Juddering in 4th below 70kmph

[DEREK SLINGSBY]

Can anyone please advise? My 1992 R4 GTL judders bad when below 70kmph. I can remove both 1 & 2 leads off the dist cap at he same time and the tick over doesn't change, remove 3 or 4 and it stalls. The leads are ok, the plugs are new, new air filter, dist cap. I'm at a loss, I've even set the valve clearances, those on 1 & 2 were very small.

 

[petak]

Is timing set correct?

 

[DEREK SLINGSBY]

I haven't changed it at all for the 6 years that I've had it and 3 & 4 seem fine.

 

[Geoff in the Gully]

Are the leads on the right plugs?
Sounds like neither 1 or 2 are pulling their weight.
Try swapping - just to see...

 

[DEREK SLINGSBY]

1,3,4,2, 2 is at the front of the cap. I have tried the cable off 4 on 1 and 2 but whatever is tried 1 & 2 are always non existent, 3 and 4 always good.

 

[Geoff in the Gully]

I think it's time for a compression test.
You've already done all the other obvious things.
Other possible issues would affect all cylinders.

The low valve clearance hints at valve seat recession, though I'd expect resetting the clearance to have made some difference.