1988 Evinrude 90HP VRO low power

[mvortex]

I think there is a weak cylinder. One cylinder plug is cleaner than the rest and its piston has alot less carbon build up. I have swapped the plug, coil and plug wire. The motor is on a ProCraft 165 bass boat. Motor runs up to 2900rpm and the boat will not get on plane unless my passenger moves up to the front pedestal seat. Then the motor will continue to rev and the boat will plane at 3200rpm. The passenger can then move back and the motor revs to 4200rpm WOT @31mph. Any ideas? My next step was to check the reed.

 

[12Footer]

Re: 1988 Evinrude 90HP VRO low power

Welcome to iboats, Mvortex. What I've got to sugjest pains me.. It could very well be water injestion. The plug is being 'steam-cleaned". A blown head gasket is the hopefull cause (because it is the cheapest to fix).<br />Run a compression test.<br />I'm not that familiar with the moitor you have, but if it has exaust port plates on the side, the gasket may be leaking into the combustion chamber there instead of the head.

 

[OBJ]

Re: 1988 Evinrude 90HP VRO low power

Hi mvortex....<br /><br />I will ditto 12footers suggestion. Another indicator would be poor idle until ya' get the throttle plates cracked open a little. You may also see higher than normal gas usage. If ya do the compression test, do one with the engine cold and then warm it up to operating temp and do another. The leak may be heat related. Good Luck!!

 

[mvortex]

Re: 1988 Evinrude 90HP VRO low power

Thanks for the replies. I was also thinking that it could be getting water, too. I have done a cold compression check and all cyls are right at 100. When I get a chance I will try it cold then warm it up. Also, I have checked plug temps with a infared temp gun and the cyl in question never gets up to 90 degrees while the three others got up to 115 before I stopped. Roughly a 20 degree diff after about 5 mins at 2500-3000 rpm.

 

[mvortex]

Re: 1988 Evinrude 90HP VRO low power

After a long search, I have solved the problem. When the previous owner had the engine rebuilt, they put the top carb.(cyls 1&2) back together incorrectly. The jets in the bowl were installed worng. It is supposed to be a 26c on the air side and a 56c on the fuel side, well they put both 26c's on the #1 cyl side of the bowl for both air and fuel. Then on the other side of the bowl #2 cyl they had the 56c jets. So basically one cyl was running real rich and another was running real lean. After putting everything back together and switching to a 13x17 4blade Comprop she now runs 38mph@ 5300 WOT and planes in no time. Next outting I will switch back to the 13x19 Alum prop that came on it and see what the increase in pitch will do.<br /><br />Also, I am running 92 octane. I have read in other posts that 87 might be better. What do you think?<br /><br />Thanks<br />Mark