Fuel Vapourisation

[AndrewHarris]

Hi Everyone I am looking for some advise / guidance please? Having had my 912 HC engine set up on a dyno just before this hot spell and all was running great, however after a 350 mile round trip to Castle Comb this weekend including enjoyable track time, my engine has a little misfire but only when it get hot throughout the rev range although continues to pull and develop good power. Coolant is fine and never gets above 90C but as the temperature under the bonnet raises the misfire get worst i.e. stuck in traffic, once moving in cool air it's good. I am 99% sure it's fuel vaporisation which these HC engines are prone too, I use Shell V power but even this is less stable then fuel from the 80's. I do have a fuel filter/regular under the bonnet which has increased the length of hose to the carbs which I fitted when I had a aftermarket fuel pump, however now I have the standard Electronic SU pump, so I might remove this or maybe fit it in the boot on the output pipe so that I can have a short as possible route to the carbs from the fuel flow value which I could also potentially insulate?
So basically anyone else had this issue and fixed it either in Elite/Éclat's or Excels?
Thanks
Andrew

[Hawaiis0]

I know its the other end but how is the fuel filter?

[Pete Boole]

Ignition coils can also falter if they get too hot.

Pete

[Marten]

Ignition coils can also falter if they get too hot.

Pete

And where does the intake air come from?

[DavidOliver]

Have you fitted steel braided fuel line, close to anything hot?
Take a wet rag and put temporarily over filters, etc.

dave the cog

[AndrewHarris]

Morning All, Thanks for the feedback and I will try to answer all the questions in one? Fuel filters new, one from the tank to pump and one in the regular engine end. Ignition coil is a epoxy type which is not prone to failing when it get hot as I have found out before now with a oil filled coil. I have steel braided pipe from the fuel value to the carbs and they do not run close to any individual hot item, generally the whole under bonnet get hot this weather? I also have a fresh air duct from the rad intake directing air towards the air housing intake too.
My current thinking is the under bonnet regular pre heats the fuel a little before routing the carbs so initially I take this out of the circuit and see it it helps as the SU pump should correctly pressure the carbs now? With these engines with modern fuel running close the wire?
I am of course assuming the floats are set correctly in the carbs?
Thanks
Andrew