Other Mid range vibration

[hillbilly550]

Sorry for the long post but thought i would give some background info, the question is at the bottom

So i have a 750 engine with a 650 stator and flywheel and sbn44. The carb has NOT been tuned to this engine. Bought it from a guy complete with conversion plate for a 550 and I had some free time so what the hell, Installed it in a 550.

It had a horrible vibration. Pulled it back apart. I replaced the coupler because it looked to be drilled oversize with a hand drill and vise, then taped. That was verified by the vise marks and a runout check on a lathe. So a new coupler was modified by a machinist.

Put it back in and had a mid range vibration. Idles smooth. Part throttle back of engine vibrates like crazy then smothes out with more throttle. Going to pull flywheel tomorrow if I get time and check for issues with it and stator. Pistons seem to be in sync (180 apart) but I haven't checked it with a dial indicator yet. I have shimmed this thing every way possible and it dosent change so i would think it's got to be internal.

So I'm looking for out of balance flywheel, out of phase crank, or bent crank?



Could carb out of tune cause a mid range engine vibration? It's violent, the hole ski shakes on the cart but only at part/mid throttle. I am looking at pulling the motor back out and tearing it down if there are no other possibilities but I decided to throw that out there

Thanks.

 

[Austin]

I would check the crank. Does it feel like it has full power?

 

[Yellofury]

could it be anything in the driveline that causes the vibration? ie can you pull the pump and run it and see if it vibrates? that would at least start the elimination process.

 

[tshank123]

Are you sure its really a problem? Every ski will vibrate at a certain RPM, although I've noticed its usually at lower RPM. Its physics, you cant cheat it. Resonant frequency of the hull.

 

[Austin]

From what it sounds like, its more intense than your normal vibaration at low rpm's

 

[509freerider]

Could it be a bad pump bearing? Incorrect alignment could cause a issue also. I would would water test it to see if it goes away, I know my 550 made a horriable vibration when I would rev it up out of water and would run just fine in water.

 

[hillbilly550]

It's pretty violent. I'm going to pull the coupler off the back of the motor and put it back in to run it. That will give me an idea if it's engine or driveline. The prop shaft and pump shaft turn smooth and are in good condition. They are set up the same as they were before I took them out. I think I'll put my tach on it to see what rpm range it is so I can see if it changes with different shims and such.

The engine sounds great and fires right up.