tryna' learn from the jetting/plug reading master class...
Been holding off posting on this thread until I could do some adjusting and riding on my own to try to understand decision making on jetting without constant feedback. Instead of making a change, riding it, pulling plug, taking photo and posting here for advice.. I am really trying to understand how everything relates and why to make different changes by using the plug symptoms, feel and sound to make educated guesses instead of shooting in the dark. Plus it was raining for half a week when the atomizer came, then once it stopped raining it was cold as all hell here for riding (34 feels like 24) on the few days I had some time free to mess with this so I didn't really have much time to do it all at once.. instead made incremental changes over the past week or so and sat on them and thought about them for a few days before making another change.
First thing I did was switch to Jack's suggested 120/BE5/125 MJ stack and the 48/160 idle. Ran fast, but hot and sputtered a bit quarter to half throttle. I thought it was rich, but decided to go up to be safe and make sure it got worse going up before going down. 128 MJ got better was almost clean in 2nd from crawl to wot but temps were still hovering around 300F on mid throttle city streets. So I went to 130MJ and it still felt clean and strong with only the small four stroking/stutter in the first 1/8-1/4 throttle. Temps seemed to come down to around 250 mid throttle. At this point I said f' it im gonna keep going up until the bogging starts happening in 2nd from crawl to wot. Bogging started happening on a 135 mj so I figure this is my upper limit of too rich MJ. I believe my target MJ is a 130, but stuck a 132 in just to be on the safer side (as this 132 still runs clean).
Then I went on a higher speed run in 4th to see what the upper limit of the temps do. I am very clearly seeing the CHT get cooler when I give it gas and rise slightly before coming down when let off gas. I did notice that holding WOT the CHT seemed to still be slowly climbing over 300F and didn't look like it wanted to stop, so I backed off and went back to garage to think about it.
Pulled plug and checked at this point. Plug looks chocolate, but a bit dark still. (first photo attached below). I had checked the plug at each change of MJ and even at the leanest 125 it still looked a bit dark. So I went back to the conversation in my thread from about a year ago where we discussed how to read a spark plug for various symptoms. I was wondering if maybe my B9ES plug was too cold and the reason why the plug looked too dark even at what seems to be the ideal MJ. I had been looking for that demarcation line on the grounding electrode for the edge of dark to light burn mark right at the middle of the bend (just as the image Ginch posted a year ago and is shown below:
My plug didn't look clearly distinguished at the middle of the bend like that. So that was another clue that maybe I needed to go next hottest plug, in order to burn off more fuel on the ground electrode to the correct point on the bend.
So a few days later, I swapped a slightly used B8ES plug in to get the next hotter heat range and run it around for a few miles on the same 132 MJ and see how it changed the plug color. This is where the plug started looking the correct tan/lightly charred marshmallow color, and now I could see the clearly demarcated line on the bend of the ground electrode right at the middle of the bend.
Sat on it for a few days with a couple miles here and there to decide how I felt about the jetting/etc and keep looking at the plug as more miles put on it. Didn't get much miles on cause it was freezing. But while I was sitting inside due to the cold, thinking about the plug, I started wondering if maybe my ignition timing is still not set at the "correct" timing, but just set at a generic suggested timing based on someone elses correct timing for their exact setup, which is close to mine, but not exactly ideal for mine. So I figured I needed to work on finding the correct ignition timing for my specific setup first. I also remembered from that same discussion on my thread a year ago that the center electrode should have a crusty fuel film going from the ceramic center up to about 1mm from the tip of the center electrode. My plug never seems to have that crust line, but just seems smooth dark from top to bottom, with only the slightest white/tan line right around the corner of the tip of center electrode. So I started wondering if maybe my ignition is too retarded and needs to be advanced a little bit at a time to burn off some of that dark fuel on the center electrode tip, hopefully opening up that thin white/tan line only around the hard cornered edge of the top of electrode into a wider 1mm thick clean tip.
Today was the first time I was able to get back out with warmer weather and start messing with it. So I advanced my timing 1 more degree from 23 to 24.. which would make my variable timing 24 to 20 (idle to 7000 rpm). I do not want to go too far advanced as I don't want to start destroying the piston from detonation.. so I only went that one degree more advanced to do a run. Didn't hear any obvious pinging or detonation noises after a quick run, nor did I see any signs of detonation on the plug when I pulled it after that. So I decided to go for another 20-30 mile drive on it with the new B8ES plug, 24 degree timing and 132 MJ combination. It runs great as is, feels strong all the way up to wot (just a little 4 stroking or stuttering in the first 1/8-1/4 throttle). Temps for the CHT would go down with gas, slowly climb up to 300 if held at mid to high throttle with high rpms, but would come down with quick WOT pulses. Temps would go slightly over 300 to maybe 325 if I let off gas at high rpm or if i held wot for over 15 seconds.. so I think the temps are still a bit off from being able to hold wot for days on highway.
Pulled the plug after that long run on 24 degree ignition and the plug looks so much better. Still not seeing the ideal crusty center electrode with 1mm thick clean tip at the end. This makes me wonder if I should go more advanced, or more retarded with the ignition. I'm just not sure if the crusty tip symptom only comes after many miles of riding, or if it should be showing up within 20 miles of hard riding all over the throttle range. Any advice?
My inclination is to think that I could go maybe 1 degree more advanced with timing.. and my mj could go down to 130 or maybe even 128MJ. The trick is how to keep that WOT temp from wanting to keep climbing instead of stopping at the upper limit. I feel like I need to continue down this path of figuring out the correct ignition timing, before progressing any further with the MJ stack.
As mentioned.. first photo below is on the colder plug, 132 MJ stack and 23 degree ignition. All other photos below are on the B8ES hotter plug, 132MJ and 24 degree ignition.
B9ES, 120/BE5/132MJ, 23-19 ignition (idle-7000rpm)
B8ES, 120/BE5/132MJ, 24-20 ignition (idle-7000rpm)
1 point hotter spark plug and now I get the burn line on grounding electrode to the middle of the bend as desired.