Insufficient fuel from tank to carb ?

[subarumy98]

HI All

Here are the symptoms:

• Accelerate hard 1,2,3. Half-way through 3rd, the motor will die. You can throttle back, and she will pick up again and accelerate some more. Then I ran out of road.
  Go to 3rd

, and keep the throttle on half, accelerate gently, will pick up speed at a constant rate then suddenly accelerate harder as she goes lean, then die.


In both cases, as you throttle back, the sound is the boowang, banggg bangg boowang.

So here's what I'm thinking:
The fuel is not flowing fast enough. Somewhere between the tank breather and fuel tap.

• If the fuel level was too low, then by accelerating slowly, you would not induce the condition, as the fuel will replenish fast enough.
  If the main was too small, it would not accelerate to top revs in 1st and 2nd.
  If the main was too large, it would not rev cleanly in 1st and 2nd.

Please check my logic and post your thoughts..


btw:

1983 500XC
45 pilot
430 main
std needle and jet
new needle & seat
everything is clean
2000m altitude



 

[bigk]

Faulty fuel tap or blocked vent in cap. Had it happen a couple of times with one result being a stay in Hospital & a long recovery period. It was a brand new aftermarket fuel tap as well, so don't be fooled into thinking your new fuel tap is not at fault.
K

[cyclegod]

I had a similar issue with my RM500 too but I fitted a very large fuel filter which adds a lot of volume to the fuel line to the carb and eliminated the fuel starvation at full throttle intervals despite the tiny RM tap.

[Davey Crocket]

I do that to all my bikes cyclegod.

[Freakshow]

What happens if you give it more pilot jet ?

[subarumy98]

HI All

I have progressed quite some since the previous post.

- more pilot - no effect

To ensure good fuel delivery, I have done the following:
- Drilled out the fuel tank cap breather to 5mm
- Removed 2nd fuel filter from inside the body of the pet cock
- Drilled out the bottom half of petock to 8mm
- 45 pilot
- 340 main
- 2.0 slide
- 0.7 air-jet
- 40:1 Belray
- 2t airscrew
- altitude of 1500m
- NGK B8ES

I am a LOT cloaser now.
Will not run at extended full throttle in 4th, is starving for fuel.

Next steps:
Even bigger fuel hose if I can.

[Curly3]

Cut the valving part off the standard petcock leaving just the mounting flange, drill & tap for 1/8 bsp and fit an airline ball valve.
I've seen it on several Dirttrackers running methanol.

[subarumy98]

SWEET !

Excuse me while I go kick myself.
Been sitting here trying to work out how to dissasemble the petcock to get inside to drill out, when the answer is a whole lot simpler

Will go find something tomorrow.

Thanks very much

[subarumy98]

Finally sorted !
The last key to the puzzle.


http://www.facebook.com/#!/photo.php?fbid=10150407548079343&set=a.10150104189549343.305921.522719342&type=1&theater



Thanks to everyone all across the world that has helped me with ideas, suggestions and actions.

Now we are in business !

Trevor

[subarumy98]

First race after jetting completed.
This is a completely diferent bike. I need to learn it from scratch.

In practise, I would ease through the big sandy corner, then gassed it hard and instantly I was sideways and down.
The only evidence was a large hole in gthew sand that used to be a berm

Learn to ride 101...

[Kane Mcguire]

so did you change to a bigger tap? i run the same main jet 340 and it runs great up top.

[Mike52]

Finally sorted !
The last key to the puzzle.

http://www.facebook.com/#!/photo.php?fbid=10150407548079343&set=a.10150104189549343.305921.522719342&type=1&theater

Thanks to everyone all across the world that has helped me with ideas, suggestions and actions.
Now we are in business !
Trevor

Beauty Trevor but not all of us have a facebook account , so what did you find ?

[subarumy98]

HI All

Basically I had to re-look the fuel supply chain.
Everything from the gas cap vent was drilled out to the petcock mounting and finally the petcock is from a plumbing supply store.

What also led me astray, is that the 500 main jetting is far smaller (340 as opposed to 430) than the 430WR motor.

All is now peachy and very fast. A great treat to ride and certainly demands respect now.

thanks again to everyone for all the input.

Trevor