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914World.com _ 914World Garage _ Another stupid d-jet question:
Posted by: DRPHIL914 Nov 29 2021, 08:06 AM
calling all d-jet masters !
OK so yes, ive read Anders etc and maybe missed it along the way, but
how or what constitutes a part-load condition?
I am trying to get my d-jet MPS dialed in on the 2.1 build. and it had been running really well, but just a tad lean still, so after going back and reverifying my timing and other settings, checking plugs aftera 750 mile trip, its really close and realizing i was probably a bit low on the fuel pressure i made that correction and then set out to do some local highway driving to test it out, and really felt good, but maybe a bit rich at low end, idle and what i was thinking would be part-load.
BUT i think i over corrected on the MPS and now i went from being in the 12-12.5 range at idle and also cruising at 3000-3400rpm, i now am running light at about 14 on that mid-range cruising. it is good on WOT so i dont want to mess with that(full load stop) .
i should have left well enough alone because i will probably be a bit heavy at idle and low end with this motor, due to a more performance minded cam profile etc.
point is, what is part-load? if i am reading my AFR meter , lets say at 3000rpm- 3400rpm and cruising on the flat, that would be part- load condition correct? so i dont want to make it more rich at cruise or on WOT, so how can i isolate the mid range or par-load to enrich it with out messing anything else up. i already messed this up trying to just lean it out slighty and over corrected.
if i adjust the inner screw by itself it changes both part and full load.
the outer screw in will richen part load i believe lean out full- load.
the Anders chart doesnt really address it.
- also i feel i cant really get idle right, it seems too rich but that might be the way the motor will be, not sure.
the MPS is a rebuilt one with Tangerine kit and adjustor screws, so easy to access and adjust using the Tangerine tools.
I may be at the point of just going dual webber with 44 IDF's, and forsaking the d-jet - OR a more modern programable EFI...... i just dont think i am getting the most power out of this motor that i should or would with better air intake and A/F mix.
intake is somewhat restricted on a stock d-jet and the injectors can only give you so much fuel. i did see somewhere anders wrote that the stock set up could support a build up to 2270 even with the proper changes( not sure what that means either),
anyway first question is - part load definition. then how to proceed to get this mid-range or par-load adjusted into a better mix with out making idle even more rich(or WOT either)
Thanks for the help.
Phil
Posted by: BeatNavy Nov 29 2021, 08:42 AM
Phil, a couple of thoughts from me.
@http://www.914world.com/bbs2/index.php?showuser=18632 , IIRC, suggested one way to identify "part load," or that point at which manifold vacuum is in the 4-5 psi range, is to run a "T" vacuum fitting off of your MPS to a hose with vacuum gauge in the cabin. It'll give you a better sense of what driving conditions are for your engine at "part load." In my case I found it instructive, and you can base your AFR numbers accordingly. Simply cruising down the road doesn't take much load or HP in most cases, so take AFR there with at least a little grain of salt, especially if you can monitor head temps accurately.
Do yo have an inductance meter to measure what it is you are changing, or are you going by AFR readings alone? If the latter, I think that's hard to do with much precision. I think you sort of need to ballpark it at that point and see how the car feels under different circumstances.
Take idle AFR readings on a T4 with a big grain of salt. Too many variations in exhaust and O2 setup, plus the exhaust gasses move too slowly through the system to put too much stock in them. I know it's tempting (I do it too), but you need to use other clues like smell and the nature of the idle (is it too low, too high, does it react a lot with small changes in air, etc.). Your idle mixture should be primarily controlled at the ECU. I imagine the ECU "slope" has some effect on that (or not, maybe someone can enlighten us), but get fuel pressure where it should be and then use the ECU.
Don't ditch the D-Jet. Carbs present their own set of issues. Also, I'm running Microsquirt, which I really enjoy, but it's not a panacea either. Still lots of fiddling and experimenting. The upside is that it's much easier to do the fiddling and measure the results.
Much smarter and more experienced people than me can chime in now 
Posted by: emerygt350 Nov 29 2021, 10:19 AM
same boat here but with a stock 2.0. When we finished at the dyno I was still running really rich up over 4k WOT and leanish below 4k. Idle was at 13.5 which I consider rich but as beatnavy said, it idles good, smells fine, and revs correctly so I am choosing to ignore that.
