2 cycle engine issue

[helbent]

Hey fellas, Im bored.  Seeking advice so I can think I am doing something constructive.

I bought a 99 ultra 150 jetski that was not running.  I tore it down completely, rebuilt the motor and replaced some electronics.

Its been running great, everything perfect and functioning properly.  Gaining confidence in the ski I stopped premixing my fuel, started to trust the oil pump.  I also started using a non ethanol fuel, then the last couple times Ive had it out I have lost power to a cylinder and have had to limp it back home on 2.  Pulling the plugs the front one had had its gap closed up, replaced the plug ran great then dropped the same cylinder again.  What is crushing this gap closed?  Is the piston hitting it?

Looking for ideas from anyone, since you guys are the smartest people in the world, before I go tearing into the motor when I get home in a couple weeks.

Thx

[helbent]

[PAKFRONT]

I would say yes, seen it before.. Some factors to take in to account.. Don't don't take this wrong please.. I usually see it when using low quality rod and wrist pin bearings, they get loose pretty quick, (just normal tho, no worries).. Also when the engine heats, the rods lengthen a bit.. Was the head or Jugs Shaved?? Try Spark plug Standoffs.. Or cheaply, double the washers..

[rpm]

Sounds like it may be hitting the piston. Why is another story. Are you sure it's the right plug for the engine? Could be too long.  When you rebuilt the engine did you change the rods? They may have stretched.

I'd run the piston to TDC and look thru the plug hole for damage on the top of the piston.

[helbent]

Didnt shave anything, put stock pistons back in.  Had the crank re-tooled while it was out, one rod had remnants of piston in the bearings and was moving side to side a bit.

So you dont think i need to pull the heads and take a look.  I really dont want to buy another gasket set.  Have way too much money in this already.  Seems funny that this would happen after 30 hours instead of right away.

Also I have seen oil collecting in the hull.

[CAP1]

i've zero experience with 2 stroke engines.....but the closed spark plug gap.......the only thing that can do that, is the piston hitting it. pull the plug, then shine a flashlight down into the cylinder, and see if there's any marks on the piston top. that'll give ya a clue. it sounds as if something's running a little hot, and stretching a bit..........

[PAKFRONT]

Getting confused now.. New rods pressed?? New mains & seals? Old pistons? New Pistons? sorry, lol!

[helbent]

1 New rod, the center, new mains and seals, pressed (not exactly sure what the guy did).  New pistons, rings and wrist pin bearings (3).  The center cyl was the initial cause for the rebuild.

So, if it gets hot, the rods stretch. (could be because it runs fine for a bit then i drop that cyl)

By not mixing my fuel, could be causing excessive stretching?

[PAKFRONT]

If you made solid contact, it would have smashed the plug.. Probably just the bearings loostening up.. They do that.. I have LOTS of 2stroke exp..

By all means, I would pull the head.. But that's me.. Still, if you made solid contact, the plug would be smashed! Use plug indexers to lift the plug a bit higher..

Assuming you know the oil injector is working, oil won't be a factor in that.. By stretching I meant natural expansion of the rods length, due to normal heating.. There is sometimes little spare room for error..

[CAP1]

1 New rod, the center, new mains and seals, pressed (not exactly sure what the guy did).  New pistons, rings and wrist pin bearings (3).  The center cyl was the initial cause for the rebuild.

So, if it gets hot, the rods stretch. (could be because it runs fine for a bit then i drop that cyl)

By not mixing my fuel, could be causing excessive stretching?

 by not mixing the fuel, you could be running a little hotter, thus causing a slight bit more stretch. the oil lubricates, and cools.

[helbent]

OK, this is my plan,

check the piston for damage, extend the plug, keep trusting the oil pump and keep using the no ethanol gas.

hopefully this works for me

appreciate the help fellas.

If i get time to mess with it when I get home in a couple weeks, ill be sure to let ya know how it worked out.

gonna be cold, but have wetsuits =)

[PAKFRONT]

 

[CAP1]

i wish i could've been more help, but like i said.....i've got zero experience on 2 strokes. for whatever reason, i've just never had a reason to have worked on them. looks like pakefront got ya covered though. 

[Dadsguns]

Are you using the recommended plugs for Kawasaki or are you using regular automotive plugs not the (NGK's)?  I have a Kawasaki 1100 STX, only seen that happen when not using correct plugs.

[homersipes]

my 2stroke experience is with sleds, and no expert by any means.  Seems as thogh if a piston slapped the plug you would hear it, and it may create a hole thus loss of compression.  Hard to say not knowing lol.