97 SPX 787 Mag cylinder is hot?

[BlakRat]

Hello, I just put a fresh 787 in my SPX... I set the carbs to stock needle settings and run pre-mix as well as the oil injection for the first outing... The thing ran great but fouled what i think was the rear plug ... It started vibrating and seemed like it cut down to one cylinder after about a 2 minute full throttle run, it started running fine again when I started alternating the throttle setting again... both plugs had a brownish sootie look to them but the PTO one was wet and the Mag one was dry... When I got home and flushed it on the tap, I also noticed that the rear cylinder was running very cool and the front was very warm to hot... Whats going on with the variance between the two cylinders? Should I give it a little more fuel to the High end of the Mag cylinder or lean the PTO side?

Thanks, Dave.

 

[mikidymac]

First if it is anew engine you should not be doing any full throttle runs. A few things to check are...
1. All carb adjustment screws should be set the same on both carbs per the service manual.
2. Did you make sure that the carb filters and internals were nice and clean. As well as checking the pop off pressure of both carbs?
3. Are you positive that the (2) 1/2" hoses that connect to the back of the head are not switched. IF the coolant flow is not going in the right direction it could definitely cause one cylinder to run hot.

 

[BlakRat]

Thanks for the reply...

I had about an hour of varying RPMs settings with a couple stops for cool down, and then took it back to the dock to check it out, and then about another 20 minutes of the same before I did the short WOT run... I figured that was enough for a short burst.

#1... Yes, but I will check again to be sure.

#2... Yes, but I did not check Pop off pressure... I read somewhere that I really shouldn't have to if I wasn't having issues before. I will check it though.

#3... I reinstalled according to the manual, I will double check this as I have been known to be dyslexic at times.


Thanks again.

 

[dannyual767]

Pinch/clamp the hose aft of the flush port fitting

According to the Sea Doo Shop Manual on page 02-02-01, you need to pinch the water hose just to the aft of where you connect your flush hose. It says, "This prevents water from exiting through the outlet socket."

I remember forgetting to pinch off that hose on one of my 96 XPs a couple of years ago and one of the cylinders seemed to run a good bit warmer than the other. I scratched my head and then realized that I forgot to pinch/clamp off that hose. I clamped it off aft of the flush hose fitting, started the engine, turned the water on and all was good. Nice even temps on both cylinders. For me, it was the hose pinching/clamping that fixed it. It's free and easy. If you didn't already do it, give it a try and see if it works.

 

[BlakRat]

Okay, I will give this a try this coming week when I return home and will report back.

Thanks for the reply!

 

[BlakRat]

Okay dannyual, you were correct, I should have read the manual and pinched the line, I just took it for granite that it was like my little yami. I took it out today for a second run and kept tweaking by reading the plugs, it runs really good right now and seems to stay relatively cool... Holy crap, this thing can sure sail over the boat wakes! It sure sucks the fuel though, but is a load of fun

Thanks for your Help!

 

[dannyual767]

BR, I'm happy to hear that all is well with your ski. I've also own Yamis and they require no hose pinching for proper garden hose cooling.

Yeah, these things are very thirsty! Gas guzzlers for sure but the smiles that they provide are priceless.