05-13-2009, 08:56 PM #1
1995 SLT 750 - Motor failed AGAIN!!
Last season, my PTO piston blew, and I rebuilt the top end, installing a triple outlet mikuni pump, and converted over to pre-mix. After 2-3 hours of break-in, the same piston burned through again. I have yet to tear it back down, but I will in just a couple weeks.
I need to know if anyone else has been through the same issue, and what they did to correct the problem. Here is what was done during the rebuild:
Triple Mikuni fuel pump conversion
Honed all three cylinder sleeves, and measured with a micrometer
installed all new fuel line (the clear blue stuff)
installed new pistons, wrist pins, bearings, lubed thoroughly
rebuilt all three carbs
made sure the cooling system had no restrictions
Break in procedure used 20:1 premix, ran 10 min, cool, 15, cool, 20, cool, etc, up to a full hour, left it sitting for a week. Took it back out, ran for 20, cool, 45, cool, 1hr, cool, and took it up to full throttle, and about 20 seconds into WOT, all power was lost!
Let me know what yall think, and some of you guys that helped last year may still be around!
05-13-2009, 09:06 PM #2
05-13-2009, 09:10 PM #3
05-13-2009, 09:23 PM #4
05-13-2009, 09:25 PM #5
05-13-2009, 09:32 PM #6
- Join Date
- Jul 2007
- near Toronto, Canada
Were you checking piston wash or spark plug condition during break-in?
Were the needles and seats replaced when the carbs were rebuilt?
What carb settings were you using?
What do the other two pistons look like?
Pictures when you pull the heads?
05-13-2009, 11:41 PM #7
- Join Date
- Oct 2006
- Cleveland OH
What do you mean piston blew? Does it have a hole in it?
If there's a hole, you ran lean (lack of fuel).
Did you ever run a leak down test. (air leak)
Have you done a crank index? (piston timing issue)
What are the carb screws set at right now?
Did you check the burn characteristics while performing the break in? (read plugs or piston wash)
05-13-2009, 11:43 PM #8
Sorry, I meant 32:1, not 20:1!! And that was without injection, as I removed the oil pump and installed blockoff plate.
05-13-2009, 11:47 PM #9
Carb screws of the front two cyls were set just past factory, maybe 1/10 of a turn past, because I wanted it to run slightly rich. PTO was set at a half a turn past factory.
Piston wash and plugs looked fine all the way through the breakin, and just before another hole was burnt through the piston.
Do you think the leak down test should be the first thing checked? I would have to put a good piston in the cylinder before doing the test, correct?
05-13-2009, 11:48 PM #10
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