1998 MXZ 670...Need Advice - Snowmobile Forum: Your #1 Snowmobile Forum

skidoomxz670MI · 12-07-2006, 08:35 AM

I have a 98 MXZ 670 that is running really rough. Ran good for about 20 miles then went downhill from there. It acts like it is running on one cylinder. Changed the plugs numerous times and the problem is still happening. Compression is at 141 psi on each cylinder. The exhaust has a few leaks. Could this be my problem? Possibly Ignition Coil? The sled will top out between 45-60 MPH with a lot of smoke coming out from the vents in the hood. I am also running K&N filters with the stock air box removed. I would appreciate some advice. Thanks.....

**smallengineguy** · 12-07-2006, 03:53 PM

Is only one plug getting wet? We need a little more info.

upersleder · 12-07-2006, 07:50 PM

check your plugs, if one is soaked change it, see what happens. to figure out which cylinder is not firing if the plugs look ok when you first start the sled put some snow on each side of the exhaust manifold and see which one burns off quicker, if one side is not firing the snow/water wont burn off. like SEG said, please give us a bit more info so we can help.

mmrosshere · 12-08-2006, 01:55 AM

Is the smoke from the belt by chance? Did your filters get iced over? Brake locked up? Actual y w/the high comp. readings I think You may have dislodged a nest in the exhaust and then it pluged up solid down the line the smoke has to come out somewhere. The more you push it the more backpressure you get there

"The sled will top out between 45-60 MPH with a lot of smoke coming out from the vents in the hood."

Just a thought with the limited info we have

skidoomxz670MI · 12-08-2006, 08:53 AM

Thanks for the info. Here is some more info about the problem. When it starts to run bad I will turn it off and switch the plugs because on plug does not follow. The belt side is the good cylinder. That plug is very wet and looks good. It is just really weird because it will run really rough and then it will rip for about 30 seconds and then it will die down and not run.

skidoomxz670MI · 12-08-2006, 08:54 AM

I did have to rebuild the brake. I believe that I bleed it properly. Are the brake cylinders known to go bad?

skidoo kid 102 · 12-08-2006, 09:12 AM

sounds like one cylender isn't getting gas? Don't know?

98mach1 · 02-22-2007, 11:43 PM

ill bet its in that teather switch not making good contact. it will cause it to smoke like crazy as well not making good contact. if hes got good spark,compression and fuel. thats al i know of the 670 HO having an issue with. make sure the teather is clean and making good contact to the ignition and back to computer

**RJ Gleason** · 02-23-2007, 01:47 AM

The clutch side one is the problem cyl. the plug that is wet is the one not firing.
You will need to get a spark detector and see if there is any spark after it is running.
Either the coil is the problem or you just have a bad connection from the wire to the plug boot.