Bonneville America Forums Forums Technical Forums Performance Mods Plug color discussion

I just installed the Freak, and I'm happy with it, but I am still experimenting. I have put on about 150 miles with the Freak and new plugs. Last night I pulled the plugs and they are almost white, with only the faintest sign of grey residue. I know, I'm running a bit lean. I am running 150s based on some comments of BikerThug, who had at that time a very similar setup to mine. I'll probably try the 160's soon.

So here is what I am thinking:
Most of the time I am riding around at under 4000 rpm, boulevard and highway cruising. But, say I am accelerating away from a full stop. I hit 2nd or 3rd gear and whack the throttle. At around 3500 to 4500 I can feel a surge of power where the mains really start to kick in. So that tells me that the mains aren't really being used except when I am really romping on it, or on the highway at high, mainly extra-legal speeds. So, the question is, how much do the low speed and mid-range carb circuits figure into plug color? I have seen instructions where you whack the throttle wide open, run up to red line, and then immediately shutdown and pull the plugs for a color check. Will the plug residue burn off with additional, normal riding? I have never been able to get the desirable, light brown plug color. My plugs have always had only a light grey color, and I have tried a large range of jets. That was before the Freak. Now I'm starting the process over again. I think plug color depends somewhat on riding style, gas additives, ethanol content, etc. Maybe I am just overthinking this.

Any comments?

Cody

Around 3600 or a bit faster is where you transition from the pilots to the main jets when the engine is under load. So, run it a bit on the road holding the engine speed around 2500 and check the plugs. I'm thinking that is where you are running extra lean. If so, a little bigger pilot jets and maybe Thunderbird Spot needles with a shim or two should help.
Unless you are able to hold a fairly constant speed for a couple hundred miles, you won't build up any significant deposits on the plugs, and slowing the bike with the engine running can give you a false reading. That's why you will constantly be told to disengage the clutch and kill the engine first, then stop. Even then, your best place to look is deep inside the plug where the ceramic is in contact with the metal base. That's where the ceramic runs coolest and deposits will condense more.

So how long do you think someone should run at 2500 rpm before cutting it? 5 min? A mile or two? I'm gonna have a hard time finding that stretch of road!!

Greybeard,
Thanks for the feedback. I agree with your prognosis. I'm already running 45 pilots. I tried 48s for a while but it just felt like it was sloshing. I'm thinking the TBS needles and maybe a shim would fatten up my midrange. (not to be confused with fattening up my middle, I don't need more of that!)

Cody

these are aluminum heads tho so puling the plugs right away is bad no?

Frank

If the low speed mix is off either way, you could have the same effect. Something I have seen a couple of times is that the mixture can be so rich as to wash the plug clean and look extra lean. I really doubt this could happen with these bikes though, at least not without making huge amounts of black smoke.

Hey Cody,

This was posted in another thread recently, but I don't know if you saw it or not.



It's a good little graph that helps explain where and when everything functions on our carbs. It comes from this article on CVK carbs, which is a good primer for tuning our carbs. As you can see, and others have said, it sounds like your problem is down low with the pilot jets and needles.

Quote:

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I like to go at least 20 minutes to soot up/burn clean the plugs.

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I can probably find a stretch of road to go down for a while in 5th at a reasonable speed. Thing is cutting the engine and pulling over... Yikes! Also, how does one pull the plugs on a hot engine?

very carefully!!

no kidding!! Seriously tho, any danger to the threads? How bout the whole burnt hand thing?

I've been checking mine quite a bit lately as I dial in my carbs and have had no problems, I just don't use gorilla strength when tightening.Once I break it loose I take the ratchet off but leave the socket on the plug.this removes my hands slightly from the heat of the engine.A thin pair of leather work gloves helps also.Don't forget mind control,you know, like walking on hot coals!!

Here's another hint. Wrap a bit of 1" masking tape around the top of the socket. Gives you just enough friction so it won't slip.