Engine stumbles off the line
Thread Starter
Racer
Joined: Feb 2014
Posts: 275
Likes: 14
From: Gahanna, Ohio
Engine stumbles off the line
So I have a question for any Holley Carb guru's. I have a mostly stock 350 in my 74, except it does have a torker 2 intake, Holley 750, 1.6 roller rockers, HEI with vac advance. This car runs perfect, no issues with starting, driving etc. Has good vacuum readings and plugs look as they should. Car has great pick up with no bogs or sputters on mild take off. My issue is when I mash the pedal fast it does stumble and bog down, then quickly takes off. A friend suggested moving the vac advance to manifold port which I did with no noticeable improvement. I have car timed to 8 degrees btc, the accelerator pump was set up using YouTube videos and Holly's website, this was the first thing I looked at.
So I am curious at what I am missing, carb is in great shape but was a swap meet buy. I am just trying to bark the tires a wee bit and not sure even with bog fixed it will do that, but more curious about why it's bogging when pedal is mashed.
Thanks for all input and suggestions.
So I am curious at what I am missing, carb is in great shape but was a swap meet buy. I am just trying to bark the tires a wee bit and not sure even with bog fixed it will do that, but more curious about why it's bogging when pedal is mashed.
Thanks for all input and suggestions.
Racer
Joined: Jan 2020
Posts: 272
Likes: 69
From: Reno, NV
You may have seen this thread, but I had the same problem and received a ton of good advice on this thread. For me it ended up being just not tight enough on the acc pump linkage, due to the need for clearance at WOT. Yes, 8* advance is low.
https://www.corvetteforum.com/forums...post1605152607
https://www.corvetteforum.com/forums...post1605152607
Le Mans Master
Joined: Apr 2001
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
What size squirters are you running? What is the total timing you are running? You should look for Lars paper on setting timing. What transmission do you have? Is the engine stock other than what you mentioned? A 1974 corvette had 195 hp with the L48 or 250 with the L82. Neither will be a big performing engine if you have an automatic.
Is my vette stock?? HAHA
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move initial timing to 15* withg the vacuum advance disconnected and the port plugged, then reconnect it, and it will be very close to all in at 3000 rpm. Thats problem number one.
NUmber 2, is it an auto or standard. If its a standard you have to get above 2000 rpm if you are just going to mash it and let out the clutch. An auto should light them up even a lame one with the timing set correct and the accelerator pump working
Number 3 would be how is your idle set screws set and your throttle set screws set. You could be into the transition circuit at idle if it all isnt set correctly. Do you know your vacuum setting at idle and what power valve you have?
If you dont go big on your timing you will never get anywhere, but with your cam start at 12, test it with a burn out and increase 2 degrees and try again. Dont go above 18*, with your cam you may not notice above 14 anyway, but the 1.6 rockers will help you out there giving it a bit more lift and duration
NUmber 2, is it an auto or standard. If its a standard you have to get above 2000 rpm if you are just going to mash it and let out the clutch. An auto should light them up even a lame one with the timing set correct and the accelerator pump working
Number 3 would be how is your idle set screws set and your throttle set screws set. You could be into the transition circuit at idle if it all isnt set correctly. Do you know your vacuum setting at idle and what power valve you have?
If you dont go big on your timing you will never get anywhere, but with your cam start at 12, test it with a burn out and increase 2 degrees and try again. Dont go above 18*, with your cam you may not notice above 14 anyway, but the 1.6 rockers will help you out there giving it a bit more lift and duration
Last edited by Rescue Rogers; May 20, 2022 at 07:06 PM.
Is my vette stock?? HAHA
Joined: Oct 2015
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But it is there at idle and off idle, it does matter
Thread Starter
Racer
Joined: Feb 2014
Posts: 275
Likes: 14
From: Gahanna, Ohio
Thanks for all the help friends. Its a auto trans recently rebuilt and the squirters I have no idea. I assume they are what comes on 750 3310 carbs stock. I will take them out and then buy a couple size ranges up or a kit of them from Jegs. The timing will be moved to 12 and set as you describe and I'll report back. I know the heads are junk, so Iam thinking about doing cam and heads coming up to get more HP.
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Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,153
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
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Increasing squirters isnt going to do much if you arent set up properly.
More timing
Tighten the pump so it just touches the arm no space
Make sure the idle settings are correct
Bring your idle up to 800
More timing
Tighten the pump so it just touches the arm no space
Make sure the idle settings are correct
Bring your idle up to 800
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
So I have a question for any Holley Carb guru's. I have a mostly stock 350 in my 74, except it does have a torker 2 intake, Holley 750, 1.6 roller rockers, HEI with vac advance. This car runs perfect, no issues with starting, driving etc. Has good vacuum readings and plugs look as they should. Car has great pick up with no bogs or sputters on mild take off. My issue is when I mash the pedal fast it does stumble and bog down, then quickly takes off. A friend suggested moving the vac advance to manifold port which I did with no noticeable improvement. I have car timed to 8 degrees btc, the accelerator pump was set up using YouTube videos and Holly's website, this was the first thing I looked at.
