Dropping onto 1 cyl.

[AMCQ46]

There have been a few of us lately who have had the bike decide it want to become a lardy 500 single, and it happened to me on Saturday. Although we worked out it was the rear pot that was not running, we didn't find out what the problem was and after 10 miles of 1 pot racing it stated to splutter back into normal operaation and ran better than ever!

The usual root cause of water in the front head isn't an option as it was baking hot and dry. The coil failing could be an issue but they are stick coils and when it sorted it's self out the bike as back to full power! S what could it be??

Both the way it died and the way it came back to life felt like a fuel problem...like running out of petrol, it effected the low throttle (pilot jet) first and then the mid throttle was lost and finally the wide open throttle and main jets cut out.

So today I took the carbs apart and stripped the petrol tap and guess what I found? ... Absolutely nothing All clean and working as normal.

So what else couldn't be....?

The only other clue was that it happend 5 miles after brimming the tank and letting the bike sit in the sun for 30 mins while ady consumed the regions brown sauce allocation could it have been the tank Getting a vacumn lock? I never thoughts try and open the filler cap, but why would it effect only one cylinder?

Any ideas team?

[lloydie]

My first though was carb icing but its to warm for that .

[AMCQ46]

Yes a bit too hot for carb icing and why would it effect only 1 cyl?

I didn't say in my 1st post, but we diagnosed the rear cyl 2 ways. 1) you could touch the exhaust and 2) when I unplugged the rear coil there was no difference in the way it ran.

So I am looking for something that only effected the back pot / carb. Figured the float needle was blocking and the float was not filling up... But no sign of any contamination.

[VTRDark]

Change the spark plug first, before chasing down other possible causes.

(:-})

[lloydie]

Al if you'd like to borrow a set of carbs to rule them out let me know

[Ckennedy]

I am assuming you have looked for chaffed wires and bad connections in the plugs for the stick coil on the rear cylinder? Afraid I can not be much more help than that. Don't see carbs on the trucks I work on

[AMCQ46]

Change the spark plug first, before chasing down other possible causes.

(:-})

Plugs were new last month, and it's running better than ever after it came back to life. Bottom end is running cleaner if you crack the throttle in a higher gear from low revs.

I cant figure it out!

[AMCQ46]

I am assuming you have looked for chaffed wires and bad connections in the plugs for the stick coil on the rear cylinder? Afraid I can not be much more help than that. Don't see carbs on the trucks I work on

Yup, that was my 1st thought on the roadside, and I thought I had found the problem when the revs lifted as I manipulated the wiring harness for the coil.....turns out that ziggy thought it was going to stall so had blipped the throttle

[Ckennedy]

If I have any more thoughts I shall post them up. Chances are I won't but hey. I'll keep thinking.

[VTRDark]

Plugs can die at anytime a bit like a tensioner. The same thing happened when we rebuilt marty's bike. I checked to see if it was sparking and the rear was, but was not as clean a spark as the front. I blamed it on the bright sunshine not showing the spark as well. I checked coils, fuelling etc etc. It was bugging the life out of me, we even changed the fuel in case it was a bad batch. In the end it turned out to be the plug that's why I said change the plug. I felt like a right tw@. If you have one it's worth ruling it out or just swap them around and see if the problem reverses.

(:-})

[AMCQ46]

I have put a spare old plug in the toolkit and if it does it again I will be able to check

[VTRDark]

have put a spare old plug in the toolkit and if it does it again I will be able to check

Is this an intermittent problem then. One more thing you my want to check is to see if the ECU is all good and hasn't got moisture around the wires.

(:-})

[agentpineapple]

i'm with carl, just to rule it out. but the bit where the bike runs fine again sort of suggests its not the plug. is there anyone local who has the stick coil conversion, maybe you could do a swap, just to rule out a bad coil. you could also drain the tank and make sure theres no crap in the bottom, also a new fuel filter might be a good idea.
don't it run like crap on one cylinder.....
i hope you find it buddy....

[Hairy biker]

When you find the cure could you let me know please, I've the same problem!

[AMCQ46]

have put a spare old plug in the toolkit and if it does it again I will be able to check

Is this an intermittent problem then. One more thing you my want to check is to see if the ECU is all good and hasn't got moisture around the wires.

(:-})

Yes intermittent, did it once for 10 miles and then was fine for the next 300, and still good today. It got progressively worse like running out of petrol, but I struggle to understand why only one cyl effected.