SX/SXi/SXi Pro 750 sx will not stay running.

kass727

kass727

Location
Long Island
hi hopefully someone will be able to help me here. ill start with the problym im haveing and hopfully some one will be able to give me a hand here. the ski will turn over no probylm however once it starts it only runs for 30 secs or so and than it stalls out on its own or if i rev it up when it starts up it stalls out almost imediately. the ski has a jetted carb to match the rull west coast race exaust, has vortex air intake with aftermarket flame arrestor and has been modified to be premix oppose to oil injected. i did a compression test and it came up in mid 150's wich is average from what ive read, also checked spark and replaced plugs, seems strong. the only other place seems to be fuel delivery that could be causeing this problem. i plan on replaceing fuel lines and maby flushing the pickup. ide rather not rebuild the carb until ive pritty much run out of other options. i noticed that there are no inline fuel filters on my ski, is there one that is easily changed inside the carb? aslo would it be a good idea to add an inline one while im replaceing the lines? also could this be caused by my set screws being out of tune, if so how do i reset them? any help or suggestions would be greatly appreacieated, wanna try nd get out a few more times bfore the season is dead here in N.Y.
thanks a lot
 
ger87410

ger87410

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Fort Worth
Does the 750sx have a fuel pump? If so, check that. If not, check the pulse line for starters, then see if you can feel suction on the fuel inlet side.

If you feel suction, verify you have the fuel lines connected correctly and check for blockages and cracks. For kicks and grins, check the 1-way valve on the fuel tank while you're at it.

If you're sure the lines are hooked up correctly, take the tank outta the mix and try running with the hose going to a cup full of gas.
 
kass727

kass727

Location
Long Island
thanks for the responce, what do you mean the pulse line for starter, what is that and ware can i find it. and im assumeint that this model doesnt have a fuel pump bc there are no wires going to the fuel pickup.
 
ger87410

ger87410

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Fort Worth
If a fuel pump is used, it'll be in the fuel line somewhere. The ones I've seen are mounted on the hull right in front of the engine.

(I only know mikuni's, so that's what I'll describe. The other brand of carbs should be the same.)
There should be 3 lines going into your carb. Fuel pickup, fuel return, and pulse. The pulse will go to the engine block, the other 2 to the fuel tank.
 
kass727

kass727

Location
Long Island
ok its deff does not have a pump i just checked it out. so i should take the pulse line off on the carb end and crank it to see if theres a suction is that right?
 
ger87410

ger87410

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Fort Worth
No.

The pulse line causes the diaphragm in the carb to move with creates the suction on the fuel inlet side. Check the pulse line for cracks/leaks. Even the smallest will keep it from working.

If you got a mikuni carb, the fuel inlet nipple has an arrow pointing away from the nipple to indicate intake. The return line will have an arrow pointing toward the nipple to indicate flow direction.

When was the last time the carb was rebuilt?
If that's unknown, when was the ski last ran?
 
kass727

kass727

Location
Long Island
the ski sat since mid july havent been around most of the summer to use it and i have no idea when the carb was rebuilt. ive never rebuilt a carb before seem verry intericate work, is there a place i can bring it to have it rebuit or does that cost an arm and a leg to have done? im gonna go and check that pulse line now if i dont have suction there what would my next step be? if i do i know i have to work my back down the fuel system undtil i reach the pick up searching for clogs and kinks and cracks and if all elce fails rebuild carb, but will be completely lost if my pulse has no pull.
 
ger87410

ger87410

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Fort Worth
If your pulse is broke, you're looking at an engine rebuild.

I'm wagering on the ski was put away without sta-bil and the fuel left a residue on the diaphragm preventing it from moving.

Rebuild the carb yourself. It's incredibly easy. Be careful to turn the 2 needles all the way in, carefully taking note of exactly how many turns and fractions of turns it takes to reach bottom. That way you can set the needles back to where they were after replacing the o-ring.

Assuming you got a mikuni, download the manual for it. That will have a blow up of the assembly.

For a temporary fix, U can try spraying some wd-40 into the fuel filter reservoir, put that back on, the constrict the air intake so as to force fuel flow through the system. The wd-40 should hit the fuel buildup on the diaphragm and dissolve it.

