Topic: Single sooty plug...air screw?

[aperry]

I've been attempting to tune my 750K3 for pods (I know, I know, but I don't have the stock airbox, and it's a cafe build). The bike also has 4-1 with a cherry bomb muffler and a small ineffective baffle.  The system is probably about as open as it gets. 

Obviously I've been dealing with a lean condition and I've made some gradual changes to get it closer to normal.  I've recalibrated to 26mm float height, rejetted the mains to #123, dropped the clip position from default position 4 to position 5 (bottom). I have a set of #42 slow jets on order.  The air screws are about one turn out.  These are 657a carbs.

My question:  my last change was to drop the needle clip position (raise needle), and I also changed the air screws to about one turn out (I had mistakenly set them at two turns out initially). Following a ride of about 15 miles I pulled the plugs and found that number 1 was pretty sooty, whereas the other three looked pretty lean (fairly consistent among the three).  What is the likely cause of 1 cylinder looking much darker than the rest?  Should I start with the air screws?  Or is it likely that I messed something up while dropping the needle clip position?

Until yesterday, all four plugs were looking consistently lean, as expected. 

See photos below contrasting cylinder cylinders 1 and 2.

Thanks,
Aaron




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[flybox1]

under what conditions did you do your plug chop?

[aperry]

Unfortunately this wasn't really much of a "plug chop".  I did about 15 miles, 10 of which were on the highway.  Some was at WOT, but most was under 1/4 throttle.  I was just surprised at the differences in the plugs and my main question is whether the air screws alone could lead to plug color inconsistencies like this.

I suppose I should do a more precise plug chop to figure out if this is an issue with lower throttle, or a problem with the mains at WOT, or what.

Sorry, I'm pretty new at all this.  I've read several threads on jetting for pods as well as plug appearances, but I had trouble finding information that would answer this question directly. 

Thanks again,
Aaron

[lucky]

Not ready for any plug chops yet.
I would go back and see if the needles are all in the correct position and no clips fell off.

Also re check the idle jets by taking them out and looking through them.

Use compressed air to blow them out if possible when they are out.

Then put it all back together with some #115 main jets and ride it for a few days to get the mixture screws set to where there is no popping on decel and then do another plug reading. Always wait for a while after riding to pull the plugs out when it has cooled down . Use some anti seize on the threads of the spark plugs. Do not over tighten the plugs.


ALSO: Quote: "Until yesterday, all four plugs were looking consistently lean, as expected.  "

It would not be running lean unless you have air leaks.
Not with 123 mains,42 idle jets and the needles raised up one increment. Did you lower the clip to the lowest notch counting from the top???

[aperry]

Not ready for any plug chops yet.
I would go back and see if the needles are all in the correct position and no clips fell off.

Also re check the idle jets by taking them out and looking through them.

Use compressed air to blow them out if possible when they are out.

Then put it all back together with some #115 main jets and ride it for a few days to get the mixture screws set to where there is no popping on decel and then do another plug reading. Always wait for a while after riding to pull the plugs out when it has cooled down . Use some anti seize on the threads of the spark plugs. Do not over tighten the plugs.


ALSO: Quote: "Until yesterday, all four plugs were looking consistently lean, as expected.  "

It would not be running lean unless you have air leaks.
Not with 123 mains,42 idle jets and the needles raised up one increment. Did you lower the clip to the lowest notch counting from the top???

Thanks Lucky.  This is all very helpful.  For clarification, the #42 slow jets haven't arrived yet so I'm running stock #40's right now.  Also, yes, when I say "clip position 5", I'm talking about the bottom slot on the needle.  So the needle is being raised as high as possible.

From what I gather, people seem to get fairly dramatic effects just by increasing from 40 to 42, so I'm hopeful that'll move me out of the lean condition.  Most of my riding is in the lower throttle ranges, so I'm not sure if the mains are having all that much impact on my plugs.

I will start by looking at all of the slow jets that are currently installed.  I expect they're free, because I rebuilt these carbs a few months ago with a kit (that I believe included new slow jets).

Aaron

[aperry]

Thought I would follow up on this for anyone's benefit:

First, I have what seems to be a pretty good pod tuning config.  No throttle hesitation and not much popping on decel at all.  I did the "ton" (mph version) for the first time today.  I should also mention that this is my first CB, so I'd love to ride someone else's stock setup before claiming victory.  For my 750K3, I found the following pod config to work nicely:
123 mains
42 slows
one turn on the air screw
clip in bottom-most position

I have cheap pods and a Kerker muffler.  I had a cherry bomb, but I think it was too open, and *way* too loud. 

I also managed to get rid of the blackened plug and it's not running a nice dark brown.  I think it may have been a combination of leaky carb boot, and too high float level. 

Having a lot of fun on this bike now!  Few more bugs to work out, but I'm having a ton of fun on it now.

Aaron

[lucky]

Good to hear Aaron!

The main jet and idle jet seem right .

Just a little adjustment on that mixture screw could get rid of that popping on decell.
Try 1/4 turn either way and see what you get. Leave it in the new position for at least one day to decide. Unless it is very obvious.