Stall when hot
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
Stall when hot
Hi,
I know there are several threads about this topic, but just looking for some fresh ideas of what may be my problem... I have a 1970 base original engine (350/300hp) with a 3-speed automatic (THM400) which was finished last Nov after a 19 year restoration. I picked up my car last Nov and drove about 600 miles to bring it back home. Didn't notice anything out of the ordinary during that trip where I stopped a few times for gas and all that. Got home, drove maybe once after that before having to put it up for winter storage (added Stabil to the gas).
So this spring took it out, drove it a bit near my house, and notice a "hesitation" at times from a stop to get going. It didn't stall but I could feel it hesitating.
Let me start off by saying that I purchased a used Quadrajet for it last Oct and had it rebuilt by Lars last Oct/Nov, so I know that it was done right, and am not looking for anything related to the carburetor. Car starts good cold, starts good hot, idles good when cold, idles good when hot... idles good when in gear at a stoplight (around 650rpm I believe)... so I'm looking to see if my issue is related to something other than the carb, because I know Lars' reputation and he is the best out there for Quadrajets.
So this past weekend decided to take it out with some Corvette friends for a longer ride (50-60 miles). When I left my house it obviously wasn't at maximum temperature, and we stopped at a couple of places, and I didn't see any issues. So we kept riding and did about 30-40 miles, and on the trip there were some hilly areas, and going up a hill under load, I could feel like it didn't have all it's power, it seemed like it was hesitating... on a straightaway at speed 40-50-60 mph and if I accelerated, it felt normal. We stopped again for a while, and after we took off I could feel it hesitate (almost stall) from a standstill. Drove some more, and we came up to a stop light... when the light turned green, I pressed the accelerator as normal, and it stalled. Put in neutral, started it no problem, and gently feathered the accelerator so it wouldn't stall. Arriving near my home it did it a couple of times, from a standstill if I pressed on the accelerator, it stalled. If I very slightly pressed it so that it wouldn't stall, then it would be ok. But a little unnerving if you have to turn left and it stalls in the middle of the road.
I know that I also have a vacuum problem because during the ride I had to use my wipers (the wiper door raises fine), and when we stopped at our destination and I turned off the engine, both my headlights popped up and my wiper door raised. Can a vacuum issue like this cause a stall issue?
Anyhow, just wanted some fresh ideas form guys who know a lot more about these cars than I presently do...
Thanks...
I know there are several threads about this topic, but just looking for some fresh ideas of what may be my problem... I have a 1970 base original engine (350/300hp) with a 3-speed automatic (THM400) which was finished last Nov after a 19 year restoration. I picked up my car last Nov and drove about 600 miles to bring it back home. Didn't notice anything out of the ordinary during that trip where I stopped a few times for gas and all that. Got home, drove maybe once after that before having to put it up for winter storage (added Stabil to the gas).
So this spring took it out, drove it a bit near my house, and notice a "hesitation" at times from a stop to get going. It didn't stall but I could feel it hesitating.
Let me start off by saying that I purchased a used Quadrajet for it last Oct and had it rebuilt by Lars last Oct/Nov, so I know that it was done right, and am not looking for anything related to the carburetor. Car starts good cold, starts good hot, idles good when cold, idles good when hot... idles good when in gear at a stoplight (around 650rpm I believe)... so I'm looking to see if my issue is related to something other than the carb, because I know Lars' reputation and he is the best out there for Quadrajets.
So this past weekend decided to take it out with some Corvette friends for a longer ride (50-60 miles). When I left my house it obviously wasn't at maximum temperature, and we stopped at a couple of places, and I didn't see any issues. So we kept riding and did about 30-40 miles, and on the trip there were some hilly areas, and going up a hill under load, I could feel like it didn't have all it's power, it seemed like it was hesitating... on a straightaway at speed 40-50-60 mph and if I accelerated, it felt normal. We stopped again for a while, and after we took off I could feel it hesitate (almost stall) from a standstill. Drove some more, and we came up to a stop light... when the light turned green, I pressed the accelerator as normal, and it stalled. Put in neutral, started it no problem, and gently feathered the accelerator so it wouldn't stall. Arriving near my home it did it a couple of times, from a standstill if I pressed on the accelerator, it stalled. If I very slightly pressed it so that it wouldn't stall, then it would be ok. But a little unnerving if you have to turn left and it stalls in the middle of the road.
