BBC 396 wil not idle with any carb

[Beast496]

Not sure on what you mean square up transfer slots.

They are the slits in the butterfly valve bores, visible from below, they should make a square as a baseline for tuning. Atleast, thats the way i was taught.

 

[Rustisbest]

Make sure you're plug wires are on in the right order.

In the 1st pic you're choke isn't wired up so it's gonna flood fairly quick since its gonna stay fully closed.

Looks like you're vacuum hose for the advance is hooked up to the metering block which is ported vacuum. Put it on manifold. Should the fitting on the left of the baseplate.

4 corner idle mixture screws baseline is 3/4 turn out
2 corner is 1 1/2

 

[legopnuematic]

@Beast496 beat me to it

If the transfer slots are over exposed, by the butterfly being open too far, it will be running off of the transition circuit not the idle circuit, which will render the mixture screws basically useless.

You must be registered for see images attach

An engine will run with them over exposed, but will display poor tuning attributes. Lack of responsiveness to adjustments. An easy way to get an idea it the butterfly if open too far is if you have a vacuum signal at idle on a ported vacuum port. If it’s idling on the idle circuit there will be no vacuum to a ported source at idle. If it’s idling on the transition circuit there will be vacuum at a ported source at idle.

If you have a poor intake gasket seal (large vacuum leak), it will show on a vacuum gauge. Doesn’t have to be idling to check, if the needle bounces from 12-20lbs (this number depends on what vacuum the engine will make, it will vary) to zero being held at a constant rpm there’s some sealing issue, as it’s drawing air through the leak rather than the carb, thus the loss of vacuum signal.

What is known about this engine? You mention it has .03 over pistons, so it’s been over bored, and presumably decked. If it has been decked, there is a potential there is an angular stack up that might promote poor intake sealing, or it the China walls were not machined the intake could be held up by them preventing a proper seal. Lot of potentials here.

 

[Adriank]

Make sure you're plug wires are on in the right order.

In the 1st pic you're choke isn't wired up so it's gonna flood fairly quick since its gonna stay fully closed.

Looks like you're vacuum hose for the advance is hooked up to the metering block which is ported vacuum. Put it on manifold. Should the fitting on the left of the baseplate.

4 corner idle mixture screws baseline is 3/4 turn out
2 corner is 1 1/2

I did not know that on the 4 corner mixing screws. Thanks! Since that picture was take i have moved the vaccum to manifold. That particular carb which is on that picture has had everything on the choke removed. Thats why i it wasnt wired up.

 

[Adriank]

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.

I will have to try this weekend

 

[Adriank]

@Beast496 beat me to it

If the transfer slots are over exposed, by the butterfly being open too far, it will be running off of the transition circuit not the idle circuit, which will render the mixture screws basically useless.

You must be registered for see images attach

An engine will run with them over exposed, but will display poor tuning attributes. Lack of responsiveness to adjustments. An easy way to get an idea it the butterfly if open too far is if you have a vacuum signal at idle on a ported vacuum port. If it’s idling on the idle circuit there will be no vacuum to a ported source at idle. If it’s idling on the transition circuit there will be vacuum at a ported source at idle.

If you have a poor intake gasket seal (large vacuum leak), it will show on a vacuum gauge. Doesn’t have to be idling to check, if the needle bounces from 12-20lbs (this number depends on what vacuum the engine will make, it will vary) to zero being held at a constant rpm there’s some sealing issue, as it’s drawing air through the leak rather than the carb, thus the loss of vacuum signal.

What is known about this engine? You mention it has .03 over pistons, so it’s been over bored, and presumably decked. If it has been decked, there is a potential there is an angular stack up that might promote poor intake sealing, or it the China walls were not machined the intake could be held up by them preventing a proper seal. Lot of potentials here.

They are the slits in the butterfly valve bores, visible from below, they should make a square as a baseline for tuning. Atleast, thats the way i was taught.

Ok thank you i will have to check this.

 

[Ricko1966]

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.

Go back and read carefully what I said about the dipstick,vacuum gauge etc. I'm trying to determine if you have a vacuum leak under the manifold a vacuum gauge on the dipstick tube with all other openings plugged will show this.

 

[Adriank]

Go back and read carefully what I said about the dipstick vacuum gauge etc. I'm trying to determine if you have a vacuum leak under the manifold a vacuum gauge on the dipstick tube with all other openi gs plugged will show this.

Ok will do. Going to check on this weekend and will be back with update

 

[cadillac_al]

Is that an HEI ignition or points?

 

[Adriank]

Is that an HEI ignition or points?

Running MSD HEI