Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Location: London UK
Plug mid throttle on new ac attached.
Since these photos, I've tried 108/be3/130 and it runs just as good with no stutter. Gonna leave it as is and tweak the af screw now.
Cm22, it idles a little high in the video because i didn't touch the af screw or idle screw after changing the ac.. just left it same. It won't take much to reset the idle a little lower. Was just being lazy and wanted to see how it ran as soon as i finished drilling the new ac.
You are inhuman. I have no idea how you can tell all that from that video. Hopefully i can some day. Seriously 10% more power and i might crap myself at top speed!
Would certainly seem like it's getting there. Pilot is too lean, so is the main. Timing is low as well. What's the next level after holy crap? At least 10% more power to come yet. 132 main and 52/140 pilot. Timing up a couple of degrees too.
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Location: So Cal
Joined: 19 Jun 2007
I've held off on updating this thread for the past 2-3 weeks because I realize I post too much with minor incremental updates, so instead I've been doing a lot of experimenting with jetting and timing on my own while pestering Jack over PM with questions to confirm my own decision making.
I finally feel like I have some basic grasp on how to jet and time these damn things. Insane amount of work with random guesses for the past two years, but the last 2 weeks have been very deliberate and intentional now that the si jet system has started to click in my head. The last frontier was timing which was a mystery to me until the past two weeks where that also started to click.
Down to the nitty gritty... past year or more of having jetting issues came down to one major thing set wrong.. ignition timing. I had been setting it to the default 21-24 degrees at the vape T mark which works out to 17-20 degrees @6000 and 14-17@8000 rpm. This is just too much advance for my top end. What it ended up doing was forcing me to go really rich on the main to try to cool the piston and cylinder down at wot. So this cascaded into way too lean idle to get the jetting to feel right throughout the throttle range. I spent months working on every iteration of idle and mj stack and got it real close many times where the temps were close to 300f or less at any throttle range below wot, but temps would keep climbing over 300F towards 400F at wot.
The main temperature response I have been seeing for months is one where half-3/4 throttle looks great on the CHT at 250-300F. Give it full throttle and CHT immediately jumps to 350-375F for 15 seconds +/- then would drop rapidly to 250F where it would then slowly start its climb from 250-350/400F even at really big mj. What I've come to understand regarding this symptom is one that Jack has been mentioning all along.. way overly rich MJ causes temps to get hot because unspent extra fuel from being too rich fills the free space in the squish causing compression to get really high and hence temps get hotter. I was thrown off by this because I assumed the hot bump prior to the cool was normal, and the immediate cool drop after 15 seconds was telling me my mj was good. This is obviously not true. I was at or around 100/be3/128MJ for the past week or two trying to figure out how to get the temps to stop climbing slowly. But I'll get back to this overly rich main jet because this leads me back into the ignition timing knowledge that has started to click in my head over the past two weeks.
I had been thinking I needed to go way more retarded timing for a month or so, but every suggestion was to stay around 18 degrees at 6-8000 rpm. Something Patrick had detailed in one of his CHT/EGT posts in the past had started coming back to mind in my head over the past few months... ignition timing is a seesaw between CHT and EGT, and the goal is to find the right timing to balance them both out and keep one from getting too hot while the other is too cold. Going back 6 months or so ago and prior, I had never really been able to register EGT temps on my gauge except few rare occasions of lugging it, but my CHT temps were always up high. This should have been obvious as a symptom the timing was too advanced, but hey, I didn't fully understand it at the time and the past 6 months of struggling with it really allowed me to digest the information and understand it. The other symptom which should have also tipped me off the ignition timing was too advanced, but at the time I was assuming was a jetting issue was the fact that I could never see the clean ring on the tip of the center electrode with tan carbon deposit below it on the center electrode. I figured this was a jetting issue, but in fact was a second clue the timing was off. What I've come to realize was my overly advanced timing was burning off all the carbon deposit on the center electrode leaving it clean, because the timing was making the piston and head too hot.. which also relates to going extra rich on the main trying to combat it for cooling. Over the last few months that clean center electrode was sticking out in my mind and started to make sense regarding too much advance on timing. So I tried going a little lower to 20 degrees at the T mark (16 degrees @ 6000). This is where I finally started seeing the beginnings of carbon deposit on the center electrode. But I was still hesitant to keep going more retarded with timing because all advice was telling me not to go too retarded. This is where I mentioned it to Jack and he said I was good to try going all the way down to 10 degrees @ 8000, and that his o-tuned P200 was set to around 10 degrees @ 8000 due to the tight squish.
