runs like pooh at low RPM...seems hot.

So I just got this new bike running. 85 Maxim XJ700N. Ran pretty good in short bursts, but I took it out today for a longer shakedown run. As time went on it needed to be run and a higher and higher RPM. Anything too low and it would sputter and miss and try to die on me. I have been working on cars for some time, but truth be told, this is my first bike and I don't have much experience to compare it with. I don't really know if it is running to hot, but my gut is telling me it is. I am going to chance the oil since I can't think of many other things too cool and air cooled motor down. I haven't checked the timing, sync'd the carbs and I haven't adjusted the valves, so I'm sure there are a number of places to look, but I think it is a matter of the engine getting hot. Like I said, runs like crap at low RPM only after it starts getting warm, and gets worse as it gets hotter. We are talking ride the clutch at 5000 RPM to get through an intersection crappy. Any help would be much appreciated.

 

Pull the Plugs and inspect the Ceramic surrounding the Center Electrode.

If the Plugs are Clean ...
Clean is Lean.
Too lean generates too much heat.

Do it right away.
You feel its running hot?
It very well might be running too hot.

Check it!!!

 

Sounds rich to me. Rich mixtures burn more poorly at higher temperatures. Lean condition on the other hand runs better when hot.

Pull the plugs like Rick says. They will tell the story.

 

IF the temps check out......
Could be once things warm up, you're opening up an induction leak. In fact, I'd be willing to bet that's the problem to begin with, as a lean running engine will get HOT-quick!
Try this:
When it's hot & running crappy, spray some WD 40 on and around the intake boot rubbers between the carbs and head. If the idle changes pitch/RPM, you have a leaker.
If you have a digital infared temp probe, point at the exhaust pipe where it curves downward and compare temps before and after warming up. EGTs should be consistant and even across the board. A high EGT (exhaust gas temp) reading will point to a lean cylinder a whole lot faster than waiting for a plug to color up. A ColorTune plug will do the same if you have one available.
Now, we're not talking about a Maxim X which is water-cooled, right?
Just askin'......

 

So after posting this, I decided to check the plugs...go figure. I expected lean, but I was wrong. New plugs completely covered in soot. Like I said, it might not be that hot, I just don't have much to compare it to. My next thought is...could it be that I have the old air filter back on it now?? I ran it in the garage and up the street without the airbox because I was going to make one...then decided I was dragging my feet and needed a filter. The thing looks pretty bad, and it really didn't start this until I put it back on...hmmm. That almost seems like to easy of a fix, but hey, why not??

 

...and it is an XJ700N...air cooled.

 

a plugged air filter will cause an over-rich condition, yes. Stock components?

 

I'm so jealous. I have an 85 xj700 and I cant get my plugs to darken at all!


Good luck.