20-04-2022, 02:37 PM
I haven't used the Pytchley much over the last year. Having converted it from twin SU's to a single 1" SU, I detected considerable harshness in the engine and feared the worst. The engine is the first I ever built up, back in 1982, and it has done service in several specials over the last 40 years. I suspected that there could be a problem with the bottom end, which has an original crank and rods.
Part of the conversion to a single carb involved changing the cylinder head, from a planed low comp to a bronze 9E1. I spent the other afternoon trying to sort it out and establish the problem. It seemed to be ignition related. It has a Bosch distributor but it is an old Skoda unit probably 30 years old, in other words, not a rubbish repro unit.
To cut a long story short, it turned out that my problem was nothing more than a set of duff spark plugs. I fitted a set of known old plugs and set the mixture and timing up from scratch.
Today being a lovely spring day i did some road testing to fine tune the mixture and ignition settings. Starting from my driveway opposite the Church there is a slight rise through the village, a water trough on the right hand side defines the end of Sector 1. Leaving the village there is a road junction on the left which is the end of Sector 2, then a left hand bend and a long drag up a hill of about 1 in 8 to the end of Sector 3 at the gates of the 'big house' at the top of the hill.
My dashcam records each run and the sector times and speeds are useful for analysis. Before anyone accuses me of road racing I would point out that the top speed recorded on any of the runs is 35 mph. This is less than the average speed of cyclists who pass through the village with the apparent blessing of the authorities.
When the Pytchley had twin SU's the time recorded was 75 seconds for the climb, with the single 1" SU I recorded two times of 72 seconds, on one run I lost a second or two having to slow for a pair of partridges on the road. A third run had to be aborted as there were three horses up ahead.
Part of the conversion to a single carb involved changing the cylinder head, from a planed low comp to a bronze 9E1. I spent the other afternoon trying to sort it out and establish the problem. It seemed to be ignition related. It has a Bosch distributor but it is an old Skoda unit probably 30 years old, in other words, not a rubbish repro unit.
To cut a long story short, it turned out that my problem was nothing more than a set of duff spark plugs. I fitted a set of known old plugs and set the mixture and timing up from scratch.
Today being a lovely spring day i did some road testing to fine tune the mixture and ignition settings. Starting from my driveway opposite the Church there is a slight rise through the village, a water trough on the right hand side defines the end of Sector 1. Leaving the village there is a road junction on the left which is the end of Sector 2, then a left hand bend and a long drag up a hill of about 1 in 8 to the end of Sector 3 at the gates of the 'big house' at the top of the hill.
My dashcam records each run and the sector times and speeds are useful for analysis. Before anyone accuses me of road racing I would point out that the top speed recorded on any of the runs is 35 mph. This is less than the average speed of cyclists who pass through the village with the apparent blessing of the authorities.
When the Pytchley had twin SU's the time recorded was 75 seconds for the climb, with the single 1" SU I recorded two times of 72 seconds, on one run I lost a second or two having to slow for a pair of partridges on the road. A third run had to be aborted as there were three horses up ahead.