haunting idle problem

[perfectsoldier2]

hay fellas i have a slight issue.i have a 350 with a eddy carb that i just rebuilt and replaced intake gasket.The problem is that while i was observing the engine run it seems to idle up and down on its own.Sometime is takes a few for the change.It has a pretty hot cam in it so i usuallt idle it around 1100 rpms.i had it set at 1500 and it will drop down to about 950 then surge back up again.it will keep doing this over and over.when put in gear the rpm drops pretty low then stalls.kinda weird to me but heck i dunno.does this seem more like an intake manifold leak or carb problems?ill take any suggestions before i rip it all apart again.

ps the flots are set at approx 7/16 and approx 15/16.has good fuel pressure.

[sparky2263]

I'm wondering if you have enough initial timing. A vacuum gauge would reveal that as far as a base setting goes. Increase timing to max vacuum and back off 1/2". Works good for a start.

Other problem could be the power valve springs could be to tight. Easy to check. Loosen the power valve retaining screws just enough to slide the retainers over to the side so you can see 'em. Crank it up and make sure they pull down and stay that way.

Stock springs can be a bit tight for a lopey cam and allow the enrichment rods to jump up and down.

[perfectsoldier2]

im useing an hei dist with drag racing springs.i do not use a vaccume advance.im certion the timing is right on.i rebuilt the carb only for the fact it was dirty and i like my stuff nice.as far as powervalves i assume your talking about metering rods and springs?it is an eddy.i reused the same springs and rods for they were in perfect shape.the only thing i changed were gaskets and pump shot spring which was alittle stiffer than the old one.im still not certian that a vaccume leak on the manifold would cause this,could it be my flotes depleting and not filling fast enough?im running at about 6 to 7 psi with a mechanical pump.thanks

[sparky2263]

If you're not using a vac advance with an HEI, initial timing is going to need between 12 and 18 btdc. An HEI, w/o grinding out the advance cams is only good for around 16-18 of mechanical advance. I'm not doubting your diagnosis, only making sure we're on the same page.

Yes, I'm speaking of the power enrichment rods. Like I said, a real easy check to make sure the spring selection (and vacuum) is correct.

6-7 psi is perfect for the carb. At idle, a starvation problem really wouldn't be an issue, so bowl filling is a non-issue.

I'm only harping on timing because the eddy is pretty foolproof, so the only other thing that comes to mind is that, since you had to re-set the dist.

[perfectsoldier2]

im still wondering about the intake manifold causing this problem.It almost seems like it will leake then something will block the leak for a second then leak again.the dist is good im sure of it.it has i high perf kit in it and im pretty good with timing.i dont use a light but i play it by ear.i set it by wot untill the popping goes away and set for max advance at idle untill runs the smothest for i use no vacc advance.it acts like the metering rods are moving up and down slowly but when i look in to the carb i hace no fuel comming form the to so that tells me the rods are all the way down.its kinda a stumper to me.Think i should pull the manifold and reset for a vacc leak?or look elswhere?thanks

[sparky2263]

Propane works good for finding a vacuum leak. You can even remove the PCV and pump it in the crankcase to see if it's leaking underneath the intake. No worry of an explosion as the oxygen level in the crankcase isn't high enough to support combustion.

[perfectsoldier2]

how will i know if its leaking?it didnt seem to do it today but i had storms roll in but it only did it hot.it was strange.i run about 6 in vaccume and it bounces slightly with the cam i have in it.any mor tips would be nice thanks

[1JohnnyO]

Is this a street car or race only? If it's street, why aren't you running vacuum advance? Just curious. Also, Edelbrock carbs dont like high fuel pressure, and 7# is too much for that carb. 4# is plenty, although I doubt that is causing your idle problems. I would think it's a vacuum leak somewhere. The surging up and down indicate that. You really need to set your ignition timing correctly before you go messing with adjusting the carb and looking for problems there. That's why I asked about the vacuum advance. If you're on the street, you really need to run one.

[perfectsoldier2]

i do not run the advance because i run a mechanical curve.timing is right on the money.i run 6 psi on fuel with a mechanical pump.the cam is wild but set up to run on the street.kinda overboard for the street but hay i love it.truck smokes everything in its ways lol.im goona pull the intake and check everything for flatness and reseal it because i seem to be gettling alittle water out the left bank pipe.i dont rhink i used enough sealent on the front and rear of intake.plus i didnt seal around the water passages.thanks for the suggestions and ill write a follow up after mission complete.

[1989lsccars]

I would check for a vacuum leak first. Sounds like it was ok before you changed intake gasket. I usually get a spray can of carb cleaner or starting fluid and start spraying where it could leak and if I hit a spot that causes engine to surge up I look for a leak,usually a carb or intake gasket or a hose. Just my 2 cents Jake

[perfectsoldier2]

well i got the idle problem fixed.but i still seem to be getting some water out of my left tailpipe.thought it was condensation but took for a drive and still wet.no bubbles in coolent or anything just wet with a very slight steam.i sure hope it aint a cracked head.im kinda a poor boy lol.head gaskets are ne also so ahhhh who knows.also in first gear it smokes nice under heavy acceleration.bad valvguides or seals?i dont believe its rings because i have no power loss or uneven running.last time heads were off everything was shiny.if it is heads wheres a good plase to shop and get heads that dont cost 1500 bucks a set?or should i do a valve job?who knows thanks.

[1JohnnyO]

I doubt that valve guides would smoke under acceleration, they usually do it on De-celeration, and when you get back on it again. I would do a cylinder leak down test...borrow a gauge and learn how to use it, and do a leak down test...that will tell you how your rings are sealing. Then you'll know for sure if that's the problem or not. I wouldnt go pulling heads and other stuff without knowing what the problem is for sure.