Help with a miss

[jas1200]

I've got a miss and not sure what it is. Ive checked the float level and the accerater pump, the points gap and I've run sand paper in the gap. The coil is new and so are the points and condenser.

The miss only comes on when the engine is under load and warn, its runs fine when the engine is cold.

Any thoughts

[classicdat]

Plugs or leads, changing one may mask the other.
An increased resistance in the HT circuit can cause a miss under load, warn plugs, plug gap that is too big to jump or plug / coil leads breaking down can cause this resistance.
Also a faulty Dissy cap or Rotor could cause it also.
Lean mixture can also combine to cause this sort of miss. (Hence running well when Choked)
All the best.

[jas1200]

Great, thaks for that. Sounds like i,ll need to get hold of a resistance meter and i'll pull the plugs out and check the gap and colour tomorrow.

[classicdat]

Also check how square the shoulders on the centre electrode of the plugs are.

[jas1200]

Ok will check for that. Found a reistance metre on TM for $8....new, sounds to cheap.

[jas1200]

Think I've fixed it....

I took the plugs out, they were all black except for 1 and 2 that were black with grey electrodes. The shoulders were fine. I cleaned them and replaced #3 and #4 HT leads, its runs sweet now. After a test drive all the plugs are grey/ brown.

Thanks classicdat....