Piston wash help

[ajmccracken]

I just rebuilt my motor. Top to bottom. I finally got it running decent after many changes. So i pull the head to check piston wash and this is what i find.

Jets are 72.5/132.5
42 psi popoff
Ada head 37cc domes
Bpipe
170/170 compression
Dual 38s

Im thinking air leak but want other opinions too.

 

[JC-SuperJet]

Front (right side) Piston has a Head O-Ring leak. Does Steam come out of the Pisser?

And both Piston Tops look black which indicates a Lean condition. Or excessive Heat. What Ignition do you have?

Are you running 93 Octane?

Did you air-leak test the Engine before installing it? This test will find all Air leaks.

You rebuilt the Engine. Did you rebuild the Carbs with genuine Mikuni kits too? Smart to rebuild Carbs along with a fresh Top End.

Did you fine tune the Carbs with a good Tachometer? Normal jetting is 75/135, but what you have will work. Slightly different Low and High Screw adjustments though.

And why is the Head Pipe Water Fitting capped-off or is it? The Stinger needs to be fed from this Fitting. What is that capped-off Barb Fitting?

 

[ajmccracken]

I didnt look at pisser steam.

91 ethanol free

I did not air leak test... Yet

Rebuilt carbs with genuine mikuni parts

Yes, fine tuning with tach

That capped off barb fitting was originally an extra water injection from a long time ago. I believe there was a microcontroller that injected more water at a certain rpm with the ski had the old riva kit in it.

Water is being fed into the bottom and comes out at the fitting right above it.

Im also being told i need to go past ada head torque specs as 18 is not enough.

 

[JC-SuperJet]

"Torque Specs: instead of 18 ft-lbs for Cylinder Head final torque, do 20-22 ft-lbs; instead of 23 ft-lbs for Girdle final torque, do 30-35 ft-lbs for Girdle Bolts."

 

[ajmccracken]

Ive heard this from someone but was too scared to strip things out. Is this a known issue?

 

[kevbo]

Head bolt threads can be easy to strip but they are also easy to repair. Sometimes you can just use a longer bolt and pick up enough fresh threads. It is difficult to get a lot of useful information from the goo on top of pistons. You can get better and faster information with a tachometer.

 

[Sparkplug]

I say piston wash is the number one way to tell the long term tuning of a 2 cycle.

Yours is hot. As hell. Timing. Gas. Jetting. Or a combination of all of them. I smoked a motor last month that looked the same just prior. Mine ended up being lean jetting combined with added compression I didn't consider from going larger bore.

Fix those o rings. Go a half turn out on the highs. And check static timing. Is where I'd start. I run 91 on 180 psi and don't have issues.

 

[wmazz]

Your front cylinder is obviously hot, and your rear cylinder looks
like it is gas fouled (which makes me suspect pop-off test results)

If the rear cylinder is running poorly, than that is a reason for the
front cylinder running hot.

When you disassembled the engine for overhaul was the flywheel
and bendix rusted?


Bill M.

Was that a recent compression and pop off tests, or was the
compression and pop off tests performed right before you
removed the head?

 

[ajmccracken]

Compression was 170/170 right before i removed the head. I was having a kawi racer tune it for me so ill back off those screws.

Bendix and flywheel were not rusty and in great shape. Pop off was 42psi on both a week ago. Timing is stock and stock ignition.

 

[Freakie]

Piston wash looks very lean...send pics of underneath the pistons...will verify lean issues for sure.
pop off is way too high.....surprised the ski can even rev with no hesitation....get it down to 25 ish..else you lean in mid revs as well.
I have stuck pistons on 75/140 with b pipe (wfo open...not surf conditions)....go richer...not harm at all.

 

[ajmccracken]

I have tightened the head up to above specs

I will take a pic when i get a chance. Just a thought, i dont have the intake mani blocked between the 2 carbs. If one carb is messing up, could the other be trying to compensate causing the issue?

Ive opened the rear idle screw a quarter turn more and it helped but not enough. Highs are both 2 out. I can confirm engine now never gets past 140 deg F

 

[wmazz]

I just rebuilt my motor. Top to bottom. I finally got it running decent after many changes.
So i pull the head to check piston wash and this is what i find.

The differences between the front and rear pistons leads
me to believe it was not running decent, or perhaps it
was running decent or poorly and something changed?

Jets are 72.5/132.5
42 psi popoff
Ada head 37cc domes
Bpipe
170/170 compression
Dual 38s

All this looks fine, but which reeds and impeller are you using?

I would avoid changing stuff like your jetting or lowering
your pop-off to a specific psi, it is not your problem. It
may help in the future, but you are trying to diagnose
a problem right now.

Your problem is the engine is not running the same on
both cylinders. There is a short list of possibilities. Keep the
list small.

I'm thinking air leak but want other opinions too.

First, Serious vacuum/pressure leaks (by themselves) only cause
carburetor problems like hard to start, or engine dies while
idling.

It is possible to have a vacuum/pressure leak on a new front main
seal if you used too much grease on the main seal.

I recommend you to test the pop-off on both carbs fully assembled,
because the carbs can cause cylinders to run different. Inspect carbs
for something that will cause rear cylinder rich (maybe include the
reeds) and front cylinder lean.


Bill M.

I thought I saw something in the front cylinder picture. Would you
please post a couple pictures of the front cylinder at BDC.

Did the engine ever stall or die at WOT, and then restart immediately
after as if nothing was wrong.

 

[ajmccracken]

I can get puctures early next week. It has never died at wot.

Stock reeds and hooker 10/16 impeller with fresh pump rebuild.

I did some more testing. Opened the highs and lows to 2 turns out. After just idle, both plugs are wet but if i open it up, front is wet and rear is dry but better than it was before which is making me think a jet got clogged.

Its the first motor ive built that isnt lawn equipment so i appreciate all the help i can get. Gotta start somewhere i guess.

 

[kevbo]

Actually tuning a leaf blower is very similar to a jet ski. It’s nearly impossible to hurt an engine that’s set rich of peak power. A piston that is fitted with less clearance may run forever with a cooler main jet and then seize the first time combustion temps rise. Always start too rich and slowly lean until rpm begins to peak or throttle response suffers. It’s the safest way to tune.

 

[ajmccracken]

Thats the idea. Sounds like ive got some work to do. Going to pressure test, open the carbs up and see if anything is clogged. It isnt a race ski, just for chasing boats at the ozarks. We did replace the high jets on the water so im thinking something went wrong at that point.

 

[ajmccracken]

I was able to take a look at the carbs tonight. Both still have the 42psi pop off and i dont have any jets clogged. I ordered block off plates from jetmaniac so thats the next step. My gut says one of the o rings on the ada head isnt sealing correctly causing the issue.

 

[kevbo]

If the head and cylinder is not flat it will leak regaedless of the O-ring. Look at the pisser stream when riding, If there is a head leak it will be broken. Solid stream means no leak.

 

[Mike W]

If you have the chrome/silver needle and seats, replace them with the Mikuni brass ones. The chrome coating flakes off inside where the needle rides and causes you to chase all kinds of tuning issues.

Also, Group K has interesting and informative write ups that could help you out. This one is very helpful. https://groupk.com/index.php/rear-cylinder-piston-seizures/

 

[ajmccracken]

Ive been going through the groupk right ups. Theres a lot of information there. The one you linked to was saying how the crank torsions and changes the timing of the rear cylinder. Which has me thinking i should retard the time to compensate but that sounds like the wrong way to fix it.

 

[ajmccracken]

I have 2 pissers. One comes off the front of the head and Ts to the pipe stinger. The other goes to the bottom of the bpipe. That one is not steady.