Smoking like a good un

[jonno]

Just rebuilt top end after a rebore and new piston.I use rock oil fully synthetic oil at 3 to 4 %. The motor smoked as expected before new piston but now it seems twice as much.Ring gap is between recommended size in stickys book, in the advanced engine build section.0.33 mm. CR250 piston in steel lined TS1. Anyone got any ideas as to why the extra smoke? The smoke is blue btw, so I dont think its the drive side seal.The only difference is the new piston has 2 larger windows,when the old one had 1 hole about 20 mm.

[St George]

Choke stuck open ?

[Wack]

If it's been stood a while has the oil settled to bottom of carb and tank? Does it leave a smoke trail when riding? I prefer Rock oil synthesis for autolube systems as it stays suspended in the fuel better.

[jonno]

No it hasnt been standing.The oil is synthesis 2moto x.There is more smoke ehen revved.Pretty sure the choke is off.Dont need it to start.

[dave411]

If you don't need the choke to start,surely your running rich.I would expect any 2 stroke set up correctly to need choke from cold.

[jonno]

Drained the tank and carb.new fuel with castrol racing @ 3%.Its a little better,but not much.Dave I agree,but its been dynoed several times and as its a sprinter has been deemed ok.Surely with the much larger windows in the piston its going to allow more fuel in,than the older piston with 1 smaller window/hole?

[dave411]

What clour is your plug?

[jonno]

Wet and black and struggling over half throttle. Definitely too rich.Shop that did the work said the difference in the piston shouldnt make any difference,but wasnt expecting such a difference.I have a 160 main in the carb is A 34 delly.

[Scooterlam]

Id put a new plug in. I've had fouled/failed plugs that give same symptoms.
Might not be your issue but not a lot to lose.

[dave411]

I would be looking at the carb.Also,double check your choke is completely off,as suggested earlier.
I re built a carb the other day,and when I tested the engine,it was smoking like a good in.Rough as,just no power.Took carb off and stripped it,and found to my amazement the main jet in the float bowl