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Sooted plugs on R51

Posted: Mon Feb 25, 2019 3:18 am
by Bigsieuk
Hello all,

I have a 1939 R51 with Bing 1/22/61-62's from the R51/2.

It keeps sooting both plugs up though after a very short while (minutes). I've checked the points gap (0.4mm) changed the coil, condenser and plugs. I've tried reducing the jet sizes but this hasn't helped.

The only things I haven't changed are the HT leads and the points. One plug sooting up could indicate a problem with a single carb but both makes me think is a spark issue?

If it makes a difference both carbs have the schutzschraube.

Any ideas?



I have never owned anything

Posted: Wed Feb 27, 2019 6:00 pm
by Twocams
I have never owned anything that old & I was built in 1949. But let me give it a try. Where I live there is snow on the ground, in other words cold. So if I was to run an engine for a few minutes it would soot up too. Have you tried to get the engine up to operating temp? And see if it will burn the soot off. Also the heads and pistons could have soot build up. And when you start the engine it blows soot onto the plugs?
So that's just my .02

sooted up when hot

Posted: Fri Mar 01, 2019 8:00 am
by Bigsieuk
The problem started on a run home. After about 5 miles its started spluttering and won't even get up to operating temperature. I'm inclined to think this is a spark issue.

I've replaced coil, condenser and plugs. Next to check is points, rotor and leads - hopefully this weekend.



I only lived in England for 5

Posted: Fri Mar 01, 2019 2:32 pm
by Twocams
I only lived in England for 5 yrs. But how is your petrol your using. Its newish, clean, no water in the tank. Nice blue spark from the plugs is always better than a weak Orange spark. You have checked the timing & its good? Im just throwing some stuff out there.


Posted: Mon Mar 04, 2019 3:41 am
by Bigsieuk
New petrol this weekend didn't help unfortunately.

New plugs this weekend too, it idled but the engine was missing when on throttle and sooted the plugs up within minutes.

I dropped the needles a notch which seemed to make a difference and it idled a lot better. I ran out of time (British weather) and didn't get a chance to ride it out on the road. I'll double check resistance through the leads and cap this weekend to see if I have a rotor/cap/lead related issue.


Update - Resolved

Posted: Wed May 08, 2019 9:50 am
by Bigsieuk
Thanks to Peter Ardron, he found that it was an intermittent ignition board problem that was interrupting power to the ignition system causing a no-spark condition.