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06-23-2017, 06:04 PM
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#1 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 06:57 PM
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#2 |
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Moderator
 
Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,157
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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... 
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06-23-2017, 07:39 PM
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#3 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 07:41 PM
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#4 |
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Registered User
Join Date: Sep 2014
Location: Richfield, Oh
Posts: 112
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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.
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06-23-2017, 07:48 PM
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#5 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 07:52 PM
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#6 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 07:53 PM
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#7 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 07:55 PM
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#8 |
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Moderator
Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,157
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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...
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06-23-2017, 07:59 PM
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#9 | |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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Quote:
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06-23-2017, 08:05 PM
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#10 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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Re: Drag racing
Could there be an electrical issue?
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06-23-2017, 08:34 PM
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#11 |
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Senior Member
 
Join Date: Jun 2005
Location: Winona Lake, IN
Posts: 6,212
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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
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06-23-2017, 08:45 PM
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#12 |
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Registered User
Join Date: May 2017
Location: Parker, CO
Posts: 130
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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.
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72 Chevy C10 383/465 69 Corvette convertible 454/650 |
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06-23-2017, 09:20 PM
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#13 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 09:22 PM
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#14 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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Re: Drag racing
If was a faulty pressure gauge
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06-23-2017, 09:25 PM
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#15 |
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Moderator
Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,157
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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
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06-23-2017, 09:40 PM
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#16 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 09:41 PM
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#17 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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Re: Drag racing
I run 91 octane at the pump then I add octane booster
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06-23-2017, 09:46 PM
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#18 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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Re: Drag racing
It is powered by a 7.5 mechanical fuel pump
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06-23-2017, 09:46 PM
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#19 |
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Registered User
Join Date: May 2017
Location: Parker, CO
Posts: 130
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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?
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72 Chevy C10 383/465 69 Corvette convertible 454/650 |
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06-23-2017, 10:04 PM
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#20 |
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Registered User
Join Date: Jun 2017
Location: Davis ok
Posts: 91
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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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06-23-2017, 10:42 PM
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#21 |
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Registered User
Join Date: May 2017
Location: Parker, CO
Posts: 130
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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.
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72 Chevy C10 383/465 69 Corvette convertible 454/650 |
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06-23-2017, 10:53 PM
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#22 |
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Who Changed This?
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,095
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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?
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06-23-2017, 11:06 PM
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#23 | |
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Registered User
Join Date: Jun 2017
Location: Davis ok
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Quote:
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06-24-2017, 12:02 AM
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#24 |
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Special Order
  
Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,863
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Re: Drag racing
All rubber fuel line? Possibly it could be collapsing
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06-24-2017, 12:15 AM
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#25 | |
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Registered User
Join Date: Jun 2017
Location: Davis ok
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Quote:
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