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914World.com _ 914World Garage _ Air/Fuel mixture gauge
Posted by: HansJan Apr 30 2020, 08:53 PM
Will an A/F gauge make me happier, or will it drive me nuts?
The 914 is carburated, and it runs great. But still have explosions in the tail-pipe when engine breaking. To add to the drama, 90% of these tail-pipe explosions occur under freeway-overpasses.
Whats the verdict on the Gauge Yes or No?
Thanks in advance.
Posted by: nditiz1 Apr 30 2020, 09:00 PM
You could just use it temporarily. Once you know you are dialed in you could remove it so it won't drive you crazy.
Posted by: michael7810 Apr 30 2020, 09:36 PM
You could just use it temporarily. Once you know you are dialed in you could remove it so it won't drive you crazy.
I totally agree. remove or disconnect the power once the engine is dialed in or if you're like me will spend too much time looking at it.
Posted by: djway Apr 30 2020, 09:58 PM
One T4 carbed engine I had popped on decel like that. After several nights of reading I went with a smaller idle jet and it went away.
Put the gauge in, you can always unplug.
I plan to put them in my future builds.
Posted by: infraredcalvin Apr 30 2020, 10:06 PM
https://www.innovatemotorsports.com/products/lm2.php
I have one of these that I use for my turbo. It datalogs too, so you can plug it in, record a trip and analyze on a computer afterwards. Rpm and afr are easy to hook up out of the box. Can buy an optional spark plug clamp for rpm, and a tail pipe clamp for reallly simple and temporary setup.
BTW big deep popping on decel is usually caused by rich fuel mixture...
Posted by: rjames Apr 30 2020, 11:23 PM
I bought a Bluetooth PLX with a head that is hidden behind the center console so car retains stock look, and the gauge is on an app on my iPhone. Once I got it dialed in I rarely open the app anymore. No distractions. I can also buy a physical gauge that will plug into it too, but I don't see the need.
Posted by: wndsrfr May 1 2020, 06:52 AM
Take it to a dyno session at a tuning shop... they'll use a a/f probe and you can get the jets right...no need to install one...
Posted by: Olympic 914 May 1 2020, 07:30 AM
Have one installed. Do look at it a lot. but I am running D-jet and used to tune the MPS. Some times just a small throttle change will take if from too lean to a better reading.
its still running a little lean. I want to hook up a vacuum gauge and compare them so I know where to make the changes.
Also have one on the Harley.
Posted by: veltror May 1 2020, 07:40 AM
I have a PLX and I leave it in.. jetting is an interative process I doubt i will ever be happy with the jets
Posted by: BeatNavy May 1 2020, 07:51 AM
I want to hook up a vacuum gauge and compare them so I know where to make the changes.
I did that based on the suggestion of Frank in Germany (I think?). It was pretty instructive in terms of what throttle positions corresponds to part load, WOT, etc.
Posted by: Mark Henry May 1 2020, 11:22 AM
I wonder if there's a market for a rental unit kit complete with jet reams, some jets sizes, jet sizing gauges and a SS bung and plug?
What do you think peeps would be willing to pay for this kit rental? How long of a rental? One week, two or three weeks? It would be rental plus any supplies used.
Hopefully the kit could then be shipped direct to the next guy.
I have a perfect temporary 914 cable for a 14point7 SLC wideband already made, real stealth easy install, hard part is welding in the bung. One connector and a keyed positive and ground at the dash. I might be able to figure out a ashtray mount for the meter.
I only would need to get the jet sizing gauges and a collection of jet sizes for both the IDA and IDF carbs. I have every thing else.
What else would be needed for a complete tuning kit?
Posted by: HansJan May 1 2020, 12:30 PM
I wonder if there's a market for a rental unit kit complete with jet reams, some jets sizes, jet sizing gauges and a SS bung and plug?
What do you think peeps would be willing to pay for this kit rental? How long of a rental? One week, two or three weeks? It would be rental plus any supplies used.
Hopefully the kit could then be shipped direct to the next guy.
I have a perfect temporary 914 cable for a 14point7 SLC wideband already made, real stealth easy install, hard part is welding in the bung. One connector and a keyed positive and ground at the dash. I might be able to figure out a ashtray mount for the meter.
I only would need to get the jet sizing gauges and a collection of jet sizes for both the IDA and IDF carbs. I have every thing else.
What else would be needed for a complete tuning kit?
Good idea:
However I feel that with carbs we never stop tinkering. Hence the need to own.
They seem to wonder off all the time, or change with the weather.
Wishing FI would be in the stars...(but that’s beyond my abilities and/or paygrade).
Posted by: infraredcalvin May 1 2020, 02:47 PM
I wonder if there's a market for a rental unit kit complete with jet reams, some jets sizes, jet sizing gauges and a SS bung and plug?
What do you think peeps would be willing to pay for this kit rental? How long of a rental? One week, two or three weeks? It would be rental plus any supplies used.
Hopefully the kit could then be shipped direct to the next guy.
I have a perfect temporary 914 cable for a 14point7 SLC wideband already made, real stealth easy install, hard part is welding in the bung. One connector and a keyed positive and ground at the dash. I might be able to figure out a ashtray mount for the meter.
