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Old 10-29-2012, 01:06 PM   #16
kellymac530 OP
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OK so its back to the drawing board...and this discussion board for help.

I pulled the entire motor to make it easy.
I plugged the vent line that operates the fuel pump from the crank case.
I made a cap for the carb intake with a threaded hole in it and a schrader valve and gauge
I pulled the U manifold from the exhaust and made a blank off plate and seal that up.
I finally put about 10 psi into the valve and it held just fine and very slowly bled down.

Not sure if I was leaking out of one of my blank off plates on the intake/exhaust or not, but the bleed down was slow and tookj a few minutes to drop down...not positive, but I would think that is tight enough to at least run ok.

Any more ideas on where to turn for help?

As far as the comments on changing everything and then wondering why it wiould not run...It did not run when it was parked. It ran for a few minutes then would die. That is a common problem of an exhaust leak on a jet ski or an ignition issue on any motor getting hot.

That is the reason why I replaced the waterbox, it had a hole in it and was not water/air tight...that should have solved the dieing issue from oxygen choke out.

The other chages were all done trying to address the new issue of starting but not reving up.
The motor was tired and had sat a long time with some water and carbon in it so I did a complete crank swap and a fresh bore and surface check for flatness and sealing and rebuilt it all...no problem, easiest thing in the world on a Jet Ski and I have done dozens of them over the years with no issue.

The carb repairs and ignition/magnetto swaps have all been done one at a time from a known running ski to check if that is the problem...no success. Fires up after a long cranking and then putters for a bit and never quite revs out and dies.

HELP PLEASE. I am at my wits end and can not start my rebuild on a perfect BMW R80G/S that I am dying to clean up and ride until this pig is gone.
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Old 10-29-2012, 04:57 PM   #17
baloneyskin daddy
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Just for the hell of it try swiching the plug wires from one to the other.
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Old 10-30-2012, 02:26 PM   #18
baloneyskin daddy
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I know my request sounds stupid but sometimes its somethig stupid thats the problem.
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Old 10-31-2012, 05:02 PM   #19
kellymac530 OP
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Thanx Baloney,
Yes I have tried that early on. I made an extension for the front wire that needs to be longer by using one of those spark testers that you plug inline to see if there is spark and I ran it that way...more popping less running. so that is not it but was worth a suggestion, thank you.

Any more ideas? ANYTHING is welcome at this point.
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Old 10-31-2012, 05:14 PM   #20
ragtoplvr
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have you actually put a timing light on it and made sure the spark is close.

Also, weak coils or amplifier can look good on a spark plug but blow out under compression. Use a regular plug gap at .120 and see if you get a good spark.


Rod
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Old 11-01-2012, 07:37 AM   #21
baloneyskin daddy
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Are you absolutely sure the pistons are in correctly, not backwards, and are the correct ones. It sounds like port timing is way off. Its also possible the crank is indexed wrong and the timing is off. Is it a new or rebuilt crank. 2 Strokes are so simple it almost has to be something stupid.
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Old 11-01-2012, 02:18 PM   #22
kellymac530 OP
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Yes I am sure that the pistons are the rite ones, for a piston port, and I matched them up next to the OE pistons to make sure they are the same port styles. I have pulled the head and barrels to double check that they are oriented correctly.
Arrows point towards exhaust, and looking thru the intake and exhaust manifolds the ports line up propperly.

As far as timing, a light is really hard on a jetski because the magnetto is inside a sealed case on the front of the motor, I can see it now since I have been running it with the cover off, but I do not see any timing marks off hand, I will look better. It is a magnetto and not a distributor so it only fires the plugs while the motor is turning quickly enough to generate spark.

The spark trigger plate only has a few degrees of adjustment, maybe 15* total. I have tried it at every increment possible, all very similar results.

As far as coils, I have swapped out the ignition from another known running ski and no change. I have swapped out all of the ignition components to no avail. Put the old ones on the other ski and it is fine. I am losing it. Never been stumped like this.

I really appreciate the help though and I do go and verify all replys just to make sure...
Sure feels like it is something simple or dumb.
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Old 11-01-2012, 06:50 PM   #23
baloneyskin daddy
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I know its a rebuilt crank but it might be a bad crank seal, the one between the 2 cylinders. you'll have to pressurize one cyl and see if air leaks into the other.
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Old 11-02-2012, 01:48 PM   #24
kellymac530 OP
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I think that is my next test then.
Thanks a ton Baloney and everyone else.

Any more help or ideas are still very welcome.
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Old 11-11-2012, 09:01 AM   #25
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Any news?
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Old 11-13-2012, 12:06 PM   #26
kellymac530 OP
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It held air in all test...pissed me off so I stripped it down, easy on a Jet Ski motor, no trans, and it looks like the bore may have been too tight. They are Hyperutectic pistons and had a coating on intake side and exhaust side that was probably a few thousands thick. I think they bored it to the piston top measurement and did not account for the coating thickness.

This has now worn off almost totally and scored the cylinder walls badly and the pistons are all scored like a dry seizure looks when you run a 2T without oil. It dropped to about 90 psi compression before I stripped it so I am guessing that may be adding to it.

I am going to try honing it and see if I can get out the scratches and then gently sand the scratches out of the pistons and check clearances, if decent I will reassemble and see if that runs. If that helps I guess I can bore it over and get new slugs and try again.

I do have one question, the new pistons are the same height, shape, skirts everything, but there are 2 small holes on the exhaust side of the pistons just under the rings that go thru to the inside of the piston. The old pistons do not have these. I am curious if that is just a modification from the high performance piston manufacturer or if that could be part of the problem here bleeding off too much bottom end pressure??????

Maybe the pistons are for a different year...they are deffinately labeled for this year motor, and not for the reed valve model 550.

One more stupid mystery...I am going to call the manufacturer and ask....been really busy with a kitchen remodel for the little woman...that will buy me some garage credit....lol
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Old 11-13-2012, 02:34 PM   #27
baloneyskin daddy
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I can't imagine holes below the rings at the exhaust port affecting anything, probably allow a little extra oil at a notorious hotspot. Rings with insufficient end gap will scar cylinder walls also.
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Old 11-16-2012, 08:32 AM   #28
kellymac530 OP
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Thanks Baloney,
I will check that before reassembly.
I do not think tight rings would eat the hyperutectic patches on the pistons, but I guess if they scored the cylinders then the scoring could grind up the patches.

I thought that the holes might just be a lube vent for better performance/cooling/modification.
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Old 11-16-2012, 08:35 AM   #29
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Is there a time when the holes are open to the exhaust port. If so then this is an issue.
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Old 11-16-2012, 06:19 PM   #30
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Yes they are open to the exhaust port. They are immediately under the ring. They are about 1/4" or less in diameter and are on the exhaust side, at least according to the arrow on top of the pistons which is supposed to point the direction of flow....at least it has on every other ski I have built...That would suck if that was the entire answer after all of this time.
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