Chasing down a ghost problem, help?

[mennobike]

Going to try to make this short and sweet:

'97 E model
Runs great for 20ish miles (if I'm being nice, bit less if I'm hooning about)
Then starts surging backwards (dying sporatically, dunno the best term for this) and dies after doing this for 2-3 minutes.

THINGS I'VE DONE CHASING THE PROBLEM:

Flipped to prime as well as reserve. Nothing.

Opened the gas cap after it started happening. No help.

Removed air box, carbies and and boots in search of a vacuum leak. Boots looked a mite cracked on the outside, but were sound inside. Boot o-rings were trashed, so I replaced them.

Also replaced the o-ring that lives in the float assembly base in the carbs (I don't know what this is called. Think it deals with the idle?)

The idle got stronger after the o-ring replacements, but the dying problem persists. Any ideas? Doesn't seem like there are really that many more places that could be messing stuff up this badly.

Thanks!

Menno

[EdChen]

I feel that most of those problems would manifest itself regardless of run time (maybe except the fuel vent).

I would consider looking into something heat related, possibly the coils? Or valve clearances as things expand and contract?

[prmas]

It sounds fuel related to me. Check the two fuel taps for restriction. As it makes no difference on Prime or Reserve it has to be something that is common to all circuits. It may be a partially clogged strainer in the tank. 

Macka

[mennobike]

Thanks guys, I was wondering about the petcock or the valves myself...

Macka, what do you mean by "taps"?

[Janx101]

If not a fuel issue.... check the condition of the harness connectors and wires that live under the tank towards rear of valve cover... those connections cop a lot of heat and the wires on mine (after close inspection) were partly melted (tricky to spot though) and intermittent shorting/sparking. ... ended up affecting head light, ignition circuit and starter circuit....

All the issues were mostly not present on a cold motor but started to randomly manifest after bike was hot and wires expanded/wiggling because hot.

[prmas]

Thanks guys, I was wondering about the petcock or the valves myself...

Macka, what do you mean by "taps"?

Sorry Menno, I did already reply to to you but it has not appeared here yet.
It is a difference of expression between Continents.
What we call a Fuel Tap or Petrol Tap you call a Gas Petcock.     

Macka