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Discussion Starter #1
Perhaps some of you recall my ongoing saga of repairing my TW200 a.k.a. Betty Boop, following a bent valve incident following a fuel starvation scenario. I installed a serviceable head given by the ever so generous Admiral and buttoned up everything but engine runs terrible despite trying to confirm everything ok.
Symptoms are engine starts fine with half choke tonight in 40 degree temps but only runs at a rough few thousand r.p.m.s irregardless of throttle position, then stalls after 30 seconds or so. Sounds rough and possibly rich, really only wants to run with full trottle, although at only 2000 rpm max.

Things I have already checked and may need to double check:
valve clearance
cam sprocket timing
air leaks around carb
clean air filter
good spark
good fuel delivery to and through carburetor
fresh fuel
float level set while disassembled then confirmed with clear "pitot tube" once on bike according to manual supplement ( Betty is a 2003 with ~9000 miles and a stock engine and exhuast)
air in tires

So, what am I forgetting? Symptoms sound familiar to anyone?
By the way I never really identified cause of fuel starvation.
I do have brand new mixture screw and float valve/seat/o-ring but did not install them as old ones seemed undamaged.
Any comments will be greatly appreciated.
I can video and post engine sounds tomorrow if anyone thinks this might be diagnostic.
 

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I am sorry to hear this news Fred. Since I am not a mechanic I will bounce off of here and make room for the smart people. I hope there is a quick fix and you are off and running soon. Take care.




Tom
 

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I had the same problem with my 2005 TW after a carb cleaning. The main nozzle fell out while the carb was apart and I was unaware of it, and reassembled the carb and and put it back on the TW, and it ran like crap, similar to your conditions. I removed the carb several times, hoping to find the problem, to no aval. I went to the pole barn for something else when I found a shinny little metal thing laying on the floor,and wondering what it is for. Still disgusted with the TW, I removed the carb again and took it apart, and shure enough, that little part was for the TW, put it in, reinstalled the carb, started it up and went for a nice ride,smiling ear to ear, it ran great. I hope this helps you. That shinny thing is called a main nozzle on the TW carb parts breakdown, item #12, which you can find at www.stadiumyamaha.com
 

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Hey Fred That's is a bogus. Check your sparkplug by swapping out another
just on a off chance. The holy trinity of gas engines are fuel, compression and spark.
Sounds like you've ruled out fuel, how is the compression? Need min 100 psi to run. You can kinda guess based
on how the kick starter feels compared to before. If fuel is ruled out, compression ruled out
then it's spark, more specific is amount and timing. Lizarbrth had a great thread on testing timing. But a timing light
is the tool required, need to make sure you have strong spark all the time and it's advancing proper. Easiest test
is to swap a known good CDi unit if there is someone nearby with one you could borrow.
Wonky advance in ignition will mimic fuel problems as will low compression. Big chain parts stores
rent out compression gauges and timing lights. Good luck
 

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So Silverwing could have a point, could the perp of the valve collision been
part of your carb? If so it would be in the exhaust but wouldn't explain
your failure to be conclusive on the original "fuel starvation" problem. But wouldn't hurt to
pull header pipe and shake it out and or pull carb and search for missing parts.
 

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Discussion Starter #7 (Edited)
Thanks guys, will check all the above. Never thought to use my compression tester as I assumed that was solved. Thanks for reminding me of my favorite admonition: Test Your Assumptions. Always good to differentiate that which you know from that which you think. For example I think I reassembled carb correctly, no missing nozzles or clogged passeges. And while NGK plug seems to spark strongly why not test with that E3 plug hiding somewhere in the parts box?
What else? Would she even fire if 180 degrees out of time?
Maybe I should have pulled muffler for a shake out. Nothing was in headpipe but I'll pull muffler mañana.
 

