Running fault. Carburation?

[Kryten]

Was out on the SZ last week and noticed an interesting bit of behavior from the bike when running.

Background to bike is carbs fully rebuilt to stock sonic cleaned new seals gaskets O rings float valves, mains and pilot jets, etc.

K&N filter in standard airbox (new clips, and rubbers)

Mershall Deeptone 4-1

Ignition is stock CDI driving Andrews Coils with Taylor Leads

Carbs were balanced. Valve clearances set to factory.

Engine(R701) has had no work done to it to take it away from standard.

Starts from cold with choke, hot no choke required even when in a biblical downpour!

However (prior to downpour) at about 3000 rpm/steady 60mph it felt as though the engine was loosing power or that the engine was being throttled back, obviously the butterflys were staying open as I was not moving the twistgrip. This was not hugely obvious but enough to be noticable.
There was no obvious misfire or cutting onto 3 cylinders and by either opening the throttle or closing it had the expected result. Performance was generally good although when reopening throttle from closed (eg slowing to match speed with another road vehicle) sometimes produced a little hesitant response.

During afore mentioned downpour bike behaved realy well with no cutting out or misfires. But I did notice what could have been HT earthing through the clutch lever and my water logged glove. But then again that might have been my dodgy nerves in my left hand/arm playing up.

I am thinking that it could be diphragms or the springs but all were very carefully checked.

It's done about 600 kms since going back on the road and been run mostly on Esso premium unleaded.

Was going to see if there was a dyno in my area (North Norfolk) to check the fueling throughout the rev range, but not got that far yet.

Any ideas?

[johnr]

ok, heres something to check. many moons back id a similar problem on my sz, i had dyna coils fitted which were slightly fatter than the stock coils. when the bike had a full tank, the weight made it sit on its rubber mounts, and the coils would occasionally earth out onto the bottom of the tank giving an occasional missfire in the wet, drove me potty till i spotted it. worth checking that your tank isnt touching your coils when its sat on the frame. ditto clutch cable pressed against either coil or ht lead.

[Kryten]

Hey John.

I think you may well have something there. I fitted a pair of big fat Andrews Coils that give fantastic sparks, but looks like the HT leads exiting forward from the coils have been rubbing on the bottom of the tank. Going look at swapping them over today and see if it improves.

[johnr]

i spotted mine by running it in the dark whilst looking under the tank.