Whats going on?

[Thunderbutt]

HP500 w/ ZX drive in a Warlock deckboat w/ 24 pitch four blade.. Getting on plan you have to ease the gas, if you hammer it to fast it will baug down the motor. I've checked the compression, took a leak down and everything is ok. the carb is an 850 Holley with 84 prim. and 90 sec. The secondariers open all the way. After it is up it runs fine. Thanks Jim

[celeb1]

I had same problem and it went away after I took off a four hole carb spacer, I think it was leaning out too much on my setup. I played with everything, accelartor pump cams, holley vac advance springs, timing advance, you name it I checked it.

[Thunderbutt]

I had same problem and it went away after I took off a four hole carb spacer, I think it was leaning out too much on my setup. I played with everything, accelartor pump cams, holley vac advance springs, timing advance, you name it I checked it.
Thanks celeb, I don't have a four hole spacer, the carb sets right on the manifold. Jim

[SmokinLowriderSS]

I'm gonna suspect an accelerator pump problem then. Is this a sudden problem? Was just fine before?

[Thunderbutt]

I'm gonna suspect an accelerator pump problem then. Is this a sudden problem? Was just fine before?
Both pumps are fine. It has been an on going problem every since I put the motor in. Like I said, after it gets on plan it runs fine. Yesterday we had it out and had it up to 5000 rpm and 70 mph. I think I will go back to the 26 pitch prop.

[OMEGA_BUBBLE_JET]

what is the timing set at and how fast does it come in?
Omega

[celeb1]

could also be an air leak in the carb, I have seen the same thing happen from a missing vac plug or a removed choke.

[SmokinLowriderSS]

OK, 24 pitch prop, (I'm a jet guy, I get 5Krpm almost instantly).
What is your RPM it holds up at on opening the throttle too fast? Since a prop won't just rev free like a jet, I'm suspecting a carb just a bit too big if you can't find an air leak. Is it a mechanical seccondary carb? What size accel pumps are in it? My 4150 is a 700CFM'er and has a 30cc in the Pri and a 50cc in the sec side. I am also ONLY running a power valve in the pri side.
Too big of a carb and too fast an opening will cause signal loss to the venturis, reducing fuel flow just when you are wanting more for acceleration.
I'm betting the 26-pitch prop will only make it worse, slowing your engine's wind-up even more.

[Thunderbutt]

OK, 24 pitch prop, (I'm a jet guy, I get 5Krpm almost instantly).
What is your RPM it holds up at on opening the throttle too fast? Since a prop won't just rev free like a jet, I'm suspecting a carb just a bit too big if you can't find an air leak. Is it a mechanical seccondary carb? What size accel pumps are in it? My 4150 is a 700CFM'er and has a 30cc in the Pri and a 50cc in the sec side. I am also ONLY running a power valve in the pri side.
Too big of a carb and too fast an opening will cause signal loss to the venturis, reducing fuel flow just when you are wanting more for acceleration.
I'm betting the 26-pitch prop will only make it worse, slowing your engine's wind-up even more.
The HP500 motors come from Mercury with the 850 carb, Yes it is a mechanical sec carb, timing is 36.

[SmokinLowriderSS]

Man ... you gotta make this HARD Thunderbutt ................ float levels too low maybe? Low floats will make the carb have to get a stronger than normal vac signal to pull fuel farther uphill to the main venturis. Would have similar effect to oversize carb.