Carb or electric (1987)

[fishx65]

Working on the old 87. Just replaced the stator, ignition coil and rebuilt the carb. The main problem of running for 5 minutes and then dying was finally solved with a new ignition coil. It must have been heating up. Still trying to solve another problem: She cruises along just fine at low RPM but as soon as I rev her up she starts missing and sputtering. Not sure if it's electrical or carb related. Anything that's common with this condition I should be looking for?????

One other thing, the 87 ignition coil had two wires coming out of it. One goes to ground and I believe the other runs to the CDI box. The cheap ebay coil only had one spade terminal which I used for the run to the CDI. Seems to be fine without a ground wire.

 

[frit91]

I am not sure about the coil wire situation, but let me relay some info to you. The previous owner of the 02 I now own had the same issue as you. It would run fine at idle to just less than half throttle. It fell on its face and backfired above half throttle. He took it to the yamaha dealer who said it was electrical and changed the stator, cdi, and coil and that did nothing for it. He dropped it off with me and after jetting the carb down one size on the main jet it ran just fine. Buy a new plug and do a plug chop to see if its too rich or too lean, then jet accordingly.

 

[fishx65]

Thanks Frit. Put a few miles on her tonight and I'm starting to think it is a fuel delivery problem. Feels like she's not getting enough fuel when I hit the throttle. Gonna yank the carb in the morning and see if I can figure it out.

 

[frit91]

Check the float level. It's easy to overlook that and end up chasing your tail.

 

[bomber315]

you probably need less fuel at WOT. sounds like too rich to me.

 

[fishx65]

Went through the carb again and everything seems to be fine including the float level and accelerator pump. I also ran a new fuel line to make sure the filter wasn't clogged. Since the cheap new ignition coil helped so much I'm thinkin about ordering a Mr. Electrical or Caltric coil to see if it solves my problem. Anyone running either of these???? I did install a Mr. Electrical stator which, of course, didn't solve the problem but seems fine.

 

[frit91]

Jets are cheap. What size main is in it? Did you ohm out the stator and coil and spark plug cap? Lots of things to check before dropping more money on a guess. Did you do a plug chop? Try a main jet 1 size smaller and see if that helps, or maybe you need a size bigger. A plug chop will tell you which way you need to go, leaner or richer. How many turns out is the air fuel screw? Clean all grounds. Are the parking brake wires bypassed? And for reference Caltric parts are cheap, and remember you get what you pay for. If I remember correctly the parking brake can affect throttle response a little above idle. Search the forum for past threads and you will most likely find your answer. If you don't mind, post the answers to the questions I asked and that will help us answer you a little better. Good luck bud.

 

[fishx65]

New stator checks out fine but I never checked the plug cap. Spark plug looks to be on the lean side. Carb is completely stock besides a few rebuilds and all grounds are solid. Not sure if the old 87 had any parking brake wires but it's been blocked off for the 20+ years I've owned it. I did use the old plug cap on the new ignition coil so I'll check to see if I have another one laying around. I did end up ordering another coil last night and this one comes with a new cap. Thanks for all the help!!!!!!!!!!

 

[ksowin87]

Not sure if you checked or not but see if there is a crack in the intake boot on the carb... Will cause same problems... Happened to me twice...

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[fishx65]

Not sure if you checked or not but see if there is a crack in the intake boot on the carb... Will cause same problems... Happened to me twice...

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Thanks but it's the first thing I checked cuz I've been down the torn carb boot road before. It's a long road!!!!!