300/440/550 JS300 Newbie Tuning/Diagnosis.

[johnnyb]

Hi there, you might have noticed I'm new here, also new to Jetskis so bare with me.
I recently purchased a JS300, At a guess its a mid eighties model looking at pictures, Pink, Green and White. "Hawaiian Style" (according to the decals)
Its pretty rough and gutless, but the bloke who sold it to me, told the story that he was given it, in pieces, with some form of engine failure. He says he had the Jet unit rebuilt, and 'rebuilt' the motor, then it never saw any water time untill I brought it.
Apparently the oil system has been disconnected, I'm having trouble making sense of the plethora of fuel/oil lines running everywhere though. I'm currently running 50:1 premix, How does this sound?

My problem is this, I can't seem to tune it very well, just about no position on the jets seem to make it much better. It doesn't run bad wide open, but anything below say, 80% throttle, it bogs, surges and generally runs hairily.
Very difficult to get it to idle consistantly, and if you pull the plug after stalling it, it won't be very black, but still damp with fuel.
Will only restart if you hold the throttle wide open.
I know this sounds like its running far too rich, but in my last effort to tune it, I had the low speed jet screwed basically all the way in and it still runs.

Up to this point I've generally just been backing my truck down to the water, tying it to the truck, and fiddling away with it running in an attempt to find its sweet spot..

So, sorry for the long and possibly confusing read, but what do you lot suggest I should focus my attention on next? Air leaks? Carb?

Thank you
John

 

[King of the Js550]

Needles control fuel. Turning them in closes off the fuel, making it more lean. Low is lower on carb, high is higher. Pop those plastic caps off. When seting the needle be sure not to mash it in,

Base settings, assuming you still have the BN34 carb:
low speed 1 15/16
hi speed 15/16

 

[jetski9010]

could be dealing with a leaking needle and seat. The the needle or seat is bad or the pop off pressure is to low its going to make fuel push past at low RPM's and make it run rich and bog down then once you hit high RPM's when the needle is sposed to open up from pop off pressure normal its running lean because your turning all your screws in to try to get rid of the rich spot in the low end. Might want to try to take your carb apart and check it out. The arm for the needle and seat should be lined up somewhere close to paralle to the surface of the carb. If not bend it so it is. Also pull the needle out of the seat and make sure there is no dirt in there and also that the tip of the needle is not worn or have a deep indent.

 

[jetski9010]

If you take the air filter off the carb and look down it while its running at idle a lot of times you will see fuel drops dripping down the middle of the carb if its pushing past the needle and seat.

 

[johnnyb]

Needles control fuel. Turning them in closes off the fuel, making it more lean. Low is lower on carb, high is higher. Pop those plastic caps off. When seting the needle be sure not to mash it in,

Base settings, assuming you still have the BN34 carb:
low speed 1 15/16
hi speed 15/16

By this do you mean for the low speed 1 and 15/16ths turns out
and for the high speed 15/16ths of a turn out?

If you take the air filter off the carb and look down it while its running at idle a lot of times you will see fuel drops dripping down the middle of the carb if its pushing past the needle and seat.

Thank you I will try that and then pull the carb apart if I cannot make sense of it.

 

[johnnyb]

Also, my the hull # is JS300B-102169, does this mean its about a 1988-'89?
I might try and purchase a manual for it to aid in the ownership of it..

 

[johnnyb]

Alright I ran it for a bit quickly with the snorkel/filter off and it definitely looked like there was a bit much fuel, especially in the lower range. Pulled carb off and stripped down what I could, the 'fuel pump' type thing and 'float valve.' (forgive my terms, this carb is not quite like much I've opened up before).
I couldn't see any obvious dirt, blockages or worn bits, but did my best to blow out everything and give it a bit of a wipe. I've just popped it back together now and it seems to be definately better just running it on the back of my ute for a few seconds, no fuel pouring in and splashing back out of the carb.
I set the jets LS- 1 & 15/16ths turns out
HS- 15/16ths turn out
I plan on taking it out tomorrow so I will report back with how it goes.
Thank you very much.
Also, is 50:1 an ok ratio to run these on?
And how exactly is the standard oiling system supposed to work, it looks rubbish/confusing.
Here is the carb

And has anyone seen this colourscheme before? I can't find any like it on the net, perhaps it is a one off? Here is my friend on it a few weeks ago.

 

[jetski9010]

Sounds good try it out and let us know. If there was no dirt in there you might want to try bending the arm that the spring pushes down. This will rise the pop off pressure a bit and help keep that needle closed. I know you already have the carb all back together so just try it as is but if it keeps giving you problems try that.
Stock oiling system just has an oil pump run off the flywheel that pump oil into the intake track below the carb.

 

[Mitchell]

it's probably just something that the guy had painted the pole bracket is anodized red which was stock and there's that sticker around the gas cap. I think your ski is an 86 or 87 because i know the year after one of those they went to the super small rounded hulls that look more like a 650.

 

[King of the Js550]

it's probably just something that the guy had painted the pole bracket is anodized red which was stock and there's that sticker around the gas cap. I think your ski is an 86 or 87 because i know the year after one of those they went to the super small rounded hulls that look more like a 650.

