Accelerator Pump - 77 Vette
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
Accelerator Pump - 77 Vette
Last year I had my quadrajet rebuilt by Lars. Now I have symptoms of a bad accelerator pump. Could it be something else? Before I put the car away for the winter I added gas stabilizer and filled the tank. Can the alcohol degrade the accelerator pump that quickly? If so, can I get one designed to handle the 10% alcohol better?
Race Director
Joined: May 2006
Posts: 18,690
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with the engine off and the choke open do you see gas squirt into the primary side of the carburetor when you open the throttle? Lar's rebuilds typically have a alcohol tolerant pump. What are the symptoms you are experiencing?
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
I will take a look later today to look for the squirt of gas. If I slowly increase the throttle to full throttle it pulls well. If I try to quickly floor it, it stumbles and almost dies and then will recover and accelerate. Last year it ran great.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
I knew he would and that is what was throwing me. I took off the air cleaner with the car off and the accelerator pump seems to be giving a decent squirt into both primary barrels. It must be something else. I wonder if it could be the timing advance weights.
Race Director
Joined: May 2006
Posts: 18,690
Likes: 2,572
have you checked the tension on the secondary air valve flap, it would have been correctly adjusted during the rebuild but I guess the set screw could have loosened. You should feel some resistance when pushing down on it with a finger and the engine off.
when the engine is fully warmed up and running is the choke completely opened?
when the engine is fully warmed up and running is the choke completely opened?
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Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
have you checked the tension on the secondary air valve flap, it would have been correctly adjusted during the rebuild but I guess the set screw could have loosened. You should feel some resistance when pushing down on it with a finger and the engine off.
when the engine is fully warmed up and running is the choke completely opened?
when the engine is fully warmed up and running is the choke completely opened?
I tested the accelerator pump yesterday after I drove the car and it was fully warmed up and the choke was fully opened.
The odd thing is that if I floor it slowly, say in about a second, it accelerates nicely. If I quickly floor it it almost stalls, kind of bucks and then goes. Around 4K RPM the acceleration drops, but I think that is not too out of the ordinary with a '77 L48.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
I"m having the same issue on my 77 l48. Had a rebuild by lars too. But mine has had some stumbles since I put it on. I thought about moving the accelerator pump rod to the second hole to give more fuel. Have not fiddled with it much though being that I rarely floor it.
Last edited by Strokemyaxe; May 22, 2015 at 12:42 AM.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
I looked at more things this evening and so far haven't found anything definitive. Before it was fully warmed up I stabbed the throttle and the hesitation wasn't as bad, so perhaps I have a vacuum leak somewhere causing it to run lean. I checked the hoses I could and made sure the heat riser was open and checked out everything external on the carb I could see. I also made sure the distributor was tight. After the car was fully warmed up I stabbed the throttle again and it hesitated more. If I gradually go to full throttle there is no hesitation. It revs well up to around 4K RPM and then the engine is weak, but think that is typical of the L-48. The engine was rebuilt by the PO around 3,000 miles ago, but I don't know the details. I did add a dual exhaust with no cats and it is nice.
It sounds like you may have a different issue than I do. Have you recently checked to make sure the carb is torqued to spec on the manifold? 12 lb/ft or 144 lb/in.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
Before Lars rebuilt the carb it ran poorly. It stalled on me once and was often hard to start. After having Lars rebuild the carb, setting the timing and changing the plugs, wires and distributor cap it ran great for the Fall season.
I looked at more things this evening and so far haven't found anything definitive. Before it was fully warmed up I stabbed the throttle and the hesitation wasn't as bad, so perhaps I have a vacuum leak somewhere causing it to run lean. I checked the hoses I could and made sure the heat riser was open and checked out everything external on the carb I could see. I also made sure the distributor was tight. After the car was fully warmed up I stabbed the throttle again and it hesitated more. If I gradually go to full throttle there is no hesitation. It revs well up to around 4K RPM and then the engine is weak, but think that is typical of the L-48. The engine was rebuilt by the PO around 3,000 miles ago, but I don't know the details. I did add a dual exhaust with no cats and it is nice.
It sounds like you may have a different issue than I do. Have you recently checked to make sure the carb is torqued to spec on the manifold? 12 lb/ft or 144 lb/in.
I looked at more things this evening and so far haven't found anything definitive. Before it was fully warmed up I stabbed the throttle and the hesitation wasn't as bad, so perhaps I have a vacuum leak somewhere causing it to run lean. I checked the hoses I could and made sure the heat riser was open and checked out everything external on the carb I could see. I also made sure the distributor was tight. After the car was fully warmed up I stabbed the throttle again and it hesitated more. If I gradually go to full throttle there is no hesitation. It revs well up to around 4K RPM and then the engine is weak, but think that is typical of the L-48. The engine was rebuilt by the PO around 3,000 miles ago, but I don't know the details. I did add a dual exhaust with no cats and it is nice.
It sounds like you may have a different issue than I do. Have you recently checked to make sure the carb is torqued to spec on the manifold? 12 lb/ft or 144 lb/in.
Thanks
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
If Lars rebuilt that unit last year and it is now having "problems", he would want to know about it and also offer ideas on what the problem might be. You should just contact him at V8FastCars@msn.com.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
I don't think it is the carb. Last night I had the car warming up while I worked on putting the kick panel back on. The choke had already come off and it was idling a little rough. A minute or so later the idle was suddenly smooth and I took it for a drive and I noticed no hesitation. I have some kind of intermittent issue, perhaps with the distributor and timing or something vacuum operated. I have noticed once in a while the car idles at 500 RPM and at other times more like 650 in drive. When it idles at 500 it feels rough by comparison. Plugs, wires, distributor cap and rotor are almost new. The heat riser has been disabled in the off position.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
Weather has been so bad here lately, I'm thinking about modding my vette to a boat. I'll keep you guys updated with my progress on that.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
Sooo. My hesitation/stumble seemed to clear up a bit with the tightening of the carb! Thanks a lot for that tip. I use the thick spongy gasket as opposed to the thin one for my carb to manifold and I guess I was just leaking at the base of the carb on acceleration.
Weather has been so bad here lately, I'm thinking about modding my vette to a boat. I'll keep you guys updated with my progress on that.
Weather has been so bad here lately, I'm thinking about modding my vette to a boat. I'll keep you guys updated with my progress on that.