Wich Jets For Mikuni Carb.?

[dan williams]

Hmmm if mixture then it should be worse when air temp is cold. Could be ignition timing. Advance could be shifting when the stator heats up. Sounds like your engine is just on the edge of lean. Did you try raising the needle a notch. The problem with an engine that's this close to right is richer mixture/retarding the ignition timing/higher octane gas can all "cure" it even though they may not be the problem.

Could even be something even dumber like a partially shorting kill switch or plug wire.

There are days I really wish Betas had on-board diagnostic computers.

Edited February 16, 2010 by Dan Williams

[samo]

Simptoms are the same as when you forget to open fuel and before engine dies, you hear "ping, ping.." sound in cylinder.

Yes, I try to raise the needle for a notch, but than mixture was too rich. Engine didn't run smooth..

140 is smaller than 145 and it will be leaner yes Liviob, but I'll try anyway. Maybe is Pilot too small-27,5 I'll put 30 and will see..

[liviob]

You may also have a partialy blocked fuel delivery. When you feed the motor alot of fuel the delivery cannot keep up and the motor goes lean. Maybe you need a new fuel filter or see if there is a partial block in the tank at the tank valve. There is a brass belll that mounts under the main jet, and float bowl drain plug extender for the rev3 mikuni availiable through Beta. This will also help keep the motor from going lean at bigger throttle settings.

[dan williams]

Agreed, sounds like the poor thing is starving for fuel. Check for the blocked breather hose on the cap. I believe there is a check valve in the cap to keep fuel from leaking after a crash. That valve could be stuck too. Should respond to a shot of carb cleaner. Perhaps a test run up a hill with the cap cracked open a bit will tell.

[samo]

Agreed, sounds like the poor thing is starving for fuel. Check for the blocked breather hose on the cap. I believe there is a check valve in the cap to keep fuel from leaking after a crash. That valve could be stuck too. Should respond to a shot of carb cleaner. Perhaps a test run up a hill with the cap cracked open a bit will tell.

Which cap Dan? Could you be more specific?

[dan williams]

Sorry, Gas cap. If the vent /hose thingy in the gas cap gets blocked then riding the engine under load, like on an uphill, can cause the bike to use enough fuel to cause a vacuum in the tank. Tends to interrupt fuel flow into the carb so the bike will run lean under load but seem perfectly normal when just idling or puttering around.

[samo]

Sorry, Gas cap. If the vent /hose thingy in the gas cap gets blocked then riding the engine under load, like on an uphill, can cause the bike to use enough fuel to cause a vacuum in the tank. Tends to interrupt fuel flow into the carb so the bike will run lean under load but seem perfectly normal when just idling or puttering around.

Ok. I understand. I'll check this today.

Thanks

[ioan_vapi]

Hi,

I bought an used Beta Rev3 270 - 2005.

Does someone know the stock jets, needle and air screw setup for this bike?

Also, please tell me a popular online store where I can order Beta spares. I never found all I need in one place .

Thanks.

[viking]

30 pilot and 150 main if i remember. Mixture screw 1.5 - 2 turns out.

[nzralphy]

Simptoms are the same as when you forget to open fuel and before engine dies, you hear "ping, ping.." sound in cylinder.

Yes, I try to raise the needle for a notch, but than mixture was too rich. Engine didn't run smooth..

140 is smaller than 145 and it will be leaner yes Liviob, but I'll try anyway. Maybe is Pilot too small-27,5 I'll put 30 and will see..

Not sure if i have it right here but it could be a knocking noise. Most Beta's do that at a constant throttle. Go back to a 30 pilot and some fresh petrol. I took my Beta head off and polished the top of the piston and the head. It helped but didn't cure it. Just avoid a constant medium throttle up a hill.

[samo]

Not sure if i have it right here but it could be a knocking noise. Most Beta's do that at a constant throttle. Go back to a 30 pilot and some fresh petrol. I took my Beta head off and polished the top of the piston and the head. It helped but didn't cure it. Just avoid a constant medium throttle up a hill.

I solved the problem already a year ago. I put the 30 pilot and 140 main, but it was stil knocking to hear so I turn the ignition 2-3mm to the left and it was perfect No knocking animore.

[ioan_vapi]

30 pilot and 150 main if i remember. Mixture screw 1.5 - 2 turns out.

That is what I found too. Thanks.