I should be 4800 rpm...

[ghuskin]

at WOT, per the searay prop chart. I'm only getting 4000 rpms. Does anyone know the possible causes? I'm running a 15 X 17 prop (chart indicates 14.5 X 17), would this make that big of a difference?

New plugs
new fuel pump
pertronix ignition
new cap/rotor

Thank you for your thoughts/comments!

Gregg

 

[stevea661]

at WOT, per the searay prop chart. I'm only getting 4000 rpms. Does anyone know the possible causes? I'm running a 15 X 17 prop (chart indicates 14.5 X 17), would this make that big of a difference?

New plugs
new fuel pump
pertronix ignition
new cap/rotor

Thank you for your thoughts/comments!

Gregg

I was kind of where you were a couple of weeks ago. Were you ever able to get 4800 out of it? My boat is a learning experiance. After the new motor about 3400 rpm and 30 mph wot. New carb and pertronix, took it out again, No change. Pulled the distributer, brought it in to a distributer guy, had it curved, springs were loose, took it out again, no change, but I ate the prop on that trip, on the way in, on a rock. Replaced my 15.8X 15 solas with a 15.5x15 hustler prop, added 2 quarts of boost 108 and 30 gallons of 91 octain to the 50 gallons of fuel already in the tank advanced the inital timing to 10 deg btdc, took it out again, got to 3600 rpm. Had the wife run the boat while I was down in the engine compartment at wot and advanced the timing till it just started to ping and backed it off a hair, 4200 rpm and 32mph, cruise on plane at about 24mph and 3400 rpm. I still haven't been able to get it above 4200, but now its like the thing is starving for fuel or emptying to bowl too quickly. It starts to hunt rpms at 4200.

 

[tobnpr]

"Charts" are just a place to start...not necessarily the right prop.
SteveA's first question is the right one- is this a change that would indicate an engine problem (were able to hit 4800 previously), or is this a new-to-you boat that you haven't run before?

Each inch of pitch roughly equates to 200 rpm's, so in your case you're looking for alot more than that...Are you sure that your throttle cable is getting full extension at the carb at WOT?

 

[stevea661]

"Charts" are just a place to start...not necessarily the right prop.
SteveA's first question is the right one- is this a change that would indicate an engine problem (were able to hit 4800 previously), or is this a new-to-you boat that you haven't run before?

Each inch of pitch roughly equates to 200 rpm's, so in your case you're looking for alot more than that...Are you sure that your throttle cable is getting full extension at the carb at WOT?

"Are you sure your throttle is getting full extension at the carb at WOT?" That's an easy one. I've just been screwing with mine for so long I forgot about that one:grin:.

 

[ghuskin]

Yes the bowls are opening. I found a loose wire on dist. I still need to check for slop inside dist as well as timing. This is third season with boat and she seemed to run stronger last year after new fuel pump and pertronix. Need accurate shop tach and timing light. Rain today and maybe tomorrow. Thank you for your thoughts. Gregg.