Quick question about spark timing....

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UFS207
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Quick question about spark timing....

Post by UFS207 »

I was wondering if someone could tell me the symptoms that would most likely be experienced with overly retarded spark timing on a KDX? Would it mimic a bike that was jetted to rich?
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Post by IdahoCharley »

MY thoughts on the effect of overly retarded spark timing

1. The engine would not rev up quite as quickly.
2. Over retarded timing would also lose some of the power pulse force so the bike would have less power.
3. Don't know if the spooge factor would be increased - but I THINK it would increase.
4. The rpm point where the pipe comes into its own would change.
5. Spark plug would be darker than with more advanced timing.

Bottom Line - I think it could mimic an overly rich condition.
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Post by Bailey28 »

OVER ADVANCED:

Hard to start
revs quickly in neutral
pings under load
detonation
quick initial throttle response bottom and mid
comes on pipe sooner
slightly more bottom end torque at the expense of top end over-rev


OVER RETARDED:

easy starting
slow revving
comes on pipe later
runs hotter
smooth(er) power hit
less bottom end and mid response
bike will rev to the moon, will feel like a 125 on top

I would imagine that you could jet a little "richer" for advanced timing for safety reasons. Eric Gorr and Rich Rohrich wrote something about this a while ago.

I haven't played with the timing on the KDX, it is set in the middle between the three notches. I have found that by retarding my 04 YZ250 smoker by 1mm that it smoothed the power hit and gave me some over-rev.
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Post by IdahoCharley »

Bailey - I was thinking UFS was refering to 'overly retarded' to be BEYOND the point where the bike will have extended over-rev. If you go pass that point and pushing more fuel out the pipe would not the engine be running cooler? Just looking for information or thought process. The rest of the symtoms make sense to me.
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Post by UFS207 »

I was basically trying to determine if my KDX220 was timed correctly. The bike has been almost completely unresponsive to jetting changes and fouls a plug every few rides.

I have gone over the basics time and time again: clean carb, proper float height, properly functioning choke, new reeds, no airleaks, good main seals, clean pipes, no exhaust leaks, excellent compression (165+), properly functioning and timed KIPS, hotter plug ("7")....you name it.

The bike displays many of the characteristics mentioned above so I'm hoping I'm finally on the right track.

I will be checking the timing this weekend, I just wanted a little food for thought until I get the chance to play with it. Both of your responses have been helpful and informative. Thanks.
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Post by Bailey28 »

I have found that over advancing and over-retarding the timing resulted in both higher operating temps. I pesonally found that over-retarding caused a lack of power, so the operator was compensating by adding more throttle constantly, making the engine "work" harder to produce the same result. I'm guessing that due to a late spark lead, the engine was way less efficient. In both situations, the engine ran hotter, but not hot enough to overheat.

I posted above with the intent to provide symptoms of what may happen when the timing is moved either direction past the theoretical "0" or baseline set by Kawi at the factory. Going waaaaay past either limit line may produce very undesireable results. Someone here a while ago even stated that Gorr stated you could move the mark past the max advance line and still get good results. I has been stated in my YZ manual, that 1mm /.040" of stator plate movement is the maximum the stator plate should be moved.

I have read on the DRN board that a CDI box was built using different components that allowed the bottom end timing to be advanced significantly while the new parts "retarded" the top end enough for good over-rev. The person actually melted away the epoxy on the stocker and changed out capacitor value or something. I myself wouldn't mind learning more about this. More bottom timing advance, and more top timing retard, sounds good in theory.
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Post by IdahoCharley »

A weak ignition coil, bad spark plug wire, or bad spark plug cap can also lead to unresponsiveness to jetting changes. Good Luck on finding your problem
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Post by IdahoCharley »

Bailey - thanks for the information. I agree that advancing the ignition does lead to higher engine temperatures and the need to jet richer for the increased advance.

My experience with a sled - I retarded the ignition on my Formula III (triple cylinder triple pipe) snowmachine a few years ago and the exhaust temperature went down so I compensated with leaner jetting. My exhaust temperatures came back up but the sled did not have the horsepower to pull the clutch set-up that it perviously had done well with. This was part of the bases of my thoughts on over-retarding a two cycle engine.

P.S. The PVs on the bikes in the last ten years have negiated the need for us older riders to be looking for mopowereverywhere like we once did. :cry:
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Post by m0rie »

>|<>QBB<
Bailey28 wrote: I have read on the DRN board that a CDI box was built using different components that allowed the bottom end timing to be advanced significantly while the new parts "retarded" the top end enough for good over-rev. The person actually melted away the epoxy on the stocker and changed out capacitor value or something. I myself wouldn't mind learning more about this. More bottom timing advance, and more top timing retard, sounds good in theory.
That sounds like the CDI work that Jaguar was doing. Pretty cool stuff and seemed like it really worked well for him.
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Post by IdahoCharley »

Haven't the MX guys had 2 stage CDI advance curves for some time?

Aftermarket had some for both 2 and 4 stroke models a few years back and I read a few write-ups on the boxes. At least one had a handlebar mounted switch for switching between the two curves.

Could be wrong but I'm thinking one or more of the gasgas models has a "mud" and 'normal' ignition curve (user switchable) on one of their bike models.
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Post by m0rie »

Yeah there have been switchable ignition boxes for a while. Vortex makes one with 10 different maps that you can switch between. The gas gas models have had the option to switch between a sunshine and mud map for the last couple of years. Last year there was a handlebar switch and the 2 or so years before that the option is there you just need to run a couple of wires off the cdi and into a switch.
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Post by fuzzy »

And hear I thought the bike would just drool, and speak incoherently. :cool:
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Post by UFS207 »

Sorry to resurrect this thread but I checked my timing a couple of weeks ago and it was spot-on, exactly between the two timing marks. I also checked all the electrical connections associated with the ignition with a digital multimeter for resistance and everything was within tolerance. I just flipped my service manual open to the ignition section and went right down the line testing against every value printed...nothing was even close to being out of spec.

