engine is surging while driving

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duster360

duster360

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What would cause the engine to surge while driving, low speed and at highway speed? I can notice it better at highway speed because I am running at a steady speed.
 
Hmmm I wonder if its related to your timing issue?
Idles good but not good under load?
Dist bushing worn? Bent shaft?
 
Back in the 70s I had a Duster that did that. Turned out to be the prefilter on the pick-up in the gas tank.
 
Oaktree said:
Back in the 70s I had a Duster that did that. Turned out to be the prefilter on the pick-up in the gas tank.
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I need to check all the filters front to rear. Meant to do that before I fired this new engine. Got excited and ahead of myself.
 
I'm gonna throw a guess out that you are experiencing lean surge; fatten up your carb just a tiny bit.
 
Oaktree said:
Back in the 70s I had a Duster that did that. Turned out to be the prefilter on the pick-up in the gas tank.
Click to expand...
This. Surging is usually related to a fuel delivery problem. I had it happen when my later year (70+) tank venting system wasn't hooked up properly. Pressure would quickly build in the tank and cause surging.

To rule out a fuel tank pressure issue try driving without the gas cap and see if it goes away.

If not you have several places to look:
pickup screen on the sending unit
crap in the tank
clogged fuel filter
faulty fuel pump
clogged carb jets/crap in carb/incorrect float height

if all of those fail to show any results you may need to increase the jetting on the carb at cruise, or metering rods depending on the carb
 
Carb is holley 670 street avenger. Engine is a 340 that made right at 400 HP on the dyno
 
buell564 said:
I had one of those carbs on my 340, did the same thing. I swapped out for a 650 double pumper I rebuilt and it went away.
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I just happen to have a fresh 650 double pumper on the bench. I will give it a try.
 
I'm positive this is not your problem, but I had the same symptoms and it turned out to be the stock plastic timing gear was so chewed up and out-a-round, the chain was flappin. Especially when 40+ mph at cruising.
 
j par said:
I'm positive this is not your problem, but I had the same symptoms and it turned out to be the stock plastic timing gear was so chewed up and out-a-round, the chain was flappin. Especially when 40+ mph at cruising.
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Thanks for sharing that info. But it has a new Cloyes true roller double roller chain and gear set.
 
i had this issue with a brand new dui distributor. they kindly refunded my money and now back to factory dist and fbo plate
 
unplug the vac advance hose on dist if you are running one . it should run smooth as a kitten. Had same issue with a commando with big cam .
 
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