Bogging on higher speeds - '75 Evinrude 15hp

[Bobbywolf]

I just got finished with rebuilding the carb, and replacing the points and condensors to try and get rid of bogging that is occuring as you go full throttle. From idle to about mid way, it progresses nicely, but then starts to smoke die out. I tired adjusting the rich/lean mixture on the front of the motor, but I beleive that is only low speed setting anyways.

Could my timing be out of whack? I have a timing light, but this motor is manual start. Can I use an external battery with the light somehow so I can time it like it says in the manual?

Thanks!

Rob D

EDIT: I got the timing light set up properly, just pulled my car up near the barrel for 12v. Couple more things I'd like to add. While idling at a good speed (what my ear tells me is 1000rpm, I have no tach), I check the timing marks, and the marks on the flywheel are about 1cm in front of the marks on the throttle plate (likely wrong terms, but hopefully you see what I am getting at.) In the manual I have, it says to check that the marks are centered on one another, while running at 1000rpm. The marks of course move farther apart as I apply throttle, but they only really line up when idling as slow as it'll go. Hopefully this makes sense.

Last part of the equation. My plugs don't seem to be sparking completely regularly. Every few dozen flashes there is a blank, and it seems to be random, and coincide with the coughing of the engine. This doesn't seem to affect my ability to go to full throttle with a good throaty roar (before starting to smoke and bog down again).

Thats about all the info I can think of. Let me know where you think I stand.

Oh yea, I'm New! (as if you couldn't tell).

Rob D

 

[Xcusme]

Re: Bogging on higher speeds - '75 Evinrude 15hp

Welcome to iboats!! Rob, A couple of things to check. When you gapped the points. Align the crankshaft key with the rub block on the point set, then set the point gap. Rotate crank 180 degrees and again, align the crank key with the rub block and adjust the other point set. Your motors' timing is set with the crankshaft key. Look to see that the key is not partially sheared, which would throw off the timing. Clean off the crankshaft taper, use no lubricants, dry fit and torque flywheel nut. Are the coils newer? perhaps you're dropping a cylinder from a leaking (cracked) coil at higher rpm's. Check to see that the coils are properly mounted. Their bases should be flush with the mounting bosses upon which they sit. If the coils are mounted too far out, they'll rub on the flywheel, too far in and they won't develop full voltage. You're right, the only carb mixture adjustment is the low speed idle mixture screw. The high speed jet is fixed. You did soak the carb in cleaner to remove any crust and blow out with compressed air, and properly adjust float level...right? Lastly, check the link and sync. Make sure carb butterfly just starts to open when the throttle cam roller contacts the advance cam at the mark indicated.

 

[Bobbywolf]

Re: Bogging on higher speeds - '75 Evinrude 15hp

I basically set the gaps at .022 at their farthest opening, but I will go back and do as you suggest. The carb was completely torn down, with core plugs removed and soaked. I'm 99% sure it isn't the carb causing this.

I'm leaning a bit towards the coils, since this problem was present to a lesser extent last year. (It would only occasionally bog down, and only a bit at full throttle, slowing you somewhat). I do have a 9.9 Johnson of the same year which I can rob parts off of, so I may grab the coil packs to see what that does for me.

As for the link and sync, that is new to me. I didn't pick anything like that up in the material I have. I'll post up again tomorrow as I try things out. Maby I'll even grab a vid of what it is doing.

Rob D