1115 will not reach 5000 RPMs at WOT

[Skippy the skipper]

I am working on a 115, 1978 that will not reach 5000 RPM at WOT. I have done the link and sync, rebuilt the carbs, checked the fuel pump and inspected everything I can think of but it still will not reach 5000 RPM. Compression is at 125 on all six, good spark on all six with the sparky. Let me give you guys some history on this engine. I am the 3rd mechanic to work this jewel. 1st guy replaced some ignition parts (don't know why but he never even checked compression). 2nd guy found low compression on 1 cyl and did a rebuild. I get the boat it dies while put in gear and will not wind up. I also find the carbs had not been rebuilt and were leaking gas horribly when the bulb was depressed. Ok I'm thinking this engine is drawing too much fuel out at high RPM so I rebuild the carbs and do a link and sync. Runs smooth and does not die now. Hooked up my trusty tach to #1 and only get 3800 at WOT, recheck link and sync (21 at max advance at WOT with the timing light) still no go. I have not worked on these distributor mercs all that much, could I be missing somthing? In did the link and sync found here in the forum and it was much better than my manuals. But I still feel that it may be an electrical problem. BTW I noticed a small drop in RPM when I would try and trim the engine at WOT, instantanious when I would hit the switch (possible stator problem)? Any help would be greatly appreciated thanks in advance!!!!

 

[Laddies]

Re: 1115 will not reach 5000 RPMs at WOT

There is a very good chance then then engine was rebuilt it got a piston and rings, who ever did the repair either did not check the cyls for taper or out of round, they also may have thought that it was close and wood run those engines won't. We found that out the hard way about 20 years ago on one of our rentals that we thought we would freshen up like the other rentals, factory sent a mechanic over and we tore it down, it was less than ,002 out on taper when he said that was the problem, we thought he was just trying to get on the road and said we've been getting by with more than that for years on our rentals, he said if that don't fix it I'll pay for the rebore and come fix it on my own time. Well that fixed it, so we were red faced for a while thank god it was our engine. That engine acted just as you describe, since then we have redone about half a dozen that other shops did and it fixes them every time the owners hate to hear the problem but that seems to fix them. As a footnote ever one of the engines we redid showed 110+ lbs. compression, that maybe why the oldtimers at Mercury said compression means nothing on a 2 cycle.

 

[Skippy the skipper]

Re: 1115 will not reach 5000 RPMs at WOT

Thanks!!