Royal Enfield Constellation engine running with left exhaust pipe removed during investigations.

Almost at my wit's end now and getting desparate, I removed the left side exhaust pipe in case there was a problem where it joins the right side pipe, but it just showed the problem must be something else, somewhere else.

[@andrewslattery403]

Curiouser and curiouser...

[@michaelmouse5210]

Slightly bent or sticking valve would be my best guess. You will get there Paul. I'm sure of that.

[@derekgee8504]

We are watching with bated breath Paul

[@norsehall309]

G'day Paul, racking my brain for what can fix it, I'm going for a ride with club members and I'll ask the question ❓ will leave another comment if someone has a solution, cheers mate, Neil 🤠.

[@michaelmouse5210]

Also, I'm not sure if the twins suffer , but I have seen and heard of similar problems with a loose valve seat. Just a thought. This was on Bullets though.

[@thra5herxb12s]

Is it possible somehow that the fuel is sucked into one cylinder more than the other by some kind of uneven turbulence, or could that not happen. I did hear tell of some BSA's needing a deflector inside the manifold or was that just a myth..

[@obi1kahnobee549]

I was working on a 900 Kawasaki many years ago and could not get it to run right it wasn't until I removed the head and block I found all the rings on all cylinders were broken and yet the compression was ok. so I suggest you do the same.

[@danproctor15]

Could you run a spark gap between the lead and plug and watch it at low speed? or a current clamp on a scope if you have one. Its certainly a puzzling one. Good luck!

[@hermangibbs8163]

Thanks Paul.

[@peterwilson8797]

Can you measure the valve lift on all 4 with a dial guage and a degree disc. Clutching at straws. Dont sound like a shot cam when running.

[@neilmcintosh1200]

No, not the pipe. The hidden gremlin is sniggering at you.

[@anthonyhull2998]

I wonder if one of the valves is very slightly bent ?

[@pw601]

Can you do a leakdown test?

[@pw601]

head gasket failing?

[@baronlowie]

I know you have checked it Paul but this is surely a compression issue. Just don't ask me how!

[@chrislaunders8283]

Could you have a cam lobe worn flat??

[@nickmarshall9192]

I had almost exactly the same symptoms with an xs650
But this had twin carbs
It'd idle on one anthe other side cut in when revved
It turned out to be the inlet rubber perished
I realise you are running a single carburettor but is it possible its pulling a lot more air in one side ?

[@paulhenshaw4514]

You may be onto something - watch out for future installments!

[@dungspreader]

I think your dad is fckn right .😅
I reckon that seperate heads and a single manifold is a poor idea from RE .
Is there a chance that the surfaces aren't flat or there's a void in the LHS branch ?

[@briantaylor5815]

I think I'd replace the LH lead and spark plug next

[@JohnBennett-cw1ri]

Refresh my memory please, has it had a compression or cylinder leak down test?

[@paulhenshaw4514]

The compression is very good and equal on both sides.

[@stevetee4145]

Check valve clearances, rings and valve timing.

[@andrewlengert2558]

Strange how all brit bikes sound awful without the downpipe(s), but sound lovely with downpipe and no silencer

[@mickhardstaff6605]

I personally think it is electrical Paul, HT lead or plug cap even the spark plug could be faulty .

[@billykershaw2781]

Oh.....damn...

[@SapoPeta-c6x]

Tell the owner to get a Commando