650sx carb issues

K

killcraft

Location
virginia
Hey guys looking for some help. I'm not great with carbs just throwing that out there as a warning.
i have a 650sx that's completely stock and it only runs when i pump gas in from the primer. i've rebuild the carb and ultrasonic cleaned it ive also bought a used carb and tried that and it does the same thing. i know its getting fuel and i know the crankcase hose is connected....what am i missing?
 
C

Colby

Location
Harvey's Lake PA
Hey man i'm not great as well at carb tuning. What carb do you have? On all my 650 motors I run a 44 minuki sbn. I had one with it stock and hated it. I don't mess with carbs ill clean them but tuning no fu@#ing way. Id check a couple things. 1 Your gas could be bad or not have a good mix.2 does it have the oil tank if so get rid of it and premix it? Once you answer those I may be able to help.
 
K

killcraft

Location
virginia
Colby said:
Hey man i'm not great as well at carb tuning. What carb do you have? On all my 650 motors I run a 44 minuki sbn. I had one with it stock and hated it. I don't mess with carbs ill clean them but tuning no fu@#ing way. Id check a couple things. 1 Your gas could be bad or not have a good mix.2 does it have the oil tank if so get rid of it and premix it? Once you answer those I may be able to help.
Click to expand...
Stock 28 carbs new gas and I premix
 
wmazz

wmazz

Location
Riverside, CA
killcraft said:
i have a 650sx that's completely stock and it only runs when i pump gas in from the primer.
Click to expand...

Probably the most common carb problem on a 650. The needle and seat
isn't opening because of a vacuum leak

Stock 650 carbs are 34mm (not 28mm) and were later upgraded to a 38mm
carb.


Bill M.
 
mikidymac

mikidymac

Location
California
wmazz said:
Probably the most common carb problem on a 650. The needle and seat
isn't opening because of a vacuum leak

Stock 650 carbs are 34mm (not 28mm) and were later upgraded to a 38mm
carb.


Bill M.
Click to expand...

That isn't correct, the 1986-1990 650 used the 28mm Keihin carb with the remote fuel pump, the 1991-1993 used the 38mm Keihin with integrated fuel pump.
 
wmazz

wmazz

Location
Riverside, CA
mikidymac said:
That isn't correct, the 1986-1990 650 used the 28mm Keihin carb.
Click to expand...


Really!!!

That is myth, not fact. Just look at a Kawasaki jet ski specification manual
or the X2 repair manual.

If you use the same logic that a CDK34 is really a 28mm carb, then try
applying that logic to the Mikuni SBN carburetors.

Sbn 46 would actually be a 42
Sbn 44 would actually be a 40
Sbn 38 would actually be a 34
Sbn 34 would actually be a 28


Bill M.

Below is a tutorial for rebuilding Keihin carbs

Remember your needle and seat isn't opening. That is why it only runs when
primed. That is a common problem and you need to fix the vacuum leaks
that cause the problem.
 

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Last edited:
newbee

newbee

Soo 100% off topic but my carb bigger then yours. Lol. How do you measure them? I always went off the butterfly.
 
mikidymac

mikidymac

Location
California
wmazz said:
Really!!!

That is myth, not fact. Just look at a Kawasaki jet ski specification manual
or the X2 repair manual.

If you use the same logic that a CDK34 is really a 28mm carb, then try
applying that logic to the Mikuni SBN carburetors.

Sbn 46 would actually be a 42
Sbn 44 would actually be a 40
Sbn 38 would actually be a 34
Sbn 34 would actually be a 28


Bill M.

Below is a tutorial for rebuilding Keihin carbs

Remember your needle and seat isn't opening. That is why it only runs when
primed. That is a common problem and you need to fix the vacuum leaks
that cause the problem.
Click to expand...

Your correct, Group K, Hot Products WSM, are all wrong because they call it a Keihin 28mm for the 1986-1990 650, it's not "my logic". And yes, I owned a 1989 650SX for many years with the little remote pump Keihin. It has been known commonly as the 28mm since it was introduced in the 80's regardless of what the actual throat diameter is.
 
wmazz

wmazz

Location
Riverside, CA
This is how it got started, look at my attachment from the early X2 manual.
it clearly lists the carb as a CDK34, but for some reason Kawasaki listed the
venturi diameter as the size. I have always measured at the flange or spigot
of all motorcycle and watercraft carbs. It is close enough.

Look at picture #1 it demonstrates why vacuum leaks are so prevalent on
Keihin carbs.

Back when the 650 was new, I tried an experiment to measure how much of
a vacuum leak occurs when you reuse the carb base gasket 1 time. I used the
idle drop test in a test tank, and the pilot (low speed) screw required 1/4 turn
richer after reusing the oem metal gasket.


Bill M.CDK34.jpg
 
catpower

catpower

Location
iowa
I might be way off but here goes my 2cents. Does that 650 have the drain plug on the bottom of the case like X2 650's. I struggled with same 28mm and changed out carb to larger one. I never finished that ski as it wasn't mine but I think the drain plug on case was leaking air. The only way it would run is just as you describe. full choke or (primer) and drown it with gas.
 
G

gtjacket

Location
Gainesville, GA
Hey I also have a '89 650sx with the 28mm carb that has the remote fuel pump. Would I be better off rebuilding the current carb/fuel pump, or switching to the 38-42mm keihin carb that is coming off of my 750sx? (being replaced by sbn44)
 
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