Thread: still rough idle

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need some help again,put 350 ci. 290 hp crate engine in ,pulled 305 ci out all new parts from fuel pump to distributor ,idles rough, removed intake and carb replaced with edlebrock intake and carb (600) put distributor in at o degrees tdc ,rotor at 4 oclock and have wired no.1 from there,fuel pump pressure and volume its okay,set timing at 10 degrees idle shaky set it at20 runs better no backfire, slight hesitation in throttle then it revs up,vacuum is
16 when timing at 10, vac is 18 when timing at 20 ,but vac goes from 18 to19 to18 then 17 back to18 slowly not rapidly,no black smoke,has a catylatic converter (new) i dont know if i have too much back pressure,compression test was 125 psi all the way around. what have i missed ?
thanks soup

okay denny i will try it, if it doesnt hold vac what is problem ?

denny i just checked at 1500 and vacuum drops up and down by 1 ,feels like slight miss.

If you're running power brakes, and I assume you are, don't forget to check those fittings and hose as well.

I had a similar problem recently with the very same engine in my '69 Camaro. Every time I was checking the vacuum, and adjusting the idle screws on the carb, I was also disconnecting the hose from the vac. adv. on the distributor. Vac readings were fine, but it still felt like a vac leak. I checked everything, several times. Well, almost everything, it ended up being a faulty advance module on the distributor. I found out once I put a 'T' in the line for my vac gage.

Originally Posted by DennyW

Check all your connections, and around your gasket areas for vacuum leaks. A can of choke cleaner works good. Just use little squirts at different points, and watch the gauge, and listen for rpm changes. Don't forget the throttle shaft. It sure sounds like a vacuum leak. Fuel is ok, right ?

Another thing that works well for this is a small propane torch. Turn it on (with no flame obviously) and run it around the gasket areas. When the RPM's change, you've found the leaking area.

thanks for the help guys i will check out things in a week ,we have a salmon derby on right now and i am it.need a break from project.
soup

a place i tend to find that problem in the shop often is at the carb gasket, a lot of people tend to snug the carb down unevenly, or they have a spot where the carb body is in the way so the use a wrench instead of a socket and just dont get it tight....

well i did vacumm leak tests, with carb spray, propane and hand over carb no difference,no leaks ,checked exhaust {catylatic} okay there .rough idle almost seems to be timing, have slight hesitation , have to check tdc again?

checked vacumm advance and mechanical working ,new distributor from jegs
but this morning i found two plugs not firing right,changed coils and modules have new wires on ,i now suspect bad magnecic pick up or connection,buddy has another distributor will try it and let you know
soup

found problem,one wire on magentic pickup streched not full contact,broken or frayed, resolder and runs like a charm now.must not of been crimped right at factory ? thanks for input guys
soup

Originally Posted by soup

need some help again,put 350 ci. 290 hp crate engine in ,pulled 305 ci out all new parts from fuel pump to distributor ,idles rough, removed intake and carb replaced with edlebrock intake and carb (600) put distributor in at o degrees tdc ,rotor at 4 oclock and have wired no.1 from there,fuel pump pressure and volume its okay,set timing at 10 degrees idle shaky set it at20 runs better no backfire, slight hesitation in throttle then it revs up,vacuum is
16 when timing at 10, vac is 18 when timing at 20 ,but vac goes from 18 to19 to18 then 17 back to18 slowly not rapidly,no black smoke,has a catylatic converter (new) i dont know if i have too much back pressure,compression test was 125 psi all the way around. what have i missed ?
thanks soup

MAKE SURE YOU DONT HAVE A INTAKE LEAK,,THIS WILL CAUSE ROUGH IDLE.ALSO MAKE SURE YOU HAVE NO VACUMM LEAKS AROUND THE BASE OF THE CARB,, ALSO BAD WIRES ,FOWLED PLUGS,,START FROM THE SIMPLE THINGS AND DO A TROUBLE SHOOT,,THIS WAY YOU WILL HAVE TO FIND THE PROBLEM,,GOOD LUCK!