Hi there,

I bought an old (1982) XJ750 a few months back, which I have been fixing up. She has got nearly 80000km on the clock.

Currently I have problems with the way she is running:

She starts ok, idles a little unevenly, but rides away ok.

As she warms up, literally after 2 or 3km, she develops a "flat spot" at lowish revs (2000 to 2500 rpm). This gets worse and worse as she warms up, till (after 8 or 9km) I have very little power at anything under 3000 to 35000rpm, making slow riding almost impossible. She feels really flat as I try and accelerate, and then a surge of power as the revs gets over 3000rpm. She sounds fine at higher revs. And if I stall her I can not get her to restart.

Oh and she didn't have this problem when I got her, she had other things wrong with her, but was not doing this...

I changed oil, air filter and plugs when I bought her. The new plugs have some carbon now, so guess she runs a bit rich.

I suspected the carbs, so took them out and cleaned out the float bowls. Haven't balanced the carbs yet (as I don't have vacume guages).

If anyone else has had these symptoms, or knows how to go about solving it, I would be very grateful.

Thank you from a newbie on this site,

Alan.

It could be the float levels set too high causing a rich mixture, coils cutting out when hot, poor battery (alternator giving better charge at higher revs-stronger spark) or dodgy plugleads.

What you are describing sounds like typical running rich which could also account for the rough idle. Also balancing the carbs on these bikes can make a world of difference to the idle and general smooth running and quietness of the motor.

Hi Alan, I agree with the previous comments about running rich, but would suggest you check the needles and emulsion tubes for wear, unfortunately its a carb strip down job though!