RM250 new problem

[cz400]

got the reed block in

[OverTheHill]

Has got a crank seal in the RH side? [don't like to ask but clutching at straws]. Only ask that because i think you said it ran ok despite being worn out [etc] & now smokes badly [primary case oil] so that rules out carb unless something outside the square has gone on in the carb. You haven't got a new slide & it's got the guide slot on the wrong side causing a super rich run [cutaway wrong way around]--or--someone's drilled the needle jet [emulsion tube jet--main jet screws into], seen them drilled for alky [methanol] then put back on petrol. No thick washer [any washer] under main jet, although if it has a hat thingy the main jet screws through then it would takes the place of that washer. Sorry, doodling & not thinking hard. Something gone amiss with the choke, like rubber pad gone out of end of it. Something [crumbled old airfilter] got into the air bleed to the emulsion tube. Good Luck.

[Hardo]

Few things I would try:
Try a hotter plug. If it has a 9 in it - try an 8.
Try running it with the fuel cap off? Fiddling with the tap keeps it going you say? Maybe the tank cap is creating a hydraulic lock and not breathing correctly? That doesnt really make full hydraulic sense - but its free to try.
Did you check the reeds? A cracked / chipped reed could cause similar issues?
Try raising the jet needle one clip to lower the needle and lean it off a touch.
Check crankcase breather tube isn't blocked.
Check earth is super clean at coil. Bikes can give erratic spark when revved and foul a plug in a nano-second.

Hope those help.... if not get a green one....   

[pokey]

For an engine to flood is has to have either no spark to burn it but yours fires so its not sparks. This leaves the carb being the problem, only one way for fuel to get in and thats the needle and seat, this also turns the fuel off when its full.  if it doesnt.. it floods.

AS  mr crocket has said Mikuni do a few different types. make sure the needle you have matches the seat you have.

 if its right main seal the gearbox oil usually goes milky.
could pay to pull the tap and check it for crud while you have the spanners out. you may have more than one problem confusing the issue but I would start at the needle and seat

[tony27]

While you're dealing with the needle & seat drop the float in a container of hot water, if it has a leak it will start fizzing as the air inside it heats up. Have had similar problems with my yz465 & a cracked float on 1 side was the problem

[OverTheHill]

my thoughts for the day--if it was float valve [needle & seat] related then fuel would be pssing out somewhere [overflow/breather etc]. Not being suzuki orientated i didn't realise it was water cooled but regardless if rh crank seal was stuffed it'd let tranz oil in [smoke] but run lean from too much air--umm--unless gearbox breather was blocked i suppose. don't suppose the piston has windows like yamaha as have seen one back to front causing headaches [lean & gaspy--very gaspy]. We're all waiting with baited breath for the final outcome. thanks.

[DR500]

Sounds like the needle and seat are not closing off, there are a few different types off needle/seats for Mikuni's, I alway's put a brand new carby on every resto......30 plus year old carb's are fraught with problems, cheapest part you will buy to make your bike run properly.....under $200 with the correct/extra jets/needles bla bla. Ring T D Hatrick in Townsville tomorrow.

As my fellow mechanic said, don't stuff around with 30 yr old carbys, we've been there done that! $200 and another 30 years of use.

[vlxk]

Well I pulled the carb again and checked out the needle valve. I remember when I first went through the carb at rebuild the needle looked good to me. There wasn't even a hint of wear on the tip of the needle. I polished it slightly just because and reinstalled it.

The reeds are perfect. Crank seals are new with the rebuild. Since it cleans up and runs good as the fuel level drops I don't think it is an electrical issue. It does have the hat thingie under the main jet. I will try the hot water test for the floats next weekend, maybe one is heavy? They both seem to float pretty well in the fuel in the bowl.

So today I had a thought, what about pulling the bowl and hooking up the fuel line and do a test to see if I could stop the fuel flow. I can stop the flow using my finger to raise the float lever dealie. I realize even the lightest pressure from my finger is probably more than the floats raising the lever. But now I am not sure about the needle. I guess $20 for a new one would just eliminate the needle as the problem.

Does anyone know what the number on the seat means? Mine has 3.0. I have searched the interweb and there many different options available. Some have 1.5, 2.0, 3.5. I suppose the number is a reference to flow rate but I'm not sure.

I'm off to work tomorrow so I won't have any updated news until next weekend.

Have a great week and I'll check back in a few days.

[Momus]

That number is the inlet orifice size, the port diameter, that the needle seats against.

The bigger the number the more flow- and the more pressure head trying to push the needle off the seat.