I have dual weber 40 idf's. I cannot get the mixture correct no matter of the changes that I have made. I foul the plugs with dry black soot in only minutes. The car runs fairly well. Could be fine tuned however right now I am working on gross tuning. Heres the background info-

Setup-
-1.7l case now 2.27l by changing jugs to 96mm and crank to 78.5mm
-2.0l heads (I also have stock 1.7l heads, I have had the same issue with both heads)
-A "fairly aggressive webcam camshaft setup for carbs". I do not know the exact lift and such. The previous owner increased the displacement from 1.7l to 2.0l. He changed the cam when he rebuilt the engine. When I rebuilt the engine, I used the same cam. I had this rich mixture issue before and after my rebuild.

Carb info-
-Dual weber 40 idf's freshly rebuilt with new needles and seats
-main jets 120
-air correction jets 200
-tubes- f11
-idle jets 50
-vents 32mm
-floats set at 10mm (rich mixture), 11mm (rich mixture), 12mm (rich mixture)
-fuel pressure at 3.5

Other Info about my engine-
-MSD 6al ignition
-MSD Blaster 2 Coil
-Bosch 050 distributor with pertronix
-Autolite 63 spark plugs gapped at .030

I have tried a few things however I have not been able to change the problem. I only have a set of larger mains which obviously didn't help the issue. I have checked to make sure the needle is seating properly. I have removed the air correction jets to see what would happen- no major change in the mixture. I have a set of 34mm vents on the way however I doubt that will change much. It seems to me that with the carb setup that I currently have, I shouldn't be fouling the plugs after running the engine for only a minute.

Any ideas would be greatly appreciated.

(Yes, I did post something similar on 914Club. I am trying to look for as many ideas as I can find).

I was helping you over on the Club site. Can you describe the symptoms besides the sooty exhaust and fouled plugs. Does the car fall on it's face and bog down? Does exhaust reek of fuel? When you press the throttle down does the engine lag and stumble a bit before reving up?

NGKs in the same or hotter heat range (BP5 or 6ES is a decent range for a lower compression engine. I dunno squat bout Autolites ) & gapped to .050.

Its difficult to explain because I have only driven the car for about 10 minutes in the past year. I have not gotten the engine to WOT yet (I usually work on the car at night. I don't want to wake my daughter).

Here is what I remember from my drive last week. Accelerates quick at about 1/2 throttle. Lower RPMs are ok but then high rpms seem to stumble. Not sure if this is connected but when the engine is hot, the rpms go to about 3k when idling, after about 10 seconds the rpms drop down to the point of almost dying.

I'd check the float valves to make sure they are seating properly. What fuel pump are you using?

He checked the float valve assembly and he says it doesn't leak. He's running a CB rotory.

Hunting at idle is a symptom of a rich condition. Hunting is different than reving to 3K and then almost dying. Do you have any carb pops with this (backfiring out of the carb)? I can't see the engine reving up to 3K with the butterflies closed. This one sounds like a bad vacuum leak when things get hot and move around. Check around the manifold gasket for leaks. Use the thick gaskets.

Are your 50 idle and 120 main jets new? If not the PO might have opened them up. Some guys have even bought "new" jets that have been opened up.

Have you sync'd the carbs and adjusted the linkage? (not the root of your problem but causes issues)

[/quote]

He checked the float valve assembly and he says it doesn't leak. He's running a CB rotory.

Hunting at idle is a symptom of a rich condition. Hunting is different than reving to 3K and then almost dying. Do you have any carb pops with this (backfiring out of the carb)? I can't see the engine reving up to 3K with the butterflies closed. This one sounds like a bad vacuum leak when things get hot and move around. Check around the manifold gasket for leaks. Use the thick gaskets.

Are your 50 idle and 120 main jets new? If not the PO might have opened them up. Some guys have even bought "new" jets that have been opened up.

Have you sync'd the carbs and adjusted the linkage? (not the root of your problem but causes issues)
[/quote]

You clearly know your stuff. I forgot to add something. I had the high rpm issue last week. I checked my intake manifolds and found a huge crack. I purchased new manifolds and now have them installed. The things that I have tried have been with the new manifolds. I have not driven the car yet with the new manifolds so I am not certain that I still have the RPM issue.

My jets are new. I purchased them from aircooled.net. I have synced the carbs with a snail and have confirmed the linkage.

