Hesitant revs below 3,000 RPM when hot.

[JezzaPeach]

I think it helps narrow down the options. eg if just 1 pipe warms up slower/not at all (I had 1 faulty plug, or it could be one carb blocked), then if it’s 1&2 or 3&4 points towards carburation as the fuel is fed to them in pairs (eg a blocked fuel tap gauze or pipe might slow the flow to one pair) or if it’s 1&4 or 2&3 more likely ignition.
I had a problem where I believe one worn HT lead was not connected well to the cap on 3, and it seemed to affect both 2&3 warning up, but produced other issues like less power once warmed up.

I’m going a bit off track but I think can be useful to eliminate possibilities or other things adding to the problem making it harder to detect.

[JezzaPeach]

PS I don’t want to ‘mis-promote’ a product, but I am testing Sta-Bil ‘storage’ which seems to help cleaner running, given less smooth, older delicate carb innards ‘may’ be likely to attract more blockages. Something may be clean, but still less ‘non stick’ compared to brand new. Only my theory!

[JezzaPeach]

When my 2&3 were playing up a bit 1&4 used to put out slight vapour for some reason.

[Bradders]

Thanks for the suggestions guys. I will start her up tomorrow and see how the headers warm up.

[Bradders]

It could be a coil or a cap is failing as the engine warms up, when it's cold it's fine but any heat makes them start to fail.

Any chance you can borrow a set of known good coils and caps for a test to see if it still does it?

Is it possible to test coils / caps whilst they are still on the bike?

[Bradders]

Thanks for your advice oddjob. I did look at Ash’s coil repair but it seemed a bit daunting to me. (I’m not the best mechanic in the world.)

[JezzaPeach]

If you manage to check the pipes heating up, even if it’s not conclusive, I won’t regret replacing my 49 year old coils with DSS, plus old caps and plugs. Along with points and condensers that were 20+ years old - it is running really well now, and should for a good long time.

[JezzaPeach]

Certainly a saving if one has time and skill to do it. I didn’t and at £72/pair the DS were much cheaper than some, and should last another 50 years! I’ve kept my old ones in case I get time to do the leads, or to sell to someone who can. My leads were certainly poor. I wonder if the wiring within the coils can also deteriorate after 50 years.