Weber IDF always rich- Please help! Options

[tornik550]

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).

[jmill]

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?

[J P Stein]

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.

[tornik550]

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.

[IronHillRestorations]

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

[jmill]

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.

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)

[tornik550]

[/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.

[jmill]

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.

[rhodyguy]

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.

[Root_Werks]

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? (IMG:style_emoticons/default/confused24.gif)

[Root_Werks]

Here's more of what I was talking about:

[jmill]

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?

So are my carbs normal or should I be looking for parts? (IMG:style_emoticons/default/confused24.gif)

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

[Root_Werks]

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?

So are my carbs normal or should I be looking for parts? (IMG:style_emoticons/default/confused24.gif)

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

Kinda what I thought, thanks!

[tornik550]

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!!!!!!! (IMG:style_emoticons/default/smilie_pokal.gif)

[jmill]

Glad it all worked out for you. (IMG:style_emoticons/default/cheer.gif)

[Root_Werks]

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?

[Silverstreak]

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

[tornik550]

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.

[tornik550]

sorry forgot to add the link

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

[tornik550]

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.