My 83 XC500 get a Lectron carb (pix)

Clean the screen above the fuel shut off in the gas tank. Bubbles and lean means the gas isn't flowing fast enough.

there is a thread on this on Ozvmx...CR 500 Honda pinging...lengthened the idle jet with a bit of thin fuel line and it helped immensely

If your seeing massive vibration could it be the swing arm tubes in the case are the newer ones with the larger diameter holes?

no idle jet in this application

was just sayin its a common problem with the bigger bikes that gets overlooked.

radical head mods were touted for the CR's and YZ's of that era to stop them pinging and it was a simple fix all along. frothing fuel in the bowl.

Update:
I removed the inline glass re-usable fuel filter, and fitted a new 6mm pipe with nice gentle routing - just to be sure.
Quick test ride around the block - all seems good.
Then popped her onto the bike stand, hooked 6th and tried to simulate some load - all is still well.

I am very hopeful that we might have solved the fuel starvation issue.

Next step is onto the track...

Thanks again to everyone that is following or commenting on this thread.

Track results:
Close, but no cigar

I can get to 3rd, the carb will drain and the engine will die.
Coast a while, and the engine will come back, but no sustained high-speed for sure..

@Motoz:
Larger float bowl ?
Deep bowl drain plug ?

All suggestions welcome.

Check the flow rate of your fuel tap.

There could be a restriction in the tap itself.

What about the fuel cap and over flow hose are they venting?

I have in the past disassembled fuel taps and run a drill bit through the holes, you don't necessarily need to open the

holes up, just cleaning up any badly cast passages.

Cheers, Dave.

The intank filters can block up they are a very fine mesh.

check the headstem pipe is clear if your tank vent hose goes in there. a relo had a yz 400 and it would go about 5kms then die. took 15 mins to restart. shop pulled it down twice (charged him a fortune) for no better result.
I rode it and noticed it starving on the main jet after a hard blast. stopped, opened the tank cap and heard a large intake of air. Some &*$%#@ had ball bearinged the tank vent hose. Some ones chooks were "let out of the pen" at a later date.

Hello.

I had massive fuelstarving problems on my Cr500 and i solved it by mounting a PWK39 AND a mikuni fuel pump-
Never had any issues after that.
The PWK runs a 1.5mm needlevalve so it won't flood and the pump is a mikuni DF62.
http://www.mikuni.com/c-fuel_pumps.html

HI All

Carb vents are clear.
Tank gas cap and its' vent is clear
Foam filter in bowl is clear

Fuel line is 6mm
No inline fuel filter fitted....

@Moto,
I will extract and assemble all the detail and send as requested.

I think You have something loose and floating around in the fuel tank and or the petcock. For some reason its passing the sitting still tests not the riding tests. I'd try another Tank and Petcock. It doesn't need to look pretty a plastic bottle and no petcock might answer what's going on.

my cr500 used to do this also , 6mm ID fuel hose and a big filter solved it . the little cone filters wont flow enough . you need one with the convoluted material in it that has more than 3 square mm of cone thing for a filter .

is it worth using some cheap crappy clear hose instead of fuel hose so you can see if the tap or the filter is your restriction

this is ok

this is not

1/4" gas hose, is the vent in the gas cap clear?

Post #95 above Bill !

It almost sounds like a vibration issue. Are the carb stubs too long, and touching something they should not ? Mainly on the engine side. That would airiate the fuel in the bowl, and as it got lower would be sucking air from the bubbles. Just a thought.