On my 79 308, when cruising and I step on the gas hard, it stumbles...if I accelerate slowly....all is fine. How can I tell if the accelerator circuit is to rich or to lean? Image Unavailable, Please Login
I always start with simple tasks. What octane gas are you using and have you changed the fuel filter ?
Premium...did not notice the octane Changed the fuel filter a few years age....so probably 5000 miles or less ago
First diagnostic step is to just visually confirm/deny that each accelerator pump jet is squirting when you quickly open the throttle and that the volume of fuel squirted by each seems about equal.
Unfortunately, that's the only thing in the 308 carb design that comes into operation "when cruising and I step on the gas hard". About the only other simple thing to check is that the distributor advance mechanisms are working reasonably (i.e., at a reasonable cruising RPM, the amount of advance is in the right ballpark).
Yiu are on the track but this will take effort. IF your car retains the matching, correct jets and tubes and foat level to original specs, that would be a blessing because it means no one has f&*^&^ed it up. Now, there IS a corrective set of jets, emulsion tubes, all that jazz, to run 10% ethanol gas, and it's out there somewhere. This is no for the faint hearted obviously. I watch that guy in the UK complain about "a whistle" at full throttle and I think "be damn gald you are not hearing an explosion at full throttle!
Steve points out a great point on these cars: "Nine out of ten carb problems are ignition…." LOL Go up two heat ranges on your plugs and report back...
Check for any broken strands in wires to points under the ignition advance plate that could be causing an open or short during spark advancement as the plate rotates.
It could be all manner of reasons but I would say the problem is in the accelerator pump circuit, check the diaphragms have not gone hard and deliver the correct fuel to each barrel, simply looking down each barrel is not enough as you cannot determine the correct volume is being delivered. Each jet must deliver the EXACTLY the same, from memory its about 23cc for the 0.35mm jet Rapid opening of the throttle causes a temporary leaning out or enrichment of the mixture due to the sudden change in air volume entering the engine & drop in vacuum, without the correct fuel to go with it your engine is stalling until things can catch up with you , make sure the small non return valve is working too, any bleed by can cause fuel to be dumped back to the fuel bowl and starve the Acc pump circuit from delivery the right amount. Incorrectly set floats or to high fuel pump pressure can cause the same issue tony
In order to pass my Smog check in California Jan 2020 for my 1978 308GTS ... Rebuilt carbs and replaced the accelerator pump diaphragms. Ran a small copper wire through all accelerator jet nozzles. Two were plugged and two needed cleaning. Idle Jets from 55 to 65 Main Jets from 125 to 130. Also verified my carb throttle plates were fully opening with accelerator pedal at its stop. They were only opening about 65 degrees, I adjusted to about 85 degrees to minimize strain to throttle cable at full throttle. Adjusted idle mixture screws accordingly for the road. Runs great, accelerates way better than before and engine temperatures now always run at normal operating temps.