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Premium Member
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Discussion Starter #1
I've seen a few posts from folks regarding using the Colortune plug to analyze their combustion, and I'm considering buying one. I'm curious -

  1. if you have one, was it worth the purchase
  2. If the Colortune plug shows a blue burn, would that be the correct air/fuel mixure to eliminate the backfire, but yet be hot enough to cause engine problems?
  3. If you no longer need it, would you be interested in selling it?
 

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Premium Member
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I believe "kanuck69" uses or used one; if he doesn't show up here shoot him a PM and he'll probably share some info. ;)
 

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It is not the really the fuel mixture that causes the "backfire"..and here I am guessing you mean the de-accelleration "popping" , not true backfiring.

The popping is caused by the "clean air" system which introduces fresh air to the exhaust port. Blocking or removing this system can help to eliminate this, but I doubt jetting alone would.

But real backfiring, which is not a "popping" sound but more like a large bore gun going off, IS a result of improper mixture.

You did not say if your bike has a diffrent intake, e.g. an "earshave" , or other possible carb problems, so I am unsure why you believe rejetting is a solution unless you have altered other systems on the bike.

The colortune plug is usefull for those building a bike from scratch or if they heavily modify the engine. Or they simply do not know how to read a spark plug.

Enough folks here have done an earshave so jetting reccomendations that seem to work are available without buying anything.


KM
 

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Discussion Starter #4
I haven't done an earshave. All ive done so far is plug the reed valves, and turn the air mix screw. The popping has since stopped.

I'm trying to understand the relationship between the turning the air mix screw, the burn in the cylinder(viewed with the colortune), and the popping.
 

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All ive done so far is plug the reed valves, and turn the air mix screw. The popping has since stopped.

I'm trying to understand the relationship between the turning the air mix screw, the burn in the cylinder(viewed with the colortune), and the popping.

Again, the popping is caused by the "clean air system" or the intake of air via the reed valves. (See my reply in your other post)


The only relationship of the "burn in the cylinders" to popping would be how much fuel goes unburned..this you will not see with a colortune.

Turning the airscrews out only adds a bit more fuel to the idle mix..which is lean from the factory to begin with. Popping gets it's fuel from open throttle...when you slow down, down shift and close the throttle fuel is still sucked in due to the engine speed not "imeadiately" slowing..the unburned fuel from this action is then ignited when the fresh air hits it coming off the reed valve.

And that is why marbling is suggested to help eliminate popping. Turning the air screws out just produces a better mixture at idle so the bike runs smoothly.



KM
 

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Discussion Starter #6 (Edited)
I guess i'm dense. As long as the crankshaft is turning, isn't a spark still being produced? So if some amount of fuel is still being sucked into the engine on downshift, why doesn't it just combust within the cylinders, instead of being passed into the pipes?

I had already plugged the hoses coming into the reed valves, and it was still popping. Tonight, i turned the screws out to 2.5 turns, and the popping on decel stopped. It's now idling around 1100 rpms, definitely smoother, and just a bit higher than just under 1000 before I turned them.

There's obviously still a part of the combustion process that I am just not understanding. I'd kind of like to understand what's going on in there, even though it's working fine.
 

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Giggity!
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Or they simply do not know how to read a spark plug.


KM
There you be! I don't trust the variance I see in the plugs & try to determine what I'm seeing. I liked the ease of being able to see what was going on in there. Yes I feel it was worth it but I like tools. A good mechanic can read plugs, I'm just a monkey with a wrench.:rockon:
 

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during the combustion stroke all the fuel is not burnt, what's left then exits the exhaust port and then its my understanding that air is introduced out of the combustion chamber, and when that air mixes with the unburnt fuel you get your popping sound. this is especially present when decelerating as the amount of air entering is greatly reduced while the amount of fuel supplied takes a second to be reduced thus causing more fuel to remain unburnt.


I guess i'm dense. As long as the crankshaft is turning, isn't a spark still being produced? So if some amount of fuel is still being sucked into the engine on downshift, why doesn't it just combust within the cylinders, instead of being passed into the pipes?

I had already plugged the hoses coming into the reed valves, and it was still popping. Tonight, i turned the screws out to 2.5 turns, and the popping on decel stopped. It's now idling around 1100 rpms, definitely smoother, and just a bit higher than just under 1000 before I turned them.

There's obviously still a part of the combustion process that I am just not understanding. I'd kind of like to understand what's going on in there, even though it's working fine.
 

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Sparky!!!
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during the combustion stroke all the fuel is not burnt, what's left then exits the exhaust port and then its my understanding that air is introduced out of the combustion chamber, and when that air mixes with the unburnt fuel you get your popping sound. this is especially present when decelerating as the amount of air entering is greatly reduced while the amount of fuel supplied takes a second to be reduced thus causing more fuel to remain unburnt.
I have to agree with every one on this one, and ryn summed it up prety darn good
 

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Discussion Starter #10 (Edited)
Ok, i follow all of that - until we get to the part where turning the screw CCW and enriching the mixture eliminates the popping. But you know what? I think I'm going to leave it at that, and just enjoy the smooth running... Thanks!
 
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