I only would need to get the jet sizing gauges and a collection of jet sizes for both the IDA and IDF carbs. I have every thing else.
What else would be needed for a complete tuning kit?
And don’t forget about an nice long, detailed video of how to...
As for the bung, get one of these, and a long enough cable for the o2 sensor instead.
Posted by: 914Toy May 1 2020, 03:21 PM
I have been on a steep learning curve since installing Webers on my 911 2.7 with headers. I have an O2 meter in each header about 6' downstream of the collector, a few inches before the muffler couplings. I have installed the Innovate Motorsport double A/F harness from the O2 gauges into their single gauge that shows separately each A/F. I have found them extremely helpful along with a carb air flow gauge to adjust the carbs. While I watch the gauges a bit neurotically, I get comfort from knowing how the carbs are performing at any time.
Posted by: HansJan May 1 2020, 06:11 PM
Thanks every one for your input.
I will order one.
Be ready for a boatload of stupid questions, ones it’s installed.
Posted by: HansJan May 25 2020, 09:09 PM
Alright, I installed a gauge last week.
My readings were:
With 1.70 Main Jet
Idle: 15.0
Halve throttle: 10.0
Full throttle: 10.0
Periodic back fire at decel.
Understanding that ideal reading is around 15, I decided to install smaller main jet.
This changed the reading to:
With 1.55 Main Jet
Idle: 19
Halve throttle: 13.5
Full throttle: 11.1
Less back fire.
The question remains. Do I install even smaller Main Jets?
According to the jet size chart, this 1.55 Main Jet is already smaller then recommended.
The engine is:
4 cylinder
2.0 type with 103mm cylinders (2.3 l)
aftermarket cam
Dual EMPI HMPX 44 carbs.
Venturis 36mm
Air jets 2.20
Idle 0.70
PS: The car runs fine
Posted by: yeahmag May 25 2020, 10:43 PM
If you are on E10 you are looking for around 12.5:1 under load. If you are on E0 (pure gas) 13.5:1. Your idle is way too lean and with a 70 idle jet I suspect a false reading. Where is the O2 sensor installed?
The 155 is closer, but you can probably drop down to a 150.
Posted by: HansJan May 25 2020, 11:24 PM
If you are on E10 you are looking for around 12.5:1 under load. If you are on E0 (pure gas) 13.5:1. Your idle is way too lean and with a 70 idle jet I suspect a false reading. Where is the O2 sensor installed?
The 155 is closer, but you can probably drop down to a 150.
Thanks Aaron,
I use E10 gasoline.
The sensor is about 6” in front (upstream) of the muffler.
The idle readings (in both scenarios) have been very consistent (15:1changed to 19:1).
Maybe I should keep it like this. If the idle become even leaner, with a smaller main jet, we could do some damage. 0.70 is the largest idle jet I could find.
Posted by: Mark Henry May 26 2020, 08:13 AM
It's all about load, lean at idle will do little or no long term damage because there's no load, same with lean on decel. It's also common to be lean at idle on carbs, in fact it's near impossible to get rid of it and you shouldn't try to as it usually upsets the AFR readings and/or performance elsewhere in the RPM/load range.
The AFR reading is for the most part is only important at WOT and part load.
Posted by: MikeM May 26 2020, 08:55 AM
I wonder if there's a market for a rental unit kit complete with jet reams, some jets sizes, jet sizing gauges and a SS bung and plug?
What do you think peeps would be willing to pay for this kit rental? How long of a rental? One week, two or three weeks? It would be rental plus any supplies used.
Hopefully the kit could then be shipped direct to the next guy.
I have a perfect temporary 914 cable for a 14point7 SLC wideband already made, real stealth easy install, hard part is welding in the bung. One connector and a keyed positive and ground at the dash. I might be able to figure out a ashtray mount for the meter.
I only would need to get the jet sizing gauges and a collection of jet sizes for both the IDA and IDF carbs. I have every thing else.
What else would be needed for a complete tuning kit?
And don’t forget about an nice long, detailed video of how to...
As for the bung, get one of these, and a long enough cable for the o2 sensor instead.
I just used one of those on my DJET car but now people are saying it's too far from the engine for accurate readings?
Thoughts?
Mike
Posted by: Mark Henry May 26 2020, 11:18 AM
I just used one of those on my DJET car but now people are saying it's too far from the engine for accurate readings?
Thoughts?
Mike
The lambda needs the heat to read correctly, ideally 750F. I've measured a 100F difference just from a header collector flange (with gasket) to the muffler flange. Mufflers do get hot, but nowhere near 750F.
Ideal it's 2 feet from the exhaust port for NA or 3 feet for turbo/SC and before the cat if you have one. On a 914 the best you can do is about 2-1/2 feet from the port which should be OK.
The innovate clamp is idea I tried (home/shop made) back in the 90's/early 2000 and found it gave me inaccurate readings.
Posted by: JamesM May 26 2020, 12:05 PM
It probably wont drive you as nuts as a head temp sensor gauge does but may be more usefull to have installed when you are having running issues. If you dont mind the look where you have it installed I would probably leave it in.
Probably more usefull on a carb'd car where mixture can be easily tweaked and issues can be addressed at side of the road.
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