Popping and not pulling well?

[Biddlecombe]

I took Vera to West Firle for a meeting of The Old Farts Club, or half a dozen of my old mates. 1 pint of Harveys best and home only 9 miles each way. 

Bit of popping in the box and not pulling well in top. Checked temperature of each plug and found number 3 10 degrees C lower than the others. Any ideas?

[John Mason]

Your colder plug and presumably I cylinder to me indicates that it has an intermittent misfire. Check the ignition and plug in that cylinder if they are ok. Then check tappet clearances.
Also do a wet and dry compression test to check out valves and bore. I had this when a tappet came loose thus keeping a valve constantly closed.

John Mason.

[Timothy P]

Sorry for the delay in doing this. Split from the 'What have you done today...' thread. 
Also found a work around which meant that I could keep your photos and the bit about your trip to the pub in the other thread too.
All the best.

[Nick Salmon]

Try a different plug?

Envious of your proximity to supplies of Harveys. Many a happy pint of it was sunk in my youth.

[Colin Wilks]

My RP finally died the morning after completing the Sevens to the Sea run. I'd had a number of problems, points closing up on the Bosch distributor and carb float bowl threatening to go walk about, but the issue that stopped us in the end was the coil. The previous day the car had started misfiring quite frequently and was down on power. Subsequent investigation indicates this is a classic symptom of a duff coil. Assuming you have a good spare coil to hand this is an easy one to exclude and/or fix.

[Chris KC]

If we disregard plug temperature for the moment, if my car were popping and not pulling well I'd clean and re-gap the contact breaker points before considering anything else.

[John Mason]

By all means check the points as Chris suggests and all the ignition circuit. However the points work the firing on all cylinders so why would the points effect just the plug in one cylinder. I would check the dizzy cap for the connection to the cold cylinder together with the plug and lead. Also to check the tappets and valve for the colder cylinder. In my mind there is something stopping that cylinder firing correctly or even not at all thus keeping it cold. Is the plug oiled or sooted up.

John Mason

[Robert Leigh]

I would start like Chris K-C, but it is worth checking the contact breaker gap in all four positions. A lot of distributors have seen a lot of service by now, and wear can have undesirable effects like the points gap being unequal as the cam goes round.
Robert Leigh

[John Mason]

I take on board what you say Robert and apologies to Chris KC the point (no pun intended) of warn dizzy and different point gaping I had not considered or even thought of. To prove things you could swap plugs around to see if the coldness moved to another cylinder.

John Mason

[David Stepney]

I fitted a refurbished distributor to my RP saloon, as the top bush on my original one was worn and it made a real difference to the way the car went.