I bought a '95 EXT 530 EFI liquid cooled last week. The sled had slightly scrored a cylinder and had bad compression, so I put a new wiseco top end on it. New pistons, rings and I had the cylinders professionally honed.

Just after I put the top end on, my compression gauge read 90 on the magneto side and 95 on the clutch side.

I took the sled out to grand lake today and put about 30 miles on it. The sled runs really good, but still has low compression. 90 and 95

The only thing funny about this sled it the oil in the tank seemed to have gas in it, so I drained the tank and put fresh artic cat 50:1 oil in it. After running it all day, the oil seeems to have a FAINT smell of gas in it. I suppose this could be the left over gas that was in it.

My question is: What would cause this low compression? Could it be related to the gas that was in the oil tank?

Bad or cheap compression gage

NO=GIVE IT SOME TIME,RIDE GENTLE AND ALLOW YOUR NEW RINGS TO SEAT.
YOU'LL BE FINE.

It is likely both of the above posts. If the rings haven't seated, compression will be lower than after they haev seated.

Cheap gauges, or good ones that are not accurate will show lower than the true compression. Also make sure the gauge you use has a Shrader valve at the plug end of the hose as well as at the gauge, or the compression readings may be low as well. The hose volume has to be compressed, and with no valve there, and a a small displacement engine, it cannot move enough air to give a true reading.

Also, the 95 EXT was a 580, not a 530. The 530 was last used in 1991, then came the 550, with the 580 added in 93.

It is likely both of the above posts. If the rings haven't seated, compression will be lower than after they haev seated.

Cheap gauges, or good ones that are not accurate will show lower than the true compression. Also make sure the gauge you use has a Shrader valve at the plug end of the hose as well as at the gauge, or the compression readings may be low as well. The hose volume has to be compressed, and with no valve there, and a a small displacement engine, it cannot move enough air to give a true reading.

Also, the 95 EXT was a 580, not a 530. The 530 was last used in 1991, then came the 550, with the 580 added in 93.
[/b]

thanks for all the advice. Yes, it's a 580 (I finger fudged it).

I'll try another guage and put some more miles on it before I start worrying.

Ya I figured as much, just looked and your topic title was right anyhow. The 72mm pistons from the 530 might be a little loose in the 75.4mm 580 bore :lol: . Those would really be causing you compression issues, along with clattering off the cylinder walls trying to turn it over.