Help; severe engine miss under load

My Son has a 1983 XL600R that was in very rough condition when he got it.  Some chuckle-head had wrenched on the inside without knowing what he was doing and the cam sprocket bolts came loose and chewed up everything.  I've completely rebuilt the top end, including new cylinder, piston, rings, new head, valves and seats, etc.  I've overhauled the carbs and installed a "Ricky" stator.  The bike starts first-kick and runs great at low RPM.  However, accelerating from 30mph and up just ain't happening due to what feels like ignition cut-out.  I've convinced myself the carbs are adjusted properly.  There are no air leaks causing lean condition.  Coil checks out and of course the spark plug is new.

Any ideas?

Thank you!

Fuel level in the bowls OK?

Fuel flow out the petcock is good?

No breather/vent hoses plugged with mud, spiders, or mud daubers?

Does it get better with the choke on?

Dual carbs?

Did you sight through all the jets and jet holders and emulsion tubes looking at a fairly bright light?

New inlet needles and floats adjusted properly, fuel in the bowls and no flooding.

Petcock flow is good.

No plugged hoses or breather.

Applying choke when warmed up will kill the motor.

All jets and orifices are clean and shiny.

However, even though the spark plug is new, I have installed new plugs in other vehicles in the past that were "bad" right out of the box! 

BTW, this critter is for sale if anyone's interested.  I've put too much money in it already.  It's plated and titled and everything else works.

What jets are in it?

I`d block the air intake off under the seat a little with tape or apply some choke while running it,,,,,,if it`s better it`s lean,,,,,,,,,or try pulling the side cover to allow more air in,,if bnetter there,,then it`s rich,,,,

 

Sounds lean to me..........

 

But if the above does nothing but make it worse,,,check the plug grounded to the head,,is the fire nice and blue....

 

B

My bet is the float levels. They are so picky, an they don't run right unless properly adjust. They leave no room for any wrong adjustment. I have an 87 that had the same problem, adjust the floats to the top of the float bowl. You should be prime.

Thank you all for the responses, you've given me some things to try!  The float level is a pain in the a _ _!  It's a fine line between flooding and adequate fuel!  I put new tires, tubes, and tuned the spokes on his Yamaha XT600 this weekend so the Honda will have to wait until the next time I have "free time." 

If the bowls have a drain you can use clear line to check the actual level with everything assembled.

If the bowls have a drain you can use clear line to check the actual level with everything assembled.

That is a brilliant idea.

Didn't think of it myself, one of those completely-obvious-in-hindsight things!

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