82 Honda 250R Run on when trying plug chop!

[bradmopar]

Bought a 250R in pieces from a fella that took it apart and lost interest in it. I totally disassembled the engine and replaced ALL seals and gaskets in it. Reassembled it and rebuilt the carb. Tried it out and it was way rich and 4 stroking! Went to a 148 jet and tried it. It runs now and goes great. I tried to do a plug chop the check the jetting. I took it down a quiet road wot in 5th gear. I pulled in the clutch and shut down the kill switch and the thing kept on running. I hit the throttle and then it died. I'm thinking that its still way rich and pulling unburn't fuel from the expansion pipe. My plug is dry and black. Any suggestions?

[NeverLift]

By the term 4 stroking I'm sure you mean "dieseling". This happens from pre ignition something is getting red hot in your combustion chamber igniting your air/fuel mixture when its not supposed. I have also seen it when the slide on the carb has too light of a spring and the air speed through the carb actually holds the slide open. I would try 1 more plug chop with a new NGK plug. The post pictures of the plug for us.

[bradmopar]

The term 4 stroking is a term used when your 2 stroke is running so rich that its miss firing. Slang term referring to the power output of a 4stroke. I know its running rich. Plug is dry and black. Pulled the choke and dies out instantly. This is the way I've tuned my sleds for years. But never had an engine act like this and continue running with kill switch off on a plug chop. I'll get a new plug and try another chop. I don't trust a plug chop if the engine does this though.

[bradmopar]

I should say its running rich at mid throttle to 1/4 throttle. But need to hold on like crazy so unable to pull choke at WOT. I am wondering about my service manual. It says the main jet should be 158 and the float set at 18.5mm. My manual is listed as 81-84.I think there was a different carb on the 83-84? On the Honda part site I use they don't list a 158 main jet and the float level at 18.5mm seems way high. Carb had a 148 main in it when I got it. Honda site lists 142 to 148 main jets.

[bradmopar]

Yes it is dieseling on the top end! Switch is good.

[OldNo437]

running rich and an air leak? make sure all your gaskets, seals aren't leaking first.. my watercraft would diesel and run on with no ignition, turned out the carb gasket was leaking...

[barnett468]

put a 142 - 144 in it.

make sure plug is proper heat range.

[LastFoolerInVA]

My r would start "dieseling"- I called it death revving- when I was running out of gas... if your dieseling only when she's wide open, but runs rich everywhere else it could be something as simple as improper float height in the carb causing the float bowl to run out of fuel.. for some reason the air cooled r's are more prone to dieseling.. 158 main jet is way big for a stock 82... I think I was running a 155 with a 38mm air striker