This is only a temporary fix. You're looking at a carb rebuild anyways. <$50 for the kit if you do it yourself. >$100 to have it done.

EDIT: U shouldn't feel suction in the pulse line. That line just moves something in the carb that creates suction elsewhere. What you'll feel on the pulse line is a gentle pushing and pulling.
 
Last edited:
kass727

kass727

Location
Long Island
thanks i know im being a pain but i know verry little about carbs ware would my fuel filter reservoir be is that on the carb? there is no inline filter that i know of also is mikuni a standard carb for kawi? how would i check to know if this is the carb that i have?
 
ger87410

ger87410

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kass727

kass727

Location
Long Island
from what ive read its a keihin CDK II carb. ill comfirm when i get off work that this is right do you have any idea ware i might find a manual or assembly diagram for this? also before when i was looking at my ski there is definately no inline fuel filter the previous owner must have deleted it for some reason. do you see any gain from not haveing one? if not im going to add one while replaceing the lines.
 
ger87410

ger87410

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Fort Worth
There is definite need for a fuel filter as it also acts as a water separator. Water will get into the fuel tank, even if it's just condensation.

Besides, not having a fuel filter is extremely foolish. All it takes if 1 piece of sand to require a rebuild without a filter.

I think the CDK II carbs are A/M upgrades. No experience with Keihin here....
 
ger87410

ger87410

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Fort Worth
The advantage of using the stock filter is being able to take it apart and drain the water.

The common inline fuel filter from the auto stores cannot be taken apart, so they don't work good as water separators.
inline_filter.jpg


I've drained the water from my stock fuel filter after the water in the bubble got half full. As far as I know, I've never put water in my fuel. So water does get into the fuel system.
 
kass727

kass727

Location
Long Island
thanks so it just has to be one that i can take apart and drain. thanks again for being so help full and patient with me, ima big car buff but, but a simple as these two strokes seem they are just as complicated if not more than what im use to working on. but the more i read it seem to be makeing more sence to me. ill take a look at my fueling system later tn when i get home and hopefully ill have some luck with it and will keep you all posted for who ever is interisted.
 
ger87410

ger87410

How did I get here?
Location
Fort Worth
No prob. I have no problems helping noobs, but some on here will.....

Anyways, read up on 2-cycle theory and how they work. There's tons of sources out there.

You'll find that 2-cycles are simpler the 4-strokers. Tons easier to work on.
 
kass727

kass727

Location
Long Island
ok so i was able to play with it a little last night, the first thing i looked at was the pulse, it seemed good from you description, it was just a soft push and pull of air. also replaced that line just for my own peice of mind, than went on to check the fuel lines, disconected from carb and blew in twords the fuel tank, there was definiately no clog, however the air flow was alot slower than i had expected, even when i deiconected the line from both sides. so beleive it or not i had a few feet of fuel lines laying around my garage so i went ahead and replaced the lines also adding a inline filter, there was definately none there pervieous to me replaceing the lines. i than removed the fuel pick up and cleaned out the on/off/reserver toggle. when i fired it up it seemed to idle a little better, but when i reved it up it just died out afterwards. could this be from one my carb set screws being set wrong, if so how would i fix this. and i confirmed that the carb is a CDK II that has been jetted.
 
ger87410

ger87410

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Location
Fort Worth
Let's hope jetted correctly. :wink:

The problem you're describing is a fuel starved engine. Check the fuel filter to see if the gas is flowing. If not, pull your carbs and you could try taking a look at the part of the carb the pulse line and intake go into. That part comes off the main carb body for maintenance, etc.

I've no experience with keihin carbs. You are most likely looking at a carb rebuild.

I suggest visiting this page:
http://www.keihin-us.com/am/products/cdkii.php

That's got a Technical Info PDF that should make things clearer. #14 on the blow up diagram is the diaphragm. That's what does the pumping.

If you got dual carbs, you got 2 diaphragms to check.
 
ger87410

ger87410

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Location
Fort Worth
It's cake.

Just take the thing apart and clean it then put it back together replacing what comes in the kit. Use the parts blowup diagram as a guide.

Make careful note of the mixture screws' positions as outlined above and put them back to where they were before the rebuild.

Piece of cake and should take less then 30 minutes.
 
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