High throttle miss

[Texasdoc]

Unfortunately, I don't know what size any of the bleeds or restrictors are. This is how it came from Brent. There were no instructions or parts list in the box.

How can I tell what size they are?

[Gaz64]

The jet size might be stamped on the outside of the jet.

You could be lucky and read some numbers in situ.

I know you have a Quick Fuel 750, but specifically what carburetor have you got?

Gary

[Texasdoc]

Originally Posted by Gaz64

The jet size might be stamped on the outside of the jet.

You could be lucky and read some numbers in situ.

I know you have a Quick Fuel 750, but specifically what carburetor have you got?

Gary

It is a custom Q-750 series from Brent. The jet sizes are 74 and 82 as stated.
The idle air bleeds are 70 (on the outside) and the high speed bleeds are 33 (closest to the squirter) for both primaries and secondaries.

[Gaz64]

Ok, first thing to do is give all the air bleed a spray of carb cleaner and compressed air to make sure and clean and clear.

And double check your air cleaner gasket fit etc.

What air filter are you using, size etc?

[Texasdoc]

Originally Posted by Gaz64

Ok, first thing to do is give all the air bleed a spray of carb cleaner and compressed air to make sure and clean and clear.

And double check your air cleaner gasket fit etc.

What air filter are you using, size etc?

Will do these things. Air filter is the normal cobra filter but I have a K&N element, not the standard paper element.

Update: I cleaned the K&N just to be sure. The guys over on racingfuelsystems suggest decreasing the high speed air bleeds from 33 to 30 or 28 to lean out the transition circuit.

They also suggest increasing the base advance and decreasing the total advance. Right now it is base 16, total 37, no vacuum advance. They suggest base as high as stable, total timing around 30 with vacuum advance connected to the ported manifold port.

I guess I could start a new topic over in the Holley tuning section since the high speed miss is gone...

[Gaz64]

I would reduce the size of the idle feed restrictions in the metering block.

Your mixture screws are ultra sensitive, which says the idle jets are too large.

Even getting it to idle correctly, and the transition goes rich says the IFRs are too large.

We aren't talking much here.

If they are say 31 now, drop to 29.

I can't see how making the high speed air bleed SMALLER will lean out the transition circuit.

The smaller HSAB will make the high end richer.

Gary

[Gaz64]

I'm not a member on the racingfuelsystems website, but I have read your thread on there.

I fail to see how tuners recommendation of reducing the high speed air bleed will lean your transition circuit.

You could take out the main jet, and the high speed speed altogether or block them off, and as long as airflow doesn't start the main circuit, no amount of change to the main circuit will change the idle/transition circuit metering.

If the current IFRs have no number, get hold of a pin gauge set to measure them.

Don't muck around with bits of wire.

If they are smaller than your new HSABs of 31, then they are probably 28s or 29s.

Your mixture screws at 3/4 turn, and rich above idle says the idle circuit is still too rich.

A larger idle air bleed in the early 70s may cure all of this off idle richness.

So to me, you need slightly larger IABs, and slightly smaller HSABs for the top end.

Gary