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Discussion Starter #1
I've about exhausted what I can to figure this out.

Background - 1989 tw200ca, 10k miles; in Clear Lake, TX (essentially sea level)
has been used regularly until ~2yrs ago when it decided to misbehave - I would like to be back on the bike a bit more.

Symptoms -
Starts easily and idles fine. after driving about 200 yards it will cut out as if it has lost power. Driving at night, I noticed that the lights don't dim or flicker at all during these cutouts.
If I pull in the clutch, it will continue running fine but stutter if the clutch lever isn't pulled. When the clutch is pulled, I can rev it hard and it will ramp up RPMs quickly. It just cannot handle any load during these episodes.
After about a mile, it will run just fine (probably forever). If I stop at a light for a long time, it might do the stutter again, but not as drastically.

I'm about to ditch the bike and get a Honda, but I actually think the TW is perfect...

What has been tried (from reading other threads) -
adjustment of stock carb, air mix screw, jetting, seafoam - no joy
replacement of stock carb with Chinese clone (found in other forums) - no change
replacement of NG plug - no change, recently plug is blackish (running rich)
replacement of plug cable/coil - no change
replacement of gas tank/clean petcock - no change
replacement of CDI (found vendor on other forum) - no change
removal of superfluous cabling (LED body lights, voltmeter, external batt charger cable) - no change
removed fuel filter - no change

I'm open to ideas or suggestions -
 

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Does it sputter when it cuts out? Or does the engine just cleanly stop running? You running stock tank cap or vented? Replaced fuel lines?

Check for leaks around carb/spray some seafoam at it while idling, see if idle increases.

You could be experiencing air starvation, idle jet is set well enough that starting, idling and initial motion isn't an issue, but as soon as main jet transitions, you start dumping fuel and there isn't enough air to burn all the fuel. What size main jet? Elevation?
 

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Discussion Starter #4
Batt has good voltage. I disconnect it if I'm not going to ride for a couple of months. Good voltage when running - batt hasn't had to be charged off the bike ever.
I replaced the pickup coil, but not sure how to test the stator. I veered away from an electrical gremlin when I saw steady lights during the sputters.

Thanks--
 

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Discussion Starter #5
Does it sputter when it cuts out? Or does the engine just cleanly stop running? You running stock tank cap or vented? Replaced fuel lines?

Check for leaks around carb/spray some seafoam at it while idling, see if idle increases.

You could be experiencing air starvation, idle jet is set well enough that starting, idling and initial motion isn't an issue, but as soon as main jet transitions, you start dumping fuel and there isn't enough air to burn all the fuel. What size main jet? Elevation?
It just sputters and doesn't die completely. My reaction is to pull the clutch lever - it will then just run smoothly while I coast... I can freely rev the engine while coasting.

I have the stock tank cap. I did replace fuel lines when I put the cheap carb on.

I'm not sure the main jet size. Elevation is about 30ft above sea level. I took the stock carb off about a year ago. The newer carb made no difference.

Air starvation makes sense. I'll try the carb spray and see what happens.
 

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I'm betting the carb intake has a vacuum leak. What you describe sounds like a lean condition (revs easily unloaded, but does not handle any load) With the engine idling, wave an unlit torch around the carb/intake. (or spray carb cleaner). If the RPM's increase, you found the issue.

It's pretty common for these seals/boots to dry out, crack, leak on bikes that are 30+ years old.
 

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I replaced both boots from the carb and upon inspecting them they both had cracks and rot that was causing issues.

I had a similar problem with a Chinese carb I installed. Idles fine but would die under load. Setting the fuel mixture

fixed my issue.
 

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Discussion Starter #8
I'm betting the carb intake has a vacuum leak. What you describe sounds like a lean condition (revs easily unloaded, but does not handle any load) With the engine idling, wave an unlit torch around the carb/intake. (or spray carb cleaner). If the RPM's increase, you found the issue.

It's pretty common for these seals/boots to dry out, crack, leak on bikes that are 30+ years old.
No change when spraying carb cleaner around the carb/engine boot.
Should note that after chugging for 200-500 yds, it will run just fine.
 
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