BBC 396 wil not idle with any carb

[Adriank]

I recently pick up a motor from a guy that owns a shop and did a engine swap on a car. He didnt know much about the motor besides it ran and drove to his shop. Its a 396 BBC with aluminum elbebrock performer rpm heads "6055". Took a bore scope and found it has pretty new pistons that are 30 over. Rods looked all new. Pretty much everything was clean and new. Not much wear anywhere. Cleaned up the engine and painted. Installed in my c10 with the carb that was on the engine when running which is a quick fuel Q series 750. Fired up but runs really rich. Had carb rebuilt still same issue. I can get it to idle at about 1400rpms but only for a min. Very responsive and sounds healthy as hell. Anything under it stubbles to quick to get out and adjust anything. After it runs its floods out so cant restart for awhile. So bought a non double pump qft 750 with electric choke. Now acting as its not getting enough fuel. Only fires up if you pump the throttle a few times before starting and runs for 5secs then dies. Will not accept throttle what so ever. Acts as if its not getting any fuel. Had the carb replaced thinking something was wrong with the brand new one. Replaced with the same thing and does exact same thing. Ive advanced timing, ive retard timing, ive adjusted idle air mixers everyway possible. Adjusted the bowls. Not sure what to do. As far as the cam in the engine i can tell its a pretty decent size. Do not know what size though. Not sure how much of a factor it has? But any suggestions or ideas as to why im having such issues with fuel?

 

[Ricko1966]

Check vacuum and compression,as well check for vacuum leaks,use carb cleaner around the manifold base. Hook a vacuum gauge to the dipstick tube,block the pvc valve and tape over all valve cover openings/vents,see if you are pulling a vacuum under the manifold.

 

[Adriank]

Check vacuum and compression,as well check for vacuum leaks,use carb cleaner around the manifold base. Hook a vacuum gauge to the dipstick tube,block the pvc valve and tape over all valve cover openings/vents,see if you are pulling a vacuum under the manifold.

No vacuum leaks that i can tell with carb cleaner. Pcv valve is new and new grommets. Same with dipstick everything seems to be completely sealed off. Only vacuums on carb is to vacuum secondary which is new hose and to turbo 400 which is new as well. Compression is spectacular on all cylinders. Do not remember the numbers off top of my head though.

 

[legopnuematic]

Vacuum gauge can tell a lot.

Is the balancer new or used? Has TDC been confirmed? Pointer/mark adjusted if if was off?

If you are running a Holley style carb, pull it off and square the transfer slots up, set mixture screws 1 1/2 to 2 turns out as a baseline. Verify float height, needle and seat function, accelerator pump function.

Check both manifold and ported vacuum sources, if you are pulling vacuum on a ported port, idling, the transfer slots are too far exposed and needs more timing to square the slots up.

Carbs are generally pretty forgiving, especially under a low load situation like idling.

 

[squaredeal91]

No vacuum leaks that i can tell with carb cleaner. Pcv valve is new and new grommets. Same with dipstick everything seems to be completely sealed off. Only vacuums on carb is to vacuum secondary which is new hose and to turbo 400 which is new as well. Compression is spectacular on all cylinders. Do not remember the numbers off top of my head though.

Is vacuum modulator on trans leaking? Is it smoking a little blue? Or just black?

 

[Snoots]

It could have a bodacious cam in it.

 

[Adriank]

Vacuum gauge can tell a lot.

Is the balancer new or used? Has TDC been confirmed? Pointer/mark adjusted if if was off?

If you are running a Holley style carb, pull it off and square the transfer slots up, set mixture screws 1 1/2 to 2 turns out as a baseline. Verify float height, needle and seat function, accelerator pump function.

Check both manifold and ported vacuum sources, if you are pulling vacuum on a ported port, idling, the transfer slots are too far exposed and needs more timing to square the slots up.

Carbs are generally pretty forgiving, especially under a low load situation like idling.

Balancer did not seem to be new but wouldnt really be able to tell if it was or not. Tdc was correct on the markings though. I did check that before installing to new plugs..

Not sure on what you mean square up transfer slots? Ive done the mixture screws from 1 turn out to 1 and half to 2 to 2 and half. Primary float was alittle high so brought it down to alittle above the sight glass. Rear was just about the same on the sight glass. I choked it still same results and open choke same results.

I have not been able to check vacuum gauge cause i cant get it run long enough to get a reading without being pretty high idle.

 

[Adriank]

Is vacuum modulator on trans leaking? Is it smoking a little blue? Or just black?

New modulator, nothing seems to be leaking. No smoke besides fuel

 

[Adriank]

It could have a bodacious cam in it.

If thats the case what would be the best solution to be able to get to run it?

 

[Snoots]

If it's a 'loaping' cam, you'd have to change it. Since the engine ran before, like others have said; vacuum leak. I'd start there then, go to timing before the carb.

 

[Adriank]

If it's a 'loaping' cam, you'd have to change it. Since the engine ran before, like others have said; vacuum leak. I'd start there then, go to timing before the carb.

It pretty high lopes on it. But nothing to crazy that i can tell but thats also just coming from my experience. Definitely not stock but not full blown chassis rocker.

 

[Donald vonMinden]

I agree with snoots. A high lift camshaft will idle really rough and "lope" at idle. Also, check for leaks around the gasket between manifold and cylinder head, especially if you have eliminated the possibility of a vacuum leak there. Generally, a leak below the throttle butterflies will cause idle problems, but not so much from above them.

 

[Adriank]

I agree with snoots. A high lift camshaft will idle really rough and "lope" at idle. Also, check for leaks around the gasket between manifold and cylinder head, especially if you have eliminated the possibility of a vacuum leak there. Generally, a leak below the throttle butterflies will cause idle problems, but not so much from above them.

Whats going to be the best way to check for leak on the manifold? If i cant get it run long enough is there way to do it with out the car running? Its has all new manifold gaskets on it but that dont mean it cant be leaking.

 

[Tonimus]

A smoke machine will do it.

 

[Ricko1966]

Whats going to be the best way to check for leak on the manifold? If i cant get it run long enough is there way to do it with out the car running? Its has all new manifold gaskets on it but that dont mean it cant be leaking.

Set your shop vac hoses to blow,put an air cleaner with a snorkel on the carbureator,put rags in the exhaust pipes, pot your shop vac hose on the snorkel and tape it up,turn on the shop vac and start spraying everything with soapy water look for bubbles.Alternately you can blow in the exhaust and seal off the top of the carbureator.