Triumph Repair: Fluxuating loss of power at 80-100km, engine temp, gas filters

Question
HI Jim. I have a 77 spit. New gas tank, new/rebuilt SU carb, new gas filters, new mech pump, fuel lines away from engine to reduce vapour lock (i hope). Starts great, idles great (minor black smoke), runs great for first 10/15 minutes. Once up to normal engine temp, and up to 100km, I experiance fluxuating minor loss of power. Doesn't stall. Idles fine at normal temp when I reduce speed or stop. I suspect its starved for fuel due to speed/load on engine. Could it be a temp issue or a fuel starve issue? If so - what remedies would you suggest? Thanks!

Answer
Nelson,

Which SU?  One of the HS?  Or an HIF?  If it's an HS, it's easy to check the fuel level, make sure it's correct.

One good test for a fuel issue is to take a plug cut.  Find a quiet back road, get the car up to speed then shut it off and coast to the shoulder.  Let it cool a few minutes then pull the spark plugs.  If the insulator tips are bright white... too lean a mixture.  Which is either needle, or it's float bowl level.

I'd also check the ignition timing, if that's off it can give a similar symptom.


Cheers,

Jim