Surge

[98ciHemi]

Having some issues with getting the new motor tuned. It has a surge at part throttle, most noticable in third at 35 mph. I have checked for vacuum leaks, checked and rechecked timing and vacuum advance, and jetted the carb up two sizes with no improvment. I am at my wit's end. Ideas?

[squirrel]

Re: Surge

Did you try backing the timing off a bit?

What rpm is it running at that speed?

[TC]

Re: Surge

Having some issues with getting the new motor tuned. It has a surge at part throttle, most noticable in third at 35 mph. I have checked for vacuum leaks, checked and rechecked timing and vacuum advance, and jetted the carb up two sizes with no improvment. I am at my wit's end. Ideas?

What all did you do to the new motor?? Is it just a stock rebuild??

[98ciHemi]

Re: Surge

Engine is a low compression sort of bastardized stock rebuild. 89 1.9 block and dished pistons, 83ish 1.6 hemi head and OEM flat tappet cam, 82 1.6 carb and intake, 82 exhaust manifold, and 1.6 flywheel and clutch. I can't say for sure what RPMs I am turning, give me a few minutes to figure that out. Third redlines at 70 mph, so it's happening at high cruise RPM. I shift to fourth usually at about 40.

[JOES66FURY]

Re: Surge

does it do it at idle or only high RPM's, I ask becasue I had an issue like you described with my mother in laws bronco II..it would surge, or buck and rock at higher RPM's....after exhasuting all possibilities we found that the clutch was installed improperly....

[SpiderGearsMan]

Re: Surge

what do you mean by a surge ? a bog ? a flat spot ? a shake ?
timing marks ? a lot of times with a belt - tightening the tensioner causes the cam to move , that is why when you time it , you crank the engine over a few times to ensure the marks line up

[98ciHemi]

Re: Surge

By surge I mean bog and shudder as if going to slow in the gear selected. It almost only happens at whatever RPM correlates to 35 in 3rd, and it goes away if you dump in the second barrel. I am sure the clutch is in properly installed since the car does 75-80 without a twitch. ;D I think I found a vacuum leak so I will attack that next. Naturally it appears to be on the underside of the intake manifold where you can't get to it..... but, I will persevere. Timing belt was installed outside of the car and I rotated the engine through about five time before I was satisfied that she was good. Ignition timing change had no effect on this issue, so I have it set with the distributor lined up on the OEM marks.

[98ciHemi]

Re: Surge

Evaporative emissions.... I don't need no stinkin' evoporative emissions lines..... ;D ;D

[Scott Liggett]

Re: Surge

Go up another couple jet sizes in the primaries. That's what you're using at cruising speeds.

[98ciHemi]

Re: Surge

I fixed it. There was a vac leak somewhere in the evap system, which is now unhooked.

[min301]

Re: Surge

Hows it run now?

[SpiderGearsMan]

Re: Surge

building engines is cool

[milner351]

Re: Surge

remove the charcoal canister from the vehicle if you've unhooked the evap system... the canister can be a bit of a fire hazard, and is dead weight anyway.

nice going on the troubleshooting / diagnosis.