Last night, I found something that may be a the problem. On one carb, I have a choke assembly. On the other carb there is only the block off plate. I took the choke assembly off the one carb (I did not work on the other carb). I took it off because I tried to move the choke lever and it was stuck. I found that the starter valves do not move (I thought they were supposed to move up and down). I didn't have time to see if they were stuck open or closed. When I rebuilt my carbs, I did not work on the starter valves. I will work on this later tonight.

I believe you have found the root of your problem. With your current jetting you should be in the ballpark, if not a tad lean on both your idles and mains. Chances are (I hope not but suspect it with your current jetting and cam) when you get that fixed you'll be asking us about lean transition issues. On a SWAG I'd say 55 idles and 125 mains are what you'll end up with. Make sure you reset your float level to 10 with the gasket. The F11 is real sensitive to float level.

perhaps i've missed it. what effect do the idle air adj screws have on the idle when you run them in, one at a time, to fully(gently) seated?

the linkage may be binding when the engine is hot. try backing one carb's idle speed adj off of the stop. if you've tried to balance the carbs using the idle speed adjs, you're wasting your time.

sometimes the home rebuild route is not the best path. a firm such as AIR COOLED ENGINEERING can set the carbs up for your SPECIFIC application and they can be installed 'out of the shipping box'. they're not cheap by any means but less than a new engine if you burn things up by washing lubricant off the cyls when running pig rich.

I went through and cleaned out one of my IDF's this weekend, made a big difference, I still have to do the other one. There was a bunch of "gunk" on the bottom of the bowl. Not from a bad fuel tank or anything, I think just becuase the car sat for so long. Up in this thread, I noticed it was mentioned the fuel enrichment parts were in one side and not the other. Both my carbs have the block off plates, but when I removed the one side, I noticed there were no parts? On later IDF's did they simply keep the casting the same and just not drill out the passages?

I don't have a running rich problem or anything, but have heard very bad stories if you remove the arm cover for the block off plate and don't keep the two parts in the carb as well as make sure they stay down with a little set screw or something.

So are my carbs normal or should I be looking for parts?

Here's more of what I was talking about:

Your carbs are normal. They kept the casting and didn't do the machining or add the parts.

Kinda what I thought, thanks!

I have kind of an embarrassing/funny story. Tonight, I decided to take the my carbs apart completely to see if I had missed anything when I rebuilt them. I found that ALL 4 of the starter valves were completely stuck. They would not move at all. They looked like they were closed however I think they were slightly open dumping fuel into the engine. I slowly worked them free, cleaned everything again, reassembled everything. Started the engine. Still had some black smoke but nowhere near as bad. I thought that the engine ran rough but not horribly bad. I checked the spark plugs and they were much better. I then realized that I forgot to reinstall the jet stacks!!! What an idiot!!! Anyways, I reinstalled the jet stacks and the engine runs so smooth. The spark plugs look perfect! Now I can fine tune everything.
I greatly appreciate everyones help. There is no way that I could have fixed the problem without everyones assistance. THANK YOU!!!!!!!

Glad it all worked out for you.

Cool!

Before I was told my versions don't have the ports drilled for starter valves, I did some reading up on it. It seems like if you remove the cover/arm for just the plate, make sure the valves stay all the way down.

I wonder what year they (weber) stopped putting the starter valves on the carbs?

Victory!!! I hope I am as victorious with my DRLA's.

Unfortunately, it appears that I didn't actually solve my problem. I think that I was having a few issues that were making the rich mixture impossible to diagnose. I had the stuck starter valves which screwed everything up. Things got better when that was fixed however I am still getting a super rich mixture. I also found that I when I purchased my main jets, they had actually been drilled out. I had 140 mains and purchased 120 mains. I measured them recently and found they were identical. Since then I have purchased 115 mains and have drilling them out trying to get the right mixture. I found that around 130 is good for high rpms.

My problem now is that I am rich at idle. I have 45 idle jets which were the smallest that I could find easily. I did see that you could get slightly smaller however it doesn't seem like I should need such small jets.

I tried to do an experiment. I turned all of the idle mixture screws in and put a new park plug in to see what would happen. I started the car and ran it at idle only for 1 minute. I then removed the plug and it was fouled. I tried this with seven different types of plugs and I got the same results with all of them.

I have tried float settings of 10-12.5 and had fouling troubles with all settings. Is there anything else that I can try?

