Jerky / being held back when cruising

[Mr Morris]

Went for a good long drive in my car today. All was well overall but when I get to the 40 / 45 mph mark it seems pretty flat out. Also at this speed it feels lumpy / jerky as if it wants to go on further but it's being held back by something. The timing is fine, carb seems fine, air filter fine, brakes not binding. I'm not sure what the problem here could be. Can anyone help?

[mike.perry]

Are you sure that the timing is ok and there is no fault with the distributor?

[Mr Morris]

I was starting to think distributor problems could be the answer. But I'm not sure how to diagnose a distributor as I've always stayed away from them - what can I do?

[tomas.geoghegan]

Had Egsactly the same simptoms.its like driveing in to a head wind
Sounds like the distributor. My vacume unit was not working either.
Put a new one on and now pulling like a train.
Tom Geoghegan

[Mr Morris]

Thats interesting Tom - did it give the engine more speed too as mine feels like it's got in there somewhere but something is pulling it back. I think I will replace it and see what happens!

[tomas.geoghegan]

Yes i got my distributor from www.simonbbc.com and cost £40.94 a bargin i think .comes with points condenser and rota arm
and ready to go As a vacume unit is Around £20 on its own. and have seen distributors At £60 plus.
I went for the 25D Dissy with points.
Personaly i would try it.
Hopefully will sort it out?
Please let me no how it goes.
Good Luck Best Regards
Tom Geoghegan

[bmcecosse]

How do you 'know' the timing is fine ?? Is the air cleaner element NEW ? Are the valve gaps correct? Have you done a compression test recently? What colour are the spark plugs? And yes - well worth testing the vacuum advance - although it doesn't usually affect top speed so much as acceleration. R

[Mr Morris]

Just to update on this, I checked most of what Roy suggested and the spark plugs were a little darker than tan but not too bad, so i cleaned them. My friend gave me a whole new (used) distributor from a MM he no longer uses and it's solved the problem completely. Thanks for your help everyone.

[bmcecosse]

Oh well - it would be good to find out what is wrong with the old dizzy - so you can carry it as a 'known good' spare.

[tomas.geoghegan]

Hi Glad to hear it.
well done!
Tom

[beero]

So it could just have been the points in the old dizzy. Did you check them?

[bmcecosse]

Or the condenser or the 'low volts' lead