Part throttle cruising can be leaner than 14.7 and be ok since you are not loading the engine. In my old CFI mustang it will bounce around 14.3-15.3ish while cruising. When we were tuning it on the dyno (tangerine setup as well) part load settings seemed pretty good.
I just got my AFR meter in the mail today for the porsche. As soon as it warms up a little I will get it installed and check out what mine is doing on a non-dyno afr.
Posted by: DRPHIL914 Nov 29 2021, 10:48 AM
i do appreciate the input. and i can post a few pictures of the plugs which actually looked really good if not slightly lean, eventhough the AFR seems to indicate more rich which leads me to believe that the AFT is not that accurate, especially at idle,
you cant compare to a mustang and i would say that if your running 14-15 you are way too lean for an air cooled motor and your head temsp will be high. when i raised my fuel pressure up to 34-35 my head temps improved, my AFR was reading more in the 12.5-13 range and plug color is almost perfect. i prbably am not running that rich just going by the plug color.
at this point id be happy if could go back a day and NOT make that last adjustment,
i need to increase enrichment at part-load with out making idle more rich or WOT/full load.
I can put that T in and check that vac load at cruising or slight acceleration to see if i am in that 5psi range if thats what we define as part load. too bad there is not a in line vac gauge that had blue tooth conneciton to be able to hook up and monitor while driving.
Phil, a couple of thoughts from me.
@http://www.914world.com/bbs2/index.php?showuser=18632 , IIRC, suggested one way to identify "part load," or that point at which manifold vacuum is in the 4-5 psi range, is to run a "T" vacuum fitting off of your MPS to a hose with vacuum gauge in the cabin. It'll give you a better sense of what driving conditions are for your engine at "part load." In my case I found it instructive, and you can base your AFR numbers accordingly. Simply cruising down the road doesn't take much load or HP in most cases, so take AFR there with at least a little grain of salt, especially if you can monitor head temps accurately.
Do yo have an inductance meter to measure what it is you are changing, or are you going by AFR readings alone? If the latter, I think that's hard to do with much precision. I think you sort of need to ballpark it at that point and see how the car feels under different circumstances.
Take idle AFR readings on a T4 with a big grain of salt. Too many variations in exhaust and O2 setup, plus the exhaust gasses move too slowly through the system to put too much stock in them. I know it's tempting (I do it too), but you need to use other clues like smell and the nature of the idle (is it too low, too high, does it react a lot with small changes in air, etc.). Your idle mixture should be primarily controlled at the ECU. I imagine the ECU "slope" has some effect on that (or not, maybe someone can enlighten us), but get fuel pressure where it should be and then use the ECU.
Don't ditch the D-Jet. Carbs present their own set of issues. Also, I'm running Microsquirt, which I really enjoy, but it's not a panacea either. Still lots of fiddling and experimenting. The upside is that it's much easier to do the fiddling and measure the results.
Much smarter and more experienced people than me can chime in now
same boat here but with a stock 2.0. When we finished at the dyno I was still running really rich up over 4k WOT and leanish below 4k. Idle was at 13.5 which I consider rich but as beatnavy said, it idles good, smells fine, and revs correctly so I am choosing to ignore that.
Part throttle cruising can be leaner than 14.7 and be ok since you are not loading the engine. In my old CFI mustang it will bounce around 14.3-15.3ish while cruising. When we were tuning it on the dyno (tangerine setup as well) part load settings seemed pretty good.
I just got my AFR meter in the mail today for the porsche. As soon as it warms up a little I will get it installed and check out what mine is doing on a non-dyno afr.
Posted by: 914_teener Nov 29 2021, 11:08 AM
calling all d-jet masters !
OK so yes, ive read Anders etc and maybe missed it along the way, but
how or what constitutes a part-load condition?
