yesterday as I was riding home form work, I was going uphill in 2nd gear, mid-range, and had a loss of power and pretty much coasted to a stop

the bike was motor was making strange noises; instead of the normal rat-a-tat-a-rat-a-tat-a it was making more of wumph-wumph-wumph sound

I pulled over immediately and backed off the throttle and let the bike idle and it seemed fine so I continued on my journey home

same thing happened again today on the highway at 55 mph! so I pulled over to let it idle and again it righted itself and off I went

the bike also seems to pull well at lower rpm in each gear when colder, and then pulled better in mid-range when warm but loses any gains at top speed in each gear; i.e. 55 mph and open throttle and engine speeds up but not bike

was thinking it was clutch slip when warm and may just need an adjustment? or is it carb intermediate needle adjustment?

but the noise and loss of power is not clutch related

I put new pistons (.030 over), rings, cylinders on the bike. Took a few days to get the Tillotson re-adjusted to what it is now; manual says start at 7/8 turn out from lightly seated and when I turned the idle and intermediate screw in, they turned at least 2 full turns in!

it did not idle well so I turned out the idle screw 1/8 turn and the intermediate screw 1/4 to get it to smooth out again and it had much better performance in the low to mid range in each gear when cold but the low end seemed a miss when warm (slow acceleration not unlike clutch slip), so will adjust again as per FSM (i.e. when warm) when I have some time tomorrow

but what really confounds me is the loss of power and the weird sound.
it was happening before I replaced the jugs, pistons and rings also which i thought was a sign of worn out jugs, but not now as i have replaced the pistons, jugs, etc.

so what now?

pretty sure it is not air intake leak as the manifold seated very well with new O-ring rubbers in place and then electrical taped to hold in place and clamps set very tightly; have checked its stability and it is solid

only leak I can find is the exhaust pipe and heat shields seem a tad loose even though they are fully clamped shut; 2-in-1 header with re-pop muffler from nosparts (when they were still allowed to sell to North America last year)

help? I would lover to go for a longer than 15km ride without having to pull off and let idle or turn off to cool down

 

sounds like a fuel restriction, start by checking flow out of the pet ****, then if ok move on the the float,

 

Seems like a peculiar problem. I am not familiar with the Tillotson carb so i cannot help with that. But i agree that making sure it is best set up is important. Given that it runs so well in some circumstances it cannot be a serious engine problem.

If you have an external fuel filter in addition to the one in the tank i would eliminate one of them; if you are using an automobile fuel filter i would eliminate it for sure - they expect a fuel pump and will not flow fuel in a gravity system.

Remove fuel line from tank and watch the flow into a container.

When the fuel level in my Keihin was too low the bike would sputter at hiway speed in 4th gear, then pick up when i reduced speed.

Your problem might be a thoroughly clogged fuel system at some point, probably in the fuel filter. A classic sign of this is running well for a while then running poorly, then picking up again after a pause, during which the bowl fills again.

only leak I can find is the exhaust pipe and heat shields seem a tad loose even though they are fully clamped shut; 2-in-1 header with re-pop muffler from nosparts (when they were still allowed to sell to North America last year)

To seal the exhausts at the heads ...

1. ensure that there are 4 cuts in the header not just two; make more with a hack saw if needed; no deeper than the ones already there.
2. use a pop can shim between the clamp and the pipe, especially if the clamp is already fully closed; this makes the clamp much more effective
3. apply some Permatex Ultra Copper RTV to the inside of the pipe before installing the pipe onto the head. There is Ultra Black, Red, and a few other colors. The copper has the highest heat resistance; lots of us use it for this application.

These are the ones to try for OEM NOS parts that i know of ...

http://www.tomsnosparts.com/ <- Tom ran the USA NOSParts for the European owner
www.OldDude.com
www.SportySpecialties.com

rdns@genesco.net <- decals & transfers

www.NOSParts.nl <- does not ship to North America
www.JWBoon.com <- does not ship to North America

 

thanks Mick,

the fuel flows fine as I had the tank off recently and the gas poured out the 1/4" line no problem. I only use the in-tank filter, no inline filter. I recently had the tank off to reattach the filter as it had come off in the tank and I had the same problem before when there was no filter.

I cleaned the passages of the carb when I took it off to replace jugs and pistons; or so I thought, but will have to check the diaphragm float needle I guess

will take it for a ride so, to warm it up and adjust carb as per FSM and see if that helps

could be timing? bad condenser? although I replaced the points and condenser a couple of years ago I suppose they could be bad already

or perhaps a bad spark plug when heated up? by why would it correct it self once idling for a minute or 2 ?

 

Does not sound at all like an ignition timing problem to me. I have very little experience with points ignition other than following this video one time ...

http://www.youtube.com/watch?v=mKVh4pbyh2A

I have heard a few times that the new points parts are very unreliable. But if they have worked well for a couple of years? Perhaps replace the condensor regardless?

I use only NGK spark plugs and have never had a problem with them.

 

You said that the fuel line flows....for how long? Have you checked your filter? I have heard of cases where you get some bad gas (say right after the tanker visits the station and stirs up the crud in the bottom of the fuel tanks) you pump it into your tank and it partially plugs your filter. As you are riding along, it sucks more to the filter essentially plugging it off and the motor sputters. You stop/decrease the demand for flow and the extra falls off the filter allowing more flow until you ride a little longer and it happens again.

Dave