Air/fuel

Fourdy

Fourdy

Well-known member
How do you change the air/fuel ratio that runs between 14.5 and 15.1 at 50 mph? I run a blown 276, timing is correct.

With the blower, I understand that I should be a little richer. Carb is the 570 holley, electric choke, vac secondaries.

Change jets?? Or??

Thanks in advance

Fourdy
 
If the question refers to a "Cruising", constant throttle position, at 50 MPH there is no need for a richer mixture than what is stated unless the engine is operating poorly. If the engine is running good and if the fuel system adds adequate enrichment during acceleration there will not be damage or other undesirable characteristics.
 
Thanks JWL. A/f does drop to +/- 13 when I step on it. Can you tell me what part of the carbonation would be adjusted to change A/f?

Fourdy
 
If you are looking to change a/f at full throttle, you could change jets in the secondaries. This would not affect your cruising a/f.
 
As Flatjack mentioned, changing the main jets is one of the methods and can be altered between primary and secondary, and both, to get close to your goals. There is also the option of increasing the Power Valve orifice diameter if the aim is to enrichen acceleration-only activities. For more tuning the air bleed diameters can be modified, and finally the whole metering block can be altered or exchanged for a tunable block with a series of vertical jets.

The level of boost the engine is getting will determine how concerned to be about the A/F at all RPM levels. For moderate boost and intermittent WOT operation, simple main jet adjustments should satisfy the requirements.

I think JSeery made a good point which is--- the more sophisticated the tune-up request the more sophisticated the equipment and the operator needs to be.
 
Assuming you are pulling adequate vacuum at cruising speed you can drop the primary jets a couple of sizes. That should lean it out a little. I removed my 4160 390 after fighting it for over a year and went to 1403 500 Edelbrock. Cured my problem.
Good luck
 
41ljh - -
I don't want to lean in any more. Just trying to make sure I am not too lean with my blower. Sounds like I am okay.

Thanks for your info.

Fourdy
 
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