This is where all this information really started clicking for me and feeling a little more confident in my own decision-making regarding jetting and timing. With the confirmation from Jack that my hunch over the past few months was valid, I jumped into really making changes with the timing, specifically going way more retarded than what most have been suggesting. I felt I had some wiggle room to do this because my EGT temps are consistently low and CHT temps are consistently high. So I went down 1 degree at a time over a couple days starting from my original 23@T (19@6000). I ended up at 17 degrees @ T mark (13@6000/10@8000) as jack had said was my low end safe limit. At this point, I could really start to see the CHT temps get closer to the target 300F and at the same time could see the tan carbon deposit on the center electrode getting closer to the tip of electrode, but was still a bit thick of a ring for what I think was suggested.
Today I really focused on not being afraid to make these changes with jetting and timing in attempt to finally getting it close. I walked my timing down from 18 to 16@T (12@6000/9@8000). This timing change made a huge difference, and I was seeing the temp responses I was supposed to see. One, the CHT was way more stable at much closer to 300 even in 4th gear at wot. Two, the EGT temps were finally registering regularly at approximately even with the CHT temps on the gauge, well within the middle safe range for both that I've marked on the gauge based on what Patrick had suggested in his post. But I still had that pesky Hot bump, fast cool drop and slow climb over 350F.
I then revisited the jetting which is where I'll finally get back to where it all actually clicks for me and I no longer feel like I'm just taking stabs in the dark. I was at around 100/be3/128 mj with more stable lower temps, but the same strange temp responses at wot. So I figured my hunches regarding that hot bump, cool drop and hot climb were symptoms of what Jack has always mentioned.. too rich mj causing over compression and heat. So I said F it, and made a huge jump down from 100/be3/128 to 100/be3/120 while also switching from 48/140 to the target 52/140 idle in order to compensate for the drastic leaning out of the main jet. Things woke up here and temps in fact started to get colder! The bump, dip climb actually reduced quite a bit, but still had the slow climb. So I walked it down to 118, and 116 mj while doing a long hard 4th gear wot run for each and checking the plug. To my amazement, the plug never looked lean on 120, 118 and 116. The plug only started to look more correct chocolate/tan with every drop in size.
My last two changes for today which I felt was probably the final large broad stroke change to both jetting and timing, was first to inch my timing 0.5 degrees more retarded (because my temps were holding stable at around 325 and my plug center electrode still had a slightly thicker clean ring on it than I would like). I felt this would be just enough to get that tan carbon deposit on the center electrode just a bit below the tip with the thinnest clean ring at the top. Second and last change was to drop from 116mj to 115 as I still felt my temps were climbing slowly high at their most stable point. Plus the plug color still looked like it had a point or two of wiggle room in terms of darkness.
This is where I finally saw the temps really stay cool around 225-250F at everything but full throttle. in 4th at WOT temps are nearly perfect at 300F with maybe the most ever so slight climb up closer to 320F but so imperceptible I am probably imagining it. I also no longer see that hot bump, fast cool dip. Finally I see exactly the temperature responses that Patrick and Jack have described all along, and thrashed it pretty hard all over the throttle range to confirm the temps really never get over 300-320F at all. Temps are so much more stable and controllable now!
Here is the plug after long hard 4th gear wot run at 100/be3/122 with timing set to 17@T mark (13@6000/10@8000) which shows the clean ring on center electrode being a bit too thick and far down from tip. But at least I could finally see the carbon deposit below the clean ring. This is where I knew I was headed in the right direction with timing.
100/be3/122 mj timing set to 10@8000
100/be3/122 mj timing set to 10@8000
And attached below is the plug after a long hard wot run at 100/be3/115 mj where I am confident this is the end of broad strokes adjustments. Now that everything clicks and Im finally on the home stretch with jetting and timing this stupid project, I have to fine tune the middle rpm range, which is ALMOST perfect, but still has a slight bit of dirtiness for a split second at the 3/4 throttle range. I'm going to do some tweaks to the air mix screw (which is currently 3 full turns out on a 52/140 idle) and possibly go to 114 mj if the air mix screw adjustments don't clear up that dirtiness. If neither of those work, then i'll experiment with the various atomizers.
Now I know some of you may be thinking "That's way too retarded timing!!" Well, the proof is in the pudding on my CHT and EGT readings at all throttle ranges. I suspect my timing would have been closer to 19@T mark (15@6000/12@8000) prior to skimming the head and reducing the squish, back when the squish was around 1.3mm. But skimming the head to have a tight squish of 0.8mm really demanded drastically retarded timing!
Those gauges were indispensable in dialing in the jetting and timing because without them I was convinced I was correct many times prior if not for those gauges telling me the wot temps would keep climbing until it seized. The EGT gauge also was indispensable in confidently knowing this drastic retarded timing was not too much.. as I can confirm the EGT never gets into the danger zone!
