Challenger Single 787 Acceleration Problem

[Ridley]

Good morning folks,

Having an intermittent acceleration problem with my 97 Challenger.

So far I have rebuilt the carbs, genuine mikuni parts and original springs. Followed the excellent step by step guide on here (thank you). Pop off was consistent at 42 on both carbs. Returned high and low screws to the settings they were at:

High: 0 Mag / 1/2 PTO
Low: 1 1/2 Mag and PTO

Cleaned and rebuilt the Raves with new diaphragms and o-rings. Red cap is screwed all the way in on both.

All fuel lines have been replaced, running the fuel selector on reserve doesn't make any difference.

Boat starts and idles fine. Sometimes it will run perfectly especially when first in the water, then sometimes either after fast deceleration, tight turn or sitting with engine off for a while the acceleration problem re-appears.
Boat will get up to about 5-5.5k rpm, just before getting on the plane, and then won't accelerate any higher. Any movement of the throttle beyond about 50% makes no difference to engine speed.

Completely stumped with what to try next, very grateful for any suggestions.

Thanks,

Ridley

 

[MDR]

I'd back off on your Rave valve adjustment

 

[Ridley]

Thanks MDR, I did try backing them off until the top of the red adjuster was flush with the cap, but it didn't seem to make any difference.

Any other ideas to try?

 

[skoolball23]

I hope you removed those tiny little fuel filters out of the carbs. Those things will get clogged very quick. It was a terrible design flaw! Then add an inline filter in the fuel line.

 

[Ridley]

Thanks skoolball, I did replace the carb filters, and i've got an in-line filter.

 

[mikidymac]

Get rid of any aftermarket fuel filters. Only use the ones that are there from the factory but new replacements obviously.
And absolutely do not remove the little internal carb filters, they are not a design flaw. They protect the jets and adjusters from anything small that make it past the fuel filter.

 

[Phuck_boi]

So frustrating, I have a similar issue and cannot find a thread that has a conclusion, just some how about try this. Boat has achieved 6800rpm but not consistent. It consistently holds at 5500rpm and about 30+ MPH. Why??
cleaned carbs, rebuilt raves, rebuilt pump, new fuel lines, unplugged rectifier, and still can’t get it to run right.