KHK Rear Plug Fouling

Production K Models

KHK Rear Plug Fouling

Postby Geodoc » Sun Jun 03, 2018 6:27 pm

The KHK that got it's top end re-op has been back with the for a couple month now and seems to have some of the same problem that it had prompting it's repair work - a recurring issue with the rear plug carbon fouling. The heads had plug inserts fabricated to allow 14mm short reach plugs and it's been running BR6HS NGK's. Most of his riding is in town a moderate speeds.

After running the bike on the dyno for break-in the idle and high-speed mixture settings were set for best power. These settings seemed to be fine for hiway running, but would result in popping on the over run. A richened idle mixture cured that. He does not use much if any choke to start with the warm(ish) temps here. However after a few miles on new plugs the rear plug will quite often carbon foul. The front plug shows a nice color and no sign of fouling ever. The rear plug does not look like it's an oiling issue - dry, black carbon that shorts out the center electrode.

So - a manifold leak seems unlikely as it would (you'd think) affect both cylinders. All adjustments are correct - spark timing, valve clearances, etc.

Is this something that was an issue with KHK's or other K Models for some reason?

Tempted to install an iridium plug in the rear, being more resistant to fouling, but that's just a band-aid over some other problem I fear.

George
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Re: KHK Rear Plug Fouling

Postby thefrenchowl » Mon Jun 04, 2018 1:47 pm

So the R in BR6HS stands for Resistor... Suitable ONLY for electronic ignitions... Get rid of this crap...

And replace with NGK B6L...

And town riding shouldn't mean any different than the open road...

Use all the revs available...

Patrick
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Re: KHK Rear Plug Fouling

Postby Geodoc » Mon Jun 04, 2018 2:03 pm

I'm running resistor plugs in my points equipped Guzzi Eldorado and well as a Dyna-S, but otherwise strictly non-electronic ign. Ducati 750 GT. Never a problem. Finding non-resistor plugs around here is pretty much impossible anyway.

thefrenchowl wrote:So the R in BR6HS stands for Resistor... Suitable ONLY for electronic ignitions... Get rid of this crap...

And replace with NGK B6L...

And town riding shouldn't mean any different than the open road...

Use all the revs available...

Patrick
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Re: KHK Rear Plug Fouling

Postby mikeslemmon » Mon Jun 04, 2018 3:22 pm

try champion J8c same as harley # 5 or (hotter)J12y same as harley # 3-4
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Re: KHK Rear Plug Fouling

Postby thefrenchowl » Mon Jun 04, 2018 4:09 pm

Hi Geodoc...

If you know better than the manufacturers, why are you asking us mortals???

I dispair with these forums... They just make the world go backwards...

I think I'll stop stating the obvious eventually...

I'll just mention: did R plugs existed when the K was born?

Does progress improves the breed?

Patrick
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Re: KHK Rear Plug Fouling

Postby Ferrous_Head » Mon Jun 04, 2018 4:33 pm

OK. We're lucky here as this is a twin cylinder bike.
Basic trouble shooting with what you think might be plugs/coil/wire problems/
Swap the plug leads and plugs. Test. Did the problem follow the plug/lead ? Yes ? Problem is lug or lead.
No. Problem is probably not the plugs or the leads. Now you have to look at the carburation.

What I suspect might be happening is a small air leak on the front cylinder. You have compensated for this by ricjening the mixture. So the front cylinder is now getting correct (sort of) a/F mixture.
But on the rear cylinder with no leak it is now running too rich.

But do the plug.lead swap and see what happens.

(Resistor plugs do just what they say. They resist voltage. That is, thy reduce the voltage to the plug. On a very good ignition system, with coils putting out 70v,000+ volts this is no problem. On a mag system at cranking speeds or a points system where voltage drops as the revs rise it's "problematic".)
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: KHK Rear Plug Fouling

Postby Geodoc » Mon Jun 04, 2018 4:39 pm

Yeah, stopping stating the obvious is a great idea.

thefrenchowl wrote:Hi Geodoc...

If you know better than the manufacturers, why are you asking us mortals???

I dispair with these forums... They just make the world go backwards...

I think I'll stop stating the obvious eventually...

I'll just mention: did R plugs existed when the K was born?

Does progress improves the breed?

Patrick
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Re: KHK Rear Plug Fouling

Postby Geodoc » Mon Jun 04, 2018 4:59 pm

One of the things the owner did before we got it was to install a new coil & copper core leads w/ the old-fashioned metal clip type ends & they seem to be functioning fine. The best bet seems to be as you suggest, a manifold leak. Actually, the intake manifold seals that we got from enfieldracing,com were a bit of a struggle to get to seal.

Ferrous_Head wrote:OK. We're lucky here as this is a twin cylinder bike.
Basic trouble shooting with what you think might be plugs/coil/wire problems/
Swap the plug leads and plugs. Test. Did the problem follow the plug/lead ? Yes ? Problem is lug or lead.
No. Problem is probably not the plugs or the leads. Now you have to look at the carburation.

What I suspect might be happening is a small air leak on the front cylinder. You have compensated for this by ricjening the mixture. So the front cylinder is now getting correct (sort of) a/F mixture.
But on the rear cylinder with no leak it is now running too rich.

But do the plug.lead swap and see what happens.

(Resistor plugs do just what they say. They resist voltage. That is, thy reduce the voltage to the plug. On a very good ignition system, with coils putting out 70v,000+ volts this is no problem. On a mag system at cranking speeds or a points system where voltage drops as the revs rise it's "problematic".)
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Re: KHK Rear Plug Fouling

Postby thefrenchowl » Mon Jun 04, 2018 5:50 pm

Hum, Geodesic George, small air leaks...

Could that be due to overzealous lightening of valves?

Image

Patrick
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Re: KHK Rear Plug Fouling

Postby Geodoc » Mon Jun 04, 2018 6:20 pm

Is that why it whistles what sounds like the theme from "The Fighting 69th" speeded WAY up just off idle?



thefrenchowl wrote:Hum, Geodesic George, small air leaks...

Could that be due to overzealous lightening of valves?

Image

Patrick
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