Lt-1 Stalls at idle
I just fixed one problem and seem to have created another. I just installed a new accelerator pump which eliminated the flat spot the car had from a standing start. Now after driving the car for about 40 min. the car will stall out at idle. When I left my drveway I was idling at 900 rpm during the ride I noticed the idle became a little rough and the rpm dropped to about 750 to 800 rpm. I checked float levels, timing , dwell all seem to be right there. Could a hot engine evaorate fuel in the manifold at idle? Also engine temp was good.
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Re: Lt-1 Stalls at idle
When you left your driveway (900 RPM idle), was that with the engine essentially 'cold' from a fresh start, or did you let it sit, idle, and warm up fully to get the carb's choke system out of the equation?
The reason for asking is to make sure that the 'idle' condition we're discussing is, in fact, the hot engine, normal curb idle profile of the carb without the carb's choke adjustment/operation playing a role... -
Re: Lt-1 Stalls at idle
Jack, the car was warm and the choke was off. I also replaced my plugs today before the ride.Comment
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Re: Lt-1 Stalls at idle
James, There may be many problems with that carburetor. The gaskets could be allowing leakage and the gasketed surfaces could be slightly warped allowing the same. It may be time to have a pro overhaul that carburetor.
Outside of that you may try to just slightly lower the floats to where the fuel level is just at the bottom of the check screw. Don't go lower because I think other things are affected like emulsion bleeds etc.
Make sure the heat riser is opening and closing.
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Re: Lt-1 Stalls at idle
Tim, the carb was rebuilt by a proffessional about 5 years ago he also just installed the accelerator pump. What are the mechanics that cause this condition does any one know?Comment
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Re: Lt-1 Stalls at idle
When the car stalls at idle is it running really rich, black smoke out the back?
Is it running extremely lean, like a vacuum leak?
Have you changes fuel at all - something with a higher ethanol content?
(will boil quickly and cause over flow throughthe vent tubes).Comment
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Re: Lt-1 Stalls at idle
Bill, it seems to have the same exhaust smell as it always had, no black smoke, these older cars always seem to idle a little on the rich side. Before the new pump was installed it idled okay. Idle always seemed to go soft when it had been running for a while. Plugs are new, points, cap, and rotor have maybe 500 miles on them. Condenser has not been replaced for a while. Very frustrating situation.Comment
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Re: Lt-1 Stalls at idle
Your car will run without any issues durring the 40 minutes, then all of a sudden act up?
Wonder if you are having an intermittent issue with the idle selonoid?
Just curious - what year is your car?Comment
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Re: Lt-1 Stalls at idle
Mine does the same thing. (70LT1, Holley 4555, correct metering blocks & jets)
Idle was originally set after idle until the choke went fully open. It would idle fine at 750 with occasional, regular burps down to 700. When I only took short joy rides just to stay in use there were no issues. I did have rough idle issues after driving it to the port for delivery (2 hour drive, mostly interstate) but I attributed that to the longest road trip in many years and forgot about it.
When I first got to Germany it was my daily driver for about a month and after about 15 minutes of casual commuting I started having hot idle problems. I found a place I could let the car idle (you can get a ticket for letting your car idle more than 30 seconds here) and readjusted at operating temperature (20 minutes stop & go, choke full open, heat riser full open) to hold 750. It was winter around 32F, and cold idle was now up to 1100. I got my other car and the vette sat for the rest of the winter away from the ice and snow.
I got my house in the spring, and my drives became longer with much higher RPM's. The hot idle problem returned. It would sit at 750 for a second, then 700, 750, 650, 700, 550, 600, 450, 500, kaput. It got to where it even died a couple of times as I came down an exit ramp with the clutch in. I re-adjusted hot to 750 and cold idle is now at 1800+, then after 5-10 minutes of low speed driving the idle is down to 1100, and after the 20 minute high speed run it sometimes still just won't hold idle (the same 750 then decay syndrome as above.) I used to have a great carb guy, but now I just have me. I am getting what I pay for. I sit at lights now watching the tach and have had to develop the heel & toe idle procedure.
Exhaust at Idle is slightly fuel rich by smell but no smoke. Idle screws are set to max vacuum.
I hope if you fix James' problem then you will also fix mine! Besides being wrong, it is embarrassing to let it die at a light.
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Re: Lt-1 Stalls at idle
Right now I am working on a date correct 3810 I purchased for my 67 and it's interesting to see the damage leaded gasoline does over the years. The surfaces need a little help with some JB weld and plate glass with 220 wet paper.
One in particular is the main body primary side where the hole is for the accelerator pump channel and it's a gasketed surface that's exposed to full manifold vacuum from the power valve feed hole.
If there are any issues after the gaskets dry these places will leak. That could be some of the problem and the only fix is a close look and patience..
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Re: Lt-1 Stalls at idle
James, I had exactly the same problem with my '70 LT1 except that mine started acting up after about 15 minutes. I was really concerned and thought that something major was wrong with the engine. I took it to a local mechanic who knows vintage corvettes and he suggested a tune up (new plugs, wires, distributor cap, rotors, etc.). Now it runs great and no more stalling problems.
Sometimes it's the basic stuff that you need to check first.
Thanks.Comment
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Re: Lt-1 Stalls at idle
My car is a 72 with the original carb which I replaced both float bowls years ago. The plug wires are about a month old as I mentioned before ,cap , rotor and plugs are all recent or new. I am going to re-tighten the carb to make sure there are no vaccum leaks. Timing is 8 degrees at idle and 31 degrees at 3000 rpm. The dwell was good, I adjusted the lifters according to D. Williams specs. Float level is just below the sight plug hole, not sure what else to check. The only ignition part which I am not sure of its age is the condenser.Comment
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Re: Lt-1 Stalls at idle
hi ---
Do you know anyone with a "loner" square bore carb?
I would say put a test carb on and see what happens. If it continues then your carb is fine and you have OTHER issues. If it runs fine, then you know where the issue lies....
Otherwise - this will drive NUTSO~Comment
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Re: Lt-1 Stalls at idle
Bill thats a good idea. I will contact my carb guy and see if he has one that will match up. I still would like to know what causes this condition.Comment
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Re: Lt-1 Stalls at idle
A few things to think about.
1. When the accel pump was replaced, was the bowl removed from the carb? If so, you may have a leak at the metering block. Now that the car has had some heat cycles, retighten the bowl screws and readjust idle mixture.
2. Have you checked the advance weights in the distrbutor? Are they hanging partially open? (advancing timing thus idle speed) and then relaxing to the point of letting the idle down and dying. Make sure they weights are lubed properly and free of corosion.
3. Pinch off the vacuum lines from the intake feeding the brake booster and all other vacuum operations. Does the idle quality improve? You may be chasing something here also.
Best of luck!
TimComment
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