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I got a question about Carbs

T

tbrodes

Regular Contributor
"Guys,

Was chatting with a

"Guys,

Was chatting with a buddy today about boats. We started talking about RPMS and secondaries, and I told him jeffs trick about looking at where the secondaries crack with regards to throttle position at the dock (mine pop at 3300 and are barely a #2 pencil width open at 34-3600 RPM)according to throttle position. He said that it wont work due to vacuum pressure opening them. How do I know if I have mechanical or vacuum secondaries?? I have 1991 stock factory 454s..."
 
Thinking the answer is q-jets

Thinking the answer is q-jets (Cliff conversation) the answer is a little of both. The throttle plates are mechanical. The operation of the secondary system is governed by the air valve. The air valve has vacuum control and will not let the air valve open until the manifold vacuum is reduced to nominally 5" Hg. Air valve closed means little air thru that path and little if any fuel flowing out of the nozzles (inadequate pressure drop to pull it out).

I'd take him a cold one and tell him the next round is his.
 
hahah thanks mark! So my think

hahah thanks mark! So my thinking and checking of secondary popping is a half way decent way to go about it...
 
I doubt you'll see the air

I doubt you'll see the air valve release if you raise the RPM while in idle at the dock.

Even my old (worn out) ears can hear the 'noise' increase when the secondaries open.
 
"Correct, but you can still se

"Correct, but you can still see the linkage that allows the secondaries to open working. Q-Jets and Holleys are like that.

Jeff"
 
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