You talking about the 300sx

 

[Mitchell]

yeah. oops. i just read the title and saw JS. Sorry.

 

[WFO Speedracer]

Do yourself a huge favor find a stock carb off of a 91 wr500,rebuild the carb that you bought, remove the stock carb throw in thrash can,install new style carb ,turn the screws till it runs well and go ride.The carb is a direct bolt on ,no rejetting required.

 

[johnnyb]

Hi there again, a bit delayed, but we took it out again on Sunday in a local harbour. Initially it seemed ok, not so much of a flatspot down low and easier to start (at first).
The longer we spent out there the worse it got, still not as bad as before in the bottom end, but seemed like it was fouling up and difficult to start, had to hold the throttle wide open and it would eventually splutter and cough its way into life.
At one point it was pretty bad and I couldn't get it to fire, so I pulled the plug, it was a nice coffee colour, but soaked, and had what looked like oily/milky mixture around the edge of the plug.
A clean plug and things were.... better for the 20 mins more or so we spent out.
Should I be pulling the head off and checking the gasket condition? Previous owner said the head had needed some welding when he got it in parts. Previous owned has also skipped the country

I had also noticed the main throttle shaft appeared to be leaking slightly on this side, I assume there will be an O-ring or similar in there?

One more thing, on the topic of the Oiler, Why is my oil tank pressurising when cranking? A few times lying out there a few hundred metres from shore cranking, the redundant oil gauge popped out of its grommet or just had air bubbling from around it... I would be quite happy to blank of Mr Oil pump and remove all the associated hoses and tank, But it isn't that crystal clear to me.

I think that wraps up my current developments and symptoms.

 

[johnnyb]

Do yourself a huge favor find a stock carb off of a 91 wr500,rebuild the carb that you bought, remove the stock carb throw in thrash can,install new style carb ,turn the screws till it runs well and go ride.The carb is a direct bolt on ,no rejetting required.

Cheers for the advice, I will keep an eye out for one. I'm quite new to the jetski 'scene' but there doesn't seem to be much in the way of spare parts around in these parts, so that may be difficult, it sounds like a good idea though.

 

[WFO Speedracer]

Cheers for the advice, I will keep an eye out for one. I'm quite new to the jetski 'scene' but there doesn't seem to be much in the way of spare parts around in these parts, so that may be difficult, it sounds like a good idea though.

My advice is to put up a WTB post either here or at PWCT and someone will have one.

 

[Jetpilot106]

One more thing, on the topic of the Oiler, Why is my oil tank pressurising when cranking? A few times lying out there a few hundred metres from shore cranking, the redundant oil gauge popped out of its grommet or just had air bubbling from around it... I would be quite happy to blank of Mr Oil pump and remove all the associated hoses and tank, But it isn't that crystal clear to me.

I think that wraps up my current developments and symptoms.

On my JS300 I just unhooked all the oil injection and went to premix. It was doing the same thing out of that gauge.

 

[jetski9010]

Hi there again, a bit delayed, but we took it out again on Sunday in a local harbour. Initially it seemed ok, not so much of a flatspot down low and easier to start (at first).
The longer we spent out there the worse it got, still not as bad as before in the bottom end, but seemed like it was fouling up and difficult to start, had to hold the throttle wide open and it would eventually splutter and cough its way into life.
At one point it was pretty bad and I couldn't get it to fire, so I pulled the plug, it was a nice coffee colour, but soaked, and had what looked like oily/milky mixture around the edge of the plug.
A clean plug and things were.... better for the 20 mins more or so we spent out.
Should I be pulling the head off and checking the gasket condition? Previous owner said the head had needed some welding when he got it in parts. Previous owned has also skipped the country

I had also noticed the main throttle shaft appeared to be leaking slightly on this side, I assume there will be an O-ring or similar in there?

One more thing, on the topic of the Oiler, Why is my oil tank pressurising when cranking? A few times lying out there a few hundred metres from shore cranking, the redundant oil gauge popped out of its grommet or just had air bubbling from around it... I would be quite happy to blank of Mr Oil pump and remove all the associated hoses and tank, But it isn't that crystal clear to me.

I think that wraps up my current developments and symptoms.

Sounds like a BN carb problem. Like the others guys said get a 34 SBN off a wr500 or a wavejammer 500 and it will be a lot better.

 

[jetski9010]

Here is what they go for brand new. http://www.denniskirk.com/jsp/produ...ain&catId=&productId=p170217&leafCatId=&mmyId=

 

[johnnyb]

Hello again. I haven't had the chance to strip anything down or have another look yet, damn this thing and its need to be attached to water.
I may get a chance to have a look this weekend, but I have a bike which is wanting some attention also. :thinking:
I haven't managed to find any WR500 carbs locally, but, What is the general consensus on JS550 carbs?
http://www.trademe.co.nz/Trade-Me-Motors/Boats-marine/Jetskis/Accessories/auction-275361751.htm
Would this be in aid of my cause?
Mounts etc look similar, but is it likely to be any better?

and the grips on it are shot, so are a set of fluro PINK grips in order?
http://www.trademe.co.nz/Trade-Me-Motors/Boats-marine/Jetskis/Accessories/auction-275126661.htm

Cheers
John

 

[johnnyb]

and a picture or two.