Notaflyguy142

Alright for starters I am new to the forums so forgive me if I goof up somewhere.

Recently I replaced a water block and a distributor to my 71 mustang grande. It has a 351C with a few aftermarket goodies. Anyway though the vacuum advance to the previous distributor was broken, hence the replacement dist.

It was running fine up to the repairs when the water block started to leak.

After replacing and timing the dist the mustang seemed to run fine. I drove it about 4 miles when I noticed it starting to lag up and backfire rather heavily. After a large backfire it started to die, the RPM's going from 1k dropping randomly and sputtering. I had it towed home to see what the issue was.

After checking a few things and the spark plugs it obviously was getting too much fuel and loading up and dying, which I am assuming is the cause of the backfiring and the dying of the engine.

Originally I had a holley 750 CFM carb on it so I guessed that maybe putting on a smaller carb would do the trick. So I bought a 600 CFM and put it on.

I rebuild the carb (a 600 cfm holley) and tried to see if that would help. Instead it still did the same thing, idling fine for a couple minutes then sputtering and dying.

The carb is fine, the float levels are perfect and the needles are working absolutely fine. I checked all hoses for vacuum leaks and found nothing out of the ordinary. As previously stated the engine runs fine around 1.5k RPM without a miss until it warms up, the electric choke kicks in, and then it starts to sputter and die.

Anyone have any ideas of what the problem could be? I am a 19 year old in college and would really like to stop driving my Cherokee around when I could have the muscle car running =]

Thanks to whoever helps me out!!

EDIT : CHOKE DOES NOT EFFECT PERFORMANCE AT ALL

kalli

if it runs 'fine' with the choke on I woiuld suggest the engine is running to lean.
First thing I'd check is for vacuum leaks. if there are none, then check the gasket between the intake and the carb. if that's burned up you might fill the intake charge with exhaust.

as you say the engine runs fine when choke on and dies when the choke switches off. how were you able to adjust ignition properly in that scenario?

anyway ... tighten the curb idle screw so that when warm the engine will still run around 1500. when that's all ok go around in circles:

- adjust ignition (with vacuum disconnected and plugged)
- adjust mixture
- lower curb idle just so much it doesn't die and start over again

this way you can do it slowly from a running configuration. when you get the car running warm at 1500 and go down slowly, let us know when it craps out

Notaflyguy142

I was wrong about the choke. The choke doesn't effect it in any way shape or form when it idles and eventually starts to die off.

We have it idling at around 2k RPM (when I say we I mean me and my dad). Its not even the choke now that is the problem. It runs fine in terms of running at 2k without an issue then starts to idle extremely rough, dropping to 1k and below. It runs smoothly without any problem for X amount of time (usually around 15-30 seconds when warm, cold about a minute) then it starts to crap out.

There were not any vacuum leaks anywhere around the carb or around any of the hoses.

Notaflyguy142

Been playing with it all weekend and still nothing working.

Checked hoses for any vacuum leaks found nothing =[

Notaflyguy142

Checked around the carb, no vacuum leak

kalli

how did you check for vacuum leaks? spray WD40 or somethign around intake gaskets under carb. check all hoses connected to manifold and carb (powerbrakes and modulator for auto transmission). if you have powerbrakes, unplug the hose from the booster and block it for a test period. not for driving just to make sure it's not pulling vacuum from there.

Then inspect the gasket under the carburetor. I once had a 351c where the gasket was burned from an exhaust crossover in the intake blowing exhaust into the intake ->cannot run

Kalli

Justin's 71

Check the power valve, on holley's anytime there is a backfire the power valve blows. Remove the front fuel bowl and metering block, and the power valve screws into the metering block. It's a cheap fix usually around $12. I have a 71 Grande with a 351C and 600 cfm Holley.

madmattmustangs

I had the same problem with my 351 cleveland.
I can tell you right now without a shadow of a doubt that the problem is in your distributor.
I have some questions though.
What type of coil are you using?
How long ago did you replace your voltage regulator?
Did you set the point gap and dwell on the distributor?
Is the engine grounded to the body?

My problem was that my aftermarket coil kept baking my condensers and once i fixed that problem i had a dwell problem which kept messing up my points.

Also check the supression wire for the system as well.

I happen to be a 19 year old student myself and can totally relate to the muscle car theme thats why im switching to the big block ive been building since i was 17


P.S. im assuming your running a factory replacement distributor so thats why i brought up the points issue.
But i can tell you for sure its not your carborator or a vacum leak although i would check the power valve and make sure its ok. My Holley 770 Street avenger took quite a beating and was fine but still id check.

Notaflyguy142

Found out my condenser had a short hehe. All better now! Thanks everyone