engine surges after H-pipe install

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ecw329

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is it necessary to retune the carb after an h pipe install, the engine has become very unstable at idle and will surge up and down from say 600 rpm to around ~1300 and will even die if left be this engine ran perfectly without the pipes installed...... just tell me if you need more info on my combo if it will help answer the question thanks in advance
 
Sounds like the H pipe leaned the carb out a bunch.
Is this an Edelbrock 600 by chance ? I had the same problem after adding a 1" HVH super Sucker spacer to my 340. I had to up the carb in the cruise circuit 2 steps to fix it.
 
yup carter 625, basically the ede 600 thats what i suspected too because i had heard it would do that, thanks for the fast reply!
 
Lean or Rich can cause a surge. I wouldn't doubt that exhaust changes could cause either condition whether it be different mufflers or a crossover.

Reset your idle mixture and idle speed after any changes.
 
i played with the idle mixture and although i did increase the rpm the surge was still present im thinking its way lean now as i had previously installed some leaner rods and smaller pump shooter chasing down a bog when romped on...anyways ill try some richer rods and see how that goes.....thanks again!
 
I ran straight headers when I fired up the new 360 and tuned the carb (Holley 750 HP) a little rich until it was up and running for a day. Then I leaned the carb back down. Had my exhaust ran out with X-pipe installed and didn't have to touch a thing. So I said all that to say this. It is a little strange that it started surging after the H-pipe install. I installed a H-pipe on a Charger I had and didn't have to change anything (Holley also). So do you think it could be something else another words?
 
dont think it could be anything else as it was the only thing changed, but maybe it could be a manifold vacuum leak??
if it helps the carb was previously leaned out so i will replace the rods and richen it up....
also, the exhaust was previously true duals with 40 series flows that 90'ed out inn front of the rear wheels and the only change was a crossover about 1 foot back from the collectors
 
ill check for vacuum leaks as its an alum intake and alum edelbrck heads so ill make sure everything is tight hope this works!!
 
You can richen it up in the mid range and WOT with smaller diameter rods but that won't do squat for idle. The idle circuit is separate from the high speed circuit.
 
fishy68 said:
You can richen it up in the mid range and WOT with smaller diameter rods but that won't do squat for idle. The idle circuit is separate from the high speed circuit.
Click to expand...

"Uhh Chuck, I am going to go with Fishy on this one".............

I agree, the idle circuit is separate and the rods are not working at that time. They only work when the step up springs allow the rods to drop and raise.
 
i had a thought, i had the + batt cable disconnected while doing the welding for the install is there a chance my msd 6al somehow got fried???
 
no, jets are for the primary and secondary circuits. idle circuit is affected only by the mixture screws.
 
there is definitely something strange going on with this carb, i tried richening up the mixture with the idle mixture screws to no avail i guess im chasing down some hidden vacuum leak that just popped up
 
is all you did to the car the H-pipe?


when i went to the X-pipe i had to go 2 jet sizes up on my holley because it was surging like that.
 
ecw329 said:
i had a thought, i had the + batt cable disconnected while doing the welding for the install is there a chance my msd 6al somehow got fried???
Click to expand...


If the Ground lead from the welder is close to where you are welding and the welding circuit does not cross any other electrical paths or your body you should not have any problems.

I figured this out when I was welding a Logging truck bunk in the rain few years ago. :blob6:
 
ya the neg welder lead was maybe at max a foot away attached to the exhaust pipe and all i did was tack it in place remove it, and finish final welding of the hpipe outside the car
 
Have you checked for vacuum leaks? There is a fitting in the rear of the carb and the front too. Should be capped off.

Make sure both rods are free to move.

bwhitejr
 
so the car had ran out of gas previously and had apparently sucked air through the fuel lines making fuel pressure inconsistant creating the surge... or so i think as the problem is gone now btw this is an electric fuel pump situated by the fuel cell...
 
I was going to say trash in the lines or air. It sounded like a fuel related problem. Glad you found out what it was.
 
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