Can’t keep engine running – fouled plugs? - 650cc

[Luv2JetSki]

I am trying to break in a new SBT 650cc engine in my X2. I have tuned it so that it starts right up with a couple of attempts and idles nicely. However, as soon as I try to accelerate under load the engine dies and will not restart (revs fine out of the water). If I let it sit for a while it will start again. Or, if I take out the plugs and clean them (just wiping the electrode clean with a rag) it will start right up again. Furthermore, if I check for spark it is none-existent, until I clean the plugs up. I assume this means they are fouling. They are coated in a wet fuel/oil mixture.

1) Should I continue to lean out the mixture? I am a bit nervous about running the engine lean while it is breaking in and I am already a full turn leaner on my idle screw then my old engine ran. Does the extra oil added to the premix for break in cause plugs to foul easily?


2) I did rebuild the carburetor (BN) but could not test the pop-off pressure (don’t have a gage). How important is pop off pressure in a single carb setup? I thought pop-off pressure inacuracies could simply be tuned out with the high and low adjusters if you were not trying to match multiple carborators up.


3) This is the latest in a series of problems I have had after getting the engine in. This has resulted in several engine starts that have been relatively short (1-5min) both in the water and on the driveway (with cooling system hooked up). Will this affect the quality of my break in?



Thanks,

Zac

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

No that won't effect break-in.


You need a gauge, or need to take the carb to a pro for a proper rebuild. Read the tech article on pop-off, you don't compensate with the adjustment needles. www.watercraftmagic.com has gauges.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

Where can I find the correct pop-off pressure for a 44mm Mikuni BN? I will call around and see if a shop will let me use their gage.

My shop manual does not even mention pop-off pressure in the carb rebuild instructions, so I assumed it was typically correct if you bend the spring arm so that it is even with the carb body as stated in the manual.

Thanks,

Zac

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

You'll probably find 20psi a good setting for that carb on a 650. I don't know what manual you're reading, but perhaps you aren' treading what you think you are.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

It is clymer manual, covers all the major carborators in the rebuild section. I looked realy close because I see pop-off pressure mentioned here a lot, but no mention of it in the manual, or at least not in that section.

I dont' have a good discription of what each part does in the carb. My take is that pop-off pressure is the pressure at which fuel is released back to the tank. Is this correct?

If it is, then I am probably running rich because my pressure is too high. This would not surprise me because the spring in the rebuild kit was slightly longer than the original

-Zac

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

Clymers sucks as a primary manual, get an OEM Service Manual.


No that's not what pop-off pressure is - read my tech article on it.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

That was very helpful, I had not noticed that tech article before. Thanks a lot for writing it. One more thing that was not included in any of the carb rebuild guids I used.

The needle on this carb has a little spring loaded pin sticking out of the back of it. The lever arm hits this little pin. Should the lever arm be bent even with the body while this little pin is pressed into the needle or with the pin extended? The lever arm currently rests even with the body with the pin extneded - is this right?


I am surprised the diaphram will hit the lever arm if it is even with the body.

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

I'm not quite sure whatyou're asking. The needle has a little wire guide that the arm goes into. The arm, when assembled, needs to be parallel to the carb body. Watch the carb videos in the video section.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

I was afraid that would not be very clear. This pin is literally coming stright out the back of the needle. If you press in the pin, it will spring back out. The controll arm rests ontop of this pin and presses down on it and thus the needle.

This wire guid that you talk about that is mounted to the needle, when you say it "goes into" the arm. do you mean there is literally a hole in the arm the wire passes through? I don't recall this, I belive the arm was solid where it contacted the pin. The oposite side of the arm had a little dimple to keep the spring in place.

If that still does not sound familure, I will take a picture tonight and post it.

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

Yes, please post a picture.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

Here are some pictures I took last night, hopefully this will clear things up.

First, here is the needle section fully assembled. It is followed by a picture of the needle itself. Note that when assembled the little pin I am refuring to is extended. It can be pressed into the pin until nearly flush. So, do I bend the arm with the pin pressed in, or with the pin extended?





And when I test the pressure, I remove the pump and test with it appart like in the picture below? If so I assume the return port as indicated by the arrow is the correct place to attach the gage?



Thanks for the help. It is killing me to have just spent all the money on the SBT engine and not be able to enjoy it yet.

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

Please use the attatchment feature as it's intended, so you aren't stretching everyone's screen like that...I'll edit it for you.

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

EDIT - my mistake, I see now you did say you had a BN carb, I overlooked it in your first post. That is a Mikuni BN carb - X2's used Keihin CDKs stock. That's why you didn't make any sense.


Second, yes you run to the opposite side of the needle to test pop-off. In this case that fitting.

Third, You assemble the arm to the natural position, pin extended.

[Luv2JetSki]

Re: Can’t keep engine running – fouled plugs? - 650cc

Great, thanks for the answers this really clears everything up. I should have highlighted that the carb was not stock. Do you still belive 20psi is the right setting?

Has anyone ever made a pop-off pressure gage setup? I have a design in mind that I could build from parts I already have, but if somebody has done this before I would like to learn from their mistakes.

Thanks for all the help, I should able to get back to the lake at the end of this week, hopefully everything will work better once I get the pop-off pressure settings corected.

[Technical Support]

Re: Can’t keep engine running – fouled plugs? - 650cc

I'm honestly not sure what psi to set to, but I think 15-20 *should* be ok.


Yes you can make a gauge yourself - do a search, some people have given plans. In the end though, it's usually better just buy the Mikuni guage - it's high quality, works everytime and is no-fuss.