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Hi guys , ive just got a 1990 200sr ,it starts easily,idles nice ,speeds up very well on the throttle but it doesn't like holding a steady speed on the road (feels like engine is miss firing and bike is jerking back and forth) but responds well to more throttle then settles down to more jerking , any ideas ??

Sounds like it is jetted to rich.I would try moving the clip on needle up

royadams wrote:Sounds like it is jetted to rich.I would try moving the clip on needle up

will do cheers pal

No surging is a lean condition. Clean the carb, make sure there are no air leaks in the intake run/reed block and then jet properly

A miss fire sounds rich to me a lean condition will just surge like your wacking the throttle. Any one that has forgot to turn there fuel petcock on has felt a lean surge lol. Pull the choke out when in the mid range and see if it gets better or worse.either way my guess is you have a problem in your mid range jetting.

Have you thoroughly cleaned and inspected the carb? Checked for air leaks?

had a quick look,the foam filter is very dirty looking,what can I clean it with? I'll give carb a good clean at the weekend and check reeds too,
Do I use easy start to check for leaks? (ether)

I just take my air filter to the sink and clean it with hot water and Dawn dish soap and let it dry completely. Then I spray it with some K&N filter oil (you can use motor oil) and put it in a large ziplock bag so you can work the oil into it without getting your hands all oily. You don't need it completely soaked in oil, just a light coat thoughout the filter. Then grease the seal and reinstall.

You can use ether to check for air leaks but be careful. I use WD-40. If you are planning to take a look at the reeds then just be sure and reassemble properly and replace the gasket if it looks questionable. Also inspect the rubber intake boot for cracks or pinholes. A very light coat of grease on the inside of the rubber boots will make the carb easier to install and help provide a good seal.

The carb needs to be spotless and in good condition. It needs to be COMPLETELY disassembled to do this properly. Write down the jet sizes and clip position for future reference.

Thanks for your advice Goofaroo

change the plug, check all electrical connections in the ignition system, check for crank seal leakage, check that radiator fluid level is normal since a blown head gasket will waste fluid and make it run weaker.
The SR comes with jetting that is not far off from where it should be and so to think that magically it has changed and needs to be jetted leaner now makes no sense. The air filter being clogged can make it run too rich though.

Had this problem and it turned out being the float level being too low causing lean condition at cruising speeds...did you find when the bike gets up to speed, it cuts out with excess throttle and barely maintains a certain speed? I recommend also check that if you have the carb apart...

Here is a screen from the manual for reference...height(4) between the bowl's mating surface and top of float should be 16mm. With the carb upside down.