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]

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.