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RM85 Bogging

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Hello, new to the site, but a long time reader. Here's my problem. My sons RM85 seems to be bogging on the top end. It did this about a week ago. I compression checked it and it was getting like 30-40 with 5 kicks WOT. Through some oil in the top end and compression went up. Easy enough, i put a new piston and ring in it and while i had it apart i completely disassembled the carburetor, cleaned and reassembled. put it back together and viola. 120 on compression with 5 kicks WOT and she ran like a champ. We broke the piston i right by cycling it hot cold 4 times starting with low throttle working our way up each time we warmed it up. then the next time we go out after about 2 hours of riding the problem is back. The low end seems to be fine but once it gets about half way up in the rpm it just shuts off and will even rev like its bouncing off a rev limiter on a 4 stroke, just not as fast. We are running about 36:1 maxima 927 with 93 octane. jetting is (bare with me) 128 main, 50 pilot jet? (right next to main), didn't see anything on the air screw, F1340G 24NAA H Needle on the 2nd clip from the top. We are at about 300 ft elevation in Arkansas. Any help would be great.

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correct me if i'm wrong... but if its bouncing in rpms... doesn't that mean the bike is lean? maybe if you can try upping the main jet...

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no, i didn't check the float height, but if it was that, wouldn't it be a constant issue, instead of every other ride? i took the carb apart tonight, thoroughly cleaned it and blew it out with compressed air. still runs like crap, but it isn't surging anymore. its just not producing power at all. it feels like its missing now. 👍 its always something with this bike.

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no, i didn't check the float height, but if it was that, wouldn't it be a constant issue, instead of every other ride? i took the carb apart tonight, thoroughly cleaned it and blew it out with compressed air. still runs like crap, but it isn't surging anymore. its just not producing power at all. it feels like its missing now. 👍 its always something with this bike.

My kid just fouled a plug on his new to him RM85. I know I have to rejet this bike because it was running rich. Keep us posted on what you find with yours cause it sure sounds like a fouling plug or float hieght issue.

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will definitely keep you guys posted. He's not fouling a bunch of plugs. they seem to be about right. not overly oily or anything and they are a charcoalish color, maybe a little lean. i did notice an odd vibration that i haven't felt before in it as well. i am wondering if maybe its the clutch going on it. If that was the case wouldn't it slip and try and rev to the ceiling though? it takes a lot of feathering to get going.

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Now that you have a fresh top end, drop the clip to the 3rd groove, air screw 1 3/4, with stock jets. Once your boy gets to riding it hard the jetting is close, but the bog will not go away when he is riding it and snaps the throdle open real quick with the clip at the 2nd groove. My son's races a rm85 big wheel and we been thrue this. I know the bog your talking about and I feel that rm carb is unbalanced. Seems to have a rich pilot and lean main. Needle would fix it but I have not went that route since we are look at mods to go super mini late this year. Try 1 step leaner on the pilot and 1 step richer on the main. Our bike is all stock with air box mod right now, and it sceams off the start and down the straits with 13/48 gearing. If you guys can find a Keihin PWK28 carb (off an rm100) it will wake the little bike up, but let the kids get to the point when they are riding the bike for all its worth real well before any mods. Good luck hope it works out.

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