95 Seadoo SPX Acceptable Compression

[natem1270]

Hi all, I recently made a post about my SPX fouling plugs and got some great advice. I was told by one user that my compression seemed low (135 both cyl warm). I’m wondering what an acceptable amount of compression is on this motor.

I’m ready to rebuild the carbs with an OEM kit but have been holding off because I was unsure if my compression was the real issue.

 

[mikidymac]

At 135 it should still run fine. 150 psi is perfect and they are done at 120 psi.

 

[natem1270]

At 135 it should still run fine. 150 psi is perfect and they are done at 120 psi.

Thank you for the confirmation

 

[etemplet]

I'd monitor the Compression. 135 ain't bad but you've got wear or it wouldn't be there.

 

[Ajvdub]

I'm picking up a set of 96 spxs this week. I compression tested them cold at 138 and 135 for one ski, 140 and 145 for the other. Do these pull 150psi cold new? Also, I had both plugs out, was I not supposed to do that? I just read somewhere you should do 1 plug at a time... oops.

 

[mikidymac]

Cold or hot doesn’t matter. Perfect compression is 150 psi with fuel off, plug wires grounded and throttle wide open. Doesn’t matter if plugs out or in.

 

[Ajvdub]

Awesome, thanks for responding to both my posts so quickly. I did not have the fuel off or the plugs grounded. Would the fuel on show lower compression and does not having the plugs grounded hurt the ignition system?

 

[mikidymac]

No, won’t change the numbers just prevents flooding.

You want the plug wires grounded as it hard on the ignition coil’s to build voltage and not be able to discharge.

 

[Bowser]

Huh I was wondering why it's recommended to ground the plug wires, TIL

 

[mikidymac]

Because it can damage the ignition coil if it builds up a charge and can't discharge. Grounding the plug wires prevents the coil from building a charge.

 

[tobytd]

Safety also…fuel..vapors…….spark….BOOM!

 

[natem1270]

Just want to throw this here in case anyone else is wary about their compression. I've used it twice now runs great and feels very fast with 135 lb/s compression.

 

[MSMartin]

Just did a compression check on my 97 GTX with the 787 engine. I got 135 psi in both cylinders cold.
I did not open the throttle up at all. Does anyone know if the fact that I did not have the throttle open would affect the 135 psi number much?

 

[etemplet]

I don't open the throttle when checking compression and I don't know how much of an effect it would have. I'm only looking for a number. You're numbers are not bad at all.