Lunging and Hesitating

[Uncle Jetski]

We've resurrected a 1982 GS450T, cleaning the carbs thoroughly and fixing some electrical problems, and so now it runs. But between 3,000 and 5,000 RPM, it bucks - alternately lunging and hesitating. This happens no matter how fast I roll on the throttle.

I can minimize the problem a little by putting on a little choke, but then it idles at 2,500 RPM. What is causing the problem? And is there a "better" solution?

[mark]

Did you take the carbs apart and soak in carb dip? Set floats correctly? Replace o-rings in the carbs? Do a carb synch? Valves adjusted? All that's pretty basic for a carb rebuild. Where are your mixture screws set? (I'm not that familiar with the 450).

Seems as if your running way to lean. If you do a plug chop at the throttle position where your having trouble, you can confirm it. Other problems could be air leaks at the manifold boots, air box leaks, or even a malfunctioning petcock.

[Uncle Jetski]

Tore it apart 3 times

We acid soaked the carbs, and tore them apart 3 times. We replaced the head gaskets, freed the valves, and synced the carbs. Spraying hotstart shows no more air leaks. Replaced the petcock. Both plugs are white (lean!)

What is a "plug chop?"

[Billy Ricks]

I'm thinking float height could be wrong. That's pretty much the range fuel level in the carbs has the most effect.

[Uncle Jetski]

Floats were set

We set the floats with a gauge, so we believe them to be the right height.

[Philly_Chris]

A plug chop just means to ride the bike holding the throttle position where the trouble is showing up then pulling the clutch in, killing the engine and coasting to the side of the road to examine the plugs.

[Billy Ricks]

We set the floats with a gauge, so we believe them to be the right height.

Another thought, did you get the needle assembly on the slide back together in the right order?