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Discussion Starter #1
I need some assistnace. My 68 GTO runs well, however it will surge when cruising and accelerating. It is a 400, 4 barrel, 4 speed, 355 rearend, new 750 edlebrock carb, edlebrock performer intake, new thumer comp cam (475 lift, 107 lobe seperation), manual fuel pump. Starts up and idles just fine, but will hesitate and surge when cruising down the road. I have always ran a manual fuel pump and had no problems. Any ideas?? Do I need an electric pump?Thanks
 

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I need some assistnace. My 68 GTO runs well, however it will surge when cruising and accelerating. It is a 400, 4 barrel, 4 speed, 355 rearend, new 750 edlebrock carb, edlebrock performer intake, new thumer comp cam (475 lift, 107 lobe seperation), manual fuel pump. Starts up and idles just fine, but will hesitate and surge when cruising down the road. I have always ran a manual fuel pump and had no problems. Any ideas?? Do I need an electric pump?Thanks
no you dont "need" an electric pump. are you sure its even a fuel problem?
 

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Discussion Starter #3
I may need to check my timing. I am running 9 advanced at idle right now. As I said I just installed a new thumper cam last week and set it back to 9 advance. I may need to advance the timing more. I called Comp Cams and they said 15 advance at idle, that sounds like alot to me.
 

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Could be electrical also. Coi,l bad plug wire or spark plug. I would shut the car off and pull over on a test drive when it acts up and pull some plugs to see whats up.
 

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I may need to check my timing. I am running 9 advanced at idle right now. As I said I just installed a new thumper cam last week and set it back to 9 advance. I may need to advance the timing more. I called Comp Cams and they said 15 advance at idle, that sounds like alot to me.
I'd recommend setting timing to 33-34 degrees TOTAL at oh... 2800 rpm (use a timing tape on the balancer or an 'advance' timing light) and just let your initial be whatever it falls after you do that. See if the motor likes that ---- then add a degree or two more at a time until you find the point where power starts to drop off, then back it off to the peak.

Which part number cam is it... or what's the intake/exhaust duration at .050? If it's a lot "rowdier" than stock your carb might need a little recalibration in order to deal with a reduced vacuum signal. (Larger air bleeds and such).

Bear
 

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I just fixed the same problem in my '65 GTO with tripower. I thought it was lean jetting or fuel. Turned out, I was getting too much spark advance. I took it down from 50 degrees to a total of 35 degrees and solved all of my problems. You can limit the amount of vacuum advance by installing a stop for the vac. advance rod on the vac advance........
 
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