If needed- here is a video clip that I posted on one of my other posts. I was talking about a different issue on the video so ignore that. I didn't show the black smoke form the exhaust. It is present but not horribly bad. I do not kjnow if the video would help, just thought i would post it since I have it.

sorry forgot to add the link

http://www.youtube.com/watch?v=uAvoM4DpyyM

I just noticed something on a weber idf diagram. In the diagram, it shows that the idle jet is placed into the idle jet holder and there is an o-ring around the idle jet holder. My holders do not have o-rings. I must have left them off when I rebuilt them last year. My holders are not loose.

I realize this is a very unlikely but could leaving the o-rings off cause a rich issue like this. I am searching for zebras now.

With the O-ring missing you'd suck more air from around the jet holder instead of more fuel from the fuel wells. If they leak you'd be lean. To suck more fuel you need to suck less air and pull more vacuum on the fuel wells. Plugged air ducts would do it. Are the air ducts ( orifice above idle jet ) unplugged?

45 idles are too small. Something isn't right. You should be around 50 to 55. How many turns out are your mixture screws?

BTW - you need to get those O-rings in.

There are a total of 4 O-rings per carb, very important.

I am no expert but I got a suggestion lately that helped with my rich idle
problem.

An old school VW guy told me to open my air bypass screws 2.5 turns as a
baseline to help get more air into the mix at idle. I was turning my mixture
screws in too much to try to get a lean idle and it was causing a stumble
getting on the throttle. 2.5 air bypass with 1.5 idle mixture screws worked
much better for me. Open the air bypass screws more to synch barrels
and carbs with each other not less.

If you are still blowing black smoke then I would guess something else is
wrong not just adjusted incorrectly.

John

when your car is ilding, is fuel spilling/dribbling out of item #12( the pump jet)?

in addition to the little o rings for the idle mixture screws there should be little metal caps that the springs push against. these caps are not shown in the diagram you have posted. do you own a copy of Tomlinson's Weber Manual?

I had two o-rings so I put them on the idle jet holders on one carb. I also check the air ducts and I can see the idle jet through so they are open.

I believe that my problem is primarily with the idle circuit.

Turning the idle mixture screws do not seem to make any difference at all. I have them all the way in and I still have the rich issue.

I rechecked to make sure that my float needle and seat were seating ok. I tried to shot low pressure air into the fuel input with the needle closed. I could not hear any leaking air.

I also checked the compression on 3 of the 4 cylinders. All were around 140 when the engine was half warm. I got a phone call so I didn't check the last cylinder until the engine was cool- it was 110 but I am not sure the compression tester hose was on all the way. I do not think that the 110 cylinder (#1) has anything to do with my problem cause I have the rich issue with all cylinders.

I should also mention that I am running a CB performance fuel pump. I was running a fuel pressure regulator however I recently found that it wasn't working properly (it would surge). I have removed it so I do not have a fuel pressure regulator or gauge hooked up now. I had this rich problem before and after having the fuel pressure regulator on however I do not know if the regulator was working properly. I have a new regulator and gauge on order.

I agree that something is clearly very wrong and I doubt that it is a jetting issue since I am already using small jets. I just cannot figure out where the fuel is coming from.

I checked looked several times to see if fuel is spilling or dribbling out of the pump jet. I have never seen any at all.

I don't have tomlinson's weber manual (I didn't know it existed). I do have Haynes weber manual.

Here is a brief summary of what I have tried to figure out the problem. Some may sound stupid but I have tried everything I can think of. I am referring to rich idle only. Nothing has changed anything. I realize there may be some tricks to get rid of the symptoms however I want to figure out and fix the source my problem. I am absolutely lost and frustrated.

-tried different idle jets (larger was all I had but it was just a shot)
-different main jets of many different sizes
-idle mixture screw adjustments to all extremes
-tried 7 different types of spark plugs at different heat ranges
-checked to make sure pump is not leaking
-tried different float heights- anywhere from 10mm-12.5mm
-confirmed float needle is seating properly
-confirmed air ducts about idle jets are patent
-tried to run without air correction jets just to see what would happen- no help
-rebuilt choke system after I found the starter jets were stuck- no help. out of frustration, i then tried to plug the starter circuit so there would be absolutely no leakage- no luck
-tried various timing setting- no change in rich issue.
-found crack in one intake manifold- no change
-tried different spark plug gaps (0.28-.45)
-tried different venturi size (why not give it a try)- tried 32mm and 34mm
-added the needed o-rings to the idle holders that I forgot- no help

