can u swap 580 or 650 into 720 ski?

[derek]

hi. i have heard horror stories about ignition timing differences burning up smaller motors in 720 set-ups. i don't get it. you put the mag from the 580 in and the mpem will change the timing? there is no tdc sensor if i am correct. how does mpem know what to do with timing? is there an equivalent to vacuum or centrifugal advance? (done electronically of course). or is the timing static at wherever it is set? what am i missing? why will it roast pistons in less than a minute? thanks.

 

[robin savell lloyd]

I am not sure about that one. I thought I have read that if you take electical from smaler engine and put it on larger engine it would work. I believe I have read this in diferent forums like pwc today. you may want to do more research and find the info from well known pwc mechanics. good luck as I can be wrong. Robin :cheers:

 

[robin savell lloyd]

I did a little search for you and this is what I found not mine but seems correct The 720 eninge is a good engine and if left stock, is very reliable. It makes a great upgrade to replace a 580 motor. If you use the 720 bedplate for the eninge, it will bolt right into the older hulls.
Try to find one with carbs, airbox and exhaust system and the swap is not difficult. You will need an impellor from a pump used with a 720 engine. Forget trying to put a 787 into your hull. It can be done but not easily. The electrical should even be the same unless you have a xp with a 580 in it then you will need to change engine electical and flywheel. good luck Robin :hurray:

 

[derek]

i was actually going the other way. i put a 580 into a 720 ski to get me thru the last 3 weeks of season. 720 was dead. 580 was paid for and alive. it ran 30 seconds. i thought i burnt it like all the seadoo dealers and engine builders said. turns out i got a piece of something hung up in the rotary valve and stopped it. took a couple of teeth off rotary valve gear. i am still curious about ignition timing though. thanks.

 

[robin savell lloyd]

Yes you were right I was backwards I noticed lastnight. I still do not see where there would be a problem though if you can go larger than you should be able to go smaller. you may want to change impeller to a 580 impeller for better bottom end. :agree:

 

[derek]

hi again. i replaced the rotary valve gear and valve. put correct cover on rot valve. put motor back in 93 explorer (exploder?) where it came from. started it up...BANG!! same thing. wiped out another valve and gear. thank god they use brass gears and a way to let them ratchet instead of killing crank gears. turned out it was a piece of cylinder sleeve that broke off. ebay cylinders. ups prolly dropped them and cracked a piece. anyway, when putting a motor together, check EVERYTHING. these are simple little motors. easy to work on. but they are strong enough to hurt themselves if you give them half a chance.

 

[robin savell lloyd]

I am sory to hear about your bad luck. I hope you have beter luck next time. Robin :cheers: