750 ZXI Problems

[cbeastwood]

Man, the ski keeps getting slower and slower. I think I'm too rich on the highs. Does anybody know the stock settings of the high speed screws? It gets out of the hole fine, but max's out around 35. When I give it full throttle, it drops down to around 30-31.

Any other ideas, other than the carb settings? I just rebuilt the carbs with the SBT kit, and I'm getting good compression from both cylinders. And I just installed new plugs...

Thanks,

Craig

[Technical Support]

make sure your pop-off pressure is set to 20. I will give you the spec for adjustment on monday if you still need them

[cbeastwood]

...More problems. Turns out I was concerned because I was reading 150/150 compression WITH the Group K sleeper head. A month ago I was getting about 175 PSI. So I started feeling around...

Two of my PTO exhaust studs were LOOSE. I'm thinking this was the cause of the loss of compression and also the resulting loss of performance. I took everything apart and chased all the threads of the studs and bolts and will re-install.

1) Do I still need to use those metal exhaust gaskets if I have similar paper gaskets? Should I use both? One or the other?

2)Anybody got a used 750 ZXI exhaust manifold? One of my bolt holes looks a little sloppy.

3) If in the future I need to replace the pistons, can I do it in the boat, or do I need to remove the engine and crack the case? I've never installed pistons before, so I don't know if it's possible to just pull the cylinders off, replace the pistons while the rods are still attached to the case, and drop the cylinders back over the new pistons...Thoughts?

Thanks,

Craig

[cbeastwood]

...Well, it turns out two of the exhaust studs had come loose from the PTO piston. I took the exhaust apart and re-installed the studs and everything else.

I went from 150 psi before I took it apart to 175 psi when I put everything back together. Guess I fixed the problem!

- Craig

[cbeastwood]

Re: 750 ZXI Problems

Ok, so I've dusted off the ski and I'm trying to get it back into shape. It's got a new stock SBT engine and everything else is back to stock as well, except for the impeller, which was blueprinted by Impros.

It's bogging at WOT and only goes about 30 mph at WOT. It feels like I've got another 2,000 rpms left in the ski that I can't hit. I do not have a popoff gauge so I cannot test the carbs but I'm thinking I'm running too rich.

Could you please give me the stock settings for the high and low screws for this '95 750 ZXI.

I think it's running rich judging by the plugs but everything else I've read on here makes it sound like it's running lean. I'm very confused and just want to get it running well for the weekend.

[Technical Support]

Re: 750 ZXI Problems

You are going to need to rebuild the carbs again after sitting so long.

http://www.sbtontheweb.com/forum/showthread.php?t=13981