Sooty plugs.

[K2-K6]

Now I am sort of giving myself a kick up the arse here. I had a nice run out yesterday on the k3 but quickly realised only 3 cylinders were firing. This is the second time this has happened to me this year on this bike. I got back home and checked cyl 2 and the plug was just sooted up then checked the rest and they were all sooty. Then the penny dropped that I had replaced the pilots with 45’s instead of 42’s but had made no compensating adjustment to mixer screws. As most of my running around here is in the lower to mid range rpm it stands to reason that it is getting slightly too much fuel! The reason I changed the pilots was to improve cold starting which it did do. So today I will make an adjustment to the carbs and take for another run, since it is a nice day.

Some thoughts on original posting/question and to look at it from different perspective.

The change to pilot Jets 42 to 45 gives a plus 7% shift in the idle circuit flow potential.  If that's paired with the main jet as being roughly half the size of main, then at idle to approximately half throttle operation will give from 7 diminishing to 3.5% additional fuelling in that range. Ultimately still 2% at full throttle too. Effectively its richer right across the board by a diminishing percentage as rpm /throttle is increased.

The experienced "sooty plugs" evidence that this is in place.

To just raise mixture at base of idle, you'd be better in considering std pilot jet size and evaluation of more fuel set on adjustment screw, say 1/2 turn out further than the existing.  This should just bring up the initial mixture fuellling level at "closed " throttle position,  while leaving general running mixture alone.

[Johnny4428]

Nigel I understand what you are saying and makes complete sense. The only reason I upped the pilot jet size was because of poor starting, certainly sorted that out. Even after cleaning out the old pilot jets about three times I wasn’t making headway. The bike ran very lean evidence of that was in the plugs and midrange hesitation cured temporarily by pulling the choke. I was going to buy new pilot jets anyway to try but thought I would increase slightly the size. I haven’t been out with the bike again since my last adjustment on the carbs but I think I’m going in the right direction with No 4 plug looking like we have a good fuel air mixture. If I can’t stop the fouling I will of course replace pilots with the correct 42’s.

[Johnny4428]

Managed a nice run out this afternoon 60mls or so, bike was running great. Blew the main fuse again but thankfully had a spare not sure yet what is causing that. Checked the plugs when I returned and was pleased to see an improvement with uniform colour across the 4. Maybe a little tweak yet.




Sent from my iPad using Tapatalk

[McCabe-Thiele (Ted)]

Thats not a bad colour imho - depends a tad on how hard it was ridden.

[Johnny4428]

Not ridden hard Ted. Just up in the mid range mostly. Sticking mostly to the legal limit!😜

[McCabe-Thiele (Ted)]

I'll fess up, I've not had the plugs out of my 400 since I finished the rebuild. It runs well, no hanging throttle, no flat spots, good idle. It's only done 400 miles, there is no black smoke out of the exhaust and the end of the tail pipe is not heavy with soot. I see no reason to remove them until the engine has done at least 600 miles unless it starts to misfire, have starting problems, excess smoke, oil consumption, or a cold cylinder.
 
Spark plugs are designed to effectively self clean, on a cold engine with choke the plugs will be pretty black, once the engine is hot then plugs will burn off the carbon reaching the right colour. As you know  ideally you might want to look at the plug colour when the engine is hot and has been running 4k revs or higher for a few miles. By the time you have reduced the revs,idled for a minute, then reached home the plug colour will not full represent the situation.

On my 500 due to the fuel pipe fiasco and having to take the carbs off again I checked the plugs they were pretty black. Now I have the 500 carbs back on, with it now running evenly, I hope I can put a few  hundred miles on her before I need to check the plug colour unless I develop an issue.

What I'm getting at Johnny is don't get too worried about plug colour alone, it's not a very precise diagnostic tool imho unless you have other running issues. It's not as if these old Honda's are modern lean burn designs with injection & O2 sensors.

Now you are happier with how it runs, I would be okay with that plug colour, I would worry much more if one was very lean.

[Johnny4428]

I agree Ted that if everything is running fine no need to remove the plugs however I twice lost a cylinder because of excess “sooting”. This prompted me to return to the fuelling issues, only this time it seemed to be getting excess fuel. It dawned on me then that by increasing the size of the pilot jets to improve starting had an impact of course on running from idle upwards too. It seems now that I have achieved an acceptable runner by tweaking the idle mixture screws.

[McCabe-Thiele (Ted)]

That's a good outcome then Johnny are you back on the original 42s.👍👍👍

[Johnny4428]

No Ted still on the 45’s.