Intermittent misfire!

Hi all, i've got a problem on tick over and when increasing rpm (1600 tp) It's an occasional cough / hiccup/ pop/miss type noise from the exhaust , out on the road i drives fine, whether it does it under load or not i don't know. My Hawk analyser which hooks up to the coil and earth jumps around on the low rpm setting, i wonder if this is any sort of fault indication in itself ?.
All i've done so far is check the idle jet, clean inside dizzy cap and rotor arm and re set tick over and idle mixture. Engine had new pistons, barrels and heads 1k ago. Any thoughts greatly appreciated.

 

Have you checked the points and leads?

 

Sounds like a timing problem, have you adjusted the dizzy lately?

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It's electronic ign on a 034 Bosch dizzy. Timing set to 30 deg @ 3000 rpm yesterday. Pretty sure it's correct.

 

Can you narrow it down to one cylinder? What sort of electronic module? There is evidence on here that they can give intermittent problems.

 

Cracked plug cap?

 

Not sure what make, it was on an 009 dizzy that came with the van. HT leads haven't done much mileage, plugs about 1k.
The popping is very random, not a distinct miss fire.

 

Hiya, i'll pop back out soon and visually check and have a feel around caps with engine running.

 

I had a cracked cap not long ago. Random misfire, not obvious when driving. I noticed when I pulled the relevant lead a little way off the distributor making the spark jump it idled better even though it wasn't particularly aware it was idling badly. Doing the same with the uncracked ones didn't alter the running. I don't know what the science is.

 

As it turns out Milo- Steel was on the money !. I got my mate to check the timing yesterday as i had timed it to marks i had physically measured on the o/d of the pulley, i got him to check with his new- fangled pre-setable type strobe gun. Thought we'd adjusted it from 27 to 30 degrees. Just re checked & with my old Gunsons strobe to my 28-30 degree marks and it was about 15 degrees out . I've now re-set it my way and all seems well.
Checked HT caps, all good

 

Cool well done for sorting, it just reminded me of mine when it did it, somebody had rebuilt the the engine wrong so the dizzy was 180 degrees out

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Thanks for that. Although i've fitted a Bosch 034 dizzy after issues with a Flamethrower the rotor arm is 90 degrees out the same as with the Flamethrower?. HT leads rotated accordingly.