Those carb parts I mentioned won't be in most aftermarket rebuild kits but you can get oem ones separately from a Yamaha shop. I used to wrench for the local dealership so I've run into this issue before. It's common on older single cylinder bikes since they vibrate and some spend a lot of time idling, therefore they wear the needle out in that spot. The tolerance between the needle and the tube it runs in has to be quite tight at closed throttle especially.

I’m sure you are excited!!! I’m so happy for you kiddo. Now you have to put that thing in some mud and show us some videos!! Cant keep up them 14 hour days, all work no play is not good for anyone !

Nice looking bike. I like the radiator mount. I’m a little leery of drilling holes in the exhaust. Should not have to do that, I disagree with ya having to do that, the amount of back pressure allotted for the engine is a design/performance thing. If there is an issue like that it’s a tuning thing. Do some research on the TPS for your bike. Look on YouTube. I’m sure it will open your eyes to some tuning tricks. Im sure your very excited!! It’s a bad as* bike. Be careful with that power.

Thanks Frank Angerano! Schedule is every Thursday 21:45 my local time ( +3 hours Eastern European Summer Time )

Those little tri zingers are worth a grip and lose value as you mod them. I would think routine maintenance such as carb refresh and so on would be the extend if what I'd do to it. I've looked for a decent one for a while and there just aren't any here. The few that have survived are usually trashed.

Good point, I’m with you on the carburetor. @Dimelol it really does sound like it’s a carburetor issue. I would I go back and check it again and make sure all the proper oem jet sizes are in the carb, needle is set as per spec on the proper clip location and that air fuel screw is installed right and also in good condition. Sounds repetitive but worth the effort. I would still check the voltage on the battery while it’s running to make sure your getting the 14 volts at the battery and make sure your regulator is within spec just for sh*** and giggles.

I wouldn't sweat the resistance test on the coil - anytime a spec is less than an ohm this is normal. It's very difficult to get an accurate reading that low - if the coil was bad it sure wouldn't produce as rpm increases.

I just did redid 2 carbs. I work on mostly cars though. I bought a Bottom-of-the-Harbor-Freight ultrasonic cleaner. Did a great job cleaning the carbs with little effort. I disassembled, put the parts in, then went back to work doing other stuff while the machine did the work. I should have bought one years ago. I think I aid about $45-50 after the discount coupon. I am sure other brands would work as well or better. I rough sprayed the carb with cleaner. Then put in the ultrasonic. Then sprayed out all the hole with carb cleaner and compressed air. Then back in the ultrasonic cleaner again. Lather rinse repeat twice. Came out awesome. It works great for other small item too.

I would agree @spock58 but @Dimelol seems very confident the carb is good. My feeling is yes it’s a carburetor related issue. We have seen tons of times where members say they are 1000% sure the carburetor is not the problem and it turns out there is one small stupid thing that’s overlooked or just so small that it got missed. However that coil does seem very low and out of spec.

Unless you see a misfire using a spark tester I doubt that there's an ignition issue - still sounds carb related. One thing that comes to mind is the pilot screw, is the little o-ring & spring properly in place? Usually this results in a lean condition at low rpm which makes for rough idle & bogging or hesitation. Since your symptoms indicate richness (ie. black plug) there could be wear on the needle in the slide, was this replaced already? You also have to replace the piece that it slides into, at the top of the needle jet. This is a likely reason why it over fuels and is really noticed at the closed throttle position. I will see if I can show a parts diagram of this. You should try needle set #2 & nozzle #16. Pilot screw o-ring is #9 https://www.ronniesmailorder.com/oemparts/a/yam/50038fb7f870021f60a0ca5f/carburetor

Oh gosh. This is homework for me. Never really caught on to the electrical side of atvs..

The primary coil seems low so it’s obviously a concern. Have you checked your timing to see it has not jumped at all. Long shot but it definitely can happen. Purchase an in-line spark tester and throw it on to see how your spark is doing. Last thing is your pick up coil gap. Take a look at that and see what the spec is in the manual. Check the gap you have and compare the two.

Sounds like the needle valve is sticking or gummed up and not sealing good. If the plug is wet, it's drowning itself. If the 300 is like my 220 you can pull the airbox and then the carb in about 5 minutes. Pull it apart and give it a good spraying through with carb cleaner and then blow every pathway you can find out with compressed air. Pretty sure it'll fire right back up then. Check the number of turns on the idle air screw though before you pull it all apart. Tighten it counting the turns in until it snugs up. Don't tighten it as that may damage the seat, just snug. You'll need to put it back together with the same number of turns out. Sorry, I know you said you didn't want to pull the carb but you take a real chance on burning a valve if you introduce anything strong enough to clean deposits. They don't much like hotter explosions than gas.

[ATTACH]213[/ATTACH] [ATTACH]214[/ATTACH] This hauler was custom my made by my wife uncle for his truck, when I bought the atv's he gave me the hauler. If you look in the project room, you will find my new project sitting on it. It also make a great work platform for the atv's and lawn mower. [ATTACH]215[/ATTACH]

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