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My 99 TRX 300 had a stumble

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I will, hopefully, not ramble; my goal is to share a report on what I had, what I found, and what I have now, so that someone else can use it for information.

My 99 TRX300FW had a stumble under acceleration of the engine. It would happen when I blipped the throttle in neutral, or when driving. It didn't always do it, and I couldn't find a condition

that would predicate it. Sometimes it did it, sometimes it didn't. When it did, I would hit the throttle and there would be a stumble in the RPM's before they would increase; sometimes, if I didn't back off, it would quit. If I did back off and hit it again, it would rev. Sometimes, it ran 100%; sometimes, it stumbled a little, but it ran 90%. Sometimes, it was 40%. 

I posted a request for insight on HondaATV, and Goober stepped up to the plate (along with Eric the Red). Previously, I had pulled the plug and checked it- it was slightly fouled, so I cleaned it. The gap was good, and the electrode showed no erosion. Under suggestion, I checked the vent line- it was clear. I checked the screen in the petcock, it was clean. That surprised me- it had never been off, in 23 years. No crud, particles, or varnish. It was clean as a whistle. I then ordered a Shindy kit for the carb, and pulled it off once the kit arrived. The carb was as clean as the screen, with only a slight amount of varnish in the bowl. A quick spray with some 2+2 and that was gone. No clogged passages, the float was fine, everything was moving freely. I had the kit, so I put all the new parts in. It ran the same- exactly the same. I checked the intake manifold, and it looked good with no cracks or leakage at the mating surface, but I put a new one in anyway. Still the same. I had not adjusted the valves, and the shop manual (Clymer) suggested that out of adjustment valves could cause a high RPM miss. So, I made an appointment with a local shop (Superior ATV Unlimited, in Stuarts Draft, VA) to adjust them. All of my spare time was spent, so I decided to have them do it. 

They are busy (the local dealership won't look at older machines, so they get the business), so it would be a few weeks before they could do it. In the meantime, my brain churned over what else it could be, if it wasn't the valves. I didn't think that the solution would be found there. It would help, but I didn't think that it was the root issue. So, during a break in work (I have a small fab/welding shop at my home, which I work out of), I pulled the plug again. Looking it over, I ran a dirty finger over the porcelain of the plug- and a faint crack appeared. No way it could be that simple, I thought. I didn't have a new plug on hand to put in it, but I had an old one that was still good, so I threw it in. Bam, that was it. It ran like a million bucks, no stumble or hesitation. Still dubious, I took it for a ride that evening- and it ran great. Over the next few days, I rode it as much as time would allow- and it never missed a beat. The valves were adjusted (they needed it), but that wasn't the root cause- it was a bad plug that looked great during a cursury exam. I have no regrets going through the processes that I did, because I learned a lot and didn't spend much. But, for once, it really was a simple solution.

It has a new plug now, and I took it for a long run yesterday. It ran flawless, and it is 100%.

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Edited by hodge5
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Thank you for your time, it was very informative. Sometime persistence pays off... have a great day

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30 yrs doing this..and what i've learned is..never is something too small to ruin your day !. thanks for the write up !.

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47 minutes ago, shadetree said:

30 yrs doing this..and what i've learned is..never is something too small to ruin your day !. thanks for the write up !.

 

I have a habit of looking for the more complex, worse case first. In this case, I had looked at the plug first, but I didn't check the porcelain close enough. 

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Good and informative topic. It was a long walk to a short solution. Well written story.... Thanks for the insight.... BenL

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Hodge ......I'm the sameway always look for the worst case scenario which as you say, isn't always the case, and doesn't it feel good when it's a simple fix, glad you got it sorted and thank you for a very good write up..... Now ride her like you stole her lol'! 

Edited by _Wilson_™

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1 hour ago, _Wilson_™ said:

Hodge ......I'm the sameway always look for the worst case scenario which as you say, isn't always the case, and doesn't it feel good when it's a simple fix, glad you got it sorted and thank you for a very good write up..... Now ride her like you stole her lol'! 

I did, yesterday. We have a cabin that's about 2 miles off road. It is a nice ride back there in my Jeep or truck, but it's even more pleasant on the Honda, 50 degrees, no bugs, just glorious sunshine. The great running 4 wheeler was icing on the cake.

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Thanks for posting up what you found.

 

That's how most of us ended on on a forum; looking for a solution to a problem and doing a search.

 

As a Jeeper, you know the way you have to look at that now is "well at least I know the carb, petcock, and valves are good to go for awhile!"

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3 hours ago, jeepwm69 said:

Thanks for posting up what you found.

 

That's how most of us ended on on a forum; looking for a solution to a problem and doing a search.

 

As a Jeeper, you know the way you have to look at that now is "well at least I know the carb, petcock, and valves are good to go for awhile!"

Very true; I can simplify it further- well, at least I now know how to clean and rebuild the fuel system. While I don't want to throw parts or waste energy, I do want to learn.

 

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I was always taught look for fuel and spark and go from there, good find and something to keep in mind.

 

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