I bought a used 1995 Fantic Section 250 and the seller had little previous history of the bike. It starts easily, idles fine but when throttle is applied, it bogs down with no power. I thoroughly cleaned the carb and exhaust. I tried different float and needle levels. I am able to get it to run perfect for a short while. I turn off the gas valve and after about 40 seconds it runs perfect for a minute or two, then runs out of gas. It's a Dellorto PHBH26 CD carb with a 118 main jet. Any ideas what the problem is?

Sounds like it could be a leaky float needle to me: the needle can not stop the flow of fuel into the carb making the fuel level in the carb is too high this will cause it to bog down but with the fuel tap off the level reduces to the correct level and it runs properly for a while before it runs out of fuel.

I'd second that !?

A leaky float needle makes sense but then gas would come out the overflow which doesn't happen. I figured out what the problem was. There is another jet under the idle jet that I didn't see before. Real small with tiny holes that hadn't been cleaned before. After I got that cleaned out, I lowered the needle setting and now it runs correctly.

Glad you got it sorted but a DellOrto doesn't have an overflow.

The dellorto on my 83 240 has 2 vents (overflows) on it ! One on each side of the bowl ...

Glenn

As you say they are vents, any excess fuel would flow into the crankcases, take a look at the height of the vent fittings on the carb body.

At one point the floats were stuck and gas overflowed out the tube (vent tube?) and onto the outside case.

BEEN there too , and after pulling the plug and a whole bunch of kicks to clean the crankcase out Then she'd start again !!! But my vents spewed gas after a long trailer ride and a smart wack seated the float needle again to ride that day at least !.!.!

Edited September 8, 200619 yr by axulsuv