So I am curious at what I am missing, carb is in great shape but was a swap meet buy. I am just trying to bark the tires a wee bit and not sure even with bog fixed it will do that, but more curious about why it's bogging when pedal is mashed.
Thanks for all input and suggestions.
So I am curious at what I am missing, carb is in great shape but was a swap meet buy. I am just trying to bark the tires a wee bit and not sure even with bog fixed it will do that, but more curious about why it's bogging when pedal is mashed.
Thanks for all input and suggestions.
You didn't say what your swap meet buy really was in carb type, but bad single plane made for 2500 - 6500 rpm and 750 cfm is not made for WOT off idle. Increasing idle speed, squirter arm, I use a 1/2 inch wood 4 hole spacer on my single plane to increase the signal to my down leg boosters. Holley uses straight leg boosters which are the worst for off idle fuel flow. and possibly changing the carb secondary cam color to slow the secondary opening. I also didn't see tranny type.
I have a 5 speed and 4.11 rear end and I have done everything possible so it doesn't "Bark the tires" Including sticky 335 rear tires, so it takes off instead of spinning the tires
Edelbrock 5001 Small Block Chevy Torker II Intake Manifold (speedwaymotors.com)
Le Mans Master
Joined: May 2007
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From: North tonawanda NY
What size squirters are you running? What is the total timing you are running? You should look for Lars paper on setting timing. What transmission do you have? Is the engine stock other than what you mentioned? A 1974 corvette had 195 hp with the L48 or 250 with the L82. Neither will be a big performing engine if you have an automatic.
I had this bog with my old edelbrock 650 carb and also with the holley street avenger 670 I replaced it with. for me removing the slack in the squirter arm did the trick and going to an orange squirter cam helped eliminate the bog. My new QF cam didnt have the issue.
Last edited by augiedoggy; May 21, 2022 at 09:22 AM.
Le Mans Master
Joined: May 2007
Posts: 5,018
Likes: 1,118
From: North tonawanda NY
Thanks for all the help friends. Its a auto trans recently rebuilt and the squirters I have no idea. I assume they are what comes on 750 3310 carbs stock. I will take them out and then buy a couple size ranges up or a kit of them from Jegs. The timing will be moved to 12 and set as you describe and I'll report back. I know the heads are junk, so Iam thinking about doing cam and heads coming up to get more HP.
Last edited by augiedoggy; May 21, 2022 at 09:33 AM.
Thread Starter
Racer
Joined: Feb 2014
Posts: 275
Likes: 14
From: Gahanna, Ohio
You guys are giving me some things to think about. I don't think this car is set up right. I played with it today, carb had 25 squirters, I went up to 28 and moved timing up to 12 and it did improve but still has a very slight hesitation and still doesn't bark the tires. I do have a dual plane I can put on so maybe I'll do that tomorrow. I'll report back.So to sum up changing to bigger squirters and timing helped it a lot, but still not where I want it.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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keep going with the timing
Thread Starter
Racer
Joined: Feb 2014
Posts: 275
Likes: 14
From: Gahanna, Ohio
Well friends, I can report back that this Vette is like a new beast. So playing with the squirters really didn't seem to solve the main bogging issue on Sat. I had a performer manifold sitting around and decided to swap out the Torker. After installing the dist wrong and hearing lots of detonation, I realized my mistake. I put it in one tooth off and it ran crappy and sounded like marbles were busting the rods. I only ran it at idle for a few minutes and shut it off, don't seem to have damaged anything. I re timed the dizzy via the old TDC method and got it right the second time around.
She started right up and only needed a slight adjustment on timing and mixture. So I ended putting on performer dual plane, 31 suirters, and fixed the timing to 15 and now she jumps and squeals like never before. No more bogging. Thanks for all the help and advice!!!
She started right up and only needed a slight adjustment on timing and mixture. So I ended putting on performer dual plane, 31 suirters, and fixed the timing to 15 and now she jumps and squeals like never before. No more bogging. Thanks for all the help and advice!!!
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Well friends, I can report back that this Vette is like a new beast. So playing with the squirters really didn't seem to solve the main bogging issue on Sat. I had a performer manifold sitting around and decided to swap out the Torker. After installing the dist wrong and hearing lots of detonation, I realized my mistake. I put it in one tooth off and it ran crappy and sounded like marbles were busting the rods. I only ran it at idle for a few minutes and shut it off, don't seem to have damaged anything. I re timed the dizzy via the old TDC method and got it right the second time around.
She started right up and only needed a slight adjustment on timing and mixture. So I ended putting on performer dual plane, 31 suirters, and fixed the timing to 15 and now she jumps and squeals like never before. No more bogging. Thanks for all the help and advice!!!
She started right up and only needed a slight adjustment on timing and mixture. So I ended putting on performer dual plane, 31 suirters, and fixed the timing to 15 and now she jumps and squeals like never before. No more bogging. Thanks for all the help and advice!!!
The 2101 will signal a 750 3310 well....and compensate for the venturis being too large.
Put a 650 on this engine and it will run even better.......but if the 750 is going good....leave it alone.
Good job.
Jebby