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Discussion Starter · #1 ·
I just picked up a 1989 650sx that has been sitting in a junk yard for 9 years. I’ve been working on it and replaced a lot. all full lines, filters, did a carb rebuild, new battery, gas cap, looked at the reeds they are good, new gas. And it’s been switched over too premix. So…. It starts in a dime and idles great but ones I give it some throttle is goes brumm brumm brumm brumm at full throttle. So I took it too some water and it didn’t exceed 5mph. But one time I turned it on it ran like a charm for about 5 min till I turned it off. Next time I started it same thing brumm brumm. I have the mixer screws at stock 11/2 top 11/4 low. Please help!
 

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That is cool!

Start with this:

There is a simple spark test you can perform to determine if you have adequate spark for running conditions.
(1) Fully charged battery, and a good starter motor.
(2) Take two brand new non resistor spark plugs and cut the bridge off each spark plug.
(3) Leave your old spark plugs in the cylinder.
(4) Install the two spark plugs (with the bridges cut off), into your spark plug caps, and ground them against your existing spark plugs.
(5) Crank over the engine, you should see good blue sparks on both plugs. If so, you have adequate spark for running conditions.
Keep the spark plugs for emergencies like a submerged engine, they make it easier to start an engine after it has been drowned.


Bill M.

I have other ignition tests, but it will be a few hrs before I have
time to post them.
 

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Discussion Starter · #10 ·
I’m mostly confused because it was running poorly as you saw in the video and then I killed it started it again and then it ran like it did in the second video and then next time I started it and ran poorly again. So I am curious as to why it ran good all of a sudden
 

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I don't know for sure. I like to test the easy stuff first, like the "spark load" test.
But ignition problems are normally constant, or occur after the engine is warm.

Another easy test is to look for something inside the exhaust pipe or waterbox.
Mechanics will sometimes stuff a rag in the pipe, and forget it was there while
They assemble the pipe. Pressure pushes the rag into the waterbox. If the wet
rag is blocking the exhaust outlet, it will run like your 650.

Remove the hose from the end of the pipe and rev up the engine to test that
idea.

Why did you replace the Gas cap? was it cracking open on the threads? If
you did not mop out the gas tank, there may have water in the tank. Water
sits at the bottom of the carburetors float chamber, and so is the low jet.

Remove the carb and (very important) work over a cookie sheet or another
non-pours surface so that when you remove the diaphragm cover, any
water in the gasoline is noticeable.

It would be handy to make your own thick carb base gasket for reassembly.
The 34mm 650 carb has bad vacuum leaks. I have part # for gasket material
that you can get from most auto part stores or Amazon and instructions.


Bill M.
 

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Discussion Starter · #12 ·
Thanks for the reply the gas cap was not there when I bought is I also bought we’re you screw on the cap the tank did have water but I took it off and gave it a good cleaning
I will check the water box when I get home thank you
 

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When I worked on the 650, I had a granite block for flat sanding
all the intake parts. A .040" gasket on the carb base, intake manifold,
and reed gaskets will seal the vacuum leaks better than the .020"
gaskets that are commonly available. In fact the OEM intake manifold &
reed gaskets from Kawasaki were .040". The carb base gasket was
a pos aluminum gasket.

If you want to make your own gaskets, I have info for that.

Look at the bottom of the carb, or the carb base gasket. Does that
look like it is only 1 1/8" (28mm) diam?

It is really a 34mm carb (~ 1 3/8").The 300 has a 34mm BN Mikuni.
A 28mm carb would be a really small carb for a 650.


Bill M.
 

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Discussion Starter · #18 ·
No, but I did take it apart and it looks pretty good I will check it again soon I just rebuild the engine including all gaskets and crank seals. Did the crank drain block of and took it too the lake ran great then out of nowhere it slowed down and when I gave it some throttle it sounded like it was misfiring and didn’t exceed about 5 mph I’m not sure what too do anymore it kinda feels like something is sealing then unsealing any help would be appreciated
 

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The external fuel pump with factory pulse line should be more than adequate for fuel pressure. My 650 had similar issues until I replaced the diaphragm in the fuel pump and carb. With zero other repairs its been 100% for 2 seasons now
 
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