Drag racing
 

I have just started to drag and my truck surges every time I floor it. It has a chevy small block 350 with electric choke Holley 4 barrel carb. Any tips to help me out?
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Re: Drag racing
 

Have to assume you are just drag racing your street build truck...so, your surging issue could be a lot of things...

Sounds like fuel supply loss of pressure ...starting at the fuel tank...could be wrong style of gas cap, clogged strainer on the pickup, split pickup tube in tank, crushed fuel supply line, bad fuel pump, bad settings on carb float level...depending on how fast you are spinning the engine, your fuel supply pipe size may be too small..

Other possible causes, retarded cam action due to bad timing chain/gear, bad ignition timing, weak valve springs...your surge may be valve float...lack of correct advance curve...

Have fun my friend...:chevy::chevy::chevy:

Re: Drag racing
 

Ok. I did have the carb tuned and the engine timed for drag racing. And it is a street build that I drive daily
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Re: Drag racing
 

Get it to surge then kill the engine, pull a few plugs and see what the story is.

Re: Drag racing
 

Ok I did that and they r acting normal not sure what's wrong but I don't want to have it taken to the track and lose because I can't run properly
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Re: Drag racing
 

What if I ran a higher octane level would that help? Or would it make it worse?
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Re: Drag racing
 

And I just put a higher pressure fuel pump on there with a higher carb setting
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Re: Drag racing
 

I would start with my previous list...fuel cap, tank, suction lines, fuel pump...remember, these gas lines and pumps are designed for around 4000 rpm use when in perfect condition...not after 40 plus years of use...

How much fuel pressure do you have at the carb during a run? I will bet its too low...:chevy::chevy::chevy:

It's running about 23.5 for pressure at the carb. Which I'm not sure is right tho. I checked the fuel lines and the look newer but there is still some age on them and they r 1/2 inch hose. Is this to small?
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Re: Drag racing
 

Could there be an electrical issue?
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Re: Drag racing
 

23.5 psi is way too much fuel pressurefor a carbureted engine, I would bet this is the culprit

Re: Drag racing
 

What carb are you running? I have a QFT 750 and run about 6.5lbs. 23.5 lbs will cause the float needles to not seat. If you have windows on the float bowls, the gas should be about halfway up.

Re: Drag racing
 

Ok. Just checked it again and now it's running about 5 psi. And it's qjet Holley 650 cfm. I think
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Re: Drag racing
 

If was a faulty pressure gauge
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Re: Drag racing
 

23.5 is crazy high for a carb, any carb, to handle...there should be a regulator between the pump (obviously not a standard mechanical pump)...and the carb...

1/2 line ...do you mean outside diameter or internal diameter...1/2 outside is most likely 1/4 id....too small...

The high pressure small diameter line will cause a fuel starvation situation...

Double check the pressure at the carb, at idle, then under an actual run condition under load...

Tell us in detail, what you have in the fuel system, beginning at the fuel tank...including any electric pumps, filters, line size outside and material, etc


:chevy::chevy::chevy::chevy::chevy:

Re: Drag racing
 

There is no electric fuel pump it's a mechanical pump. Thr line is 1/2 diameter all the way to the pump. There is a outside fuel filter of the carb then it runs into the carb which is running at 5 psi. Then it runs to the engine. That's all I know on it.
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Re: Drag racing
 

I run 91 octane at the pump then I add octane booster
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Re: Drag racing
 

It is powered by a 7.5 mechanical fuel pump
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Re: Drag racing
 

this is probably a dumb question but exactly what do you mean by surge? just making sure I'm following you. Also if it is a holley650, on the front of the air horn will be a 4 digit number. it will be something like 4150, 4160, something like that. Do you have the site windows on the side of the bowls? mis-adjusted float level can cause various issues.

Others are also on the right track with the fuel line size, etc... Do you know if the acc pump has been changed out for a bigger diaphram?

Re: Drag racing
 

What I mean by surging is that it cuts in and out. And I just had it tuned for racing and timed at the same time and it's got racing spark plugs on it
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Re: Drag racing
 

Top things I can think of:
lack of fuel caused by insuficient supply.
Floats set too low.
Clogged fuel filter.
unlikely but possibly the tranny / torque converter slipping make it feel like a surge.

Earlier you said the fuel pressure was 5 lbs. If you have an adjustable regulator, take it up to 6 and see if it helps.

It has been too long a week to think very straight right now. At my age when you get past about 70 hours/week you start getting tired....

If something else comes to mind, I'llpost it.

Re: Drag racing
 

Unless you have updated the fuel lines in some way, I'm a little skeptical of the 1/2" number. Is that the outside diameter of the tubing? If so, that is 3/8" steel tubing, which is stock. How many horsepower are you putting out? Do you have a dyno slip?

It has a rubber hose the kid I bought it from had changed it from a steel to rubber. It makes about 340 horse. And I don't know what a dyno slip is?
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Re: Drag racing
 

All rubber fuel line? Possibly it could be collapsing

It could be. I pretty sure their newer houses tho. But I'll check them in the morning and see if they r collapsed
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