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Discussion Starter #1
From a new member, I appreciate you folks and your expertise.

I just bought a 1999 TW200 with less than 2,000 miles on the clock. Except for a miss, it's running well. It starts fine with the choke, idles fine on the choke then after a minute I can shut the choke and it idles fine. Then as you pull away, it has a bad miss. If you're just running down the road at a steady speed, it will miss. The previous owner had bought the bike from a widower whose husband had bought it new. The second owner (who I purchased from) had cleaned out the carburetor and put a serious knobby on the front wheel. I felt under the front of the carb and the idle mixture screw is still covered with the plug. The bike is 100% stock.

Question is: How do I determine what is causing the miss? Is it fuel related or electrical?

Thanks in advance for any response and/or help.

MotoRandy in Phoenix, AZ
 

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Misfires can have many causes. Examine the spark plug and wire closely. You can also watch the spark as you crank it over. Never hurts to play around with different air/fuel mixture settings. Also can check your carb boots and connections closely. And look at your air filter and airbox.

And Welcome to the forum. Let us know how your troubleshooting goes.
 

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Discussion Starter #4
Does this "miss" occur at a specific RPM or throttle position?
Can you eliminate it by throttling slowly?
Is it worsened by hard acceleration?
TW_in_BC,

Thanks for the response.

I would say the miss occurs up off of idle while accelerating away.

If I accelerate at WOT from a stop and go through the gears, there is no miss.

If I throttle up slowly through the gears, it misses.

When it misses just off idle makes it hard to control when you're taking off from a stop.

Comments?
 

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Discussion Starter #5
Misfires can have many causes. Examine the spark plug and wire closely. You can also watch the spark as you crank it over. Never hurts to play around with different air/fuel mixture settings. Also can check your carb boots and connections closely. And look at your air filter and airbox.

And Welcome to the forum. Let us know how your troubleshooting goes.
Bladgerflorida,

Thanks for your help.

I did take the plug out and the ceramic is tan. I went ahead and filed it and re-gapped it and installed it. Just to be sure.

I'll check the boots and airbox/filter next.
 

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What is your elevation? I’m guessing you don’t know what the jetting is.
 

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Discussion Starter #7
What is your elevation? I’m guessing you don’t know what the jetting is.
Gastone,

Thanks for the response!

Phoenix is 800-1000 feet above sea level.

And, you're right I don't know what jets are in the carb. The previous owner said it was 100% stock but who knows. The original owner is no longer with us.
 

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Remove the idle jet plug with a deck screw and turn the needle all the way in gently then out 2.5 turns. That might be all it needs. It being fine at WOT is a dead giveaway. Crap in the air passages might also cause this. Most people don't know how to clean a TW car properly, but my money is on the idle needle being too lean.
 

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Discussion Starter #10
RockyTFS & TW_in_BC,

Okay, I'll pull the plug and adjust it in the morning. I'll then take it for a ride and report back.

Thank you both for your responses.
 

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Your problem seems to occur only on the idle jet, which deals with the fuel flow up to 30% of the throttle. As everyone has said, that’s your starting point ……
 

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Discussion Starter #13
Gentlemen,

I did as instructed. I removed the plug with a drywall screw, turned the screw in 1 3/4 turns. I gently seated the screw. Then I backed it out 2 1/2 turns. I also cleaned and re-oiled the air filter while I had it apart.

I then went for a test ride. Wow! No miss at just off idle and pulls cleanly without using WOT. It's 80-90% better. The only remaining issue is a miss at mid-throttle while just cruising and at a steady speed. Not really a surge feeling more of a misfire feel. How can I now fix the remaining issue?

Thanks, guys I really appreciate all your input and help. You've saved me from a bunch of grief.
 

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Discussion Starter #17
Maybe open it to 2 3/4 or 3 turns.
elime,

I'll give that a try in the morning. And, I'll report back.

This is such a sweet bike. The girlfriend is going to use it as a 'beginner bike' then once she wants something else, the bike is MINE.
 

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Discussion Starter #20
Gentlemen,

I backed the idle mixture screw out another 1/4 turn, for a total of 2 3/4 turns. It's running very well now. The mid-range is smooth and steady and no miss just off idle.

I'm going to drain the gas from the tank and put it into the minivan. Then I'll go buy some fresh 91 octane gas and a couple of ounces of Seafoam and add that to the tank. That should make it a bit better.

I'm going to call it FIXED. Thanks to everyone that responded, you were a big help.
 
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