SU woes

[Speedex750]

OH!! Just had a thought.....

Have you put some fresh fuel in???

Despite the protestations from some that fuel doesn't go off, my experience is that some modern stuff does, and remarkably quickly!

Hi Hugh,

I've always fancied a Riley.........

You seem to have pointed the finger at the carbs but is there any other evidence the mixture is at fault like white plugs? All the symptoms you describe could come from ignition side weaknesses as well? And SU's are very simple things.

An air leak is usually just a problem on one carb making tickover uneven but once the revs pick up the in leakage is swamped by regular mixture and it usually runs OK. Are you getting enough fuel through, is your pump making pressure? I would hope that vapourisation isn't a problem at this time of year but blow through your fuel lines both ways (mark one mouth, I know it doesn't taste very nice). If you've a fuel filter, change it.

It's hard to envisage an engine that did run OK, suddenly not. I've heard about duff unleaded but I've found that once the engine is running it seems to work OK even with very old fuel (4 years old with my AH). Try priming the fuel chambers with fresh, or run the engine with a plumbed in can of fresh, to test that theory? Are sure you haven't got sticky valves or low compression that do fit better into a scenario of an engine standing for a while?

Random thoughts, hope of interest.

Dave