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Compression will tell you if it's cam is out of time, more than one tooth and
it probably won't run or would have valve collison. But loose chain or just one tooth off
will dramatically change spark timing. Spark in open air a differnt animal
than spark under compression with fuel air mixture. Need to jump a good 1/8" in open air.
You can fab up an air gap tool and check spark whilst running. Timing light will tell you same thing
more or less. My psychic sense is saying bad "CDI" but I put littel faith in that.
 

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Most mornings I wake up with a manana. Sorry Fred couldn't resist. I am weak.


Tom
 

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Yup. That one was for me as much as anyone else. I was chuckling like a damn school girl just typing it:D



Tom
 

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Discussion Starter #12
Arbolmano, thanks for all the helpfull ideas. For an air-gap tool could I not progressively open the gap on an old plug and test against head untill largest spark jump is achieved? I fear bike won't idle long enough to deploy borrowed timing light but I can try, would observe timing mark through upper upper observation port on left side cover, right?
As far as CDI diagnosis goes I could try to borrow CDI unit from another Reno rider and swap out. I shall try to look into this tomorrow. Least imposition would be to take my CDI unit to Adam-in-Nevada and after plugging into his bike see if problem traveled to his test bike, I would get answer right away and not have his bike down for any length of time.
 

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Fred, you're welcome to try the cdi off my parts bike if need be. Supposedly it was replaced and is new. The bike is an '89. If it solves the problem, its yours. I'll be around in the morning and then riding the rest of the day.
 

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Discussion Starter #14 (Edited)
Outstanding! What a generous offer Mike, one which I might take you up on if a quick research reveals an '89 CDI is interchangeable into a 2003 and a CDI replacement is warrented. Truly nice offer. Still not sure how to diagnose if that is my problem short of borrowing yours for an afternoon test. Driving over to say "hi" while hi-jacking your CDI does sound like more fun than R&R-ing the carb again. I am getting quite a bit quicker, having memorized the dance moves required to get the carb out and back in.
 

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Sure, anything I can do to help. Had a couple members on here help me out with tires when I needed them. We really have some generous folks on this forum. If I can help someone, it would be my pleasure.
 

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Discussion Starter #16
Unfortunately a quick perusal of Boat.net shows different part numbers for our two bikes and the schematics show obvious differences. Does not lessen my appreciation for your kind offer though Mike.
You are right, this forum has good folks paying it forward. I have been researching a Tacoma Forum and notice a big difference in the helpfulness and friendliness. We as a smaller group, can afford a sense of camaraderie a mega-site cannot. Sort of like living in a small town; one can afford to be friends with your neighbors.
 

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Darn, was hoping it was the same and you'd have Betty purring again tomorrow. Know what you mean about the mega forums, there's some great advice on them, but the generosity on here is amazing. Hope Adam can get you some answers tomorrow. Please keep us posted.
 

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I'm going to keep my thoughts to a minimum since I'm no expert. When I did my rebuild my bike kinda ran like crap somewhat to what you describe. I had even cleaned out the carb with various cleaners and compressed air. I couldn't get it to do anything well, so I yanked it off again and ran it through the ultrasonic cleaner for an hour or better. It was like so kind of instacure and thats been a couple thousand miles ago now. Hell if you were closer I would loan you my carb just to see if it cleared your problems up. I'm always amazed that things you can't even see in there will cause those kind of problems. Did you pull the stator cover off? I would check resistance in all those wires per the manual and clean contacts as you go. You may find something there. Anyhow good luck and hope you're up and running shortly
 

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Sorry to hear there's still a problem.

If you're already thinking of switching parts... This is a really big swing, but if Adam's ok with it, could you do a quick carburetor switch with him? If yours runs fine with his carb then you may have a issue with your original carb. If it runs bad with his carb, then probably something else. Just a thought.

Double check to see if there is an airway obstruction in the airbox area. I had a piece of rubber or something a long time ago got stuck in the passage somehow blocking airflow. Took off the airbox/filter cover and saw it there. Didn't think the rubber piece I found would cause the ill running engine, but it did.

That's all I got for now.
 
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