Clearly there is something very wrong. If something were this wrong it seems like it would be somewhat obvious. I think that I have tried just about everything and I am extremely lost and frustrated. I hate the thought of taking my car to the shop but I may have to. I have a young child and my wife is pregnant. I can see her getting a bit angry with me if drop $500-1k taking the car in.

you need an o ring for each idle/air mixture needle screw. the caps also. actually, Tomlinson's book is a CB item. you get it from them. i don't think you are running on the idle circuit at all when everything is hooked up. i note in your other thread you state you can achieve a stable low idle with the linkage disconnected. do the mixture screws have any effect then?

Buy a new set of carbs for $500-600 before taking the car in anywhere...

Did you ever check if your manifolds are flat and sealing well? Mine were warped from the factory and my car ran like shit until I smoothed them and got them sealed right.
Mark wrote a post about it a while back.

John

I may have just found my problem. I was having rich issues at all rpms. I previously checked and found that when I thought I was using 120 main jets, I found they were bored out by the PO.

In retrospect, I should have checked to see if the PO also bored out the idle jets- it turns out that he did. 45 is printed on the idle jet. I think he tried to bore it out to 55. I think that it is somewhere between 0.55mm and 0.60mm (I only have 55 and 60 drill bits- 55 is very loose, 60 will not fit).

Can an idle jet discrepancy of 5-10 cause a significant rich mixture issue (even with the mixture screw turned all the way in?

I did not check, I will do that.

With the mixture screws turned all the way in your car shouldn't run. You should have no fuel flow from the idle jets. There is one of 3 things going on. (1) Your mixture screws are the wrong ones or junk. (2) The mixture screw seats are all screwed up and the needle doesn't seat. (3) You have fuel flowing into the carb from somewhere else.

Remove your mixture screws and take a good picture and post it. They should look like a sharpened pencil. The DAPO might have replaced them with the wrong ones, filed them or they are just plain junk. If the seats are screwed up it's harder to tell.

I want to confirm that my engine will run with the mixture screws in all the way. I will do this when I get home. The reason that I ask is because I currently have the screws out 1 full turn and it runs. When the engine ran with the screws all the way in, I was doing experiments on other carb parts which may have aloud the engine to run. I am not sure that the engine would run if I turn the mixture screws all the way in considering that I have all the other settings around normal.

I greatly appreciate every bodies help. Imagine how difficult it would be to figure out our car problems with out forums like this. Books are only so helpful.

I forgot to mention that my mixtures screws look decent to me. I do not see any evidence of the PO filing them or anything. They look clean. The appear like a nicely sharpened pencil.

I just got in from the garage and I am very pleased however I do not know how to interpret my results.

I put new spark plugs in, attached a new fuel pressure regulator and fuel pressure gauge. I turned all of the idle mixture screws all the way in. I tried to start the engine. It started right up and ran as smooth as I have every heard a 914 run. I was shocked by how smooth it was running. It sounded like a completely different engine. I let it run for a few minutes at idle then turned off the engine. Pulled a spark plug and for the first time ever the plug was not fouled. It looked exactly like it did when the plug was brand new.

The engine is running great at idle but from what I understand, it should not be running at all with the idle mixture screws all the way in. What does this mean? I am confused (as aways )

Thanks again!

Your butterflies are misaligned. (see fig. C ) When your butterflies are closed a progression port is on the vacuum side of the butterfly. You'll pull fuel from the progression port and your car will run with the mixture screw closed. When the mixture screw is open you'll be way too rich.

Pull a carb off and turn it upside down. The butterfly should close nice and tight and you shouldn't see progression ports. If not loosen the butterfly screws and let the plates slide into place. Tighten back up and see what you have. If you still see a progression port you can buy new carbs or file the butterfly (Fig. D).

I actually tried this last week. If I back the idle speed screws out so the lever doesn't touch then the butterflies close completely and I cannot see any of the progression ports. There is one port that is very close to the butterfly edge however it is not exposed if the idle speed screws are backed out completely. IIRC there is one progression port exposed when idle screw is set to about 900 rpms.

Is it possible that all of my idle mixture screw seats are screwed up and that is causing a little leakage into the intakes? I would find it unlikely that all would be messed up but who knows.

