97' 40HP Evinrude Bogging down

[Conrod084]

Hi Guys,

Just chasing a couple of ideas. I picked up a little glass runabout on the cheap with a 97' 40hp Evinrude on the back. The motor will start fine, idles well and increases revs no problem in neutral. But when I throttle forward it won't pick up revs and just bogs down. If you add fuel to the system using the primer injection while at WOT it will pick up the revs for a second before going back to low revs. Taking the cover off the carburetors i can see that they are both getting fuel during in pick up of the throttle so i was chasing some other thoughts on what the issue might be? Pressure in the tank fuel line maybe or something more sinister? I have removed cleaned and refitted the bottom carb as initially it didn't look to be feeding anywhere near the same amount of fuel as the top but they're both pretty uniform now.

I don't plan to have this motor on for too much longer as it will be quite under powered in my opinion but for the time being it's what i have to work with until i can afford to repower.

Thanks in advance

Greg.

[chris69]

Sounds like a fuel pump problem to me,have a look at that.

[Noelm]

If you pump the primer bulb in the fuel line while it is running, this in effect, bypasses the fuel pump, start with the very basics, borrow a known good fuel tank and hose, fill with fresh fuel and go from there.

[Conrod084]

I have put a new fuel hose on yesterday along with a new fuel tank and fresh fuel and the signs were more positive with a few more revs and a slightly better speed at WOT however it is still not throttling to full revs. Every so often when i'd throttle back and throttle up it would start to accelerate the way it should a second and then the revs would cut back down. Was pumping the primer bulb while running in forward but this did not alleviate the issue. The filter on the fuel pump will be my next inspection. Thanks again for your replies.

Greg

[astro66]

put some new plugs in....

[Conrod084]

It's definitely getting good spark astro, when i use the manual primer handle to inject more fuel with a decent amount of throttle the revs increase quite well albeit for only a few seconds once it uses the injected fuel the revs cut back. Has me thinking either the fuel pump is r/s or there's air getting into the system somewhere. I checked the filter in the fuel pump this afternoon and disassembled it to check for anything obvious but there is no build of grime or perishing /damage on the o rings or the gaskets.

[Noelm]

Probably not the fuel pump, remember what I said about pumping the primer while running?, that almost rules out the pump entirely, do you have a service manual? If not, and you plan on continuing to fix it yourself.... Get one, and get a genuine one, it will be worth every cent. Replace the plugs anyway, even if they look new, as I said, do the easy stuff first, do not get fixated on one thing.

[Conrod084]

I have a workshop manual. I definitely wouldn't have got so far as disassembling things without being able to see how they go back together on paper (Billy, not silly). Whilst clearly still very novice in my understanding of these creatures and quick troubleshooting practices i am keen to learn especially on an older motor. Anything slightly modern that didn't have a carburetor and I probably wouldn't have even had the stones to remove the engine cowling.

I will take yours and astro's advice and change the spark plugs and leads too tomorrow.

Let you know how it goes and will probably look pretty silly if that's all the problem turns out to be.

Help is greatly appreciated.

Thanks Greg.

[Noelm]

Once you have eliminated all the simple to replace stuff, do a simple and quick compression check, but so far it seems like a carby rebuild and a good "tune up" by setting all the pick ups as specified in the manual will be in order, but don't go there just yet.

[Conrod084]

So i replaced the plugs this afternoon, couldn't get the leads in Rocky the closest E/R dealer is in Yeppoon. Took one of the old plugs into Bluefin and they measured the gap while i was there which showed to be a little out from what it should've been. Got home replaced the plugs and the engine started immediately with a much more consistent strong idle as well. I noticed when i put the leads back on that the coil in one of the plugs was out of whack so i re-positioned it as best i could and headed down test it out under load. Motored off from the ramp and gave it a boot. It stood up quite nicely and kicked along really well for about 10-15 seconds before the revs started picking up and down again. I'm guessing that as i was hitting the chop the coil in the plug was connecting and disconnecting with the core in the lead. So with any luck once i get my hands on some new leads hopefully i should have my problem solved. Lesson learned, simple stuff first.

[astro66]

cheapest easiest first .....it could be a couple of small things...air leak/shitty plugs/dirty carbs/ ...is the primer bulb hard when its doing it ?