250cc to 350cc carb set ups issues

[twinrock]

hey guys well i have all but finished my dt200/ rz350 hybrid how ever i have a carburation problem..
now back ground information, i bought the engine/carbs, loom,cdi as a job lot..an unknown quantity really..
the engine which currently no airbox and rzf2 250 pipes, starts easily but is really smokey..rich.!! will not idle.. i looked at the carb set up and found that it was fitted with 250 carbs and just a 240 main jet instead of the stock 180.. i rebuilt the carbs using stock rz31k specs,idle jet, jet needle,needle jet, set float level, air screw..... better but still really smokey, out of both chambers so no crank seal failure, if anything it should be lean with out the air box, i thought maybe there could be excess fuel or oil in the crank case as i have experienced this before.. but it does not clear. i have a mate with a 350 sitting in the shed 2 actually ill grab the carbs off it and try incase there is something i missed apart from that anyone got any other ideas? thanks?

[g0zer]

there is a difference in length in the float valve plungers between 350 and 250 carbs, iirc 250 is longer so a 350cc plunger wont seal the float valve. it should be ok, so long as the float plunger thingy is the original on for that carb.

its possible i suppose depending on how you set the float level, to get a short plunger to seal a long plunger carb but only if the fuel level was higher than its meant to be. normally, you would just see fuel pouring out the overflow lines alerting you to a problem.

easy to confirm as problem, setup hydraulic leg on the float bowl and open the fuel tap to prime with the bike level.

[Sean'o]

Have you ridden it? Ive found the RZ engines hate to clear smoke just idling and reving at standstill, take it for a run and see if it clears. Rich on fuel wont give you a lot of smoke, rich on oil will, take it for a run, if it doesnt clear check your oil pump settings, or if you are running premix, drop in some fresh 30:1

[Rich]

Just so I've got this straight...

You've put an RZ350 motor in a DT200 dirt bike?

Does it have motard wheels?

[aaronmvrider]

[aaronmvrider]

this thing is going to be a wheelstand weapon....

[twinrock]

man just swapped in a set of carbs straight from my mates running rz350... exact same thing... huge amount of excess smoke both sides wont idle and no power...whats going on..!!? is it possible that there is a crack or leak into the crank case from the gear box sucking oil other then crank case seal??.. i guess i can try draining the oil and run it seeing if it makes any difference, god damn why did i sell my perfectly great running tzr again.!!!!! lol

[g0zer]

hard to believe the oil is coming from the gearbox with the bike running on a stand, the gearbox oil level should be below the case split and not splashing about that much eh? also if there was a leak, the crank wells are positive pressure to gearbox- remove the filling plug from the gearbox so it doesnt pressurize the air inside as it heats up and see if it improves problem.

like sean says, just run it. i think a lot of the oil pools in the crank wells and gets flung about by the webs can take a while to lose the excess.

re: poor running. maybe there is so much oil its fouled plugs already, also what shape is your coil in? you aren't recycling a 20 year old 31k coil and leads are you (without at least testing them)? when i first built my engine i had to pull plugs a couple of times soon after first start up dripping wet with oil and black muck.

[Rich]

Ok...the silly questions...

You are running pre-mix I assume?

You didn't accidently get your oil/fuel mix wrong?

If you are running pre-mix, and you are sure the mix is good, then you have to assume oil is getting in to the crankcase...

[Commander Keen]

That is a fucking awesome bike.

[twinrock]

ok well i drained the oil from the bottom end just incase..no difference.... i also drained the fuel and put fresh 32-1 mix in, no difference,then i pulled the rzf2 250 pipes off, fuel literally ran out of them...i put on a set of pipes i had from an rd250lc that were hanging about....this made a big difference..i could now blip the throttle and rev it more cleanly how ever still pretty smokey..but im guessing that that was the exess fuel in the crank case from before... now i could actually ride the thing down the street... much better....how ever it was getting dark and there is no plat on it so i pullin back home ill mess with it more tomorrow..and keep u up dated apart from this it is finnished