engine shakey at mid speed

[AdamT]

Whats going on. I have a Dax 67 almost through 3/4 or a gallon so still running 16 to 1. grood smooth power at lower speed but then at mid speed it is rough. once it gets past that, the top speed is smooth again sometimes i can help it through the rough stage by peddling. What is going on I have my mix needle on the second from the top, or 3rd from the point. I tried going richer and leaner with the needle but second from the top works best for me. Is this normal? havent encountered any other MBs so not sure what its supposed to be like.

 

[pdxrhett]

Well, are we talking about vibrations, or shakey power? Or is the motor jerking the bike around?

 

[AdamT]

sorry its more like the enginde gets weaker at mid speed, then as i peddle it or just hang on through the chugs it smooths out with at higher speeds and gets more power.

 

[pdxrhett]

Do you have any upgrades installed?
Some upgrades only work in a certain rpm powerband (i.e. tuned pipes). Also, with a 4 stroke motor, the powerband is pretty equal (compared to 2 stroke) all the way through the rpms, but with a 2 stroke engine the powerband is at a much higher rpm than a 4 stroke

 

[AdamT]

no upgrades just an un even power band. im using premium gas and still breaking in at 16:1 almonst have a gallon through it.

 

[RMWdave]

go for a ride and try to work it out while you listen to the exhaust note. when it becomes sputtery or off tune slack off all the way down to idle and slowly bring it up in tune again.
try to do this untill you have your flat spot worked out. Sounds like a break in issue to me it may not go awa if you have ridden too hard through the top end by now, but you can try

 

[2stroketech]

Different diameter carburetors will give you different power curves. Now I know that you have a stock set up, so I would look at your intake manifold and your transfers. It is possible that they have some casting flaws in them that are giving you some hick ups.

Also While you have the intake manifold off you might want to check to see if the gaskets are matched to the ports. This will also cause you problems.

 

[AdamT]

dang yeah i have definately ridden the top end pretty hard it is almost through its first gallon now i will try to do that dave. I will also check the gaskets but i am prety sure they are in good condition. Thanks guys

 

[fetor56]

Break the engine in first & IF u still have the same problem get back to this thread.No point in trying to diagnose something from an unbroken/inconsistant engine(u don't know what's normal)

 

[RMWdave]

for sure mate, try and work out your flat spot 9 times out of ten you can in the early stages to get it all back.
the point is to not force it to top RPM (through a sputter) you want to go from base to sputter back off and again. after about ten minutes of doing the climbs and falls you should notice a slight pickup.

have it a try, you understood what im saying so let me know how it works out!
-dave