Sudden low idle and surging at constant theottle

[MyFemurHurts]

Drove the Coupe a few weekends back, and it was running like a champ. Until I restarted it. Once it came off fast idle, it was just barely keeping itself alive. I had to keep my foot in it to keep it idling.

Driving it home, I noticed it was slightly surging at constant power settings.

I have Weber 32/36's that were gone through 18 months a 4K Miles ago. Im thinking vacuum leak. Any obvious places I should start at?

 

[jamesw]

Surging is usually a vacuum leak.

Stumbling is usually too lean or bad fuel supply - like your pump is going out or line is plugged up.

HTH
James

 

[nashvillecat]

Once it came off fast idle, it was just barely keeping itself alive. I had to keep my foot in it to keep it idling.

Driving it home, I noticed it was slightly surging at constant power settings.

I have Weber 32/36's that were gone through 18 months a 4K Miles ago.

There are many possible causes for the symptom you describe, most of them*, air/fuel related. If the idle circuit (especially including the jets controlled by the idle solenoids) becomes plugged with debris, a poor idle and part-throttle operation will result. Consequently, if the symptoms persist, I would pull each idle solenoid and jet and flush them and associated ports with carb cleaner. The symptoms you describe are not uncommon. and the most sterile of carburetors when exposed to hydrocarbons, air and occult particulates can get dirty fast. Parenthetically, even if the parts are all clean - if a jet or solenoid is loose or not properly seated - this defeats the carburetor's design and leads to poor operation.

Rebuilding carbs and changing filters is good practice but neither is a complete guarantee against debris/varnish/dirt elsewhere in the fuel system ultimately fed to the carburetors. Nor are their any obvious guarantees against parts shaking loose and requiring occasional snugging down.

Good luck

*(I wouldn't completely discount the notion of ignition related problems as a loose or slightly corroded ground, coil or condenser wire can often masquerade as fuel delivery problems.)

 

[MyFemurHurts]

Got another day off (it's the small victories), and after lunch I took another look at the carbs. After an hour I packed it in with frustration.

Warmed the car up since it has a low idle when cold even when it's working.

Shot carb cleaner around the throttle shaft bushings. Nothing. Checked all of the rubber end caps. Nothing. Shot carb cleaner down the throat of the carb. Solid idle. Ok, not looking like a vacuum leak.

Ran the engine, and looked down the bores to see if one was amiss. One is amiss. While most mist fuel, this one is dropping huge angry drops of fuel onto the butterfly.

Pulled the main jet, emulsion tubes, air corrector, the aux Venturi blade and made sure everything was clean and not clogged. All things were clear, and I was able to blow air through them easily. Subsequently, my beer tastes a little bit like gas right now.

Put it back together after checking the rest of the fuel passages with some piano wire, and the problem persists. Anyone know want could be causing this?

http://youtu.be/eLvGRpN8lg0

I know. I know. Upright video. Wasn't thinking about that as I was pointing my phone straight down.

 

[aearch]

Float

Sounds like the float stop is leaking or worn out not shutting off the gas when the float is full

 

[MyFemurHurts]

Thanks for the input.

Would that cause both bores to drip fuel? Only one bore is doing this; the other one is fine. Or is one bore just the path of least resistance for the extra fuel?

 

[Stevehose]

Do you have a synchronmeter and dgav adapter? If your throttle butterfly is to far open at idle it will draw fuel in like that. Start from scratch - back both carb throttle screws out and the butterflys close all the way and the screws have no effect then turn in until they barely touch the linkage then another 1/4 turn or so. Make sure linkage is free and not binding. start the car and sync the carbs with the meter and each butterfly screw until 900 idle is reached and both carbs breathing equal air. If it doesn't start keep turning each screw 1/4 turn until it holds idle. Check for the flooding and report back.

 

[nashvillecat]

Ran the engine, and looked down the bores to see if one was amiss. One is amiss. While most mist fuel, this one is dropping huge angry drops of fuel onto the butterfly.

Pulled the main jet, emulsion tubes, air corrector, the aux Venturi blade and made sure everything was clean and not clogged. All things were clear, and I was able to blow air through them easily. Subsequently, my beer tastes a little bit like gas right now.

Couldn't access your video, but sight unseen I wonder if you don't have a funky accelerator pump diaphragm or something wrong with the checkball/spring that is also part of the accelerator pump assembly. (I have not looked at a 32/36 carb in a while and recall that while there are two nozzles (one for each venturi) some of them - presumably on the progressive 32/36 carb - only have one open port/jet. On the non-progressive carburetors, e.g., the 38/38 DGVs, the accelerator pump has two ports/jets.)

Is yours dripping - leaking? :sad: Inspect the pump diaphragm and related assembly.