Two questions Bog, and light clatter.


I'm an ex dez racer. I've posted a few questions on the forum that have had great replies. I've got a new one. I took the ol girl out on her very first desert run in one of my old haunts. I flogged her pretty hard and she did not overheat, however every time I would hit a big bad whoop section the bike would bog on the G outs, (this sucks when you twist the trottle and need it but nothing happens, except you hit the next whoop with no power and loose your rythm.)Another thing I noticed is the engine does seem to be a bit noisy. I can hear a faint clatter or light rattle. I dont think it is detonation but it could be. I put the highest Octane I can get in it. Anyone have any clues??? and yes I've adjusted the valves. Again this is my first four stroke maybe some of these noises are normal.

Thanks in advance.


I have a rattle noise too. On mine it turns out to be the clutch lever vibrating. When I put my finger on it, it stops. It really sounds like pinging when you hit the power band.

The bog might be low float level or your missing the little white cap that fits around your main jet.

It's not the clutch lever. My two strokes have always done that too. Now the little white cap on the main jet is something I have never seen. I bought the bike new 2 weeks ago did my own jetting an have never seen a little white cap on the main jet. Thanks for the reply.


If you have an aftermarket aluminum skid plate installed, then you'll get all kinds of engine noise coming back up to you at different engine RPM.

In regards to the bogging issue, make sure to first adjust the float to the spec in the service manual and see if that helps. The book only talks about the minimum float drop, but you can also adjust the maximum float drop (not disccussed in the service manual) and that may be where your problem is. Try adjusting the maximum float drop for less drop by a few mm's at a time to see if that improves things for you.

In regards to the little white cap on the main jet, its a shroud/baffle that helps to keep your main jet supplied with fuel under hard acceleration, bumpy terrain, whoops, etc. Without the white plastic cap, you might have additional fuel supply issues when the throttle is pinned across whoops or up up a rough hill, etc.

These new four strokers do make alot of engine noise. Running 20W-50 deminishes it somewhat.

I haven't pounded any whoops deep enough to cause the bog condition you have described. But the way I understand it the bog is caused by the G-forces from bottoming causing the float to sink down in the bowl which displaces the fuel up into the venturi causing a tempory rich condition. And you know how crappy that can make a big four stroke run. Two ways to diminish this effect is to run the float LOWER in the bowl which would be a LARGER measurement when setting the float height. That way there is less fuel displaced during the G-out. The other way is by making sure your carb vents and overflow tubes are not plugged.

What main jet did you end up running?


I ended up using 170 main. I have checked all the vent and overflow tubes. I have a little fear of running float to low in the bowl and then causing a lean condition on full throttle sand washes. But I may play with it a bit and see what happens.

Thanks Guys.


Everyone is right about the G-outs causing the float to move around too much. As far as the engine noises go, well, you just have to live with it. The noises are normal, and I believe they are amplified somewhat by the aluminum frame. My bike has rattlings, clackings, konkings, and so on. It varies depending on rpm, but it's completely normal. Honda apparently designed the engine for brute power and reliability, but in the process produced a pretty noisy engine. But that's ok!


oh yeah, don't worry if your oil pump is noisy when cold. Unlike the 600, the 650's oil pump is mounted towards the outside, where you can really hear it when the engine is cold. You can hear it on the 600's also, but it's deeper in the crankcase and not as noticeable.


thanks for putting my mind at ease with the noises. After carefull testing yesterday afternoon I have nailed it down to having the most noise when the engine is almost lugging and the throttle is slightly cracked open. I guess I figured being a big four stroke this thing would be happy being lugged like a tractor. It seems to be as picky about gear selection as a two stroke. I may move my needle clip up one notch to lean the mid range and see what happens, I'm in the fourth position now maybe 3rd will be better. Wide open throttle the noise all sound pretty normal. Thanks for the replies.


My engine is so noisy I had to make a mental note when I bought it new.

Yeah man, I know what you mean about the bike being a little picky about gear selection. I don't know what that's all about haha.

Anyway, if yours is properly uncorked, and running the competition needle and 172 or 175 main jet, then you should set the needle clip to the 3rd position. The bike runs too slow for my taste in the 4th position (using the competition needle). If you run the 155 or 160 jet for high altitude, still put the needle clip in the 3rd position. Works great.

Lugging the engine or almost doing so doesn't accomplish much I've found out. It doesn't stall like a YZ426 would at such low rpm, but it protests somewhat with odd noises and chain yanking noises and stuff like that. I don't do it just because it seems to put undue stress on the drivetrain.

If you want some pretty serious streetable upper midrange and top end power, try the dual sport mod; which is, stock exhaust tip modified to 34mm (inside the chrome ring, removing the packing, not outide the chrome ring which is the 36mm mod) instead of the 40mm competition unit, and using a 170 main jet. Every thing else stays the same.

Have fun!



Thanks for the info, I did uncork my bike with the dual sport mod. the only thing I did not do was remove the packing. I am assuming you mean muffler packing like on a two stroke silencer. I did do the inside the ring hole saw job and removed the restricter. Oh and the bog is gone with a little float boal adjustment. No more peeing fuel and no more bog. Thanks for all your help. and sorry for all the questions. I am still a little nervouse about switching to a 4 stroke but so far I feel at this point in my life I made the right decision. I need something I could hit the pavement with as well as rip in the Desert.


Hey Mark whats up..Anyway , yeah there is some fiberglass packing stuff around the inside core of the stock tip. When I drilled mine out to 34mm, I noticed the tip was really hard to get out of there, and then saw that packing which was holding things up. I finally got all that stuff wiggled out of there. The result of that effort was good though. My bike is still quiet, but makes some true open class power in the midrange and top end. At the time, I didn't know the general mod was to drill "outside" of the ring, in which case the packing and all that stuff comes out easily, but the bike is louder. I might try that mod sometime just to see how it runs. In the meantime, I'm using the current mod for around town, and pop in my 40mm competition tip and 175 jet for some serious off-road fun. Low end torque is totally excessive with that setup, but it's a blast! Have fun with the 4-stroke~!


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