I am trying to get my d-jet MPS dialed in on the 2.1 build. and it had been running really well, but just a tad lean still, so after going back and reverifying my timing and other settings, checking plugs aftera 750 mile trip, its really close and realizing i was probably a bit low on the fuel pressure i made that correction and then set out to do some local highway driving to test it out, and really felt good, but maybe a bit rich at low end, idle and what i was thinking would be part-load.
BUT i think i over corrected on the MPS and now i went from being in the 12-12.5 range at idle and also cruising at 3000-3400rpm, i now am running light at about 14 on that mid-range cruising. it is good on WOT so i dont want to mess with that(full load stop) .
i should have left well enough alone because i will probably be a bit heavy at idle and low end with this motor, due to a more performance minded cam profile etc.
point is, what is part-load? if i am reading my AFR meter , lets say at 3000rpm- 3400rpm and cruising on the flat, that would be part- load condition correct? so i dont want to make it more rich at cruise or on WOT, so how can i isolate the mid range or par-load to enrich it with out messing anything else up. i already messed this up trying to just lean it out slighty and over corrected.
if i adjust the inner screw by itself it changes both part and full load.
the outer screw in will richen part load i believe lean out full- load.
the Anders chart doesnt really address it.
- also i feel i cant really get idle right, it seems too rich but that might be the way the motor will be, not sure.
the MPS is a rebuilt one with Tangerine kit and adjustor screws, so easy to access and adjust using the Tangerine tools.
I may be at the point of just going dual webber with 44 IDF's, and forsaking the d-jet - OR a more modern programable EFI...... i just dont think i am getting the most power out of this motor that i should or would with better air intake and A/F mix.
intake is somewhat restricted on a stock d-jet and the injectors can only give you so much fuel. i did see somewhere anders wrote that the stock set up could support a build up to 2270 even with the proper changes( not sure what that means either),
anyway first question is - part load definition. then how to proceed to get this mid-range or par-load adjusted into a better mix with out making idle even more rich(or WOT either)
Thanks for the help.
Phil
I think Jake Raby had a quote for this IIRC....just give the engine what it wants.
In reference to "rich" or "lean" the engine needs are not always stoic.
With part load or "cruise"..the engine demands are lower so the mixture and engine will run better slightly lean.
At WOT....slightly rich.
Stoic is also a range .....so if you are looking for an absolute number then it is the number in which the engine runs best.
I know it may sound like a quantum relationship answer but that is how it works.
If you are lookng for more than 120HP then maybe a stockish type IV isn't the engine for you.
Posted by: DRPHIL914 Nov 29 2021, 11:16 AM
here are 2 plugs, this was before input them back in and then attempted to adjust the setting and messed it up.
- also my head temps and oil temp readings i think are accurate and are pretty good , not sure i am believe or knowing how accurate the AF readings are, it the plugs should give a good idea of where i was.
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Posted by: emerygt350 Nov 29 2021, 11:24 AM
Those look good to me. I just did a deep dive into previous threads on this topic. Very interesting. Things I dredged up from the past... (may just be urban legends but I doubt it)
1) Air-cooled engines like it richer
2) 14 and less seems good
3) 12 at WOT seems good
4) Don't go driving around at 15 particularly while in 5th gear at lower rpms.
5)13.5 at idle is common and seems like a happy place, some people go richer.
Let the engine decide what it likes (assuming you aren't going north of 14 at partial load or 13 at WOT).
Posted by: DRPHIL914 Nov 29 2021, 12:45 PM
Those look good to me. I just did a deep dive into previous threads on this topic. Very interesting. Things I dredged up from the past... (may just be urban legends but I doubt it)
1) Air-cooled engines like it richer
2) 14 and less seems good
3) 12 at WOT seems good
4) Don't go driving around at 15 particularly while in 5th gear at lower rpms.
5)13.5 at idle is common and seems like a happy place, some people go richer.
Let the engine decide what it likes (assuming you aren't going north of 14 at partial load or 13 at WOT).
i agree with that , it seems to be where we want to be. i do think i am a bit rich at idle and i cant adjust the ECU more than it is. i may have to settle for that. I am more like 12.5-13 at idle. just a very low idle too, i have to open up the idle air valve to keep it from bottoming out once warmed up. it had a good cold idle.
i should have left well enough alone. going to work on getting it back to where it was.
