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Problems with 05 yz85

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I'm having problems with my son's bike:banghead: ! The bike is stock and only has a fmf turbine core for the purpose of a spark arrestor. The bike has been ran for a year with absolutely no problems whatsoever. Recently the bike began bogging. The bike starts fine will run and then about 10-15mph start bogging. I checked the reeds, they look perfect. I took the carb apart and removed the jets and cleaned everything. I cleaned the airfilter and reoiled it. I swapped out the breg 10 plug for a breg 9 and buttoned everything up. I told my son to give it a go and the same thing. The plug was wet just a tad but when he went and rode it and revved it good and came back I checked it again.....The plug was a tad wet on the threads but the top of the plug and electrode were faintly brown and looked (according to the manual) perfect. It is colder than normal but we rode the bike last winter same place, same elevation with no problem. The bike has plenty compression and the motor is tight. My little guy now is gun shy on the big tracks because he fears on a big jump the bike could bog on him. Point me in the right direction please.

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The topend has not been replaced and while I do not have quarrel with the fact that installing one wouldn't hurt but for the amount of compression this engine has and the power it made just prior to the bogging, I think it should be able to operate without the bogging.

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I took the carb apart and removed the jets and cleaned everything.

But did you change anything? Have you tried adjusting your air screw? changing out your pilot? changing the clip position on the needle?

Colder weather does require richer jetting, in addition; pilot jets don't last forever, they can get clogged and need replacement. You say that the top end hasn't been replaced yet, if its 2 years old and still on the same top end, its probably way over due.

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...but for the amount of compression this engine has and the power it made just prior to the bogging, I think it should be able to operate without the bogging.

What is the compression? 2 years on an 85 top end is a LONG time.

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get a new top end. i forgot how often they should be replaced but i think its every 20-30 hours depending on how hard your ride it. read some threads between stock and aftermarket top end kits so you get whats best for your bike

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Before you by the top end kit, try raising the needle 1 position( move clip down 1 slot), and turn the air screw in 1/4-1/2 turn. This will richen it up. It's easy and will only take about 5 min. I had to do this all time to my nephews bike when it got cold.

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