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Low RPM bog

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I was helping my nephew adjust his valves and do some jetting adjustments.

We're at 5k ft ended up with a

40 pilot

1.5 turns out

168 main

The bike runs strong and starts on first kick no popping on decell.

Now he did something weird that I've never done with a bike . He'll ride down the street at about 5mph in 1st gear (pretty close to idle rpm) then dump the throttle. It will fall flat on it's face like it's completely flooded. If you roll about 2 mph faster it pulls strong after dumping the throttle.

I told him not to do that. I don't really ever see where you would actually be riding that way. Even from a dead stop race start you're rpms are up before letting the clutch out. I'm thinking it's just the way the engine runs. That it's really not possible for a carb engine to run that low rpm and handle a full throttle move. I tried a 165 and 162 main and there was no change to this bog.

I don't think there is a way to adjust this out, am I right?

04 RMZ 250

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Sounds like exactly what you said, the motor can't pull that kind of load when the rpms are that low. You could try raising the idle and then having him try again and I'm betting it'll go away once the idle is high enough. However, like you mentioned, the bike isn't meant to be ridden like this (especially on pavement where the tire can't slip) and i don't see how you would ever run into this situation at the track.

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My bike doesnt do that. If its worth the work to you( I would do it to be safe so it doesnt bog on the face of a jump or landing) Take the carb off and completely clean it. No matter where in the RPM the bike is, it should come on instantly and come off instantly.

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I'm just going to tell him not to do it anymore. He only does it when he's screwing around thats probably why I've never seen it on my bikes. When I rode his bike after adjustments I couldn't get it to do it until he showed me exactly what he was doing.

My bike doesnt do that. If its worth the work to you( I would do it to be safe so it doesnt bog on the face of a jump or landing) Take the carb off and completely clean it. No matter where in the RPM the bike is, it should come on instantly and come off instantly.

I think you misunderstood. It wont bog on a jump face or landing or even climbing a hill. Unless of course he's trying to jump with a speed of less then 5mph. Which in that case it wouldn't mater if it bogged since he'll be firmly on the ground anyway.

Do a test with your bike. Go slow enough down the street where the engine idle speed is actually pulling the bike. You will feel the bike pulling you without giving it gas. It should be about 5mph or slower. Then all in one move without feathering the clutch wack the throttle full open. Not a smooth roll on, slam it full open as quick as you can.

Next time I have my bike out I'm going to try it and see what mine does. I'm betting it will do close to the same if not the same thing.

Or if I do like tnt said and slightly raise the idle speed it will go away but that would just be an adjustment to prevent him from being a bonehead..

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I did, and it about flip me backwords. I am just telling you from experiance that these bikes should not do that no matter what rpm. Later on it could bog in a dangerous situation. I would figure out whats going on. Check your AP timing. Its bogging meaning its not getting enough gas, or its getting to much. What kind of climate do live in, because a 168 main is to lean for summer if the bike is ridden even nsomewhat hard.

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I'm a 5k ft and right now it's been in the high 90's.

I didnt have anything bigger then a 168 main but I know smaller didnt change anything. I'm going to go pick up some bigger mains and see what that does.

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You migh not notice that much of a difference... but its alot better for the bike to run rich. If you run it lean you might blow it up. We have run my bike rich for 13 months now and I just now am having to change the shims.

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