Posted by: emerygt350 Nov 29 2021, 01:06 PM
stock ignition?
Posted by: DRPHIL914 Nov 29 2021, 01:13 PM
stock ignition?
123ignition distributor but stock throttle body(completely rebuilt), brand new OEM injectors, , stock air box, etc. SS HE with one of Ben's twin tip SS exhaust mufflers
Posted by: emerygt350 Nov 29 2021, 03:15 PM
stock ignition?
123ignition distributor but stock throttle body(completely rebuilt), brand new OEM injectors, , stock air box, etc. SS HE with one of Ben's twin tip SS exhaust mufflers
Are you using retard or advance? Or neither I guess.
Posted by: DRPHIL914 Nov 29 2021, 08:03 PM
stock ignition?
123ignition distributor but stock throttle body(completely rebuilt), brand new OEM injectors, , stock air box, etc. SS HE with one of Ben's twin tip SS exhaust mufflers
Are you using retard or advance? Or neither I guess.
neither at this point - i had been using it with my stock motor, but with this one idle was so low with the vac retard hooked up ans using setting 3or4, i disconnected that and changed over to the non vac setting “C”, that’s been much better.
just went out for an hour of driving around and making some adjustments . after warming up, it was pretty lean across the board, so i adjusted inner screw out only, did this in very small increments then some driving etc, that got me out of the 14-15 range in part load down to 13-13.5, 12-12.5 on more of a full load or WOT. much better, ans seems still a bit rich on idle but if everything else is good i will leave it like this for a while and recheck plugs again after a few more drives. I am at about 35psi now for fuel pressure too and it definitely runs better with the FP at least 35-36.
There is not an easy way to just change part load, according to this chart.
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Posted by: adolimpio Nov 29 2021, 08:53 PM
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Posted by: rjames Nov 30 2021, 12:29 AM
That seems a lot leaner than what I've heard others here recommend for the type IV.
Posted by: emerygt350 Nov 30 2021, 07:56 AM
That seems a lot leaner than what I've heard others here recommend for the type IV.
Yeah, I saw that after digging through the archives.
I really wish it were easier to change the part load and wot individually. I also wish at idle they would have really bypassed the MPS altogether. Not sure why they wouldn't. They have the TPS and the ECU knob. I guess on earlier years the knob isn't an option.
I think I need a vacuum gauge as well. I suspect changes in diaphragm position might be contributing to my strange lean early rich late WOT issue.
Posted by: emerygt350 Nov 30 2021, 08:03 AM
Once the AFR is in I can see how that sign wave stuff changes in real world application (slow throttle depression rather than just WOT from the start (which I don't really do, even when driving hard).
Posted by: DRPHIL914 Nov 30 2021, 08:38 AM
That seems a lot leaner than what I've heard others here recommend for the type IV.
Yeah, I saw that after digging through the archives.
I really wish it were easier to change the part load and wot individually. I also wish at idle they would have really bypassed the MPS altogether. Not sure why they wouldn't. They have the TPS and the ECU knob. I guess on earlier years the knob isn't an option.
I think I need a vacuum gauge as well. I suspect changes in diaphragm position might be contributing to my strange lean early rich late WOT issue.
like i have written on that chart at the bottom, if you tighten the outer screw while holding the inner one, you will enrich the part-load and lean the full load out some and that sounds like thats what you need to do. would be so much easier to doe this while on the dyno rather than the stop go etc but thats what i did last night and am getting much closer to where i was. my mistake was thinking i could see that part load by just reving the motor sitting but thats not going to work you have to have some load. and if you get to the point of low and middle load and cruising is where we want it, but full load is off, then you can make a slight adjustment to the full load stop with out moving inner or outer screws.
way better to start off with it at least at the factory setting, and go from there.
also pull the plugs and see what they look like, thats going to tell you a lot too.
