Engine won't idle

[megaladon6]

like i said, i doubt it's the problem, but i've seen weird sh*t happen. and it's easy enough to do, i figured what the hell.

 

[88olds421]

I will post up what we did to fix it sometime this weekend when it is running great.

 

[88olds421]

Well, finally got the engine builder over. After cranking it a few times couldn't even get the engine to fire a cylinder. Checked the plugs and they were all fouled. He told me I needed to let the cylinders air out since they are now fuel soaked. It needs to be a nice day and we are suppose to get rain for the next few days. So come Friday or Saturday going to let the cylinders air out and put new plugs and go from there.

 

[454muscle]

You weren't very specific about your engine specs so I'll have to make some assumptions. A 421 is a huge SBC so it probably has a huge (long duration) cam. That means low manifold vacuum - especially at lower RPMs. Carburetors are vacuum operated. Pull all your plugs and see if they are fuel fouled. If they are, replace them and see if you can get it started again. Then it's time to make some adjustments.
I had a similar situation while breaking in a small block with a long duration cam and a stock tuned carb. At anything below @1800 it would choke out. The low vacuum was causing 2 things; the power valve would open (go rich) and fuel would pull through the primaries. This would cause the engine to die and be nearly impossible to start. I dropped down to a 5.5 power valve from the 7.5 that was stock in my 3310. You probably have a 6.5. I then adjusted my secondaries open just a crack. That allowed the primaries to be closed which let the idle circuit work properly. At that point I was able to run it enough to do jetting changes as necessary. Good luck.

What he said ^^ lol... I had a similar situation with a SBC I was building years ago. Had a massive cam with high lift, long duration, heads were high compression and the engine couldn't breathe right, it kept choking below 1500 RPM. But yeah DRIVEN hit the nail on the head though. Since you're cleaning the carb you could try a smaller power valve like he said and depending on your intake manifold you can get another one that might help it breathe better (a high rise).

 

[pontiacgp]

Well, finally got the engine builder over. After cranking it a few times couldn't even get the engine to fire a cylinder. Checked the plugs and they were all fouled. He told me I needed to let the cylinders air out since they are now fuel soaked. It needs to be a nice day and we are suppose to get rain for the next few days. So come Friday or Saturday going to let the cylinders air out and put new plugs and go from there.

Did he check to see if the spark plugs were getting some juice at least? It would been easy to dry out the plugs when you took them out to check them and let the cylinders air out while your doing that should have been sufficient.

 

[88olds421]

Yes we checked for spark getting to the plugs and it was, the plugs just weren't firing. They are fuel fouled. Once that happens they are junk. I have already put a 3.5 power valve in it. We will be back at on Saturday. I will post what is found.

 

[pontiacgp]

if I were you I'd try a different coil, I've seen weak coils give a spark but not enough to fire up a engine if the engine wasn't running perfect

 

[88olds421]

Before on a new set of plugs I made sure that I was getting spark to the plugs and it was a nice bright blue spark from them. The distributor is a DUI that has about 2 years of service on it. it has like a 55,000 coil in it. I will check again once I get new plugs that is fires nice and bright blue and not a weak brownish orange color.

 

[pontiacgp]

if you have a DUI then I'm probably wrong about the coil...those are great distributors

 

[88olds421]

I know. I love being able to gap my plugs wider. I am thinking the problem is probably just something really simple that I am neglecting to think of and I have over diagnosed everything. With the engine builder coming over to figure it out helps. So hopefully soon the 421 will be thundering to life and idling like a champ.