86 xr600

my friend just put a big bore 650 kit in his 86 xr 600. The kit was the piston and sleeve, the cams were from a different kit since they don't make a complete kit for that old an xr.

The deal is that when you run the bike it starts to pop and sputter near the top end like it is running too lean. He has tried to richen it up with way larger jets and clean the carbs over and over. The next test is a replacement cdi box.

Does this problem sound familiar to anyone?? Is there a squish issue something that the layman can't see??



what main jets have you tried? have you adjusted the needle height?

Is that a dual carb model also?

This is the dual carb model.. My buddy has recently put a timing light on the bike and ran it up to failure and noticed that the light fails to operate at the same time as the popping. This means that it is a ignition issue. He has swapped in a cdi box and coil (didn't help) from an identical 600 and now the only thing left is the running coils under the flywheel. Thanks for the attention Matt!!


Hart, I had an 85 600 which is pretty much identical to the 86 medel and my stator coil went out on the thing.

Also I had done alot of work to mine too. I was running 138 mains in both carbs and went from a 45 pilot to 48 if I remember correctly.

Hope this helps.

Check all your ignition connectors-on the coil, stator wires and pickup connector. You'll need to take off the seat & tank to check all these. If you think it is something more sinister, check your stator coil with a multimeter. It should read between 230-320 ohms. If it is a long way out of this range or infinite resistance (short circuit), have the stator rewound. Blown stators are common on the 1985-1990 XR600's (99% of cases). Hope this helps.

The problem you describe sounds exactly like a symptom of a damaged air cut-off valve. When we had my '83 xr500r carb (same as the 86 xr600r, except for jetting) disassembled, my buddy(Who is a veteran xr owner/machanic) pointed out that the air cut-off valve had a small crack and would need to be replaced. If that valve is damaged it will cause popping at high rmp.If the problem is not corrected with the coil/stator fix, I would definately check the air cut-off valve. It does require you to take the carb assembly completely apart, and this valve is on one side only. (The left carb, I believe)

[ April 20, 2002: Message edited by: sixr500 ]

hey- Ive got a stock 85 xr600 and it does the same thing too- cept it doesnt even like the thought of getting on the throttle- skips and pops. Im trying to squish the problem too- It started for me out of the blue when I was riding high speed over some whoops on an old railroad bed. It started to pop and die every time I g'd out at the bottom of the whoop. Mabe this is connected to your problem or such. Hope this helps- Keep in touch Ill let you know what I find---ehowe@kvtc.net

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