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British Bikes / Troubleshooting a JAP Special
« on: April 11, 2023, 12:27:31 PM »
I've inherited my father's JAP engined, Featherbed framed 'special', and I'm trying to get it setup for road-riding, it's registered and has been used in the past for road-riding and display events (eg Kop Hill), but since he died in 2021, it hasn't been used (in fact it wasn't used much before then), and I'm struggling to get it running right.
The engine is a a ~400cc* JAP 4-stud motor, with a Cooper ally small fin barrel (ie, from a Cooper race car), running an AMAL Monobloc, and a BTH Magneto.
Frame is a Slimline Norton Featherbed.
Gearbox is a 1950s Norton 4-speed.
Akront wheels, brakes are Grimeca 4-ls front, Norton rear.
So far I've got it 'running' after cleaning out the Monobloc carb and reassembling.
It starts easily and fires up fine - in the workshop**. Previous to cleaning up the carb it wouldn't tick over, now it ticks over fine and responds to revving fine when on the stands.
However - I've taken it out on the road (round the block) a couple of times, and it always does the same thing: It'll run fine for a couple of minutes - up through the gears to about 60mph or so, a couple of times, but then, within 5 minutes of starting, the power just dies away completely and it'll barely run, although it does seem to be able to tickover still.
I thought it might be running rich, so I lowered the needle in the carb (to the lowest option, from the 2nd lowest option), and that didn't seem to make much difference - although it did seem a little 'weak' at full throttle - so I'm slightly concerned I've gone too far the other way and made it lean, OR the problem is something else completely. It goes to full throttle very easily: fitted witha Tomaselli Quick Action twist-grip - only about 1/4 turn from closed to WOT.
The first time I took it out, and it started playing up, the plug came out very black and oily (but dry).
Then I checked it two days later prior to my second test-run, and the plug was actually wet with oil.
After the 2nd test-run, the plug was again black and oily, but dry (ie not sooty black, but oily black).
The engine is also pushing about twice as much oil to the head as it should - I've read (somewhere) that the Pilgrim pump should be pushing oil to the head at a rate of 1 drop every 5 seconds at tickover. Currently it's running about 2 drops every 5 seconds, so I'm going to adjust that, but before I do - would running R30 instead of R40 be the cause of a doubling in the oil feed rate? IIRC Dad ran it on R40, but I was adviced that R30 might be better during the cooler days at present (and switch to R40 during high summer or for faster riding).
The worry I now have is that oil seemed to be getting into the combustion chamber - would that indicate a leak from a valve-stem? I'm not even sure if these motors run valve-stem-seals (in the modern sense), or could it just be the 'over-oilling' overwhelming the valve-stem?
Very grateful for any advice that anyone can give!
* It's a mix of 500 and 350 parts which come out at around 400cc.
** Starts fine sitting on a paddock stand.... pull the bike out into the fresh air and it takes 10-15 kicks.... could this be due to the fact that I'm starting it on an angle? on the paddock stand it's pointing slightly 'downwards' (rear wheel is raised a couple of inches), but outside the uneven ground means it's leaning 'backwards' slightly (pointing 'upwards', rear wheel is a couple of inches below front)
The engine is a a ~400cc* JAP 4-stud motor, with a Cooper ally small fin barrel (ie, from a Cooper race car), running an AMAL Monobloc, and a BTH Magneto.
Frame is a Slimline Norton Featherbed.
Gearbox is a 1950s Norton 4-speed.
Akront wheels, brakes are Grimeca 4-ls front, Norton rear.
So far I've got it 'running' after cleaning out the Monobloc carb and reassembling.
It starts easily and fires up fine - in the workshop**. Previous to cleaning up the carb it wouldn't tick over, now it ticks over fine and responds to revving fine when on the stands.
However - I've taken it out on the road (round the block) a couple of times, and it always does the same thing: It'll run fine for a couple of minutes - up through the gears to about 60mph or so, a couple of times, but then, within 5 minutes of starting, the power just dies away completely and it'll barely run, although it does seem to be able to tickover still.
I thought it might be running rich, so I lowered the needle in the carb (to the lowest option, from the 2nd lowest option), and that didn't seem to make much difference - although it did seem a little 'weak' at full throttle - so I'm slightly concerned I've gone too far the other way and made it lean, OR the problem is something else completely. It goes to full throttle very easily: fitted witha Tomaselli Quick Action twist-grip - only about 1/4 turn from closed to WOT.
The first time I took it out, and it started playing up, the plug came out very black and oily (but dry).
Then I checked it two days later prior to my second test-run, and the plug was actually wet with oil.
After the 2nd test-run, the plug was again black and oily, but dry (ie not sooty black, but oily black).
The engine is also pushing about twice as much oil to the head as it should - I've read (somewhere) that the Pilgrim pump should be pushing oil to the head at a rate of 1 drop every 5 seconds at tickover. Currently it's running about 2 drops every 5 seconds, so I'm going to adjust that, but before I do - would running R30 instead of R40 be the cause of a doubling in the oil feed rate? IIRC Dad ran it on R40, but I was adviced that R30 might be better during the cooler days at present (and switch to R40 during high summer or for faster riding).
The worry I now have is that oil seemed to be getting into the combustion chamber - would that indicate a leak from a valve-stem? I'm not even sure if these motors run valve-stem-seals (in the modern sense), or could it just be the 'over-oilling' overwhelming the valve-stem?
Very grateful for any advice that anyone can give!
* It's a mix of 500 and 350 parts which come out at around 400cc.
** Starts fine sitting on a paddock stand.... pull the bike out into the fresh air and it takes 10-15 kicks.... could this be due to the fact that I'm starting it on an angle? on the paddock stand it's pointing slightly 'downwards' (rear wheel is raised a couple of inches), but outside the uneven ground means it's leaning 'backwards' slightly (pointing 'upwards', rear wheel is a couple of inches below front)
)