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300ex only half rev..???

16478 Views 38 Replies 7 Participants Last post by  JERSYBOY73
i have a 1998 honda 300ex and just put in new rings. has a big bore kit in it. timing is right on and no odd noise when idle. fires right up and sounds great again but for some reason it will only rev half throttle and then revs out. all power is gone at that point. need some help i have tried going one tooth back on the timing and goin on tooth ahead and does not change,.any if would be great.
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Welcome to the forums. Did it just start this after installing the new rings and was it already running right with the big bore kit before?
X3 on cleaning the carb. Carb cleaning is a good first step.
the carb was not touched when the rings were put in only thing was i pulled the old piston rings off and put on new ones.
Did the ATV sit any length of time without it being started prior to you replacing the rings? If it did, there's a good chance the carb could need cleaning. If they sit long without starting, the gas will evaporate, leaving deposits behind that can stop up the carb.
would the silonoid couse this?
No, the starter solenoid wouldn't cause that.
i was wondering if a week spark would have something to do with it i have checked 3 plugs (new) and all the same spark so i did a contitnuaty ( how ever that is spelled) test and it has a weak pass through of elect. in the starter solinode. ok and i have gone threw all the conections and all are tight and good.
All the starter solenoid does is to send power from the battery to the starter, when the start button is pushed. It doesn't have anything to do with the spark and after the engine starts, it does nothing.

If you have a weak spark, it could be the ignition coil or stator. Did you have a good, bright blue spark at the sparkplug or was it weak? If it's red or orange colored, it's too weak.
You may have a ring that is not spaced properly, when you installed the piston kit did you check the end gap on the rings before you put them onto the piston? Also when the cam was installed after the top end was rebuilt, the Lobes should have been facing downward and the 2 "-" marks allign with the top of the head. The valves are set at .004 int and exh. I'm not trying to belittle your mechanical abilities I'm just trying to get all the facts form the time you removed the old piston to the time you re installed everything.
I agree. I was going to ask the same question about the ring spacing.
Did you install the rings like in the diagram below?

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The rev limiter is built into the CDI and there is no reset.
so what is the chance the cdi is blown would it still start?
I guess it's possible, but all the ones that I've seen with a bad CDI, it wouldn't start at all.
well well well thank u all for the great advice i found the problem and it was the cdi was not grounded all the way you all have beena great help.
Glad you figured out the problem.
Yeah, hang around, don't leave now. LOL.
you all have helped it be possible for my 11 year old son drag race in the chenango county fair and the broome county fair thank you all.
Best of luck to him and have fun!!
Welcome to the forums, Justin.
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