Fuel problem?

Hi.

My bike seem's to be fine on the flat or downhill but up hill!!!! She dies and speed drops to walking pace and of course I wind the throttle up to try and compensate. Then she suddenly without warning picks up and goes off like a rocket, dangerous. If I stop for a minute she goes off normally for a few hundred metres.

I think it's a fuel problem but I wonder if it could be either the pet cock which I have just repaired (have I put it back together the right way) or could it be the fuel levels in the carbs.

Any ideas would be appreciated?

CowboyBob, it's nice to know I'm not the only old fart still riding .

Faighaigh.

 

That is an interesting problem! What is the grade for the hill? How steep is the hill?

Obviously this is gravity related... So thinking critically...

The only thing that SHOULD change when you go up a hill is liquid level. Maybe it is a level problem in the float bowls? Maybe one of your carburetor passages is not well cleaned out... Is there a passage in the front or the back of the carburetor that would be covered or uncovered by fuel when the angle of the bike changes? I don't have your type of carburetors, so I don't know this.

However, it could be a vacuum leak - such that a leak opens up when you go uphill. Maybe your carburetors are not firmly in the boots, so that a leak opens when going uphill...

The simplest answer would be that you are maybe letting off the throttle when starting uphill? That may sound stupid, but think about it next time to make sure your wrist angle isn't changing when you start up the hill. I know that my throttle angle changes when I hit bumps. (We don't have hills in Texas) :lol:

 

I don't have a clue what the gradient is but the village is built on the side of a mountain so it's pretty steep and I think you could be right re the gravity theory. If I check the float levels and have to adjust them will I have to re-synch the carbs?

Last week I fitted a new valve in the petcock and now petrol flows through no matter what position the tap is in. There is a machined groove on the valve and I wonder if I have fitted the thing the wrong way round and that is the cause of the problem.

Faighaigh.

 

I have to agree that it would most likely be the fuel height via the float levels. No you won't have to resync. On the petcock , check the round rubber part with holes in it. You probably installed that wrong. If that is right I would make sure the diaphraghm is not ruptured and you could stretch the spring behing the diaphraghm to make sure it is sealing the stop valve.

 

Of course the easy way to test a petcock is just take the fuel line off and the tank and hold the tank at the angle it would be at if you were going uphill. Then see if gas flows!

But, now that I think about it, you would have to apply a vacuum to the petcock. If you have a vacuum pump - that would be easy. I think I got mine for around $20. I don't know what that would be in euros!

This is another good reason to have a clear fuel line. I have clear on mine, and I have used it several times to ensure that I was getting a good flow.

About the float levels - you should be able to hook up a plastic tube to the carburetor drain and check your levels without dissassembling the bike at all! Just hook up the tube to the drain and then open the drain screw. Make sure the bike is running when you do it, and it might be a good idea to do it on the incline - but I don't know how you would do that. On flat ground would be a good start.