Carb Question

[Crazy]

When running at WOT on my GPS My boat is doing 32mph and when I go to 3/4 trotle the boat speeds up to 34mph ??? what can cause this ? oh ya boat is 22 foot SeaRay OMC 351 Ford 4 bl 235hp .

 

[DJP]

Re: Carb Question

RFI

 

[speed29668]

Re: Carb Question

You may be going past wide open throttle. Put the throttle control all the way down and look into the carb. The throttle shutter should be wide open. Also check your timing advance.

 

[magster65]

Re: Carb Question

Does the rpm increase from 3/4 to WOT?

 

[Crazy]

Re: Carb Question

Rpm stays the same .... just makes more noise ....

 

[magster65]

Re: Carb Question

Interesting, I can't see how it would slow down if the rpm stays the same... anyways, either your carb. is a little lean/rich at WOT or like speed says your total advance may be a little off the mark.

 

[horndog]

Re: Carb Question

your engine/setup could be not tuned right. what is the rpms at these speeds? If you are redlining the motor, your speed and horsepower goes down, which the engine is out of the power curve. the faster the rpms DOES NOT mean the faster the boat will go. tell us your rpms at 3/4 throttle and at WOT and what prop you have. What kind of noise is it making at WOT?

 

[McKenzie]

Re: Carb Question

Is it possible the prop is ventilating?

 

[DJP]

Re: Carb Question

Cavitation...

 

[Crazy]

Re: Carb Question

I'll check the RPM's out the next time I'm out .... I don't think my tack is working right ... The most RPM's I've seen is 3500 ... but I think it is spinning a lot faster then that ... The boat is like a car stuck in first gear ... I guess it could be the prop spining out , cuz if I don't trim it up .. It makes a lot of noise and it goes nowhere . I have a new spare prop I could try ... is it hard to change and can I change it in the water . Beach the boat .

 

[Boatist]

Re: Carb Question

Crazy<br />My guess is you have a problem with the secondary on you carburetor. Could be the rear float not letting fuel in or the jets are plugged. With a four barrel you do not open the rear butterflys until about 3/4 throttle. At that point can usually here the roar from the rear two barrels. If float sruck shut so no fuel for back two barrels or the jets plug up then when the rear two barrels open all you get is more air so fuel air mix is way too lean and you will loose power.<br /><br />4 barrel carb set up this way to save fuel when not at full throttle. By the way If I am right and you run at full throttle can very easily burn a piston from running way too lean.

 

[Crazy]

Re: Carb Question

Up date , Today was test and tune day ... I got some carb cleaner and cleaned out the flame arester and carb , also brought a 5.5 gal portable gas tank with carb cleaner in it and hooked it all up . I was able to reach 37.2MPH at 4200 RPM's at WOT . That's a big dif from before for WOT at 3500 rpm and 32MPH .Is 4200RPM about right ? I'd like to see 40MPH also for putts around what's a good speed or RPM to go for good MPG . I was thinking about a K&N Flame arester for a couple more HP .