@http://www.914world.com/bbs2/index.php?showuser=25740
Posted by: DRPHIL914 Nov 30 2021, 08:47 AM
@http://www.914world.com/bbs2/index.php?showuser=11449
that helps, i need to get an LCR meter!!!
our builds are similar,
2.1, my cam is almost identical to the 9550, my heads are the same (hoffman heads are just the AA castings then done up by Len)
- looks like you are running close to stock timing, but stock 2.0 FP according to the Porsche book is 34 not 29, this might run you a bit lean,
Now a couple differences is that my compression is 9.5/1
and i have a counter balanced crank( factory cranks were not).
- that idle is too lean IMHO, but you part load and full load numbers are close to what i am shooting for as well. Last night i got it close. I also stayed with the no vac hooked up and advance setting is the one that goes to 3400 rpm. I am also running a bit more advance, at 30 btdc, it seems to like that much better. This motor would probably be a lot better off with carbs , but i will keep with this for now.
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Posted by: emerygt350 Nov 30 2021, 10:16 AM
I have an LCR and as others have said, your mileage with it will vary. 150H was never even possible with my MPS. Really a range between 60 and 90 something. The numbers that pbanders puts up were impossible even with my stock MPS.
DrPhil, the problem is that afr readout in the dyno is WOT all the way. There is no partial throttle on there (we did that separately from a run). So that is WOT and the AFR changes as the motor is revving up to higher RPMs. As I richen the bottom the top gets way to rich etc. That is why I think I need to watch the vacuum as I WOT. If that is moving above what the MPS sees as WOT I could be moving into and out of partial throttle according to the MPS even though the pedal is to the floor.
I am looking at other possibilities though. I am going to put in a new coil etc. May retard the timing a bit too. Little steps of course and only one at a time.
Posted by: adolimpio Nov 30 2021, 09:12 PM
I should have mentioned that my compression is 8.2:1.
I think your looking at the fuel pressure setting for LJET, which is 35psi, but further down in the manual it says that Djet is 1.96-2.04 bar, which is 28.4 to 29.6 psi.
@http://www.914world.com/bbs2/index.php?showuser=11449
that helps, i need to get an LCR meter!!!
our builds are similar,
2.1, my cam is almost identical to the 9550, my heads are the same (hoffman heads are just the AA castings then done up by Len)
- looks like you are running close to stock timing, but stock 2.0 FP according to the Porsche book is 34 not 29, this might run you a bit lean,
Now a couple differences is that my compression is 9.5/1
and i have a counter balanced crank( factory cranks were not).
- that idle is too lean IMHO, but you part load and full load numbers are close to what i am shooting for as well. Last night i got it close. I also stayed with the no vac hooked up and advance setting is the one that goes to 3400 rpm. I am also running a bit more advance, at 30 btdc, it seems to like that much better. This motor would probably be a lot better off with carbs , but i will keep with this for now.
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Posted by: BeatNavy Dec 1 2021, 06:55 AM
with this and with Rob's ( @http://www.914world.com/bbs2/index.php?showuser=9489 ) point about Jake's advice to "give the engine what it wants." When you go beyond stock you are in unchartered territory to some extent. In your case in particular, a CR of 9.5 is well outside what Jake recommends for that cam/FI combo (he suggests around 8.5, max). That doesn't mean you can't make it work for your specific combo, and it sounds like you are to a large degree, but it requires a lot of measuring and trial and error. IMO you really need an LCR and and an understanding of how much vacuum you're pulling under different driving conditions. In terms of idle, I'll suggest it one more time: try not to obsess over a specific 'ideal' idle AFR.
Posted by: 914_teener Dec 1 2021, 12:49 PM
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Phil.....
I'd wouldn't recommend NOT using the vaccum advance on that dizzy. BTDT.
I'd hook up the vac port on the dizzy to a ported vaccum source. It is there for a reason and the reason is as an adjustment(real time sensor for engine needs) for timing at part load. By looking at the plugs at a certain AFR you could be mistaking incomplete combustion instead of AFR.
So...looks like the above is using it...and the results show an engine that runs well.
Hook up the vaccum advance on that dizzy and reset your timiing...next step get an AFR meter and see what how the engine is performing.
Mostly....you'll know by the "seat of the pants" test and how cool or hot the engine is running...so I'd also recommend a CHT gauge and oil temp gauge.
