[ssanto]

Got a 11:1 SBC 383 with a Holley 750 HP series double pumper (mechanical secondaries).

When the motor is not running, the secondaries close very easily by the spring. I can flip them open and they close very well.

I've got the primaries set to be open enough to idle at 1100 RPM. When running and I blip the throttle, the primaries close all the way but the secondaries stay open enough to keep the motor running at around 2000 RPM. With my hand I can turn the secondary throttle shaft that last bit to close it and then it'll go back down to 1100 RPM.

It feels like the motor is sucking so much air that it is keeping the secondaries open. This is a brand new carb from Pro Systems. Not sure if I need a heavier spring on the secondaries throttle shaft. Or if I need to tweak/bend the linkage between the primaries and secondaries.

Thoughts?


Thanks,
Sal

 

[johnsongrass1]

4 corner idle?
If so, front and rear should be opened the same. 20-40 thou of the transfer slot showing is a good place to start.
BLP has a stronger secondary spring.
you can try recentering the throttle plates too. Does yours have the mechanical linkage like the Holley Pro series m 20-122?
Lastly, is this a gas, Methonal or Ethanol carb?

 

[ssanto]

Yes. 4 corner idle. Gas carb. I checked and both the primaries and secondaries were open about a 1/4 turn of the screw.

It's got the stock slip linkage like this:

 

[johnsongrass1]

Might wanna contact Pro systems. They may wanna see it come back. If the shafts have liners instead of bushing they can get dirt in them.
The Holley linkage helps.
You can also try wrapping the coil spring around another turn.

 

[chasracer]

First off the secondaries are not supposed to completely close on that carb. You should be adjusting it so that the secondaries and primaries are just opened to point of providing the desired idle RPM - of course you have to involve the idle-air mixture screws into this equation too. Mechanically the link between the primary and secondary should be setup to bring the secondary back to the position that you have adjusted into it.

 

[BogiesAnnex1]

There is a secondary throttle idle screw adjustment stop screw on the right side of the secondary throttle shaft. In Holley’s wisdom it is not so accessible from underneath. With the carb mounted there is no way to see it.

Some of the Holley’s also mount an adjustable air bleed under the air cleaner stud, you’ll need to remove the stud, shine a bright light into the hole to see if there is a screw slot showing at the bottom, if there is you have an adjustable air bleed if no screw slot you don’t.

Bogie

 

[johnsongrass1]

Pro Systems will have the secondary idle adjust moved to the top so you don't have to remove the carb.