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[Clement]

Thank you all for the replies. I am now working my way through the suggested actions. Tank breather: I started the engine, removed the filler cap etc but it still conked out. Sticking valves: I’ve always checked the valve clearances and never had any issues, but (as suggested, you have to do something while in corona induced isolation – better in the shed than peeling potatoes at home) took the cylinder head off – there was some soot but valves seem to be okay. Rockers etc okay. Next step is checking the auto advance unit and the battery. The battery is one of those yellow Motobatt batteries (absorbed glass matt technology, no need for filling), but it is now 6 years old. I could still start the engine so thought that it might be okay? Have no volt meter here. Will get to the bottom of this but it might be a while. Will keep you posted. Clement.

[Andy C]

If you have a spare brake light bulb that you can rig up to connect to the battery, the battery should be able to keep the bulb at full brightness for at least 1/2 an hour, if it dosent then the battery might be past its best.

[Wheaters]

Having read this again, this does actually sound like the problem I had with my 350 when I first bought it.

It would lose compression after about 50 miles. The exhaust valve clearance kept closing up. Resetting the clearance would allow the bike to run again, until the same thing happened again.

When I stripped the top end, I found a damaged valve and seat. The valve had recessed into the seat and it looked like the seat was too soft. I had a new valve seat put in and I rebuilt it with a stainless valve from our host, which cured the problem.

[Clement]

Piston and valves look okay I think (after cleaning) - Clement:

[Bullet Whisperer]

To add to the first answer from Wheaters, who I would think is on the right track, check the fuel flow regardless of whether the filler cap is open or closed as well, because it might be down to the fuel tap itself - I have encountered numerous alloy, lever type taps on the Bullets which have a pathetic flow rate [even brand new ones] due to the tiny holes in a rubber disc inside them. These can be enlarged with care to improve them.

[Dave the Bass]

I had an ignition coil fail that caused what you you're describing Clement. The bike (a Redditch 350 Bullet) would just about start and idle roughly but as soon I picked up the rev's away from idle it'd conk.

The insulation was breaking down, as soon I put the coil under any additional load other than idle it would arc internally instead of at the spark plug! It was a pickle of a fault to find TBH.

[Clement]

I will follow up on the suggestion made by Wheaters, bypassing fuel tap etc. I don’t know if my tap is original Royal Enfield (Bullet Whisperer), it looks okay enough, but who knows. I enclose hereby a pic pf the tap. Clement

[Daiwiskers]

That's a odd clean bit by the inlet valve

Could be a worth investigating further into the head

Going stir crazy here Dai

[Daiwiskers]

To add to the first answer from Wheaters, who I would think is on the right track, check the fuel flow regardless of whether the filler cap is open or closed as well, because it might be down to the fuel tap itself - I have encountered numerous alloy, lever type taps on the Bullets which have a pathetic flow rate [even brand new ones] due to the tiny holes in a rubber disc inside them. These can be enlarged with care to improve them.

This was one of the many problems with mine Paul (Bullet Whisperer) found it

Another thought I have had is fuel lines breaking down with the stuff that is called petrol these days

[Pantherman]

First, check that you have exactly the right spark plug for the bike and that your ignition timing is correct. I had the same problem with my 500cc Bullet ; the plug was more-or-less okay and I spent hours messing around with the ignition timing etetc. Then I bought the correct spark plug. Different plugs have different heat ranges and a plug that runs a bit too hot will cause pre-ignition once the engine attains its running temperature.