300/440/550 shaking problem

crashnburn86

crashnburn86

Location
orlando
I built a 550/650 conversion and everything works excellent. Except when i ride the ski shakes pretty bad at low rpms but when i get up to plane its fine. I have completely taken apart the ski and re aligned and double checked everything 1 time already and its all perfect... so it cant be alignment or bad motor mounts because i checked all of that.... does anyone know what else this could be??? someone said my driveshaft might be messed up ?? its not bent that i can telll ... someone please help
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
harmonics. As the rpm's go up the shaking reduces. Is this dual carbs or single, if dual you may have one carb out of sync (One butterfly is open more than another). Once you get the throttle open it becomes a moot point. But at lower RPM you are feeding one cylinder more than the other.
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
I have had friends who had 550's that shook like all get out. Had good power but were just rough. May try tuning the carbs some and see if that helps.
 
crashnburn86

crashnburn86

Location
orlando
after i first built it it wasnt tuned. since then i have gotten it tunned and it hasnt helped one bit... It feels like i hand grenade is under you at low rpms. like the pump is going to explode but it doesnt... ive checked it all and it seems fine im very confused.
 
Fenix169motox

Fenix169motox

Location
Northwest Ohio
Hey you figure it out at all??
I have the SAME PROBLEM with my sxi pro. carbs are tuned perfect and so are the plates.
I think its an air leak. one cyl is producing a little more power than the other. I though at first it was the little water drain on the bottom of the engine so i made a block off plate for that. my rear crank seal has oil smooge around it so i'm guessing i have a bad leak there, sure enough i fill the hull with water till that seal is coverd and i have an oily foam from there. Ordered some seals today so hopefully that fixes it!
hope i gave you an idea dude!
 
Wilke

Wilke

X2 stole my life
Location
Indialantic, FL
Sounds like you're running on one cylinder (at least misfiring one) Check that you have good spark on both plugs. Could be that you've got a weak spark at low rpm and you're misfiring, then once you get the revs up the spark gets stronger and the misfire goes away, might want to do a compression check while youre at it. If that all checks out I agree with fenix, could be an air leak, time to leak test the crankcase (or just replace the seals).
 
Fenix169motox

Fenix169motox

Location
Northwest Ohio
Wilke said:
Sounds like you're running on one cylinder (at least misfiring one) Check that you have good spark on both plugs. Could be that you've got a weak spark at low rpm and you're misfiring, then once you get the revs up the spark gets stronger and the misfire goes away, might want to do a compression check while youre at it. If that all checks out I agree with fenix, could be an air leak, time to leak test the crankcase (or just replace the seals).
Click to expand...

Agreed, what would cause a weak spark at low RPM ? crud on the exciter coil?
 
Hfurll

Hfurll

Henry
Location
Breckenridge Colorado
How are you aligning the engine? If you’re doing it with the rubber in, you not able to fine tune with shims. The 550 bearing housing is not forgivable .
It has become somewhat amusing, all the guys with new conversions complaining about shacking and not one with any shims after “aligning”.

Align it with rubber out, shim it, then put rubber back in.
Happy wrenching.
 
crashnburn86

crashnburn86

Location
orlando
Of course i align it with the rubber out its the only way to align it. I figured out the shaking, it is my exhaust sitting against the hull transferring the engine movement to the hull. Put turf in between it helped a little.
 
You must log in or register to reply here.
Top Bottom