Carburetored type IV engine problem diagnosis., Engine idling problem. Options

[cgnj]

Removed the carbs again and inspected the float adjustment. Both were above parallel with the underside of the casting - adjusted them back to parallel. This reduced the fuel level about 1/2 inch. Inspected all four idle jets - all were clear. Inspected the jet and diaphragm of the acceleration pumps - both were clean and in good shape.
Adjusted the air fuel valves leaner and richer ( in and out respectively) with the engine close to operating temp. Was unable to find a smooth idle position - each setting eventually leading to a stall at various idle speeds. Engine still runs well above 2,000 rpm - suggests ignition is firing all 4.
Checked timing - at 3,000 rpm, setting is on leading edge of large fan bar - 34 degrees (?). Fuel pressure is at 4 lbs/ square inch.

What should I try next?

Hi,
Although too much advance isn't likely to cause this problem, IMHO, you have too much. I personally run @28 degrees. Add heat decrease performance just what you are looking for. Just on the description of the problem, you have an unmetered air leak when the motor expands, or a linkage adjustment is for the same reason.

Things that make this happen. Phenolic gaskets and the intake area of head or manifold not being true. I ran paper gaskets till I decided to check this out and found that my heads weren't true. Same with manifolds.

I don't know what distributor you are using, whether it has been recurved, but that info will help. ( I don't think this is you're problem unless you have a 009 or a 050). The curves on these two distributors are really short.
My 2 cents, feel free to blow me off.

[VaccaRabite]

I also had idle issues for a while. It turned out the issue was a defective set of gaskets from Weber Carbs Direct that did not have all the gas ports punched in them.
Zach

[Keith914]

More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests.

[Keith914]

More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests.

Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks.

Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow.

[Keith914]

More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests.

Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks.

Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow.

With damaged carb part replaced and minor final tuning, including volume metered balance, car is purring like a kitten cold and hot. (IMG:style_emoticons/default/piratenanner.gif)

[Localboy808]

More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests.

Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks.

Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow.

With damaged carb part replaced and minor final tuning, including volume metered balance, car is purring like a kitten cold and hot. (IMG:style_emoticons/default/piratenanner.gif)

(IMG:style_emoticons/default/cheer.gif) gratz! I know how it feels to solve a problem like this. I think we all do! (IMG:style_emoticons/default/lol-2.gif)