loss of power at 55-60mph

[dudload]

afternoon all!

to continue my constant stream of questions (and thanks again for the help so far) - I was out an about this weekend with a very short stretch on the motorway. When approaching 60mph the car started to surge slightly, losing power momentarily then coming back up to full power - it's strange as never experienced this before and previously it's been able to sit at 60-65mph quite comfortably.

in terms of info on the car, I've recently adjusted the timing (although my new electronic dizzy is waiting to be installed) - it was very slightly pinking at the beginning of the ride in top gear, but I got out and retarted ever so slightly until it stopped, compression tests came up as 150 across the board 3 weeks ago and I recently cleaned out the carb (although not float chamber) with some carb cleaner.

my initial thought was clutch, but I've got enough free play on the pedal to suggest all is ok and I don't notice slippage across any other gear. could it be fuel line issues?

[Tea]

I've had similar symptoms a few times and every time it has been a fuel issue. The first time it was an in-line fuel filter being crap, so I removed it and all was fine with that car after. The second time the small needle in the lid of the float chamber had managed to become stuck not allowing petrol through and the most recent one was some grit in the lid of the float chamber only allowing small amounts of fuel through.

[bmcecosse]

As above=-most likely fuel delivery problem,but fit the new dizzy to see if that helps.

[dudload]

Thanks for the replies. I've gone into the float chamber and cleaned the (tonnes) of fine brown powder out, also checked the float assembly and all looks good.

The replacement electronic dizzy will go in the weekend. Hopefully it doesn't come to this, but if I still experience the same problems above 55 mph could it be that my clutch is slipping but only in 4th?

There's plenty of free play at the pedal, but is it still possible to slip even when correctly adjusted at pedal?

[amgrave]

If the clutch is slipping you will hear the engine increase in speed but not the car, it should be obvious to hear.

[liammonty]

You really need to figure out whether it's clutch slip or not before spending money on replacing distributors and so on! As above - it should be very easy to distinguish between an engine losing power and the clutch slipping. If the clutch is slipping, you'll hear the revs increase, but the car won't speed up. When you ease back off the throttle, the revs will drop to match the engine speed again. If the engine is losing power, you'll feel hesitation, but the revs will stay as they should relative to the road speed.

[dudload]

very good shout - should've thought of that I guess. from memory there was no additional revving when surging (although the noise at that speed can be considerable!) so hopefully that does rule out clutch slippage!

[dudload]

so the one thing I won't have touched in the fuel delivery (have disconnected the metal pipe to float and the fuel pump merrily pumps away without any obvious issue), will be the jet assembly to the carb. is it possible this could have a slight blockage or could that be a red herring?

EDIT: I haven't checked fuel filter in the pump, but I guess if it's pumping ok that would rule it out?