Runs on one cylinder (front) before engine dies altogether!

[LotusSevenMan]

Had this 'fault' for two years on and off.
Engine starts fine and runs fine. Then after say a trip of 200 miles and an overnight stop it will run great but then go onto one cylinder. Normally seems to be the rear that 'goes out'.
Then, you change, say the rear plug. All OK for a good few hundred miles. Ah, so dodgy plug. Won't use that one again. OK for a long time then it does it again.
Well to cut this long story short, I have changed the plugs (several times) the ecu, the ignitor pack (as it didn't appear as if there was a spark to the rear cylinder), the coil pack, checked the fuel flow from the tank to the carbs andhat is OK.
Just done it to me again on the M20 while in the outside lane. Scary trying to cross lanes with no damn power!!!!!
Get to the hard shoulder. Try to start it and it comes in on one cylinder. Limp back home with it running on one cylinder but sometimes on two (and sometimes none!!!).
Leave it sat outside. I then remove helmet, ponder and fire it up about two minutes later to get it back in its bike garage (well pi**ed off as you can imagine). What happens? It starts absolutely fine and runs perfectly. Grrrrrrrrrrrrrrrr.
So what's left? My only thoughts are perhaps a blockage of a carb jet by some dirt/rust particle that then when the bike is sat drops back down a bit. Had that on a car carb once. Bike has done less than 15,000 miles and when both cylinders are firing the bike pulls like a train so no valve issues etc. The problem seems to occur after a refuel too which is weird but hey; this problems IS weird.
H E L P !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[benny hedges]

check your fuel lines arent pinched at the back of the tank - mine was exactly the same, the main fuel line was twisted like a pigs tail when the tank was down.
i replaced them and not had a problem since.

[LotusSevenMan]

Thanks for the reply (which kinda confirms my thoughts re. fuel). That wouldn't explain though why it sometimes runs fine for hundreds of miles before it acts up again. The rust-particle-in-a-jet is now even more favoured if your fuel starvation symptoms were the same as this though!!!
Annoying as it's running fine now but................... just a matter of time before it happens again. Hate intermittant faults.

[pariah]

could be a plug breaking down under load or maybe one of the colls giving up? Just my thought. I would have thought fuel porblem would have been more frequent

[Twinpotter]

Seems as if you've covered plenty and I can understand how frustrating it must be. Now I've not that much to add but I did think it worth checking that there aren't particles in the tank, i.e. give it a good rinse. Got a puzzle there. Hope you find the problem.

[Stratman]

Have you tried new HT leads and plug caps (or cap, I suppose)

[benny hedges]

Thanks for the reply (which kinda confirms my thoughts re. fuel). That wouldn't explain though why it sometimes runs fine for hundreds of miles before it acts up again. The rust-particle-in-a-jet is now even more favoured if your fuel starvation symptoms were the same as this though!!!
Annoying as it's running fine now but................... just a matter of time before it happens again. Hate intermittant faults.

on a motorway run i got snarled up in slow 3-4 lane traffic for 50-60 miles and it ran fine.
it was only after riding it hard for 5-10 mins that the problem reared its ugly head.
got so bad i pulled over on the hard shoulder thinking id done a head gasket or holed a piston...
had a look around it, fired it up, all ok again,, then same again, it would ride ok for as long as i took my time, soon as i gave it beans it would pop & fart & run on just the rear pot.

it's not a vacuum leak is it... on the rear cyl that works the vacuum diaphragm in the fuel tap, or the pipe that conveys the vacuum from the rear intake stub...
as i said, mine was a kinked fuel pipe.

[LotusSevenMan]

I have changed the plugs (several times) the ecu, the ignitor pack (as it didn't appear as if there was a spark to the rear cylinder), the coil pack, checked the fuel flow from the tank to the carbs and that is OK.

Stratman. Forgot to say when coil pack was changed so was the HT lead!
The fuel tap is an interesting point. I DO have a slight problem with it in that once pulled on the diapragm doesn't let go again. So effectively, once on, the tap free flows whatever the vacuum. Have checked this flow rate too in the past & even though we know 'Storms are thirsty if it can use that amount of flow then I'm ruined wallet wise!!!

I'm gonna bet on the slight piece of dirt in the carb.