Timing / High speed timing

[danew20]

Here is the deal... 92 115 2stroke outboard

The motor starts and idles just fine. When I go to accelerate the motor will hit 3800 rmp and bog out and bounce like a car hitting its rev limiter. When it starts doing that and we push the throttle arm (lever magneto control) back just a little and let it back slowly it begins to accelerate as usual.
We checked all the spacing and timing according to specs from the manual and even replaced the coil pulser but none of that helped. It is as if it is not kicking into high speed timing or the throttle is advancing to fast. Once someone kicks the lever back on the motor and it begings to surpass 3800 it runs just fine, just getting past that 4800 is the problem.

Any thoughts...

On a side note I just replaced the CDI unit assembly electrical box because before it would not spark at all, not the new one works. I thought it may be the box, because before replaced when it was running it ran fine, but the mechanic I purchased it from said if it runs at all and runs after we hit the lever then its not the box, but that is the only thing I can think of that has changed at all on the motor.

Also, out of the water it will run past 4800 no problem, just under pressure it will not.

Any info or suggestions would be greatly appreciated...... This is anoying as hell especially the fact I can only run half speed unless someone is in the boat to hit the lever on the motor for me..

Thanks again

[jb123]

if it wont run up under load, it is most likely carbs/fuel restriction.

[danew20]

Carbs have been rebuilt! It ran just fine just a month ago before we replaced the CDI box, and its exactly at 3800 rpm.

And again, if someone pushes the timing lever it will jump up and run just fine... So the carbs are doing their job as far as I know.

No we are not using a "yamaha" meter, just a normal meter, and it is a manual we bought from one of the local shops.

Thanks

[boats.net]

Have you checked the timing to see if is 25 degrees at full advance?

[danew20]

I know the low end is right around 4-5, We have yet to check high end

[Hamfisted]

Set the mechanical timing....

Set the timing mechanically just like the factory service manual describes in the "Periodic Maintenance" section. There is a scribe line on the underside of the flywheel to use as a reference point. Sounds like you may be getting too much timing advance and detonation, killing the acceleration. Rotate the flywheel to the TDC on the number one cylinder and note it's alignment with the timing marker. Make sure the number one piston is in fact at TDC, the timing marker is adjustable if it is not. This must be accurate for all other adjustments to be accurate. Timing should be 5 degrees ATDC at idle and 25 degrees BTDC at full advance.




-Mike

[jb123]

( It ran just fine just a month ago before we replaced the CDI box )

was your set nut lose and your timing adjusted itself? in my 15 yrs of running yammies ive never seen this happen.... can someone explain how this can happen?

[cyrillefrenchy]

hello
my guess is : when you start to throttle up, the first part moving in the linkage system is the magneto control lever, and after is the carburator arm to open the butterflies.
when you throttle up, the magneto arm is moving faster than the carburator linkages, to reach quickly the maximum timing advance.
when you reach 3800 under load, you shoult have your magneto arm all the way forward, sitting on the maximum timing adjusting screw and your maximum timing advance should be 25 degres.
you should not be able to move your magneto arm by hand.
disconnect the magneto arm connection to the magneto and make sure the moving part of the magneto is moving freely.i saw some hard to move, they just need some lubrification, this part seats on a plastic ring.
ckech this out and let us know.
excuse my frenglish.
frenchy

[danew20]

We replaced the linkage and the lever of the magneto and that did not help. I advanced the screw in so the longer control connected to the magneto hits sooner and the motor will get up an run, however the timing is not at 25 when it is done this way.... The timing screw could not have come loose and adjust itself, when everything is at specs according to the book it will rev out at 3800. Strange, its to the point I am taking it in to a mechanic who knows yammers, only problem is it only does it under load so it may be costly as far as labor and time....

Thanks!

[cyrillefrenchy]

if you move IN the adjusting screw, to make the magneto arm hitting sooner, you will have less timing advance and it's not what you need .
how much timing advance do you have with the magneto arm all the way forward?
frenchy

[toddingalls]

Danew-
Did you ever figure this out? I have the same exact problem except at 1900 rpm.
Mine is year 1990 outboard.
Thanks
Todd