new B motor running issue
 

Had a B motor built. Breaking in on engine test stand. Starts and runs good with the stock manifold and updraft carb. I purchased scalded dog cast headers and a burns single downdraft manifold. I had a stromburg 81 rebuilt for it. It would not run. If you pump it, it will fire but stops immediately when you stop pumping. Had another carb built and it does exactly the same thing. I have an electric fuel pump in line with 2lbs pressure. Looking for ideas of what the problem might be. P.s. the engine has plenty of vacume

Re: new B motor running issue
 

If you have 2# of fuel pressure, your problem most likely is with the carbs.
Check the flow of fuel right at the inlet to the carb...you may have an obstruction in the line or at the carb fitting.
Your trouble is not with the engine as it ran well with the updraft carb and stock manifold.
I have run many engines on a test stand with varying carbs, intakes and ignition systems, I have had similar problems. Most of the time the issue is something simple but critical. Hope you find the issue soon. Please report back.
Good Day!

Re: new B motor running issue
 

Is the proper gas cap (vented) being used. If it's the cap, it would start easily, but run for a very short period before dying.

Re: new B motor running issue
 

How many turns out are the jet needles set at? Usually set at 1&1/2 turns out for starters.

Re: new B motor running issue
 

Deleted duplicate post.

Re: new B motor running issue
 

Will it run if you choke it??

Re: new B motor running issue
 

Look real hard for an intake manifold leak. Get the old starter fluid out. Good luck.

Re: new B motor running issue
 

2 lbs. is about right for Strombergs. Because the 2 rebuilt carbs act the same, I would also suspect an intake manifold or carb base leak. 81's should have #35 main jets.

Re: new B motor running issue
 

I sure hope i find the issue. Way to much invested in the motor to not put it in the pickup. Engine is running off a lawn mower gas tank. The idle jets are open 1- 1/4 turns. The main jets are 038. I did flatten the block side and carb side of the intake.The engine turning over pulls alot of vacume. removed gas line and have plenty of fuel. Thank you for the replies.

Re: new B motor running issue
 

Check all of the suggestions. Still will not run. still looking for suggestions. I reallly do appreciate all the suggestions, but still looking for more ideas. Thanks again for any ideas

Re: new B motor running issue
 

Where are you located?

Re: new B motor running issue
 

Just a question if you pour a little gas down carb will it run and if it does can you keep it running by trickling gas down carb ?
This would tell you if it a fuel problem, because if you are pumping it to stay running it squirts gas every time via the accelerator pump so sounds like fuel problem maybe also a vacuum leak somewhere.

Re: new B motor running issue
 

Try larger main jets, something like .050

Re: new B motor running issue
 

I assume you have sprayed the intake manifold joints with starter fluid while trying to start it and keep it running. Sure sounds like extra air is getting in past the carb.

Re: new B motor running issue
 

how much dd you change at one time?try the intake with your stock manifold. My guess is between a scalded dog header and an old burns, something isn't square allowing a leak.

Re: new B motor running issue
 

Did the same guy rebuild both carbs? Maybe he made the same mistake on both. It happens!

Re: new B motor running issue
 

Try increasing the fuel pump pressure to 3 or 4 PSI and see if it runs.

Re: new B motor running issue
 

Did you have the manifolds machined if they needed it?

Charlie Stephens

Re: new B motor running issue
 

As Jim 1932 says, the intake may be touching the exhaust manifold, not letting the intake seal against the block. I have seen this before. A little discreet grinding would solve that problem.