1969 L46 350/350 Won't Idle

[David W.]

I checked the archives are there are many threads on this topic but couldn't find any identical to my situation. The car starts immediately and seems to run fine if I keep pumping the accelerator but if I take my foot off the pedal, it stalls. If I try to hold the pedal at say 2000 rpm, the rpm won't stay at that level and starts to steadily drop over a couple seconds until it stalls.

I'm leaning towards a coil issue but I don't want to just start guessing. All input most appreciated.

For background info, the original carb was recently professionally rebuilt as well as year old gas drained and replaced with non-ethanal 93 octane.

[Patrick H.]

Re: 1969 L46 350/350 Won't Idle

fuel pump age and condition?
fuel filter?

[Leif A.]

Re: 1969 L46 350/350 Won't Idle

Vacuum leaks??

[David W.]

Re: 1969 L46 350/350 Won't Idle

Thanks for your reply. I purchased the car 4 years ago so don't have the mechanical history. It was a Top Flight car 10+ years ago. The filter at the carb has been replaced but the in-line canister has not and I think you've made a very good suggestion. Even if it's not the issue, it would be wise for me to replace it especially not knowing the history.

[David W.]

Re: 1969 L46 350/350 Won't Idle

Thanks for you reply. I'm assuming that would have to be one big vacuum leak. My experience with those annoying leaks in the past has led mainly to rough running so I wasn't think about that aspect too much. Any suggestions on common vacuum culprits?
Thanks again.

[Mark E.]

Re: 1969 L46 350/350 Won't Idle

This reads as though the engine wasn't started for a year. Correct?

If yes, how well did it run before its hibernation?

At end of hibernation, was the engine started prior to the carburetor rebuild? If yes, how did it run?

Was the engine run with the old gas after the carb rebuild?

Is the new carb to manifold gasket exactly the same configuration as the old one? .ake sure it isn't leaking.

Was anything altered in any way besides installing a new kit? Idle bypass changed, MAB changed, etc.

[David W.]

Re: 1969 L46 350/350 Won't Idle

Excellent questions. You are correct, it hasn't run for a year due to a variety of stupid reasons, one of which it wasn't running well at all. It would keep an idle but at 30mph or so it was lurching. I got back to it a month ago and it wouldn't maintain an idle, kept stalling out. Started by draining the tank and changing the small fuel filter at the carb. In doing so, I managed to strip the threads on the fuel line inlet so sent the carb for a full rebuild and helicoil new threads. Work done by CustomRebuilCarbs in NJ who has done great work for me in the past. The rebuilt carb was not run with the old gas. Nothing else was changed.

Starts right up, sounds great when I work the pedal. Just won't maintain a steady rpm or idle on it's own. I'm going to replace the fuel filter canister and hope that helps. Never a dull moment. All input greatly appreciated.

[Larry T.]

Re: 1969 L46 350/350 Won't Idle

Did you flush your fuel lines prior to the installation of the rebuilt carb? If not, this can be a contributing factor with your issue. The orifices in your carb can get clogged and your needle and seat won't seal properly.

Your best bet is to get someone ( or yourself ) to baseline the car and systematically go through the necessary steps to get the car running as intended. this includes basic tuning procedures and testing of all mechanical and electrical components. You'll save a bunch of time and money in doing so.

[David W.]

[Mark E.]

Re: 1969 L46 350/350 Won't Idle

Before carb rebuild: "It would keep an idle but at 30mph or so it was lurching. I got back to it a month ago and it wouldn't maintain an idle, kept stalling out."

After carb rebuild: "The car starts immediately and seems to run fine if I keep pumping the accelerator but if I take my foot off the pedal, it stalls. If I try to hold the pedal at say 2000 rpm, the rpm won't stay at that level and starts to steadily drop over a couple seconds until it stalls."

So the engine didn't run properly before or after the carb rebuild, with somewhat different but not vastly different symptoms. It sounds like one possibility is the engine is starved of fuel... it wants to stall but then recovers when it gets a squirt from the accelerator pump. I wonder if the idle circuit and/or primary metering system is clogged. Do you pump the accelerator before cranking? This may be why it starts okay but doesn't continue to run.

Did CustomRebuilCarbs dial in the carb on a test engine before shipping it to you? If not, ask if they can (the better shops do this). Alternatively, install another carb on your engine as a test. For cars I intend to keep awhile I will get an extra carburetor to hasten diagnostics (same with alternators and distributors).

[David W.]

[Patrick H.]

Re: 1969 L46 350/350 Won't Idle

Do you still have the old fuel in the car?
Do you run 90-octane non-ethanol?

If it's not new fuel, or it has ethanol, change it.

[Duke W.]

Re: 1969 L46 350/350 Won't Idle

I checked the archives are there are many threads on this topic but couldn't find any identical to my situation. The car starts immediately and seems to run fine if I keep pumping the accelerator but if I take my foot off the pedal, it stalls. If I try to hold the pedal at say 2000 rpm, the rpm won't stay at that level and starts to steadily drop over a couple seconds until it stalls.



For background info, the original carb was recently professionally rebuilt as well as year old gas drained and replaced with non-ethanal 93 octane.

Have you checked that the choke valve closes and the fast idle cam sets properly when you floor and release the throttle pedal prior to a cold start?

If the car has only sat for a day or two do you see fuel exiting the accelerator pump nozzles when doing the above?

Once fully warmed up does the engine operate nominally including hot idle?

Where do you get "93 octane" gasoline?

The reason I ask is that since ethanol is an octane enhancer, the straight run gasoline the comes from the refinery is less the (R+M)/2 rating posted on the pump. The ethanol is "splashed" into the tank truck at the distribution point to raise the octane to the posted value.

Duke

[Dan D.]

Re: 1969 L46 350/350 Won't Idle

Dave, just a long shot here, but thinking about your situation, have you checked the vacuum advance? That is at zero at start up and under load, but goes full on at idle and at cruse.

If it is shorting out the ignition somehow when it activates it will act just like you are describing it.

It is an easy check is all. Just pull the hose off and see what you get.

Dan D.

[Duke W.]

Re: 1969 L46 350/350 Won't Idle

Dave, just a long shot here, but thinking about your situation, have you checked the vacuum advance? That is at zero at start up and under load, but goes full on at idle and at cruse.

Dan D.

The '69 L-46 is an emission controlled engine, so there is about a 99.9 percent chance that vacuum advance is "ported", so no vacuum advance at idle and likely not enough vacuum gets through to the VAC at fast idle to even start it to pull.

Of course it may be modified in various ways from original configuration. The owner needs to provide more information.

Duke