Carbs react to vaccum by mixture and jets....if you have disabled that feature for your FI it won't run well. Just saying.
Rob
Posted by: emerygt350 Dec 1 2021, 02:34 PM
Just put the AFR on mine and did some tuning.
Got partial load in a good range centered around 13 to 13.5. Give it a little and it drops to 12, take of the gas a little it moves up to 14.7 (not sure why it hits it on the mark like that but there you go). I noticed that as I approached what seems to be good partial mixtures, my idle mix was changing and that as I get closer to where it probably should be that adjustment knob on the ECU is getting closer and closer to the factory setting.
Still working on the WOT. Started out Lean across the board, backed out the stop screw and got that to around 12 never leaner than maybe 12.5 or 13 but I noticed after my partial load tuning it looks like my WOT is running a little lean again. Need to double check that when I get another chance. Sucks how all these adjustments interrelate.
My 123dizzy is running on retard (A) at the moment. I cant stand high idle. Not sure why it bothers me so much, but it does. Luckily I can access the pot without removing the dizzy so it's easy for me to switch back and forth. When I am all done I might give advance a try again.
Here is a plug after an hour of mixed driving. Looks pretty nice.
Posted by: DRPHIL914 Dec 2 2021, 08:17 AM
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Phil.....
I'd wouldn't recommend NOT using the vaccum advance on that dizzy. BTDT.
I'd hook up the vac port on the dizzy to a ported vaccum source. It is there for a reason and the reason is as an adjustment(real time sensor for engine needs) for timing at part load. By looking at the plugs at a certain AFR you could be mistaking incomplete combustion instead of AFR.
So...looks like the above is using it...and the results show an engine that runs well.
Hook up the vaccum advance on that dizzy and reset your timiing...next step get an AFR meter and see what how the engine is performing.
Mostly....you'll know by the "seat of the pants" test and how cool or hot the engine is running...so I'd also recommend a CHT gauge and oil temp gauge.
Carbs react to vaccum by mixture and jets....if you have disabled that feature for your FI it won't run well. Just saying.
Rob
Rob,
just to clarify, on a 75 d-jet 2.0 throttle body there is only a retard port, not both retard and advance, so do you mean hook back up the retard vac line to the 123 dizzy? - thats easy enough to do, are you saying hook up retard(not advance) to pull the advance that is set at 3400rpm down at ide to be more with in the desired 3-4 degrees at idle? i am going to check this tonight to see what idle timing is at as-is.
Phil
Posted by: DRPHIL914 Dec 2 2021, 08:47 AM
with this and with Rob's ( @http://www.914world.com/bbs2/index.php?showuser=9489 ) point about Jake's advice to "give the engine what it wants." When you go beyond stock you are in unchartered territory to some extent. In your case in particular, a CR of 9.5 is well outside what Jake recommends for that cam/FI combo (he suggests around 8.5, max). That doesn't mean you can't make it work for your specific combo, and it sounds like you are to a large degree, but it requires a lot of measuring and trial and error. IMO you really need an LCR and and an understanding of how much vacuum you're pulling under different driving conditions. In terms of idle, I'll suggest it one more time: try not to obsess over a specific 'ideal' idle AFR.yea, i am concentrating on my afr readings during part and full load and it’s really close now, so if reading at idle is a bit rich that’s fine, as you say it may not be accurate, now i need to see why my idle is so low, or why i need that idle screw out that far. so will do a recheck on the vac like you suggested and check my advance at idle , then may reconsider the curve i’m using and as rob is saying maybe put the vac line back on and change the curve setting back to either 3 or 4. here is the chart from 123
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Posted by: emerygt350 Dec 2 2021, 09:09 AM
I bet you are a bit low on your timing. Have you tried adjusting your timing till you get a good idle (850) and giving that a try?
Posted by: DRPHIL914 Dec 2 2021, 02:29 PM
I bet you are a bit low on your timing. Have you tried adjusting your timing till you get a good idle (850) and giving that a try?
was at stock 27 degrees@3400rpm and verified before slightly increasing it which helped
but i have to go back and recheck it at idle too and see what its at at 900rpm - one other factor thats going to effect that is the richness/leaness at idle, thats why the true AF at idle matters too. hope to get to check it tonight.
