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81 Monte Carlo SBC 357
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Discussion Starter · #1 ·
Ok well i finally finished building a 357 for my 81 Monte and im having a slight issue and im not sure what could be causing it. Ok ill try my best to explain, after the motor is warmed up you can give it all the gas you want and it will respond very nicely and it has no problems at all. the issue comes into play when the motor is under load. For example if i were to slap it into drive and try to take off quick the motor will start to sputter and stall. Jeeze i hope someone understands. Some times it will pop through the carb also but not often.

Its a 72 010 350 bored 40 over with a mild cam and 2.02 heads with 74-76 cc chambers. I thought it could be a fuel issue so i filled it up with a bunch of fresh gas and some fuel line antifreeze and got a new fuel filter. Also thought it was a timing issue but im pretty sure it isn't iv got it dead nuts were it needs to be. Also thought the distributer could be the problem so i had another one laying around that i slapped in and no luck. Only thing i haven't done yet is clean my carb which i will do tomorrow. If you need more info just ask. I am sure you will. Thanks in advance
 

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http://www.warsprints.com
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Tubbed357 said:
Ok well i finally finished building a 357 for my 81 Monte and im having a slight issue and im not sure what could be causing it. Ok ill try my best to explain, after the motor is warmed up you can give it all the gas you want and it will respond very nicely and it has no problems at all. the issue comes into play when the motor is under load. For example if i were to slap it into drive and try to take off quick the motor will start to sputter and stall. Jeeze i hope someone understands. Some times it will pop through the carb also but not often.

Its a 72 010 350 bored 40 over with a mild cam and 2.02 heads with 74-76 cc chambers. I thought it could be a fuel issue so i filled it up with a bunch of fresh gas and some fuel line antifreeze and got a new fuel filter. Also thought it was a timing issue but im pretty sure it isn't iv got it dead nuts were it needs to be. Also thought the distributer could be the problem so i had another one laying around that i slapped in and no luck. Only thing i haven't done yet is clean my carb which i will do tomorrow. If you need more info just ask. I am sure you will. Thanks in advance
What type of carb? Could be that the pump shot (squirter) is too small or the accelerator pump is not working correctly.
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #3 ·
Well to tell you the truth i dont know anything bout the carb other than its a small Holley. Actually today i gave it a very thorough cleaning and that didnt help at all.
I looked at it for a few mins and started to think that maybe it could be 1 of 2 carbs that were running on some sort of duel quad setup haha. The guy i got it from said it was sitting around for years and didnt know much about it. Ill tell you the numbers on the tag if that will help at all.

Guna swap in another carb tomorrow and see if it makes a difference at all, i have a good feeling it will.
 

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http://www.warsprints.com
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Tubbed357 said:
Well to tell you the truth i dont know anything bout the carb other than its a small Holley. Actually today i gave it a very thorough cleaning and that didnt help at all.
I looked at it for a few mins and started to think that maybe it could be 1 of 2 carbs that were running on some sort of duel quad setup haha. The guy i got it from said it was sitting around for years and didnt know much about it. Ill tell you the numbers on the tag if that will help at all.

Guna swap in another carb tomorrow and see if it makes a difference at all, i have a good feeling it will.
I also have a feeling it's the carb. Let us know what happens after you change it.
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #5 ·
Well i found out what kind of carb it is by asking here on the forums. It is a 600 CFM Holley Vacuum Secondary Carb from a Ford 351 Marine engine. Now is it bad to have a marine carb on a street motor is there something i can do to it so the motor gets more gas, maybe something like jetting but im not sure.
 

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try changing jets and accelerator pump..blubbering is usually wrong jet size,, if i remember correctly..if i'm wrong i'm sure the tech guys will correct me.
too many years and way too many beers to be sure of anything anymore..
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #7 ·
Well guys i bought another carb its a Holley 750 vac secondaries manual choke.. Unfortunately i am still having the same issue. I also popped the intake off and sealed up the intake gaskets which actually caused it to run much smother now so there was a small vac leak. But the problem is still there any suggestions guys thanks.
 

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WFO
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It's unlikely (not impossible) that two different carbs would have the same exact (it IS the same?) probs as before, but still, be sure there is a strong squirt of gas from the accelerator pump "squirters" when you work the throttle. Do the idle mixture screws have any effect on the idle speed or 'quality' if you screw them in or out? If no on either point, get back to us. If all's OK so far,

Time to time it.

DETERMINING TDC and MAKE A TIMING TAPE will assist you if there's any problem w/the timing tab on the timing chain cover OR the mark on the balancer being wrong. If your timing light doesn't read advance, go ahead and make the timing tape.

