98 GP1200 looking for the problem...

[cwehse]

I just bought a new engine from you guys and before I install it I wanted to get to the root of the problem, Bryan when you and I spoke today we figured that it was most likely and issue with the carb on the junked piston.

Well...I've got that carb disassmbled and I've attached a photo of the only thing I think looks like, detonation on the pump plate, could this be the culprit??? But that is the only thing I see that appears wrong? This is my first time doing this, am I missing something?

Also, I can get everything apart but I can't seem to get the high and low speed jets out, pictured in 1.5, I took their respective adjusting needles out, but can't seem to pry them out?

Any help, GREATLY appreciated.

[Technical Support]

Re: 98 GP1200 looking for the problem...

There's nothing that can go wrong with the plate itself. Often the wear on the gaskets and diaphrams isn't appearant to the maked eye. The jets do not pry out, they unscrew. You do not need to take them out, just squirt carb cleaner through them.

Watch the carb videos and read the carb rebuilding tech guide for Mikuni SBN.

[cwehse]

Re: 98 GP1200 looking for the problem...

Yea, I printed the guied out and am following it. I thought it showed those 2 pieces removed in the photograph in the instructions.

As far as the plate, there's a black (like a firecracker went off next to it) mark on the inside of the pump plate and the diaphram that I was curious about. Other than that, everything (seals/gaskets) all appeared to have been in great shape.

Also, the needle seems to have a small groove close to the tip, should I replace? Where do you think I can get a good price?

Thank you!

[ScottD]

Re: 98 GP1200 looking for the problem...

Your carb's have round plastic check valves in them they are held in place with rubber plugs.
These check valves get creased or worn thru stopping the proper pumping of fuel and may cause the carbs to run lean.
If you did not inspect these check valves they are more than likely shot.
Mikuni has a site that will help you out.
Needles and seats and jets can be had at you'r local dealer or ordered over the internet.
A bad set of carbs is the most probable senario in my opinion.
A leak down test is a good idea to test you'r motor is sealed tight before instalation.
I have just rebuilt the carbs from my 99 GP1200 and I am rebuilding the engine also.I have still to get my cylinders replaced or bored but in the next couple of weeks hope to get my toys out of storage and get them prepared for the upcoming riding season.

BAD carbs KILL engines.
SCOTT...

[cwehse]

Re: 98 GP1200 looking for the problem...

Thanks Scott.

Yea, just a little frustrating since all the plastic diaphragm pieces, including the check valve ones you're referring to all seem visually fine. And the needle has moreso a shiny ring on it, rather than a groove, and therefore I'm unsure if I should definitely replace it. The reason I'm so focused on this one carb is because everyone seems to pin it as the fault that seized the piston. And of course, I only want to install this new engine and not have to worry for a few years!

Is there somewhere I should look to view instructions on the leak down test?

Also, how much do I need to adhere to this step, and how exactly do I perform this?

3.4 (Below) To check pop-off pressure,you need a pop-off pressure gauge capableof registering up to 50 p.s.i. Wet theneedle & seat assembly with WD-40 orgas. Place the pump nozzle in the centerhole and pump until the pressure unseatsthe needle. Re-pump a few times to verifywhat point the pressure holds at. It isimportant that each carb be as close aspossible to all others on the craft. Ifpressure is too high on a particular carb,you can lower it by snipping parts of springcoils. Remove the spring and start bycutting ½ a coil at a time and re-testing.You can increase pressure by using aheavier spring. Never stretch a spring!

[cwehse]

Re: 98 GP1200 looking for the problem...

With this carb rebuild kit from SBT, shouldn't it include the gasket to mount the carb back onto the plate???

[Technical Support]

Re: 98 GP1200 looking for the problem...

No, no one's carb kits include mounting gaskets.

[cwehse]

Re: 98 GP1200 looking for the problem...

Ok, do you guys carry those separately? Or do you just have kits?

Also, do you know what size seat these carbs use?

Thanks!

[uncle-buck]

Re: 98 GP1200 looking for the problem...

SBT is a great company, but I have heard it has had some issues with its carb rebuild kits. Unless they have been resolved, you may want to go with the Mikuni kits.

Here's a link to a good article by Group K on air leaks: http://www.groupk.com/tec-airleak.htm

You may want to do a leak down test on your old engine if you haven't already returned it to SBT. SBT checks the engines it rebuilds, so you probably don't need to test your new engine, but it wouldn't hurt to do so. You can build a nice tester yourself for about $20 in parts from Grainger or your local hardware store. Here's a photo of one I assembled two years ago.

Good luck.

[cwehse]

Re: 98 GP1200 looking for the problem...

Thanks man, you rule!

[WATERCRAFTSERVICES]

Re: 98 GP1200 looking for the problem...

The carb kit issue had been resolved. They had a bad batch of diaphrams in the mikuni kits. I have used many kits since the problem was fixed with no problems.

[cwehse]

Re: 98 GP1200 looking for the problem...

Hmm...ok...well, I'm comparing one of the old gaskets to one in the rebuild kit from SBT...it's the gasket under the body. And the original one I'm taking out looks of much higher quality, it had a raised lip that fits into a groove. On the rebuild kit, this gasket barely has this groove, maybe 30% of what the original has...should I be concerned over this???

[ScottD]

Re: 98 GP1200 looking for the problem...

I see you are rebuilding only one of you'r carbs.
I would do all three carbs as if one is bad the rest may be close behind.
When I rebuilt my carbs last week I read that you can double up on the check valves.
I did not do this but I have another set of valves and I was wondering if anyone had up doubled or tripled up the check valves in there carbs and what the difference was.
It makes sense to do all 3 not just one carb.
SCOTT...

[Technical Support]

Re: 98 GP1200 looking for the problem...

Ok, do you guys carry those separately? Or do you just have kits?

Also, do you know what size seat these carbs use?

Thanks!

Yes, all gaskets are in our store.

I don't recal what size seats, I want to say 1.5s...

[Technical Support]

Re: 98 GP1200 looking for the problem...

Hmm...ok...well, I'm comparing one of the old gaskets to one in the rebuild kit from SBT...it's the gasket under the body. And the original one I'm taking out looks of much higher quality, it had a raised lip that fits into a groove. On the rebuild kit, this gasket barely has this groove, maybe 30% of what the original has...should I be concerned over this???

The lip is just for alignment, they both seal well.