Well, as it rained all day, i decided to have a go at the Comet...
I took the bike out last Tuesday evening for a local spin. It was almost un-rideable. Hesitation/spitting/stalling/really playing up, couldn't hold it at a steady speed, awful, something had to be done...
Methodical is always best i think, so i started the engine with the bike on the ramp, sure enough it started spitting and farting, hesitating, backfiring through the exhaustion the overrun etc..
So, off with the timing gear cover, let's check the valve timing first. The valve timing was absolutely spot on, as was the breather timing. I did a check on the ignition timing and at full retard (static) the points were just opening at c. 4-6° BTDC. It all looked absolutely fine to me?
So, what did i do last time, well i replaced the cam spigot and the exhaust valve lifter spigot. Checked them for correct end float etc, all good.
I then turned my attention to the ATD. I bought one off Tony Cooper, it looked identical to the old one, i do remember i had a bit of an issue with the bolt thread on the new one, it went on but it was tight, i had to remove the magneto and do it on the bench, but it went on and tightened up OK in the end. I removed the new one again making sure it wasn't loose on the taper, and it wasn't. Took it off and did some measuring/tooth counting on the bench, identical..
Was scratching my head at this point to be honest, so i decided o re-fit the old ATD. Set the timing as before and put the cover back on.
It started more or less second kick, and sounded good. Revved cleanly, idle was a bit low so I set up the carb, and it appears to be running OK now! I am back to the old problem of the idle hanging up but from idle it now revs cleanly, appears to have lost its stuttering and subject to getting it on the road for the acid test i would say its OK now?
My 'problem' is this though, how on earth can an ATD make the bike run rough like this? I mean it was unrideable, literally, and all I've done is re fit the old ATD and it seems OK? I know they are a very simple device, and the new one was opening/closing etc OK?
Any thoughts??