loss of rpms and top speeed

[jason9080]

1987 omc 7.5 460.
boat used to go 60mph on a flat river. now i can only get about 40 mph and 3500 rpms. also random backfires out of the carb.(thru hull exhaust makes it hard to hear and identifly where noise comes from) i have changed the fuel seperator, rebuilt the carb twice, new plugs, cap, rotor... boat planes out great and will cruise at 3200 rpms 30 mph all day however if i try to wot im only getting 3500 tops and maybe 40mph tops. also seems to be burning a lot of fuel. i have played with the timing as well but no luck.

 

[Haut Medoc]

Re: loss of rpms and top speeed

Who rebuilt the carb twice?
Backfire through the carb is usually associated with water in the fuel or a lean condition....
I think that something, (crud), was missed during the rebuild of the carb.....
Something is clogged somewhere in the carb, most likely....
A bad intake valve will cause backfire through the carb as well....
A vacuum test & a compression test will tell you if it is a valve train issue......JK