I plan on rechecking to confirm that no progression ports are exposed however I am fairly certain that none are (assuming the above conditions).

I did not see the image at first. I think that I may fall into the "C" category from the diagram when the idle speed is set. SO if this is the case (I will confirm tomorrow afternoon) then would the best way to fix be shaving the inferior butterfly edge on the progression port side?

If this is the case, how would this happen to both carbs?

I doubt all the seats would be junk. Stranger things have happened. The misalignment fits all your symptoms perfectly. Thats my best guess. I would try and loosen the butterfly plates and rotate the shaft closed with the carb upside down. The plates will center themselves. Tighten them up and see what you have.

Poor machining out of the box, improper assembly. Do they say "Made in Italy" on them? Before you go filing plates make sure they are centered.

Mine do say Made in Italy (is that good or bad). The butterfly issue does make perfect sense. I'm going to tear into them tonight and find out. I do remember that when I rebuilt them I had issues getting the butterflies in correctly.

Does anybody know if the screws that hold the butterflies in place are something I can get at a local hardware or is it a special order type thing?

I am so great full for everyones help (especially JMill). I am not sure what I can do to help everybody else but if I can please let me know.

Made in Italy is a good thing. Chances are that it's an assembly error on your part rather than poor machining on theirs.

I'd get the screws from Weber. They are metric brass machine screws. Unless you have a fantastic hardware store I doubt they will have what you need.

One more thought. IIRC the butterfly plates are machined with a slight angle on them already so they fit the bore tight. I have triple webers at the house and don't have IDFs anymore so I can't check for sure. Check to see on yours. If they are indeed machined with a slight angle you might have the plates 180 out. This would cause them to hang up high and leave a port open below the butterfly.

i just checked a set of 40s that i have. there is a bevel and the throttle plates(butterflies) are installed the orientation as pictured in the diagram. there is also a stamping of 76* on the bottom side of the throttle plates. interesting that the bevels are cut in the opossite taper on either side of the shaft. installed wrong and it the thin edge of the plates would make for the sealing line instead of the broader edge the taper would provide and the plates seem like they would ride higher when closed.

Thanks for checking that out. Whats really important is what direction the 76 faces. You can flip them upside down all day and the same bevel angle will meet the carb bore. If you hold the plate flat and rotate it to have the 76 face the other way you will reverse the bevel angle that meets the carb bore. Just remember that the hole drilled in the plate will be on the side opposite of the mixture screw.

no hole in the plates on these italians but the 76* is on the side of the carb opposite the idle air mixture screws. that would be the inside of the shaft if the carb was installed.

I just got back inside from examining my butterflies. I believe that I have a combo of issues. It appears that 3 of the 4 butterflies were very slightly misaligned. I was able to realign all of them and they seem to close and cover all progression holes. Now I am having another issue however I am pretty sure I know what the problem is this time.

After re-aligning the butterflies, I set the idle mixture screws at 1/2 turn and the idle speed screws at 1/2 turn after light contact with the lever- wouldn't start. I tried different scenarios of backing out the idle mixture screws and turning the idle speed screws in. Basically once I advanced the idle speed screws to about 1 3/4 - 2 turns, the car would start without difficulty however I was shooting black smoke out. I turned the idle mixture screws in all the way and the engine would not run (unless I turned up the idle speed screws- opening up the progression ports). I opened the idle mixture screws about 1/10 of a turn and the car ran great, no smoke.

SO am I correct in assuming that this means that my idle jets are to big? If so, I am in luck because I have smaller jets on order. Also, does turning the idle speed screws to about 1 3/4 - 2 turns sound reasonable (I get an idle of about 1000 with this)?

I am absolutely amazed with the wonderful help that has been provided here.
THank you!!!

You really want to keep the butterflies as close to closed as you can. My goal was to get it idling nice when the screws just touched. It's not usually possible but it's nice to shoot for. As you open the butterflies you move off the idles and onto the progression ports. 1000 RPM is too high. You should be able to get it down to 800.

1/10 of a turn is very little. Those idle jets you have now would have to be bored out pretty big.

I have my fingers crossed that the new jets will fix you up. What size did you order?

I ordered 40s. I figured that I can bore them out if needed. I just found my problem. JMill get the trophy. I will post pics to explain shortly.

Heres the answer. JMill had told my to check to make sure the idle air jets were patent. They were patent but-