I know that I also have a vacuum problem because during the ride I had to use my wipers (the wiper door raises fine), and when we stopped at our destination and I turned off the engine, both my headlights popped up and my wiper door raised. Can a vacuum issue like this cause a stall issue?
Anyhow, just wanted some fresh ideas form guys who know a lot more about these cars than I presently do...
Thanks...
Tech Contributor
Joined: Aug 1999
Posts: 14,375
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
Denis -
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
Last edited by lars; Apr 25, 2021 at 01:44 PM.
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
What he said. Pretty sure its a fuel problem based on the symptoms and there can be a lot wrong that's unrelated to Lars' work. Stabil is only good for about 30 days. I have quit using it. The gas we get nowadays is crap. I have a friend who worked for Shell Oil for many years and back in my flying days guys were using automotive gas in airplanes because some grades of aviation fuel were getting hard to get and car gas was cheaper. His comment was "there is no way I would ever put that stuff in an airplane - you wouldn't beleive the crap we put in it." And that was before they started putting alcohol in it. This year I had to put five gallons of fresh premium in my car just to get it to run well enough to get to the gas station. I would bet the family ranch you've got a fuel delivery problem somewhere - bad fuel, bad pump, clogged filter. Let us know how it works out.
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
Denis -
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
What he said. Pretty sure its a fuel problem based on the symptoms and there can be a lot wrong that's unrelated to Lars' work. Stabil is only good for about 30 days. I have quit using it. The gas we get nowadays is crap. I have a friend who worked for Shell Oil for many years and back in my flying days guys were using automotive gas in airplanes because some grades of aviation fuel were getting hard to get and car gas was cheaper. His comment was "there is no way I would ever put that stuff in an airplane - you wouldn't beleive the crap we put in it." And that was before they started putting alcohol in it. This year I had to put five gallons of fresh premium in my car just to get it to run well enough to get to the gas station. I would bet the family ranch you've got a fuel delivery problem somewhere - bad fuel, bad pump, clogged filter. Let us know how it works out.
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
Denis -
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
I've seen some funny stuff happen to carb parts with the Stabil additives. Do a quick check to see if the accel pump has swollen up and been destroyed - this would cause your hesitation and stalling issue when stepping on the gas. After the engine has been running, shut it down. Look down the carb's primary venturies and move the throttle lever. Verify that there is a near-instant fuel squirt from the discharge nozzles in both throttle bores. The fuel squirt should occur with very little throttle movement, and it should be a nice strong stream in both bores. If this is not happening, the accel pump has failed and will need to be replaced.
Lars
Is changing the accelerator pump a DYI project? I've already ordered a kit which includes an accel pump, and some gaskets... Can I assume that you only have to remove the airhorn and not the entire carburetor from the car? Is there something I need to watch out for if I do this? Should I put a new airhorn gasket if it is removed? Any advice would be appreciated. If this is not a DYI project, I'll find someone that can work on it.
As for additives, I'm likely going to stop using Stabil, and would it be the same thing for an Octane Booster? Should that also be avoided?
Thanks.
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Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
Quick update...
I finally got around to changing the accelerator pump in my carb... a big thanks to Lars for identifying the potential issue and for his detailed instructions on how to replace it. So after replacing the accel pump, reinstalled everything back together... started fine, and visually checked out the gas coming out of the jets, and it was certainly a steady stream instead of a sputter... took it out for a drive, and wasn't hesitating at all, never stalled, and went very well on an incline under load... it appears to have solved my problem.
So another thanks to Lars for the help.
Quick video of the jets...
I finally got around to changing the accelerator pump in my carb... a big thanks to Lars for identifying the potential issue and for his detailed instructions on how to replace it. So after replacing the accel pump, reinstalled everything back together... started fine, and visually checked out the gas coming out of the jets, and it was certainly a steady stream instead of a sputter... took it out for a drive, and wasn't hesitating at all, never stalled, and went very well on an incline under load... it appears to have solved my problem.
So another thanks to Lars for the help.
Quick video of the jets...