GTX DI top end rebuild

[nhmort]

I just put a new top end on my GTX DI with pro x pistons 88.75.

I’m in the process of breaking it in on the lake last Saturday.

Right away we were able to get about 6600rpm.

Now today, I could only get about 6300rpm.

Why would this be the case of lower rpm?

I put in a high performance aftermarket fuel pump a couple of seasons ago. I still have the old OEM pump which I think I’ll clean it up with the 50/50 toluene gas mixture.

I need to retest the fuel/air pressure again.

Is my fuel pump the problem? I’m not getting any maintenance light or beeping.

My mag plug looks fouled and pto plug looks perfect brown in color.

Of course I don’t have a Candoo to help me out.

Nate

 

[daniel12]

From my understanding, you ARE NOT supposed to go full throttle right away because the seals and rings need time to seat properly. What are your compression numbers?

 

[nhmort]

From my understanding, you ARE NOT supposed to go full throttle right away because the seals and rings need time to seat properly. What are your compression numbers?

I didn’t take compression numbers yet.

However, I’ve done plenty of research on breaking in this motor. Bill O’Neal whom is highly knowledgeable on jet skis, said that you can ride it normally after it’s warmed up. Providing you don’t use WOT, for a long period of time in yards and not miles.

 

[mikidymac]

In my 25 year experience of rebuilding skis I would never suggest breaking it in at full throttle ever! THe whole purpose of breaking in an engine is to let the parts wear together and seat with each other. There is a good chance you damaged the rings or pistons by not breaking them in. I would check the compression if it were mine. Alos if you are quoting Bill O he suggests only using OEM pistons in a DI as they are the only ones with the special coating and treatment that can survive the lean burn of a DI in his experience.

 

[jhjesse]

If it is not running rough and compression is fine, I would think that your ok.
I would run some compression numbers at different intervals of break in period.
One cylinder is probably not seated yet.
Also the mag cylinder injector might need to be cleaned if it doesn’t straighten up.

 

[etemplet]

I'll just call BS on the break-in procedure recommendations. You could have scoured the cylinders running it like that so soon.. Hence your RPM issues or lack of may not be fuel. I am still babying my GTX engine work and it's on it's third tank.

 

[nhmort]

I just read the Seadoo operating manual and it says to vary the rpm and brief WOT not to exceed 15 seconds.

This is what I did and did not run WOT all day long.

I think Jhjesse may be correct. I may need to look at my injectors.

 

[mikidymac]

You will find that there are as many opinions about break in as on oil preferences. I however don’t agree with your methodology.

I strongly suggest checking compression before doing anything else.

 

[nhmort]

I’ll test the compression tomorrow. And report back.

 

[jhjesse]

I was agreeing with mikidymac. Compression test, finish break in and see if the rings seal. After that, if problem persists clean injectors as another route.

 

[nhmort]

@jhjesse, The DI has the red fuel injectors and the black air injectors. Do I clean both?

Ive already gotten new red fuel injectors and have a spare set.

And what’s the process for cleaning the air injectors?

Would an ultrasonic cleaner work for both?

What about the carbon dam for the air injectors? The Seadoo manual says you need a special tool to install them is this true?


Thanks for the advice guys.

 

[jhjesse]

Never cleaned an air injector or even removed one as I have never had any trouble with them.

Here is what I do for injectors. exchange
Sea-Doo Bombardier BRP Fuel Injector

 

[nhmort]

Did a compression test today.

It’s 115 in both cylinders. After running about two hours.

The plugs are perfect brown in color now.

 

[mikidymac]

If your gauge is good that is really low. It should be at least 130 on a fresh engine, 135 is perfect on a DI. Good strong battery, hold throttle wide open with plug wires on the ground posts and crank until the gauge stops climbing.

 

[nhmort]

I have a cheap Harbor Freight gauge.

I did the compression test exactly how you described.

Hopefully it will get better?

I’ll ride it some more today and recheck the compression.

 

[mikidymac]

If it is correct at 115 it won't get better. I have only seen them come up a few psi when broken in. I would retest with a quality gauge.

 

[nhmort]

Thanks for the info.

 

[jhjesse]

Did the ski run good? Plenty of power and not sluggish?
If yes, then chances are good the gauge is off.
I’m with mikidymac get another gauge.

 

[nhmort]

The ski runs well up until about 5800 or so, it gets “hung” up there and sounds like it misses.

I can back off the throttle and it will climb past 5800 not always and then up to about 6200 and top out there.

Is it my fuel pump.

No maintenance lights. So it has to be fuel/air related.

I’ll have to put my test gauge on it I guess and report back the fuel/air pressure.

 

[mikidymac]

Have you changed the fuel filters? You can also clean the oem pump with a mixture of gas and toluene.

 

[nhmort]

I’ve changed the fuel filters last year.

I only run 91 octane non ethanol gas in it.

I replaced it with one of those HPF fuel pumps and that might be the problem.

 

[mikidymac]

Unfortunately yes, all aftermarket fuel pumps are junk. If you still have your oem one it’s worth trying to clean.

 

[mandriva]

Wossner piston had traitement coating ! Yes break in procedures is important! I got issues this year with proX piston in snowmobile! Poor quality!!! I don’t use it now for any snowmobile and watercraft!!! For All seadoo 650/717/787/951 (no di) i use WSM or Wossner!! For 951 DI i put Wossner!!
Snowmobile i put spi(spx) or Wossner!!

 

[mikidymac]

You must be the only one. Pro-x are basically the industry standard and the same as factory Yamaha.

 

[nhmort]

I replaced the rectifier cuz I had a maintenance light pop up.

I bought an OEM one. Now all works well.

Thanks for all of your help.