'76 6 hp, fuel pump problem?

[BF]

Hi y'all...<br /><br />So, the season's finally on here. I used my 6 hp for trolling over the weekend. There is no new problem, just the same one that's been around for >1 year. Lack of power on top end.<br /><br />It idles fine (will troll for hours), last spring I went through the ignition/points etc. All seems fine, (running on both cylinders, timing is spot on) coils are good. I rebuilt the carb last year (including float replacement). Lynch & synch is good, compression is good.<br /><br />Problem is what I think it has a lack of power from 1/2 throttle on up. It doesn't surge or anything like that, and will run steadily for several minutes this way. But it feels like you are only giving 1/2 to 3/4 throttle when it is WOT. My original thought was that I was dropping a cylinder at higher rpms (but I'm not), or that the high speed jet was partially blocked (but it is not).<br /><br />I'm wondering whether it might be a bad fuel pump. (?) It doesn't improve by pumping the primer bulb, or using a different fuel line/tank, or by blipping the choke. Or changing plugs.<br /><br />Is it possible for a fuel pump to fail by having too low of an output at higher rpms ? If so, I would expect that it should take off OK, but then start to slow/die as the carb bowl runs dry?<br /><br />Thoughts ?? Am I overlooking something?

 

[Xcusme]

Re: '76 6 hp, fuel pump problem?

Have you tried WOT with the cover off?? You might have an exhaust leak under the cover. The motor will asperate the fumes. A small leak won't cause the problem, higher RPM's could. I've sprayed dish soap/water solution at base of powerhead to ID problem. Bubbles indicate the problem.<br /><br />Another thing to check. Remove 2 fuel pump mounting screws. Move pump off of powerhead. Work bulb,is fuel leaking from rear of fuel pump? If yes,broken diaphram,replace or rebuild pump.

 

[JB]

Re: '76 6 hp, fuel pump problem?

Sounds to me like it could be a failure to fully advance ignition timing, BF. Torque at higher rpm on that engine is critically dependent on timiing advance.<br /><br />Would be nice to know what rpm it is getting at WOT.<br /><br />Do the link 'n' synch in the manual and let us know what happens.

 

[BF]

Re: '76 6 hp, fuel pump problem?

Hi again,<br /><br />thanks for the replies.... yes I had it running with the cover off and it made no difference. (good idea though) Looking for a bad diaphram also sounds like a good idea. I forgot to mention one of the first things I did was pull the cover off the fuel pump over the little screen thing. It was clean as a whistle.<br /><br />JB, I'm 99% sure the link'n synch is A-OK, but I'll double check it next time I'm at the cottage. That was another thing I was checking with the cover off, that the advance was going all the way and that the carb butterfly was opening all the way at WOT. I don't have a tiny tach, but it's obviously doggin' and rpm's are down. At WOT it's got only a bit more grunt than the healthy 2 hp that I have. Before checking into it, I would've bet money that it was becoming a 1 cylinder at higher rpms. <br /><br />I really think it's something aside from all the things I've checked/tweaked until now. None of it has had the slightest effect on the problem, but I know that it was maintenance that was overdue so I'm glad to have gone over it.<br /><br />FWIW, this used to be my F-I-L's motor. Using it years ago I recall it mostly working good, but sporadically dropping at WOT (to how it is now all the time). <br /><br />Given the cash I dropped on it last summer (coils etc) I'd be nice to get it back to 100% <br /><br />Thanks...