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How to adjust where secondaries open

rmm

Regular Contributor
"Have twin 1988 Crusader 454s

"Have twin 1988 Crusader 454s and seems the secondaries open around 3050rpm, is it possible to adjust where they open?

Thanks"
 
"Not sure which carbs and coul

"Not sure which carbs and couldn't find label, where would it be?"
 
I have the same issue--I have

I have the same issue--I have rebuilt quadrajets and they kick in at 3050. Would love to cruise at 3200RPM. Need one of the better wrenches on this board to help with an answer. Thanks

Steve
 
"If it's a Q-Jet, there is

"If it's a Q-Jet, there is a mechanical linkage that could be "tweaked" to retard the secandaries from opening--I've done something similar on an Edelbrock. A better solution, in these days of high gas prices, is to simply remove the linkage and run on the primary barrels only. Most boats will plane off on the primaries (though it might take a little longer). For good mileage, the primaries should be all te way open or shut. Anything in between is not efficient.

Jeff"
 
"The secondaries open up at 75

"The secondaries open up at 75% of your max rpm.It is a matter of your prop pitch. If your motors rev to the upper limit of 4400, the secondaries will open at 3300 rpm.}"
 
"The opening of the secondarie

"The opening of the secondaries is not tied to rpms, but throttle position.

Jeff"
 
"Your right to a point about t

"Your right to a point about throttle position. But the secondaries open by vaccum. If the motor is laboring because of wrong prop pitch, the secondaries are going to open earlier."
 
".."If the motor is labori

".."If the motor is laboring because of wrong prop pitch, the secondaries are going to open earlier."

Actually, it's the other way around--the lack of manifold vacuum as the motor struggles inhibits the secondaries from opening. Seing this is a Q-Jet anyhow, it has amechanical linkage that can be removed to make it into a nice, fuel-efficient two barrel.

Jeff"
 
"Yes they are adjustable, sort

"Yes they are adjustable, sort of. actually you adjust the air valves (butterflies) there is a wind up type spring that you adjust at the end of the shaft, spec for # of turns is in the instruction sheet for the rebuild kit. I tweaked mine to open around 3300 - works great"
 
"Fastjeff

You wrote "F


"Fastjeff

You wrote "For good mileage, the primaries should be all te way open or shut. Anything in between is not efficient""

Can you elaborate on this? I have a 4160 Holley on a F351. WOT is about 3950 and I run at 2800-3000 depending on sea state, load and how late I am for dinner. Just looking for the most efficient way to run my yot. Thanks steve"
 
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