Retarding Ignition advance

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skipro3
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Post by skipro3 »

I'm convinced that spoo is unburned fuel and that if the cylinder's charge is completely vaporized then there wouldn't be any spoo. If a retarded timing results in less spoo, then it stands to reason that the fuel charge is more vapor at the ignition time than it was at the regular point of ignition. The only 2 changes I can think of with a retarded timing are what I mentioned; a delay in lighting off the charge of fuel and the level of compression. Therefore those 2 differences are resulting in the fuel charge becoming more vapor than a factory timed motor.

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Post by IdahoCharley »

I'am going to take a shot. While the fuel has to be vaporized to ignite anything that causes the fuel vapor to be more uniformly distributed within the combustion chamber - at the ignition point - will result in a better i.e. more uniform burn of the fuel charge. That is the primary reason we all have the squish adjusted. The ignition has to be timed relatively close to opitimal: to prevent detonation on the advance side of things/ and not so retarded that vapor pressure from the burn of the fuel is not wasted. You need peak combustion chamber pressure a few degrees after the piston has reached TDC.

I can expand on this reasoning but I'll let some shots be taken first!! :lol:

P.S. I think you can have areas within the combustion chamber that are relatively rich and those that are relatively lean fuel/air ratio. A uniform burn requires a fuel/air mixture within a relatively stoichiometric range. Look at the burn patterns on the piston. Outter edges where the piston is washed from the fuel inlet ports with the build-up of carbon and the changing carbon colors as it relates to the fuel burn which starts closer to the center of the combustion chamber.

Increased compression due to static compression changes will help fuel burn at lower rpms but as the rpms rise the increased positive compression effects drops.

Ignition retarded on a two stroke will put more heat into the pipe making the pipe making the pipe more effective (dynamic fuel stuffing of the chamber) at a different rpm.
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Post by Jeb »

My understanding of basically what made a two-stroke inefficient was that, while combustion products from the previous cycle are forced or "scavenged" from the cylinder with the new air/fuel charge, unfortunately the exhaust ports are also open at this time and thus a significant amount of fuel is lost . . .

so what IC states makes sense to me: if retarding the ignition makes better use of the pipe gases, then you recover some of the lost fuel.
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Post by canyncarvr »

Ignition retarded on a two stroke will put more heat into the pipe making the pipe making the pipe more effective (dynamic fuel stuffing of the chamber) at a different rpm.
DING DING DING..A RINGY DING DING DING! We have a WINNA!

AND..he is SO right, he said it twice!! :wink:

Said effectiveness and heat will reduce spoo.

I am honored to be in agreement with him before he even said it!

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Indawoods
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Post by Indawoods »

That's the point...ain't it? :hmm:
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Post by canyncarvr »

SOME have referenced other writings that indicate the point is to make a motoracer/roadcrosser run better.

In order for the pipe effect to HAVE an effect, you need to run the engine at the RPM the pipe is TUNED to.

Whether that is the result on a KDX woods-weapon is up for grabs.

You talked me into giving that whole scenario another go. My bike runs so well on the bottom end of things now, I could lose some and still be fine.

Thanks for the nudge!

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Indawoods
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Post by Indawoods »

But CC... now you have a bar to judge from! :grin:

I simply supplied supporting documentation to a thought process!!! Usually when I thow something out there.... it is dismissed. :?
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Post by Jeb »

Inda - it was a great topic to get going, great discussing and great learning. Give us some feedback on what the timing change does for you.

Watch out for them pesky phillips head screws holding the plate in place. When I finally got mine off I saw remnants of red loctite. I replaced these screws with allen-wrench type screws to make things easier next time (and because I boogered up the OEMs!)

I'm dying to try something that may possibly add to this pipe effectiveness thing (or at least change things in some fashion). At some point in time I'm going to replace the OEM exhaust advancer assy spring with one that I got as a sample from a spring company that has a slightly lower rate. That means the KIPS valve will open a little sooner than it does now . . .

'wonder what that's going to change things along the lines of what we're discussing!? May not do a lot . . . but may just get a little extra snap kicking in a little sooner which could be a plus for a 220.
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Post by canyncarvr »

Sure Jeb. 'Gonna' do this...'Gonna' do that!!

I've got a CDI from Jag that I need to get 'Gonna'd' myself.

Usually when I thow something out there.... it is dismissed.


No it's not! We just don't want your head getting to big for your hemet, is all!!

We're looking OUT for 'ya!!

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Post by IdahoCharley »

>|<>QBB<
canyncarvr wrote: I've got a CDI from Jag that I need to get 'Gonna'd' myself.
Hope you share your modified CDI experiences with us. I suspect I need not worry. :mrgreen: :rolleyes:
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Post by canyncarvr »

I resemble that remark!

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