BAD-HABIT

I just installed the Holley Quick Change Spring Kit. I was looking at the instructions (And my wife says I never do this ) and noticed that they show that the vaccum secondary springs start to open the secondaries at different rpm's IN ADDITION to fully opening at different rpm's..... The lightest spring shows an opening point at 1620 rpm's and fully open at about 5680. The stock spring shows an opening at 2240 and a full open at 8160. The strongest spring is 2720 and NO FULL OPEN. Now my question is two fold. How do you pick the rpm range at which to throttle down to check for a bog/flat spot? I usually cruise at 33-3500rpms. If I throttle down at 3000+ I get the best results using the black spring which is the strongest spring. Secondly I am concerend about the statement in the instructions showing the spring not allowing a full opening....But yet even the stock spring will not fully open untill 8160rpms...I realize that these rpm figures are probally for stock motors. I am running a 750 Holley model 4010. It is on a 358 SBC pushing about 375hp at 5200rpms. Boat weighs about 4200lbs loaded.

BH

BAD-HABIT

Anybody

BH

Dork

Not sure if you can convert, but I think you'd be better off with mechanical or go with a 1 to 1 opening rate for the primary and secondaries. FWIW

paradigm shift

I think the RPM ratings are just a guess. The secondaries really open on vacuum signal. They pick up the vacuum signal above the throttle plates so they delay opening till the motor can handle it. Testing is really the best way to tell which spring works best for a given application. Sounds like you have done some tests already. Only way I know to tell if the carburator is opening all they way is visual. May need a helper to look at it while running. Either crack the engine hatch open (risky) or remove it for testing. 750cfm is a little big in my opinion (Not worth much ) for a 358 cubic in motor. Cam & heads make a big difference. The fact you said that the heavy spring (Secondaries open later - higher RPM) work best kind of confirms this.

Sorry I am not sure what problem you are trying to solve. Is it hesitating when throttle is pushed to WOT or are you just trying to make sure carb is opening all the way? Do you know what vacuum you are running at WOT?

BAD-HABIT

Sorry I didnt' make myself more clear ...I was wondering how to tell if the motor is getting enough fuel if the secondaries are not opening all the way. Also at what point should the secondaries open? If I use the black spring then the everything feels pretty good. Acutally the standard spring doesn't feel bad the black spring feels better.

BH

paradigm shift

My guess is that the black spring FEELS better because it delays the opening of the secondaries until the RPM is up and the motor can handle it better. With that 750cfm you should be running a low vacuum at WOT. Other than looking at the linkage a vacuum reading is the only way I can think of to tell if secondaries are opening completely. As for enough fuel well that is done with a spark plug reading best in my opinion. EGT can help. Plug readings at various RPM will tell you if you have any lean spots. Even if the secondaries are not opening it should not be lean only down on performance if anything. Fuel pressure gauge can tell you if you have fuel pressure to the carb. Hope this helps and not confuse more.