Get a timing light on it and see what the initial timing is (at idle, vacuum advance hose off and plugged), and what the TOTAL timing is.

This will require you to speed up the engine until the timing mark quits rising up the timing tape that you made- or the info on the timing light if it reads advance. Vac can still disconnected and plugged.

You want no more than 34-36 degrees TOTAL, if it is anything else, set the timing to 34-36 degrees and lock it down for now.

Now check it again at idle and see where it is. This is for starters, there is more- to come later, after you've accomplished these tasks!

Good luck, ask if there's any questions.
 

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More for Less Racer
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It is still likely for two different carbs to have the same problem if the pump shot is too small on both carbs.

What intake are you using?? A single plane will frequently need to have a larger pump shooter (nozzle) and/or a larger pump cam than the as delivered size on most Holley carbs, especially the vacuum secondary models.

Your description in the first post is classic too small pump shot symptom.

If you put your foot to the floor from a dead stop and the engine "coughs", it is always a lean condition, and if there are no vacuum leaks then it needs more pump shot.
 

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Hi,
First check for proper fuel level (fuel at bottom of sight glass)
check again for vacuum leaks, then check fuel pressure & volume have you changed the fuel filter on this vehicle?
I think this is the problem low fuel pressure caused by either the pump going bad or a clogged filter.
Rich
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #12 ·
richard stewart 3rd said:
Hi,
First check for proper fuel level (fuel at bottom of sight glass)
check again for vacuum leaks, then check fuel pressure & volume have you changed the fuel filter on this vehicle?
I think this is the problem low fuel pressure caused by either the pump going bad or a clogged filter.
Rich
Iv got an inline fuel filter that i just put on, it flows great. Also iv got an inline pressure gauge that reads about 7-8 psi so im good in that area.. Thanks tho

Also iv got a single plane intake, i believe it was an edelbrock scorpion haha..
When i get some time ill def do my timing over..
Thanks for all the help guys
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #14 ·
ericnova72 said:
The Scorpion intake is the "father" of the Victor Jr as the Vic Jr is what was the updated casting made to replace it, and just like the Vic Jr it usually needs a bigger pump shot.

Ahh i see,, hmm is there any way to tell that that is my issue. I mean there were times when i pulled my plugs and they were completely sooted over.
Im still going to do my timing just so i can eliminate that factor
 

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More for Less Racer
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What the plugs look like will have nothing to do with the pump shot. The plugs will soot over with too much idle time or an overly rich idle calibration, a cam with a decent amount of overlap, or too cold a heat range plugs.

The pump shot is just there to cover the lean hole in the fuel curve that occurs when you suddenly slap the throttle open, it prevents that backfire cough that will happen if the mixture is too lean. Once the rpm and air speed are up you don't have that problem, which is why it drives fine from a good roll but won't go without a stumble from a dead stop - the rpm isn't high enough to draw fuel out of the carb into the air stream and the engine stumbles.

This all assumes you have the timing correct first.
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #16 ·
Actually i never said it drove fine with a roll haha,, to tell you the truth the same issue happens if i am rolling and give it a little gas. It seems it doesn't matter if i am rolling or still the problems is still there. I can be driving and slowly ease in on the gas and it will still happen. I just need to redo my timing and ill give you an update. Im feeling more and more that is my issue, it just makes it more complicated that i dont have a dial back timing light. Ill make it work tho haha
 

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WFO
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Tubbed357 said:
i dont have a dial back timing light. Ill make it work tho haha
Hint- Figure the circumference of your damper. An 8" damper would be pi (3.14) x diameter (8") = 25.12".

Since a circle is 360 degrees, 10% 0f a circle is 36 degrees- which happens to also be the max total timing for a SBC w/o 'fast burn' combustion chambers.

So, a piece of tape marked at 2.5" (~10% of the circumference of 25.12") will represent 36 degrees of an 8" diameter damper, when read on the "0" (TDC) mark of the timing tab. You can just use a Sharpie and put a line on the damper if you want.

If the damper is other than 8", do the math.

EDIT- Just saw what intake you have- and a single plane intake may need a bigger pump shot.

But doing the timing is needed anyway, so no loss there. Getting the pump shot correct AND the timing curve sorted out will feel like you got an extra 50 HP! lol
 

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81 Monte Carlo SBC 357
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46 Posts
Discussion Starter · #18 ·
Sorry i havent been able to give u guys an update, iv been waiting for some decent weather and haven't really been getting much of it. Right now there is like 6 inches of snow on my car haha.
 
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