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Just spent a friend rebuild his top end. .5 over bored cylinder, new piston rings, new valves and seals. We thought his previous running problem was related to a warped head and we couldn't get the intake valve to lap. Used head problem solved with lapping. Today we got it all back together, Ran the same, Cleaned the carb twice, noticed the needle was really dull, replaced that. Still no good. No power over 45 mph. 5th gear is useless. Mine has a 118 main, big gun, 2 shims and snorkel removed. It will literally smoke his bike. Any one think cdi may be causing this? Sorry, it is an 88 we believe. Checked gas cap vent, no exhaust leaks, no carb boot leaks, New petcock. I am lost.



j
 

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CDI may not be advancing? Brakes dragging? Exhaust plugged up? Intake restriction due to mud or mouse nest? Throttle cables installed correctly and adjusted correctly? Does slide move all the way up in the carbs bore? Fuel line deteriorated or plugged or kinked?
 

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CDI may not be advancing? Brakes dragging? Exhaust plugged up? Intake restriction due to mud or mouse nest? Throttle cables installed correctly and adjusted correctly? Does slide move all the way up in the carbs bore? Fuel line deteriorated or plugged or kinked?


Brakes free and in adjustment, Exhaust is flowing freely, But am going to throw my old one on to check, air box is clean and filter was just cleaned and oiled. Throttle cables checked during carb rebuild both checked twice. The slide moved freely, but I noticed the hardware that attaches to the slide is different than my 88. I had never seen it before and have been into several tw carbs. The normal plastic square piece was copper with a spring clip in the middle. Fuel line is clear. I am hoping that swapping the cdi will solve it.
 

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Brakes free and in adjustment, Exhaust is flowing freely, But am going to throw my old one on to check, air box is clean and filter was just cleaned and oiled. Throttle cables checked during carb rebuild both checked twice. The slide moved freely, but I noticed the hardware that attaches to the slide is different than my 88. I had never seen it before and have been into several tw carbs. The normal plastic square piece was copper with a spring clip in the middle. Fuel line is clear. I am hoping that swapping the cdi will solve it.
So here is what we discovered today. An 87 tw will run with a bad cdi if the brown wire is disconnected. iT RUNS VERY HOT. not recommended but will work if you need to get the bike home. Bike ran perfect or better with the new 118 main jet with the cdi off my 87. We attempted to put the side cover with stator on from a 94 , but realized the magnito needs to be changed. Reason for this was i couldn't find any info on the extra yellow wire on the cdi for all other year tw's. Didn't wan't to risk a cdi off the bike I am going to rebuild this winter. Anyone have a later cdi on an 87?
 

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So here is what we discovered today. An 87 tw will run with a bad cdi if the brown wire is disconnected. iT RUNS VERY HOT. not recommended but will work if you need to get the bike home. Bike ran perfect or better with the new 118 main jet with the cdi off my 87. We attempted to put the side cover with stator on from a 94 , but realized the magnito needs to be changed. Reason for this was i couldn't find any info on the extra yellow wire on the cdi for all other year tw's. Didn't wan't to risk a cdi off the bike I am going to rebuild this winter. Anyone have a later cdi on an 87?
Did you ever find out the issue here? Was the CDI the culprit? I'm having similar issues with low power. I thought it was a jetting issue, but I've made almost every adjustment and still 5 gear is nearly useless, unless I'm going down a hill. Mine is a '99 with 10K miles.
 

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I just came across this post. I had the same problem TWICE. Once on my 1929 Model A Ford and then on my TW. My problem was fouled spark plugs. Spark plugs can foul almost instantly if an engine is running too rich. Seems simple but that's what it was. Driving these computerized fuel-injected newer cars makes us forget about spark plugs.

In the case of the TW, I had just rebuilt the lower end, carb, etc. It ran like crap until I changed to a new plug. Then, after more "carb tuning" it started to run bad again. Cleaned the new plug and problem solved. 150+ miles with no problems. Also, don't use any ETHANOL gas. Treat it with a good conditioner if you do.

The Model A is a longer story. After winter storage -- no power, I checked everything, It was driving me up the wall. I even replaced all the gas in the tank. Finally, I pulled a plug and it was covered with "hairy" carbon. Weird. Cleaned the plugs, got the carb leaned out, and checked the timing (it was okay) and it has run like a dream all summer, so far.
 

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I see you live in VT. Hills, mountainous terrain? Have you checked your sprockets to see what number they are? Count the teeth on the front and rear sprockets. Stock sprockets are 14 front and 50 rear. I know the West Coast boys here who ride on mountain roads complain of the same problem with no power at top end with a smaller rear sprocket. Worth a check!

Let us know!
 
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