Read Dan's Spark Plug

[Dandy Dan]

Hey all you experts out there (Jimthejet, Chanito etc), I just thought I'd post a pic of my plug so you guys could tell me how I'm running. I've never read a spark plug before but my initial thought is that I'm running somewhere between good to lean. I pulled this plug after 15min of top speed riding.



Thanks!

[chanito]

;D Hey it looks great, i would like to see the fire ring, that is what we used to call the very tip of the center electrode, it is usually a different color because that tip gets a lot hotter than the rest, just take a picture from the side with good illumination so that the center electrode can be seen good, maybe jimthejet can help us more but my first look is that you are right in the ballpark, there is not hot specks (little black dots) so i do not think you are lean, the brown color is even and dry, so you have a complete combustion, they sure put additives on the gas over there, you can tell because of the deep tan color ;D ;D

[Dandy Dan]

I won't have a chance to pull it again until monday but I'll do it then. Thanks for your input.

[jimthejet]

:)Looking good, Dan! Chanito is right. It will also be interesting to see how it looks at other throttle settings, (1/4, 1/2, 3/4). You will no doubt see a difference especially at 1/4 throttle, since we can't get various size pilot jets or needle jets / jet needles (why we have to shim, and clip diaphragm springs).

You can pull the plug after only 1/2 mile and see a color change. Just be sure to chop the throttle, kill the ignition (kill switch, and don't coast to a stop.

Here are a couple of links to rudimentary spark plug reading examples.

www.autolite.com/tech/PlugTips.pdf
www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp?nav=31200&country=US

[bluesmokeracing]

oh yeah, u do know the little flap on the floorboard comes out next to the gas flap to access the spark plug? i stumbled upon that taking the floorboard off to jet the carb and would've been real ticked off to find out that flap comes off instead of the whole floor. just askin' havent seen anything about it on the forum

[Dandy Dan]

Yeah that's how I did it. I read it in the owners manual I think. It is a bit awkward though to pull the wire off of the plug. Still way easier though than taking the floorboard off.

[Dandy Dan]

Just a question before I really start to dial my carb in next week. (I'm really busy with exams until wednesday.). Could someone please clarify the relationship between RPMs, throttle position and the diaphram (thus needle height). JimtheJet posted about how I should pull the plug at 1/4, 1/2 etc throttle but doesn't RPM have something to do with it so 1/4 throttle down hill (high RPMs) could run different than 1/4 uphill (low RPMs). The variator system makes this even more difficult because your RPMs aren't directly related to speed.

Anyways, here's what I think: the diaphram moves via airpressure which is controlled by both the throttle position (permits high flows) and the RPMs (sucks high flows through) so if you adjust the carb to work good at 1/4 throttle but you were testing it on an uphill run it may not run properly with 1/4 throttle downhill etc. For this reason the best way to dial it in would be to find a nice flat stretch and test the Ruckus at speeds in increments of 10mph or so. Can anyone think of a better way? Right now I know I'm lean on the low end and midrange so I'm gonna add a shim back and see what happens. I wish I had a tach...

[sfc]

Dan,

They usually refer to throttle position because it is the easiest reference point but what it really has to do with is the position of the, in your case, butterfly valve. Just pick a groove on your grip and see how far it travels when you go from idle to WOT and then do the math to get you to 1/2 and 1/4.

Typically you don't begin accessing the main circuit until you are past a 1/4 throttle, though that is in theory in reality changing the main will affect the pilot circuit and, more importantly, vice-versa. I have found almost a 1:1 size such that when I increase the pilot by one size I decrease the main by one size.

In speaking with Jason, the ruckus supposedly likes to run lean.

[chanito]

Yes 1/4 downhill is diferent from 1/4 up hill, ideally you want a long straight with a slight uphill and try to keep a constant rpm, then stop and pull the plug, doing it this way is so unreliable, that is why installing an oxigen sensor and a tach is the only reliable way to set this carb, the reason the ruckus and most 4 cycle scooters like lean mixture, is the very tight u turn the intake track have to make (it tries to separate the gas from the air) so if we can install a carb facing forward and between our legs we should be able to get more bung from our gas, but that is why having fuel injection make so much sense (the gas is injected right on top of the intake valves) avoiding this separation problem altogether, there my two cents

[jimthejet]

;D Dan, I agree with your analysis, and the other comments as well. The constantly variable transmission is what makes a throttle setting unreliable, and the butterfly opening is just the beginning of the chain of events in a diaphragm carb. Even with the same butterfly opening you are going to realize different pressures in the carb as a result of loading differences (hills, wind changes, etc.) causing rpm and back pressure variances.

All that being said, if you do it on a flat and hold the rpm as steady as you can, you will get a reasonable color indication on your spark plug. You probably will find, as I did, that if you get the main jet and transition to it (by shimming the needle) correct, which you certainly already have done, your transition from the pilot to the needle is too rich. Unfortunately, the needle jets and jet needles aren't available to dial it in.

And, if you create a larger pilot jet (ream out a stocker), you will be too rich on the bottom end, and it won't idle correctly. A slide needle carb with available replacement jets would be easier to tune.

[chanito]

;D ;D Jimthejet knows!

