Topic: From D8EA's to D7EA's to D6EA's...maybe

[oldbikesrcool]

I didn't find an existing message string specifically addressing 'twice-hotter plug' usage and so appologize if I'm kicking yet another dead horse topic. I'm just about out of options and am considering yet another step hotter plug...
Has anyone corrected a low speed, carbon fouling problem by using, for example, NGK D6EA's?
Suspect Bike: '73 CB750K3 (w/50k miles, 4-into-1 exh, carbs cleaned 3-times, 110 mains, 40 slows, needle clip at 2nd from top (leaner), 1-turn out on the air, new K&N air filter, D7EA plugs).
Although this sounds like a 'lean' set up, she's still carboning up. After cleaning plugs, the bike runs sweet; a smooth, clean idle and pulls like a freight train all the way to jail  . But after a short time back into the around-town-off-idle-to-quater throttle range, the tell tale load-up starts in earnest. I also wonder if the coils are being effected by the rising engine heat over the course of the ride. Am I missing the obvious?
Galen

[TwoTired]

Turn the idle mixture screws out even more.  I've had to stretch the springs on them sometimes to get them to stay put because they were turned out so far.

Or, put in smaller pilot jets.

[Bob Wessner]

I agree. I just spent several days doing the same kind of riding to sort out low speed carbon build-up. It's a K0 with 4-into-4 pipes, 120's and 40's. Same thing was happening. If I rode it long enough under those conditions, the fouling got to the point where she started missing quite a bit. Before you go to hotter plugs, experiment with turning the airscrews out more. Small increments make a big difference. Then take  it out and come back, check plugs and repeat as necessary. I'm getting as good at pulling, cleaning and replacing the plugs as I was at pulling and putting the carbs back on.. sigh! 

I should have added, it's paying off. Two of the plugs are now about as perfect as I could hope for, and two still slightly sooty, but still not accumulating.

[oldbikesrcool]

Thanks! I just knew I'd overlooked something obvious, like 'more air(!)', or less fuel through the pilots. I think I'll try the more air approach first.
So, just for arguements sake, has anyone ever had experience with D6EA's in the SOHC mill?
Galen

[Jonesy]

Just a thought, at that kind of mileage, what's the oil consumption looking like? I'm wondering if oil getting into the combustion chamber and burning could contribute to the fouling. I'm suspecting the valve seals on mine might be letting stuff past....

[Kevin D]

Fifteen minutes on the e-way at slightly illegal speeds will do wonders for 'round-town-fouled plugs.

[oldbikesrcool]

Thanks for the inputs! (Love this site). As far as oil consumption, it's just about nil. The plug fowling is not oily, just dry, black and fluffy.
The 'fifteen minutes at intra-orbital velocities' does evict the offensive black nasties straight out the noisy end...temporarily, but the condition sets up house again, right quick.
I am still curious about D6EA usage. One of our local, old school vintage bike gurus says "We'd always run sixes in 'em...no problem". I just haven't heard anyone else support, or dispell, the theory.
Galen

[Bob Wessner]

Just my $0.02, but 6's seem excessively hot, but others may differ with me.

[eldar]

I dont think I would use a 6 plug.May cause damage in the engine.

I have to agree with the turing out of the air screws. You may also want to check your float height and make sure the float valve seats are clean. Could be possible there is a too much fuel in the bowls. Happened to me that way.

[TwoTired]

One of our local, old school vintage bike gurus says "We'd always run sixes in 'em...no problem". I just haven't heard anyone else support, or dispell, the theory.
Galen

I wonder where those bikes with sixes are now?
Anyway, maybe this will help with your curiosity....
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

[oldbikesrcool]

TwoWired,- That has to be the most beautiful piece of fine literature I have ever had the pleasure to witness. My plugs are spot on "No. 3 carbon fouled"; "...causes of sooty plugs [in figure 3] are usually the result of...
(1) the plug firing-end is not reaching 400-450 degrees C in order to self clean,
(2) air-fuel mixture to rich,
(3) Trouble in the ignition system" (!... ). I'm still not completely sure my coil set is in spec. The wires are deffinitely getting'firm', kinked, and questionable.
First things first. #1 Air-fuel, #2 coil/wire set (points set to spec, timing is spot on). I'll let you know...
Galen

[oldbikesrcool]

Follow-up:
The air-fuel direction appears to be the answer. I went out another 1/8 turn equally, on all four screws, rode around town doing earrands and experienced only slight loading-up after 15 miles. I will pull plugs tomorrow and see what there is to see...definitely an improvement.
Galen

[oldbikesrcool]

Well, for the first time I'm seeing a non-fouled, brown condition on plug #4, less caked on black fouling powder on #3 and #2, and #1 although not fouled(yet) exhibited no brown-ing...close though. I'll keep adjusting...
Onward (...or would that be 'outward' ).
Galen

[eldar]

Make sure you do not get too lean though. Otherwise you will have poor running and high heat and could actually cause damage. A light tan I think is about right.