compression numbers

[my787]

well she started out of the water but not IN the water....plugs are still getting way too much fuel. Compression test is showing 120/120 on a cold engine/WOT. Is it time for a rebuild?

 

[Dr Honda]

Past time for a rebuild. But, that's why it won't run in the water, and why it's running rich.

 

[my787]

Past time for a rebuild. But, that's why it won't run in the water, and why it's running rich.

why would it dump more fuel due to lack of compression? I know for a fact one of the needles on the carbs is bent a little, so maybe fuel is getting past the needle. I thought I read some where Seadoo recommends a rebuild anything below 100psi? Do you think a cold engine would cause my numbers to be lower?

Also, what is a good rebuild kit? At this point am I looking at top end or entire engine? I'm good with cars so it shouldn't be too hard for me to rebuild.

 

[Wire4Money]

What's your elevation? I had a 94 spx with 120psi at 5000' elev. that ran beautifully. 150 is ideal at sea level, but expect 3% per 1000 ft. correction factor.

 

[Dr Honda]

why would it dump more fuel due to lack of compression?

It's not dumping more fuel, it's just not burning what being sent in. If was burning everything... it would still be making the same power.

I thought I read some where Seadoo recommends a rebuild anything below 100psi? Do you think a cold engine would cause my numbers to be lower?

No. A good running Rotax 2-stroke will make 150psi cold. You never do a compression test warm since it will cover up problems. (and never add oil to the jugs)

The only time that low pressure is OK, is if you are at very high elevations. (as noted above)

Also, what is a good rebuild kit? At this point am I looking at top end or entire engine? I'm good with cars so it shouldn't be too hard for me to rebuild.

You can probably do just a top end... but if you get the engine apart, and you feel any roughness in the crank bearings... you will need a bottom too. Also, make sure your crank seals aren't leaking, otherwise your new top end will eat itself.

 

[my787]

do i have to pull the entire engine with a picker in order to see the bottom end?