A65L Dies when hot & takes a break before restarting

[LIONELSMITH]

Background
I bought the bike with standard carbs and coils, but with Boyer Brandsden Mk 3 Electronic ignition.
As with all my bikes, I rewired, fusing each circuit separately. The Amals were badly scored so I replaced them with Wassel evolution carbs and changed the two 6V coils for a 4 ohm coil. The carbs have got 5mm Phenolic spacers and were adjusted by the book and the bike has worked fine since.
NOW
After running it like this for some time up to about 25 miles it is still good, starts first time and runs well. I trust it now so have started to go further. The problem I have is that on longer journeys it cuts out at junctions and traffic lights, if I cant keep it revving. On longer trips it cuts out and wont restart for about 5 minutes. I know it is running hot by the colour of the pipes, going from amber to blue. The plugs show it is not running lean, if anything slightly rich as they are blacker than the expected grey.
The right cylinder may be using a little oil by a little smoke on starting, which I will investigate, but I cannot understand why this change when hot. Can you help?
Could it be an oil issue in which case a n external filter might help to cool it.

[ducati2242]

Any chance the valves are incorrectly set and not closing properly when hot .

[rhyatt]

What you describe is classic electrical components failure when hot , cool off a shade and works again.
The running temperature can perhaps be caused by a shade retarded ignition , so check that obviously.
Plugs at least are a shade rich , bores and rings - do you know of engine history , if only a puff , run a bit longer to verify accurately oil consumption.

[idie]

Check coils they will breakdown when hot.

[DAVE BRADY]

Hi,

A bit of a long shot but have you checked the fuel filler cap vent hole?  Starting will be fine and the bike will run OK whilst the engine takes in fuel to overcome any partial vacuum/restriction.  As the revs drop such as during slow running or stationary the partial vacuum in the tank restricts the flow of fuel hence the cutting out.
After a few minutes the vacuum is gone and the bike will start again as the carb will now have refilled with fuel.
It is not enough to be able to blow through the cap when it is off the bike as this may seem OK but try it with the cap compressed as if fitted and see if it is still OK.
It is surprising how bits of scale can remain in the cap even after what seems like a thorough clean.

Dave.

[chaz]

another thing to check, has the inside of the fuel tank been coated with petseal, kreem or similar?
modern ethanol fuels are known to strip the coating off. This drops over the fuel tap and blocks flow. when stopped there is no vacuum and the coating rises again only to fall back down a couple of miles later