rough running

I'm trying to finish a car for a fellow. It has a (probable) 1976 350 in it, rams horn exhaust MSD ignition Edelbrock Torker intake and Holley 600cfm carb. New plugs and NGK wires electric fuel pump

I have timed it (set to tdc and tweeked it a tad) checked the firing order several times. It's correct

It will start but I cannot get it to idle. it runs rough, misses and occaisionally backfires. Gotta keep the revs up or it dies. choking helps keep it going, but it's being bad.


To complicate things:

I did not ***emble this engine, it came to me like this The fellow bought and installed the engine, claiming it was a runner. He is NOT a mechanic. I believe he put the intake on it and I KNOW he put the carb on it.

My forst thought after ignition was the valves, but it's unlikely he would have touched them. The old engine has sat at least 5 years and probably longer.

Any ideas would be good. I need it running today.

 

Ya might want to start by looking in a tune up book for actual suggested timing. I don't believe anything actually runs at T.D.C., more like 10 or 12 advanced to start with. Motors that sit prolonged time tend to create there own problems that a few run cycles may work out. Non mechanics changing Carbs and Manifolds can sure add to issues. As well as every used motor sold use to be grate before coming out of prior car. I'd start with correcting the timing and then add a Vacuum gauge to see if your air tight. Best of luck to ya.
The Wizzard

 

Sounds like timing and fuel mixture to me.

 

How old is the carb? Might need cleaned out.

 

Timing the dizzy makes no difference. The carb is new
Good suggestion on the vacuum gauge!

 

maybe it has a cam that makes the eng. do what it does. Get ahold of the p.o. and ask.

 

Have you tried twisting the distributor around while it is "running"? My car's timing marks are off by 30 degrees or so.


Ooooops too slow

 

We had something like this happen. I kept swearing it was a vacuum leak. Wound up being a broken spring inside the dizzy causing the vacuum advance not to work. Fixed the spring and work perfect. Hope this helps

 

new carbs can get dirty.

 

Sounds like a vacuum leak to me

 

Have you confirmed that the right carb gasket is installed under the carb,? sounds like its got a big air leak ..

 

As other suggested there are Lots of basic mechanical checks to make first on the way to "tuning" out the problem.

how does it respond to idle mix screw adjustments? how many turns open are the idle screws? A blast of carb cleaner thru the idle adjust screws can clear water and some debris.

 

Just hearing "I cannot get it to idle. it runs rough, misses and occaisionally backfires" sounds like a flat cam is a possibility. I've had it happen with the same problems

 

what part of the island do you live in?

 

First I would kick the timing up to about 8 btdc for starters. Spray starting fluid around the base of the carb. If there is a va***n leak the RPM will shoot up to 3000 immediatly. Set idle mixture with a tach. I've had idle mixture screws plugged on carbs that have sat for awhile. Run a oxy- acetylene tip cleaner down the idle ports to clear them. If all else fails, start with a compression check and work from there.Good luck, nothing is more frustrating than trying to figure out someone else' mess.

 

Hey cool! I live in Nanaimo, work in Parksville...
I actually did the spray around the carb trick (with Brake kleen) and yeah.. m***ive vacuum leak somehow missed before. Cleaning up the spacer and putting adhesive on the gaskets as I type (I'm tallented like that)

Let ya nknow soon.

 

have to ask. what type of adhesive? In my 45+ years of working on cars I have always tried NOT to use any adhesives on gaskets that come in contact with fuel as gas usually dissolves most of them over time. A little Gascacinch sometimes to hold a stubborn one in place is about all. If it won't seal with out goo, there is usually a problem with the part

 

Hey I agree, but when i have to keep a gasket in place i either use trim adhesive (contact cement) on big gaskets, or this spray on stuff... lemme get the can...
Permatex spray-a-gasket.. just a light coat let it tack, and it holds it in place.

I also discovered the guy who installed ths carb used co**** thread nuts on the unf studs.. but just on one side... can you guess which side the leak was on?

 

What chance is there that the intake is sealed?

 

In the '90s we had a roundy round car shipped to us from a dealership in the next state. Brandy new MSD ignition, fresh engine etc. Missed backfired balked you name it. I ran a compression check, ran through a standard tuneup didn't touch the carb other than to try and trim it. Then I took a wild hair and byp***ed the MSD and it ran like a top.

It won't cost you much to byp*** the the MSD for a test. They do get a bad on out the door on occaision.

 

It will on this one.. It's a WHOLE MSD, dizzy, coil, the works

I though of that too. I'm waiting on the delivery guy with new mounting studs.. I'm hopefull that correcting the vacuum leak will help. I couldnt hear it because the exhaust is a tad loud

 

Got a running problem, the 1st thing I look for is a vacuum leak. When I was doing tune up for a living, other shop's tune ups would come in, sure as ****.. most of them had vacuum leaks. Most were rotted hoses the mechanic broke during their tune up.

Simple 3 second test, with the motor running, remove the air cleaner, (plug any open hoses) and cup a hand over the carb airhorn. If the idle smooths out, there is a vacuum leak. The carb spray trick is the best way to find them.

Bob

 

I keep spare distributers around just for that purpose. I have pulled several bad ignition boxes over the years. A vac leak could certainly be your problem but your description sounds more like a brain fart than an induction problem to me.

I hope your vac leak problem fixes it.