- Location
- Stockton CA
Brand new 750 motor. Pulled the head off and saw this. Air leak?
SX/SXi/SXi Pro What would cause this?
- Thread starter Ballsonya
- Start date
Brand new 750 motor. Pulled the head off and saw this. Air leak?
- Location
- Arnold MO.
looks like lack of ignition, possibly cdi, plug wire or possibly a air/fuel too rich preventing ignition. Just a guess since its hard to tell just by a picture.
- Location
- Stockton CA
I cut the plug wires back and made sure it has good spark. I'm running 650 electronics. It runs good and hits hard. The carbs are synced. The plugs look good. Idk I'm kind of stumped on this. I'm gonna do a leak down test tonight and see what happens.
Philip Clemmons
Owner, P&P Performance
- Location
- Richmond, Va
The dirty one looks about like it should, but may be a touch lean. The clean one is very rich. You have some uneven jetting or fuel requirements.
- Location
- Stockton CA
The jetting is all the same. I could be wrong on the carbs being synced. These keihins are a b***h to tune. So the clean one means to rich and the dirty one is semi ok? Or is that backwards?
Philip Clemmons
Owner, P&P Performance
- Location
- Richmond, Va
It's not backwards. The fuel coming in the transfers washes the carbon/oil off. Clean means lots of fuel flowing across top of piston. The dark one means minimal fuel. There should be thumbnail size or slightly larger patches of clean piston at each transfer port. Otherwise it should have a brownish color on piston. Oil and type of pistons (cast/forged) affect it, but yours are way off.
Have you pressure tested the engine for air leaks?
Have you pressure tested the engine for air leaks?
- Location
- Stockton CA
I'm gonna pressure test it tonight when I get home. I'll post the results.
- Location
- Cruising Around
Good call by Mr. Clemmons. Could'nt the "clean" piston look like that from water ingestion? Oring or head gasket good? Is compression even?
Philip Clemmons
Owner, P&P Performance
- Location
- Richmond, Va
Thanks. I left out what "I" would consider unlikely but realize others may not. Weak ignition as mentioned, would cause a rich issue, but my assumption was the ski ran ok and didn't have an obvious (ign) problem. Same train of thought for the water. Very good suggestion, I just assumed it would have exhibited other issues and have rust in cylinder.
- Location
- Stockton CA
I don't believe there's any water in cylinders. I've had water in my cylinders before and the ski ran like junk and scored my cylinder all up. They are brand new o rings on an ADA head. There is a slight psi difference. 180psi in the rear and 185psi in the front but I didn't find that alarming since its still being broken in.
- Location
- Cruising Around
Well, if there is no water intrusion, carbs are jetted the same,reeds are good, that leave ignition? Have you tried running it with the sparkplug boots swapped?front to rear and rear to front? IDK,shot in the dark.
- Location
- Stockton CA
Well I did a leak down test. It took 8 minutes for it to go down from 10psi to 4psi.....
- Location
- Stockton CA
I take that back. One of my fittings was loose. It's holding 9 psi
- Location
- Stockton CA
So what should try next? The electronics came out of my 650 motor and they are good. Maybe pop off test the carbs? Maybe one spring is a little bit stiffer?
Fro Diesel
creative control
- Location
- Kzoo
Always use a pop off tester. Even a homemade on is better than nothing. Really makes since when you have two carbs. That way they are really sync'ed
sent from Fro Diesel using tapatalk2
- Location
- New Hampshire
Please refrain from posting the wrong information because you clearly are still learning. By looking at the brown side you must have several hours on the motor. The wash looks great. How ever the clean side I suspect is from too much raw fuel entering the cylinder and washing the carbon off. If it was water ingestion you most likely would have some detonation on the top of the piston. If its runnin fine I'd recommend leaving it, but if you dial that carb in or figure It out the ski should have a lil more response. Is it a dual carb setup?
Joker
...chaos? Its Fair!
- Location
- La Porte, Indiana
- Location
- Valley Springs, CA
It's dual carb motor has a couple hours on it
- Location
- Stockton CA
I'm pretty sure the pop off pressure was different in the back carb and was letting to much fuel pass by. Im putting some 44sbns on it and running it tomorrow. These carbs are dialed in better pop off wise.