2003 Bullet 500 4 speed kick start
Engine started to miss occasionally on a 40-minute ride, especially when accelerating. This became progressively worse. Initial thought was fuel supply, so cleaned carb, tank, checked fuel tap. No difference. Next thought was electrics so (progressively over 2 week period) replaced spark plug, installed new points and condenser, new H/T lead, plugged in new ignition coil - no difference. Probably the carb afterall, so replaced the current carb (VM28) with an Amal; no difference. Engine will start but cut out and start missing and farting when opening up. Ignition timing was double checked and tried also slightly advancing/ retarding. No luck here. All connectors seem to be okay and I have spark on the plug.
I now have to wait until this corona lock down finishes and I can take it to a real mechanic who knows how to work mukltimeters etc and takes a step by step approach but if you have any suggestions in the meantime....? Cheers. Clement
Sounds like you've checked most things but have you checked the overall fuel flow to the carb?

The tank breather in the filler cap might be blocked. To check this, fit a piece of tubing into a container / fuel can and compare the fuel flow with the cap on as normal to the flow with it loosened.
I would do a compression test

As Pete said it could be a valve issue

Yep wet and dry compression test dry first

With advice from the forum you will get it sorted

Take care all Dai
I did have an issue on my 350 with excessive lateral play on the distributor shaft which was interfering with the auto-advance (it was fouling on bits of the mechanism and sticking in or out). That was the type with iron bushings rather than bearings, just needed the bushing seating slightly further out. Wouldn't be an issue with the bearing type.

I suppose the one thing you haven't checked is mechanical issues. How's the tappets? Is compression good?

Remember standard 500 bullet pistons are notorious for crowns collapsing or even seperating.

I also had an issue with my 500 where it would occasionally misfire and did a lot of popping and banging on the overrun and it turned out to be a loose exhaust valve seat (literally finger tight). I also had a newly rebuilt (by someone else) head on a used bike I bought that ran like a piece or crap, wouldn't pull past 50mph, latchy to start. When I put the original one back on, it ran fine. I can only assume they hadn't reamed the valve guides properly so they were sticking. So a bent/sticky valve could also cause similar issues.

When was its last de-coke? If you're at a loose end for the next couple of weeks, might be worth having a poke about in the top-end anyway? Then it's done. Our hosts are still doing their mail-order service so all you (in theory) need is a head and a base gasket.
Too late to edit again

Before jumping in with compression test
Check valve clearances (spelling)

Another thought is the battery up to spec? Do you have a lithium battery? that gave me a odd misfire
It sounds like your battery is giving out, providing enough voltage to allow tick-over or low speed running but not enough to power the engine once it starts working harder.

I had this happen to me on my old T150 which petered out on a run. It re-started fine and ran perfectly ok on tick-over but died the minute I tried to rev it. After a 2-mile push home, I found that one cell of the battery had failed giving me 10.5 volts. The T150 Boyer electronic ignition is very voltage-sensitive and there simply wasn't enough volts to keep it running. Possibly the same on your bike?

A note of caution - after recharging the Triumph's dud battery, I got an initial voltage reading of over 12 volts, which seemed fine. However, it declined steadily to read 10.5 volts after a couple of hours.
I'm not sure if the Bullet uses the same cam drive arrangement as the interceptors... My 1966 Interceptor custom did the same thing . I replaced the fuel/plugs/carb/magneto replaced with points system. I checked the cam timing and all the marks lined up, but the pistons were 20+ degrees down the bores! The cam is driven by a shaft taper fit to the right side of the crankshaft 'secured' by an inadequate pin and slot arrangement. If the Bullet has a similar arrangement see if the shaft has slipped relative to the Crank!
Another thing to check is the advance retard unit I have had them break up before now
Also I had a circlip come off on the distributor shaft this caused the advance retard unit to move back and forth (in and out) causing the advance retard unit to rub on the Point's plate causing damage to the condenser

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