Topic: Spark plug fouling issue...

[freezingprocess]

First off- '76 CB550k, D8EA plugs, pods, mac 4-1 exhaust, 120 mains, stock pilots (38). Set the cam chain, valves, and timing properly. Have not synched the carbs, as I do not have the equipment yet. I've just been playing around with mixture/idle screws, trying to get it running decent enough for some test rides, which I have done over the last week. I keep checking the plugs after every short ride, and 2, 3, and 4 have been looking ok, like #'s 18-20 here: http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
The #1 plug kept looking carbon fouled. -Soft fluffy black deposits.

Yesterday I was having fuel delivery problems, mainly to the 1&2 carbs(as seen in my clear lines), and went for a ride down the street to fill up the tank, since it was only about 1/4 to 1/3 full; figuring I just needed more gas in the tank to push down into the lines. Before I could even get there, the bike choked and died. Got it started again, and it hobbled home. Did not think to switch to reserve until I got home (duh), and then fuel rushed down into the lines. Now it won't start, so I pulled the plugs; they all look the same, except this little guy. #1.

I am nervous that I over-heated the motor and did something catastrophic to the #1 cylinder, possibly from starving it of fuel and over heating. 

Just some more background: I bought this bike last fall without the carbs on it (they were in pieces), so I never ran the motor before doing a top-end cleaning and re-gasketing, and thoroughly cleaning and rebuilding the carbs. The cylinder walls looked immaculate when I pulled it apart, but lots of carbon on the piston head and valves, which I cleaned off, being careful not to damage the surfaces.

Just looking for some opinions of what might be wrong, or criticisms of what I've done. Feel free to slap me around a bit.

[Gordon]

Probably just wet with gas after the unsuccessful starting attempts.  Don't worry so much!

[chippyfive50]

The 550 specs for D7EA plugs which are a little hotter, which may or may not matter.
120 mains sound quite large, but I know there are many variables... I am running 105s with UNI pods and a
quite unrestricted exhaust, and getting a nice tan plug..
There is a load of good 550 info herehttp://www.sohc4.net/index.php?title=CB550#Tech_Info
check the carb FAQs too... have fun...

[freezingprocess]

Probably just wet with gas after the unsuccessful starting attempts.  Don't worry so much!

Thanks Gordon- I just re-read my lengthy post and it does sound like I was a little too frantic.   I'll stop worrying and give it another try. (Bike is not starting now, by the way, which I probably should have added.)

[andy750]

The 550 specs for D7EA plugs which are a little hotter, which may or may not matter.

In my limited 550 experience the 550 runs much better with D7EAs (stock for the 550 - check the manual).

good luck
Andy

[freezingprocess]

The 550 specs for D7EA plugs which are a little hotter, which may or may not matter.

In my limited 550 experience the 550 runs much better with D7EAs (stock for the 550 - check the manual).

good luck
Andy

Cool. I do have a set of those. I'll put them in and see what's what. I know the D7EA's are stock, but based on the research I did here, I thought I might be on the lean side with my initial jetting, so I opted for the colder plugs.

[TwoTired]

Here are some maybes for you to check out.

D8 is a colder plug than the D7 Honda recommends.
Once a plug carbon fouls the center electrode insulator, spark current follows along the carbon deposits on the insulator rather than jump the gap.  This makes the cylinder NOT fire the mixture and the plug becomes wet with gas.
You can try cleaning that insulator, but you should really get the correct plugs that are more likely to self clean.

Reserve setting feeds from the bottom of the tank, if your in-tank filter is compromised, that setting is more likely to place unfiltered bits-o-stuff in the carbs that really shouldn't be there.  These bits can block the float valve open, plugs up jets, and generally make clean carbs behave like..not clean carbs.

I can only imagine what you've done to the bike to warrant #120 mains.  This size is usually the domain of some 750s?  Velocity stacks, perhaps?

Cheers,

[freezingprocess]

Here are some maybes for you to check out.

D8 is a colder plug than the D7 Honda recommends.
Once a plug carbon fouls the center electrode insulator, spark current follows along the carbon deposits on the insulator rather than jump the gap.  This makes the cylinder NOT fire the mixture and the plug becomes wet with gas.
You can try cleaning that insulator, but you should really get the correct plugs that are more likely to self clean.

Reserve setting feeds from the bottom of the tank, if your in-tank filter is compromised, that setting is more likely to place unfiltered bits-o-stuff in the carbs that really shouldn't be there.  These bits can block the float valve open, plugs up jets, and generally make clean carbs behave like..not clean carbs.

I can only imagine what you've done to the bike to warrant #120 mains.  This size is usually the domain of some 750s?  Velocity stacks, perhaps?

Cheers,

I have Uni pods,TT. (I know you love them) . I did think they'd be un-restrictive enough to use 120's, but I did buy a set of 115's as well. I know the plug chop thing is next to come up, but my failure to realize that I needed a kill switch to do that has left me without one; which I will rectify soon.

In the meantime, I just want the thing to start. How about filling the tank with gas (so I'm not using reserve), putting the 115's in and the D7EA's? Before this problem popped up, the bike wouldn't start with the choke fully on, which would point towards a too-rich condition, I guess?

[TwoTired]

The fuel metering is not the sole dominion of the main jet.  There is also the slow jet and the slide needles to factor with carb jetting.
Roughly speaking:
Main jet is dominant at 3/4 to WOT.
Slide needles from 1/4 to 3/4
Slow jet, idle to about 1/4 position.

You have mechanical slide carbs, which means you position the slides directly with the twist grip.  And, that sets the dominant fuel metering device in the carb.

Choke application deepens carb throat vacuum, which draws more fuel from whatever dominant fuel metering device you have selected with the twist grip. (possibly all of them)  Temperature plays a large factor with choke requirements, too.  Cold days need more choke, longer than hot days.

Cheers,

[333]

For future reference, and just so we're clear.  A change of plug will not "cure" a jetting problem.  The wrong plug will look like it has a problem, and may contribute to a problem, such as in this case.  But, if you are running rich, changing to a hotter plug will only make the plug look better, if that.  The bike will still be running rich.