Posted by: BeatNavy Dec 2 2021, 03:03 PM
one other factor thats going to effect that is the richness/leaness at idle, thats why the true AF at idle matters too.
Idle mixture matters. You just shouldn't put too much stock in what your AFR gauge is telling you at idle.
Posted by: emerygt350 Dec 2 2021, 04:20 PM
As I have zeroed in on good mixtures across partial and wot my idle mixture has moved all over (depending on the screw I was messing with). However, my idle speed has stayed very close to 850 regardless of richness, of course it is only maybe the difference between 13 and 12. And yeah, afr at idle isn't particularly accurate but it is better than nothing.
I just twisted the stop screw in a 3/4 turn and that fixed my WOT leanness. Now the leanest it gets at WOT (under heavy load climbing hills) is 13. Tempted to go even further but it is running so good now I don't want to mess with it. I dare to say it 'throws you back in your seat' at low and high rpm when you give it some gas. 3rd gear is particularly fun from anywhere between 30 to 60.
It is fun seeing how much the TPS enrichment matters on that AFR.
When I get a chance this weekend I will record my inductance with the LCR.
Posted by: JamesM Dec 2 2021, 04:49 PM
one other factor thats going to effect that is the richness/leaness at idle, thats why the true AF at idle matters too.
Idle mixture matters. You just shouldn't put too much stock in what your AFR gauge is telling you at idle.
THAT^^^Depending on the placement of your wideband or your type of exhaust your readings at idle could be totally out of whack. With d-jet I would dial idle in by ear or vacuum gauge rather than AFR. Twist the idle knob to lean until the engine starts hunting at idle and then move it back rich one or two clicks and you should be good to go. setup cruise and WOT by AFR but idle by where it runs best.
Posted by: 914_teener Dec 2 2021, 07:32 PM
Here's a point of reference for what it's worth.
2056
Raby 9550 cam
Hoffman heads with 44x38 mm valves
123 distributor w/ vac advance profile 1
Timing 27 btdc
Fuel pressure 29 psi
Standard motor FJ67 injectors
MPS settings
- 0 inHg - 150H
- 4 inHg - 128H
- 15 inHg - 80H
AFR
- Idle 14.5
- Part load - 13.5
- WOT - 12.5
Idles nicely at 900 rpm
Engine seems very happy
Phil.....
I'd wouldn't recommend NOT using the vaccum advance on that dizzy. BTDT.
I'd hook up the vac port on the dizzy to a ported vaccum source. It is there for a reason and the reason is as an adjustment(real time sensor for engine needs) for timing at part load. By looking at the plugs at a certain AFR you could be mistaking incomplete combustion instead of AFR.
So...looks like the above is using it...and the results show an engine that runs well.
Hook up the vaccum advance on that dizzy and reset your timiing...next step get an AFR meter and see what how the engine is performing.
Mostly....you'll know by the "seat of the pants" test and how cool or hot the engine is running...so I'd also recommend a CHT gauge and oil temp gauge.
Carbs react to vaccum by mixture and jets....if you have disabled that feature for your FI it won't run well. Just saying.
Rob
Rob,
just to clarify, on a 75 d-jet 2.0 throttle body there is only a retard port, not both retard and advance, so do you mean hook back up the retard vac line to the 123 dizzy? - thats easy enough to do, are you saying hook up retard(not advance) to pull the advance that is set at 3400rpm down at ide to be more with in the desired 3-4 degrees at idle? i am going to check this tonight to see what idle timing is at as-is.
Phil
Hey Phil....ooppps I didn't know you are running the late TB on your car.
Yea...I'd try it first and see how it runs. That dizzy has a hard map to the stock settings.....but that cam will want to idle a bit higher than stock and IIRC has a touch more duration for your Hoffman heads to breathe.
Just get the timing where the motor performs well and then check your AFR's with a wide band and head temps in part load and load and that motor should run and perform fantastically.
I think I saw James post the equivalent.
Good luck and drive it like you stole it.
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