Pulls like a train in all gears at all rpms, sounds like a huge chainsaw and wicked fast.. all while maintaining cool temps! Funny enough.. my current jetting is approximately equivalent to what I felt was the correct jetting on much larger 120 AC. So I guess that says something when the same a/f ratio at two different stacks results in the same seemingly correct setup. The main difference is I don't need as much fuel now to run right, and its staying cooler with the much smaller stack. 120/be3/138-135 == 100/be3/115.
current carb specs:
3 turns a/f screw
Variable timing settings:
15.5 degrees on the vape magneto T mark
14 degrees @ idle
16.2 degrees @ 4000 rpm
11.5 degrees @ 6000 rpm
8.5 degrees @ 8000 rpm
Looking at the timing in this way makes me realize it isn't as retarded as it seems based on the T mark and 6-8000 rpm figures.. in reality its 1-2 degrees more retarded than a static ignition based on its most advanced point in the variable curve @4000 rpm. So this would essentially be the alternative method of setting timing on the vape variable ignition. Instead of choosing a target rpm for your desired timing, set the target timing @ the most advanced point in the variable curve.. or 4000rpm.
that clean ring is much closer to the tip of electrode. 115mj 8.5 degrees @ 8000 rpm
And plug is still dark chocolate tan even after going 13 points leaner!
115mj 8.5 degrees @ 8000 rpm
I'm beyond broad jetting for casual city driving now (this thing is stable at any ride around town) and onto fine tuning the meeting for punishing long wot rides in the heat of Florida.
I ran 75 miles up to my sister's this weekend and back down route 1 along the coast where half of route 1 is desolate with no lights and high speed limit. I was holding wot in 4th for over 5 miles. Temps still a bit hot at that usage with around 325-350f if pegged at wot for miles. But it's easily controllable with slight reduction of throttle to hold at 3/4 or less. Temps stay around 300-315f.
My jetting and timing for that run was 120/be1/122 and 52/140 idle at 2 turns out. Timing is low.. set to basically 13.7 degrees if it were static. But on the vape curve it's at 13 on the t Mark, 13.7 at 4000 and 6 at 9000.
Plug was still looking rich at main on that run. Jack was suggesting because i didn't remove the squish ring on the plug while I'm using the cht ring, that might be the cause for the extra heat at wot. I know the main is cooling cause pulsing wot when lower rpms causes temps to go down fast, plug the plug when pulled after miles at wot still looks rich.
So the last day and a half around town I've been walking my main down leaner trying to find the point where the wot plug starts to look lean, just to find the leanest point that i should not go below. Still haven't gotten there yet.
I'm at 120/be4/116 mj and the plug looks good, but still not lean. I'm at a point where I'm trying to figure out if the plug still looks good because the idle might be one size too rich (long idling plug looks black and fouled), causing the main to get leaner than it needs to be? The other thing I'm contemplating currently is if the main can go so lean because the timing is so retarded, but the center electrode carbon deposit looks correct and if i go any more advanced, that clean ring at the tip will only get bigger.. too clean and too advanced.
This thing runs like a beast now, but a side effect of low timing is my max speed is now closer to 65 maybe up to 70 slowly over miles of wot pegging on flat ground. I'm fine with that max speed as long as that timing allows the cht readings to stay within target forever at wot.
I'll go get video and hopefully clean audio now cause this thing sounds and runs great with torque everywhere!
Plug/piston wash photos below are after 1 mile pegged at wot in 4th gear and engine cut off at speed.
13.7 ignition timing.
13.7 degree timing still leaves a 1-1.5mm clean ring at the tip
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Hey you are working on some impressive upgrades! So jealous of that mill...and I expect a youtube series of vespa related milling projects to follow! I need more content to learn how to do more stuff I don't need to know, but just can't help myself from learning
Man - I need to get my scoot back on the road.
Still experimenting like crazy with jetting and timing combinations trying to find just the perfect setup as I'm close but not happy with it.
But I have started to notice things feel a little more rattly either in the front fork or in the engine. I changed gearbox oil today thinking maybe something was going wrong with the gearbox. Its been about 500-700 miles since my last gearbox oil change. That last one was the first one since I rebuilt the engine, and when I pulled the magnetic drain plug that first gearbox oil change there was a decent amount of metal flakes stuck to the magnet. I assumed that possibly it was leftover shavings that were never blown out of the cases from grinding/porting, or because I never cleaned up and tapped all the threads after cases were blasted. I put it out of mind until today. Pulled drain plug to change gearbox oil again and lo and behold.. magnetic drain plug is full of metal flakes again after approximately 5-700miles.
Is this normal wear and tear or should I be concerned about possibly damage going on inside the cases?
Gearbox oil looks clean and is about 200ml removed which I assume the rest is lost through clutch cover vent as my cases are crazy dirty already.
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