Hot Rods 350 SBC won't keep running

Will start, but hard to start, need to pump gas pedal.
I have to turn up idle screw to around 1900 rpm to get it ti run long enough for me to get to under bonnet to check things out
within 10-15 secs it slowly drops over about 10 secs) from 1900 rpm to 500 rpm then dies. not a sudden drop, a slow drop in rpm.

Electric fuel pump.

Just back in the car (doing air con swap and took engine out for an engine bay clean up etc).

350 SBC Vortec with 100,000 miles on it (ran like a kitten before coming out)
While out I did:

• replace intake manifold gaskets (rear seal was leaking)
• New plugs
• new plug leads
• New HEI Distributor after mine broke when knocked off bench by my daughter
• put a carb rebuild kit in the carb (Holley 650 vac secondary). Did not change jets or anything

I may need to move the dist as with vac advance disconnected and blocked I can only get about 5 degrees of base advance before vac canister hits manifold.

I have confirmed fuel pump is working (can't check fuel pressure my gauge isn't working...just found that out. I have a spare I will throw on tomorrow)
I have confirmed no vac leaks, well as best I can in 10 secs of running
I have confirmed 12v running to coil

What else am I missing ???

It could just be a timing issue and I need to reseat the dist allowing more advance.

 

Vacuum leak or tooth off...

 

can you be a tooth off with a HEI ? I thought you couldn't

 

Of course you can

 

Fuel line kinked? Is the tank vent working? Good grounds? Definately need to re-stab the distributor if all you can get is 5 degrees of advance.

 

Fuel pump primes fine but come to think of it I ain’t hearing it when running. Albeit that brief 10 secs. Maybe I’ve missed a wire. A few things to check. No kinked fuel lines and vent is perfect

 

Will it start again immediately after it dies or does the fuel pump need to run again?
Sounds to me like maybe you're not getting enough gas to your carb. Regardless, let us know once you get it solved.

 

Just a random thought, but if the fuel pump primes it for 10 seconds, should about fill the bowls, right? So even if the fuel pump does not stay on, he shouldn’t have to have the engine at near 2000 RPMs to keep it running.

 

I believe 2OLD2FAST is right. I've seen similar situation where a major vaccum leak was the cause.

 

Re-clock the distributor so as to have a full range of timing adjustment. A timing light and a mechanic's vacuum gauge will help you get a sharp base tune.

 

Easy stuff first. Get a helper with a unlit propane torch in hand. Start the engine and check for a vac leak.

 

With it running, no air cleaner, vacuum lines plugged... place a hand over the carb. If the idle smooths out and picks up, you have a vacuum leak. Look at the fuel hoses too for cracks or dry rot. Can you determine the fuel pressure? It should be close to 5-6 psi.

 

thanks all.

Re-clocked the distributor, now have greater range of movement. set base timing to 10 degrees

no air cleaner
check all fuel lines they are good

it still has an issue. I am on my own so no helper. It doesn't run long enough for me to do anything like check for vac leaks, change timing etc. by time I leave drivers seat and get to under hood, it dies within about 3 secs.

I have noticed that when it does it puffs a massive amount of fuel back out the carb, it has also backfired out the carb and caught fire once.

It's actually like it's almost getting too much fuel.

I can't check fuel pressure. a. gauge is not working ...wil fix tomorrow and b. it doesn't run long enough for me to do so anyway

the backfire has me thinking ...I still think it's a timing issue. I had to make new marks on the balancer and I was methodical in doing so, but maybe I'm not marked perfectly at TDC on the timing tape. I did check it about 15 times before laying the tape down, but there was no original mark to go off. When I hand crank it, it is TDC on the mark just after the "whoosh". I might need to pull the valve cover and check

 

oh when I put my hand over teh carb...it dies immediately...sounds like too much fuel

 

Try rotating the distributor slightly, just a smidge, in the timing advance direction a little bit at a time without regard to the timing marks or timing light. See if it likes that mo' bettah. Figure about the width of a pencil line equals maybe 2° at the crank, so don't get carried away. Bump it along about 5 to 10 total and see what's what.

Another strategy would be to advance the distributor until starter kickback occurs, and back it off some.

The idea here being that the timing marks indicated for whatever reason are not the actual BTDC timing. It helps to have the right tools but this will work for rough troubleshooting.

 

This^^^^^

 

And double check firing order.

 

Is there a safety switch wired inline to shut down the fuel pump when there is low oil pressure ?

 

bobss396 beat me to it. maybe too much fuel pressure and its flooding out . look down in the carb after it dies and see if there is raw fuel dripping .

 

no safety switch....well over 60 year old wiring

Fuel pressure was not changed at all, and car was running fine before it came out and went back in

but good ideas for me to recheck. Thank you

 

Float needle/seat issues?

 

so just did a few extra things.

1. I pulled all the vac hoses and blocked them. It ran better. It lasted about 30 secs before dying. I did put my hand over carb, idle improved for literally about 3 secs then it immediately stalled.
2. it then would not restart. it will turn over but no restart. If I leave it for 5 mins then it will restart

I think I will pull the carb give it a quick once over as this seems really strange.

I did pull a plug and it's black. That said I have been giving it lots of pumps and high idle RPM to try and keep it running so I am sure I've contributed to that

 

I also tried running an unlit propone torch around carb base and intake manifold front and rear seals before it died. no change in idle quality. But I didn't get all the way around

 

Coil,coil,coil.

 

brand new distributor (literally remove from box yesterday). How can I test if the coil is bad.

 

Easy way to test the coil is swap out one from another vehicle that runs and see if it makes any difference.

 

No matter what coil is installed new or old need to make sure the spark is hot. Pull the coil wire from the distributor cap and hold the terminal by the boot about 1/2" from a head bolt or other good ground and crank the ignition over for a few seconds. Should be a healthy fat spark. White or bluish depending on ignition type. Yellow-ish not so good.

 

I'm currently hot-wiring the 12v connection to the coil (BATT terminal) directly from the battery as I was only getting 4V through the resisted ignition wire. I did do a test on the coil (both new one and old one). Getting 1.2 Ohms across the BATT and Tach terminals. But on both coils when I test the secondary circuit (BATT to carbon button) I get OL on the Ohms meter. The old coil worked great so I know that is working. But weird I'm getting no reading on that secondary circuit test.

I think I might through the old HEI in but it has a broken cap. So I'll use the new cap but everything else from the old one.

This is killing me. Not enough changed for this to be such an issue. But weird that it runs smooth for 30 secs then just dies. I don't understand that. What changes at the 30 sec mark to make it stall out?

 

THIS ^^^^ got my attention!!
Classic action of out-of-time-issue.
Check the firing order
Give it more advance
See what happens........
6sally6

 

Progress. Got it to run for over 1 min. every time it started to slow and heads towards stall, I sprayed starter fluid into primary carb side and it went back up in RPMs. so I've nailed it down to fuel delivery issue. About to yank the filter (I don't have another but have enough fuel line to run from pump to carb by passing regulator and filter). so I will try one then the other first see where the blockage is