Weber Odd Idle

[leadrsa729]

Hi -

I've got a 72 on 40IDA Webers that is experiencing an odd idle situation. The carbs were just tuned prior to storing for the winter. Now that I have it out and running for the first time this year something is not right.

When everything comes up to temp the idle is just right at 900 RPM, but if I were to walk away from it after a couple minutes it'll just die. Starts right back up just fine but it keeps happening.

I am not very experienced in adjusting the carburetors so I was hoping you all could give me some advice on where to start without completely messing up what's already been done. Thanks in advance

[Joe Bob]

Fuel pressure, bad fuel, clogged jet, wonky fuel filter......

[leadrsa729]

Joe Bob - your post does not inspire confidence in a fast resolution to my problem. ;-)

[Joe Bob]

Well, I assume you used Stabil during storage.....you have a pressure gauge.....a filter for carbs is cheap......

I would hang around and see what carb starves out....blowing out jets requires an air compressor.

[1QuickS]

Sounds like fuel starvation at idle. Per Joe Bob there may be old fuel that is restricting flow during idling conditions. When you start the car the fuel flows enough to fill the float bowls but idling evacuates them faster than the delivery can supply.

However...are you saying it runs well enough to warm it up and then it dies when left to idle? If so then this negates the fuel starvation item and implies an idle circuit problem. Do you have a hand throttle that you use during this process?

[leadrsa729]

Hello Paul -

I do have a hand throttle that I use to warm up the car with. I have a feeling that Joe's suggestion of fuel pressure might be the issue. I'll take a look and see what I'm getting. Should be around 4 psi right?

Thanks all!

[Joe Bob]

4-5 psi is the norm.

[leadrsa729]

Thanks again Joe! And to answer your earlier questions, yes I did put it away after running some Stabil through the system. I did blow out the jets before putting it away too, but doesn't hurt to check them again.

Would either of you know how much it costs to have an MFI pump rebuilt these days. It's got a cam for a T engine in it and I'll have to switch to an S profile as well. I thought carbs were going to be easier and that's why I went with them when I rebuilt the engine. Sometimes they feel like they're more trouble than they're worth!

[Joe Bob]

MFI Pump? Go with a cheap carb pump.......

[leadrsa729]

No sorry if I was unclear, I meant the MFI fuel delivery system rather than carburetors. That's what was originally on the car.

[Joe Bob]

Might want to block the fuel return line. Carbs don't need that.

[Uncle Enzo]

I'm running 40s on my 2.7 and once you get them dialed in they are gold. The sound is simply amazing and frankly they look the business.

[1QuickS]

3.5 psi is factory specification for fuel delivery pressure to the Webers. This pressure is to be checked while the engine is running and with the gauge in one of the lines close to the carburetor input.

A thorough carb tune-up includes checking/setting float levels with engine running which would at least allow for correction for fuel pressure being too high. Excessive fuel pressure (over 4psi) will cause your float needles to leak and overfill your float bowls with fuel then being directed through the main circuit and directly into your engine.

Fuel return line to tank is a good system to use but requires some components downstream from the carburetors to pressurize the carbs and to bleed excess fuel to tank. PMO fuel pressure regulator is used before the carbs and supplies dead-end fuel supply to carbs with excess sent to tank. The assumption here is that your plumbing is in order and was functioning properly before storage.

If your system was functioning correctly before parking then something happened during storage.

I asked about hand throttle to see if the engine would run at higher RPM with hand throttle but die when left to idle. If this is your scenario then I'd check to see that the idle jets are clear of debris or dried fuel. This might explain why idling lets engine die and use of hand throttle keeps it running...partially on the main circuit.