Strange engine behaviour

[cdsdorset]

Working on an A65 with a 64 engine with singe carb head.
Starts fine, pulls well no misfires. When shutting off to change gear, come to a junction etc it appears to drop onto one cylinder?
Feels just like one carb on a twin carb engine playing up but its just a single?
Any ideas.

[limeyrob]

Try swapping the plugs, I've had no end of problems with "new" plugs.

[DMadigan]

Using resistor wires or solid copper? Copper is preferred. Carbon core breaks up with the vibration

[V500]

Have you checked the charging and battery condition? Do you have a Boyer etc fitted?

[cdsdorset]

Used various plugs. New copper ht leads and new plug caps. New battery . I have a blurtooth battery monitor to try on it when i get a chance to ride it.

[DAVE BRADY]

Hi,

If you can determine which cylinder it is try swapping the leads to eliminate the coil.
Otherwise, does it cutout completely or keep running.
It could be a fuel issue.
Make sure that the filler cap breather hole is completely clear.  Blow through it and then compress it, to simulate being on the tank, and blow through it again.  It should be completely clear.  When the bike is going along it will create enough vacuum in the tank to suck enough air through.  When the throttle is closed and or the engine revs drop this suction is not enough and a partial vacuum in the tank causes a weak mixture which can  manifest itself as a misfire or cylinder bias.

Dave.

[limeyrob]

I would try the swapping over route and see if it does change sides with various ignition components.  A condenser would be a possible candidate since they do fail. But also the plugs, I've given up on NGK because I think fakes are now in the supply chain and I've had failures after a few weeks.

[cdsdorset]

I would try the swapping over route and see if it does change sides with various ignition components.  A condenser would be a possible candidate since they do fail. But also the plugs, I've given up on NGK because I think fakes are now in the supply chain and I've had failures after a few weeks.

It has electronic ignition fitted. I know how to spot fake plugs.

[cdsdorset]

Hi,

If you can determine which cylinder it is try swapping the leads to eliminate the coil.
Otherwise, does it cutout completely or keep running.
It could be a fuel issue.
Make sure that the filler cap breather hole is completely clear.  Blow through it and then compress it, to simulate being on the tank, and blow through it again.  It should be completely clear.  When the bike is going along it will create enough vacuum in the tank to suck enough air through.  When the throttle is closed and or the engine revs drop this suction is not enough and a partial vacuum in the tank causes a weak mixture which can  manifest itself as a misfire or cylinder bias.

Dave.

Its odd. I can tell its dropping off on a cylinder but i cant work out which one it is while riding it. It doesnt feel.like a cylinder is going completely down.

[V500]

It has electronic ignition fitted. .

I know you said it has a new battery but have you checked the charging? EI going down to one pot is a symptom of low battery voltage, as you would get when slowing down or ticking over at a junction.

[cdsdorset]

It has electronic ignition fitted. .

I know you said it has a new battery but have you checked the charging? EI going down to one pot is a symptom of low battery voltage, as you would get when slowing down or ticking over at a junction.

I was getting 14v when revving it in the workshop. Going to try a run with the analyzer that sends data to my phone.

[cdsdorset]

Worked out that its the rear brake light being powered off the same line as the coils causing the problem. Just a small wiring tweek required.