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Discussion Starter · #1 ·
My 01 m600 (carbed) is running fine around town, throttle response is good and spark plugs turning light brown. At speeds above 80kph i get surging, misfiring and backfiring. Throttle doesn't really do anything unless i give it wot and wait a second, then it goes for a while and starts to do its thing. Im running stock everything except 42,5 pilot and needle clip on the 2nd richest setting. I've tried changing emulsion tubes, all vac and fuel lines replaced. Im starting to think this isn't fueling related, but i thought id ask you guys first before going through all electrics again.

Bike has recently gone through major services, including piston rings, valve check, oil and filter, airfilter, carb rebuild (floats were ok), timing belts, carb sync. I really shouldnt be getting carb icing, though it is cold here even at +8°c. I also tried running the bike with gas cap open and spent 2 days looking for a vaccuum leak to find none. I played around with the needle clip but it doesnt seem to like it richer or leaner. The problem represents itself only at higher speeds with 1/8 maintenance throttle all the way to wot roll-ons.

Last year i ran it without the carb diaphgram breather box and it was fine, now i installed it to see if it would make a difference (did nothing). When i place my right foot on the frame slider (weird detail, yes.) the surging becomes exponentially worse. The bike just sputters and engine brakes until it reaches city speeds 50-60kph and continues running like nothing happened. I want to believe the breathers are routed wrong and this is just from turbulance in the box but I've tried routing them to every place i can think of.
Any ideas?
 

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Do a Forum Search on carb problems and tuning. There is a ton of stuff already written on the subject. I’ll suggest making sure the diaphragms are working properly. Your carbs can have the butterflies synched but if the slides don’t open smoothly and together the bike won’t run right . Remember the needles move with the slides. Make sure you don’t have kinked or collapsing hoses.
 

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Try and get it to a dyno and have air fuel checked.
Have you tested compression or leakdown?
When did the problem start before or after the work listed?
Miles?
If you run the bike with tank up and air filter removed do you see the slides opening?

Are you dropping one cylindeer or is it still running on two?
Are you using any aftermarket ignition parts (coils,wires ignition boxes)?

Is it backfiring in the airbox when warmed up?
Are the plugs black or fouling?
open or closed airbox?
 

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Discussion Starter · #4 ·
Try and get it to a dyno and have air fuel checked.
Have you tested compression or leakdown?
When did the problem start before or after the work listed?
Miles?
If you run the bike with tank up and air filter removed do you see the slides opening?

Are you dropping one cylindeer or is it still running on two?
Are you using any aftermarket ignition parts (coils,wires ignition boxes)?

Is it backfiring in the airbox when warmed up?
Are the plugs black or fouling?
open or closed airbox?
I get backfiring in the airbox and sometimes exhaust, when warm. Today when I went to work it was windy and the bike acted up worse than usual. I just came from work and it was unusually calm, the problem was much less noticable but when I went over 100kmh it started to do it's thing again. It almost seems like I dropped a cylinder. No aftermarket parts, slides are moving ok and the problem started after the work.
 

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Popping in the airbox is often a lean condition. that can be due to leaks or inefficiency . If the problem started since the work I woould re-trace the steps done as the problem probably is from something touched. Go back and exammine everything done to verify there is no mistakes or defective new parts.

If a shop did the work you might start wiith asking them. If you did the work start backtracking and you will likely find something. If plugs look good then conside you have good combustion but that points at something mechanical may be happening. The more you ride it the more parts may be damaged. Start with the compression/leakdown and check cam timing,valve clearances(easy things) first.
 

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Discussion Starter · #7 ·
Thanks again guys! The problem was resolved, last year I ran it with the carb breather boxes off and had no problem. I installed a bit heftier fuel lines and ran the t-joint float chamber vent down the frame, while this was not a problem with the original hosing now it seemed to vacuum out fuel at higher speeds. It is too easy to overlook these simple things, but this problem caused me to get the new emulsion tubes and the bike's never been better ☺
 
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