[Dandy Dan]

hmm...lots to think about. I actually do have access to a wide band oxygen sensor. I've just been a little hesitant about using it because it means drilling a hole in my exhaust which I'll then need to fill somehow (perhaps I could weld it but I'd have to take it to a shop).

When I finally get a tach I could borrow the sensor too and just dial it in. What do you recommend for an ideal air/fuel ratio. I've heard 14.7:1 is max fuel economy but max power occurs at 12.5:1 or something like that which sounds potentially wrong to me because I thought slightly lean was faster than slightly rich.

[jimthejet]

Dan, you heard right about the 12.5 to 1 being max power as opposed the stoichiometric ratio of 14.7 to 1, which is best for emissions. I'd shoot for 12.7-13.1 to 1 at WOT.

[Dandy Dan]

;D It'll be a bit before I get it totally dialed but that's what I'll go for.

[chanito]

You guys need to read some of the boring stuff i read on my free time, those number are not absolute actually at wide open throttle you want to run a little lean, and during acceleration you want to have the slightly rich condition, load put a lot of strain on an engine and therefore it need to run rich, but once you get to a top speed running lean allows the combustion chamber to run a little hotter and clean itself and the valves from carbon and other chemicals who attach itself to the combustion chamber I guess later i will need to run an extensive post about this mixture mystery, but that number is not accurate anymore, the nice people at Audi have gotten the engines in their Le Mans winning engine to run (accelerate better) better at the high 13 to one mixture ratio

[jimthejet]

;D Thanks for the update, Chanito! Progress is being made using the program mapping for fuel delivery. I could tell some stories on how it used for fooling emissions testing, too.

[Dandy Dan]

This is off topic but I enlarged the air bleed hole that is in the bottom of the carb slider today (next to the needle). I didn't enlarge it much as this is a very sensitive adjustment...I made the diameter perhaps 20% larger. Anyways, I needed to add another shim on the needle to get a bit more gas flowing as the slider rises but there was a small but definite improvement in 0-5mph accel. Here's a top view pic of a stock slider that I stole for battlescooter.com. The yellow arrow is the hole I enlarged the the red arrow is where the needle goes.

[Dandy Dan]

jimthejet said:

You probably will find, as I did, that if you get the main jet and transition to it (by shimming the needle) correct, which you certainly already have done, your transition from the pilot to the needle is too rich. Unfortunately, the needle jets and jet needles aren't available to dial it in.

And, if you create a larger pilot jet (ream out a stocker), you will be too rich on the bottom end, and it won't idle correctly. A slide needle carb with available replacement jets would be easier to tune.

Here's what I think my carb is doing right now.

1) Off the line: As soon as I twist the throttle the motor sits there for a second, almost as if there is a delay in the throttle cable opening the butterfy. I'm guessing this is a lean scenario as the gas needs a second to catch up with the air that's rushing in. I'll add a bit more shim to see what this does. This was a problem both before and after I slightly enlarged the air bleed hole.

2) 1-5mph: The engine hauls. The opened up air bleed hole helps but even before that I had strong accel. because the mix is pretty good and the aftermarket variator etc. has me geared nicely. I can actually spin the rear wheel on gravel up a slight incline with no front brakes.

3) 5-30mph: The acceleration is moderate. It runs fine but not great. I think I end up a bit lean cuz the rpm's still aren't high enough to restrict airflow so I'm getting a lot of air. I think my power actually slowly rises and it feels like 20-25mph has faster accel than 10-15mph.

4) 30+mph: It runs pretty good. I can sustain pretty respectable speeds even up small/medium hills. The 90 main jet is working well but I may try the 95 for kicks when I have the chance.

Solution??? I think I need a bit more shim to help the off the line stutter or perhaps I should increase my pilot jet by one size and drop the main by one. I'm not really sure how to cure the 5-30mph bit because a bigger main may mess my top end up and more shim won't help at those speeds I think. One way to do it would be to wire in that toggle switch for the enrichment valve. I could run with the valve open up to 30mph or so and then shut it which would permit me to run a larger main for more midrange fuel and no change up top. Even if I kept it shut all the time I'd be richer in the midrange cuz I could run a bigger main with no effect on top speed air/fuel ratios.

Your thoughts?

[jimthejet]

My guess, and it is only that, is that you are lean, as you believe, off idle and up to 1/2 throttle. I say this assuming you have increased airflow at low rpms from reduced restriction (lawnmower filter, etc.) but have not replaced the pilot jet. You can ream out a stock pilot jet and it will help the condition.

I don't believe that the main jet will affect this at all unless you go way (2 or 3 sizes) over where you are now. I wouldn't change it, and you can confirm that by ******** your plug reading at WOT.

I think your air bleed experiment is promising, and cutting coils may be as well. I don't believe shimming the needle will help you. The taper of the needle will richen up the midrange quickly if you shim it much.
I wouldn't do anything with it other than fine tuning using small increments.

Don't bother with trying to ream out a needle jet. It already flows very well and only needs a different taper needle to be optimized (too bad we can't get one!).

I hope this helps!

[ZoomZoom]

I just found this site that has good pictures and some good info.
www.dragstuff.com/techarticles/how-to-read-plugs.html