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im starting to hate my tw

1954 Views 10 Replies 7 Participants Last post by  demarko69
ive done almost everything now. new carb parts 117.5 main jet. new needle and seat. carb is 100% clean. i am pretty sure it is the cdi unit. it runs rough and sputtery, almost like a lean issue, but i know it is not because i have a brand new spark plug in it and it has black on it because ive been trying to fatten the hell out of it. it backfires when let off the throttle. im not sure anymore here!? the engine is sound. it have better than factory compression and the valves looked amazing. ive been chasing my problem as a carb issue but i think im going to have to go the more expensive route with a cdi. any suggestions on where to get one for cheap and fast, how to test for it. etc? it is a 1987
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If you are 100% sure its not the carb then move on.

There are oodles of possibilities of failure before the cdi... Test test test before spending 300+ on a new cdi

Have you gone thru the entire electical system. By that i mean everything, wire shorts wire opens wire connectors wire switches key/ignition wire coil wire relays. Once everthing has been tested good and eliminated, then move on. In the past 4 months I have had 3 87 and not a 1 was running poorly due to the cdi. The one time I was sure it was the cdi, I changed it with a known good runnig 87 cdi and thought that fixed the problem. Turns out it was a broken wire inside a connector and when I change the cdi the wire remade contact due to the movement location. Another 87 had a kill switch intermittent problem. Everytime the bike was a a certian RPM it cutout miss & pop. Faster / slower was OK. The RPM made a resonant freq./vibration that was enough to make contact.

ps. still curious on the yamaha 117.5 jet. Did you get a mfg/part# on the packing list

ps.. the only way to test a 87 cdi is to swap it to a known running 87

ps...if you want help bring it over, I have lots of 87 parts
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S.O.S ? Gerry


I saw dot dot dot bar dot dot dot, I guess I need to put on my glasses
once you get it fixedand running properly you will love it.. keep us posted
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