28zx max rpm problems
 

I have a 1998 28zx with twin 350 mags 300hrsp. 2 weeks ago for tickfaw 200 boat ran fine 4 people full of fuel wot 4900 70 mph. Took the boat out last weekend 2 people 3/4 fuel 4400 trying to blow props out 63 mph. Only change was adding 25 gallons of fuel to the existing 50 gallons. Replaced fuel filters and cleaned flame arrestors which were very dirty. Took boat out today Put 28 gallons of fresh fuel non ethenol and still the same problem cannot get the rpms over 4500 and onlt seeing 62-63 mph any suggestions. Thanks in Advance.

Both motors same rpms

Forgive me for sounding basic, but are you running your trim up so that the boat is not plowing? where are your trim tabs set? the higher you go up with your trim on the outdrives, the higher your rpm's, but go too far and you'll slip and lose speed. Just tryin to start somewhere here in determining your situation.

tom

Yes it is trimmed out. Even tryed over trimming the drives and through a rooster tail and neither engine go over 4500 rpms.

its fixed it was weak fuel i added octane booster to the fuel that was still in tank and added 30 gallons of premuim to top it off and ran light it did originally

It can sometimes be caused by the Anti siphon valve where the checkball inside sticks and causes fuel starvation. Does it fluctuate the power and then get back in then out then in..... Usually see this over a certain RPM range such as 3500 or 4K. Just a thought if it happens again. Ive seen where you can have it one day and then the next its fine then it can stick again........... Good Luck

never had an issue like that. Neither engine would go over 4500 on three outings. Finally octane booster and premium fuel worked great.