Pressure testing SD 800

[rpoggiolo39]

Hello,
I resently rebuilt my 96XP and in the process of breaking it in. But after the 2nd tank of gas I noticed a loss of power and could only get about 40mph out of it. I ran a compression test and found that the mag cylinder had 100 psi and the pto cylinder had 160 psi. So I pulled the motor and I am runnig a pressure test. I have made up a block off kit for the carbs and the exhaust. Do I have to block off anything on the rave valves?
When I add about 5 lbs air to this motor I hear air leaking from the rave valves and when I take off the rave caps the air blows the spring off the rubber boot. Could I have a rave problem, could that be the cause of my low compression problem? This happens only on the cylinder with the low compression.

[seadoohx]

Re: Pressure testing SD 800

yes block raves

[Bill O'Neal2]

Re: Pressure testing SD 800

Have you looked at the fuel filters in the two carbs?

[rpoggiolo39]

Re: Pressure testing SD 800

Yes, before I installed the rebuilt motor I had them apart and cleaned the filters and the inline filter. Also flushed the gas line out and removed the gas tank and flushed it out. The first tank of gas I was having a plug fouling problem in the mag cylinder so I cut back the spark plug wires as recommeded in prevous threads. I can see inside the cylinder that has the low compression from the exhaust port and the piston and rings look fine. Next I have to run a pressure test I am having a hard time finding 1/4 rubber for the pressure test. I have 1/8 but I can't get the raves to seal Does anybody know where I can find 1/4 rubber.

[1fastski.com]

Re: Pressure testing SD 800

what pistons did you use for the rebuild and what were the cyls cut to ?

[seadoohx]

Re: Pressure testing SD 800

yeah maybe your machine shop did not get clearance correct..
depends on piston too every one is diff
even siezco pistons(wiseco) are super tight clearances.. if cut wrong forget it

[rpoggiolo39]

Re: Pressure testing SD 800

The pistions are wiseco's. The ski ran fine with lots of power first 2 tanks of gas and I made sure it was warmed up before taking off.

[Bill O'Neal2]

Re: Pressure testing SD 800

You have a stuck ring on the piston pumping 100 psi. Replace it.

[rpoggiolo39]

Re: Pressure testing SD 800

Trying to pressure test this motor I found that it was leaking air out the cooling ports on the head cover. So I pulled the head and found that half the O'ring around the front piston was gone. It was blown out not cut. Has anyone ever hear if this.

[Bill O'Neal2]

Re: Pressure testing SD 800

Yes.

[rpoggiolo39]

Re: Pressure testing SD 800

I have replaced the bad o'ring resurface the head on a piece of glass with some sand paper and put it back together it runs great. I also while it was apart I rebuilt the carbs with some sbt carb kits replaced the fuel lines and plug wires. The pop off pressure is set at 38 PSI low and high speed are set at 1 and 0 and the engine pressure tested good. But I am still fouling the plug in front cylinder? I can run around for about a hour or two before it starts to foul and run shitty. It doesen't star acting up until I bring the rpms down and try to excelerate again. I don't know what to check next maybe the coil?

[Bill O'Neal2]

Re: Pressure testing SD 800

Try clipping the sparkplug wire for a new connection at the sparkplug boot.

[rpoggiolo39]

Re: Pressure testing SD 800

These are new wires just put them on?

[Bill O'Neal2]

Re: Pressure testing SD 800

Yeah, no need to clip a new wire.