So....I guess I've pretty much ruled out the ignition as my problem. Only thing left is a fuel/air delivery problem and I've been down that route a million+ times. I am starting to wonder if my carb has a factory defect? Like maybe a small hair-line crack somewhere? Improperly cast/machined fuel/air passage someplace?

Anyways, as far as I can tell it's a lowspeed jetting problem. The bike will produce a nice tan colored plug on a WFO plug chop with a 142 main and stock needle in the middle clip postion. If ride normally though (mostly 1/4-1/2 throttle usage, very little beyond) I can pretty much expect a fouled plug within 100 miles or so. Plug comes out of the bike black and oily wet on every surface exposed to the combustion camber. I have gone as low as a 38 pilot and it still foul plugs and barely idles even with the idle screw wound in to the stop. It otherwise runs well, makes excellent power (3rd gear roll-on wheelies) and gets decent range to full tank but the problem is killing me.

I have pretty much run out of ideas here. I am half tempted to try a different carb. Don't suppose any of you 220 folks that have gone with the 35mm carb off the 200 would be willing to sell your 33mm stock carb?

Any help/suggestions greatly appreciated.
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Post by Bailey28 »

I'll take a stab at it here.

Make sure all of the carb vent hoses are open and the float height is set properly.

Also, go out on the air screw and possibly try a different needle taper such as a C or D taper, which starts later on the throttle position than your stock needle. This will make the 1/4- 1/2 throttle area leaner. Search for jetting, there is enough to fill the library of congress.

If you want, I have a few needles you can try. I have a few Q diameters, the stock R1174k, and a DGQ, A few N diameters, CGN, DGN, EGN, and a few M's, BEM, CCM,
and an EEL.
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Post by UFS207 »

I seriously have done all the standard checks/adjustments on the carb. The thing is spotlessly clean....I actually took a garden hose to every air/fuel passage last time I cleaned it and made sure a nice stream of pressurized water shoot out of the opposite end. The vent tubes got the same treatment. I blew it dry with compressed air and let it sit in the sun for a few hours to make sure it was dry.

The float height is set as per the manual and not binding or "water-logged" (ie it floats properly). I DID have a problem with the bike overflowing on it's kickstand but I replaced the needle-valve and polished the seat...this seemed to cure that problem.

Believe me, I know about the wealth of info on jetting at this site and many others. I printed out the jetting guide over at "Canadian Dave's JustKDX" site and have read it front to back. I understand the basic process but when it comes time to fiddle with my low-end jetting I just don't really notice a difference between a 38 pilot with the airscrew 4 turns out or a 45 pilot with the airscrew wound to the stop. This is the reason I'm starting to wonder about my particular carb....maybe I got a lemon.

I would like to try some of your needles if that is OK, don't really have anything to lose at this point since my next option is to find another carb to try. From what I've read the 220 comes with a R1173L needle. So I guess anything with a leaner taper would be worth a shot. Just let me know what you want for them if the offer still stands.
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Post by UFS207 »

Once again, sorry to resurrect this thread for the 2nd time but I have good news! The problem has been 100% fixed. Solution? Different carb. Forum member "foots" sold me his stock and basically brand-new 33mm carb off his '05 220R.

Now it idles perfectly and the lowend snap actually impressed my main riding friend with a bored & cam'd XR400R. Before the bike wouldn't really smooth out and pull unless you got into it a bit with the motor under load....say 1/8 or more throttle. It was also very prone to "4-stroking" if you held the throttle at a set position. See my above posts to get a general idea of how much I've screwed with my factory carb by the book....nothing made any real difference. I pretty much resigned myself to the fact that my bike's carb was a factory lemon with some type of casting/machining flaw and as of today I have no reason to doubt that hypothesis.

It is a completely different motorcycle now. I just can't get over how smoothly it pulls. My old setup had the power but NONE of the smoothness. I can bearly crack the throttle open in 6th gear, cruising at maybe 40 mph and get almost zero "fourstroking". So THIS is the KDX you guys talk about? I can't wait to take this thing out on a tight trail again.

It still needs some jetting work but it is CLOSE to being absolutely perfect. Just a couple of test-n-tune sessions and it will be perfect.

Anyways, thanks again foots, I was pretty much ready to sell my KDX until you sold me your carb.
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Post by bradf »

If it is a stock 33 then there is a whole bunch more fun in there that RB can unleash.
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Post by krazyinski »

thats great !! now go out and enjoy that thing, you should try it with a few mods done like 36 mm carb and head work its a real smooth customer. I bet your at your ends jacking with it and ready to ride.
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Post by UFS207 »

It is a completely stock 33mm carb.

As for RB mods: I'm so happy with the way the bike rode yesterday that I won't be messing with the motor for quite a while. On the type of trails I enjoy (and my current skill level) any more power would be wasted anyhow. It already has the standard FMF gnarly "rev" pipe, turbine core II and open airbox mods. I will probably eventually go that route but for now I'm good to go.
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Post by m0rie »

Well now that the bike runs like it was meant to you can invest the time in tuning up your skills...after you comfortable with it all there is a whole lot more that you now can do, but you've got a good basis to start with.
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