My Mostly Suzuki AZ50 Based build... ... Is now a Let's II

[Raizer]

Put the 115mj in this morning and had a bit of time spare to go do a WOT run to plug chop, chucked a new plug and plug spanner under the seat and set off to the beach where there's a long stretch of 100k road and normally no traffic so it should be safe for my license if I hold WOT for a while along there.
Anyway as it is running pretty well (still feeling like it's lacking a touch of fuel up high though) and I'm having fun riding it I end up taking the long way to warm the engine up, I'm about 5k/3 miles away from my workshop when the engine just dies on me!
First thought was "oh f&#k I've seized it again" but the engine clearly wasn't hot and had made no odd noises like last time, it just stopped like it suddenly ran out of gas...

Would still start and idle just fine, but any touch of the gas would kill it straight away.

Remember a while back I said I'd torn the float bowl gasket and used Yamabond in it's place?



Yeap that is a nugget of Yamabond firmly blocking the main jet, which I discovered after pushing the scooter the 5k back to my shed since the only tool I had with me was the plug spanner!

Whacked a 117mj in, was out of time to go and do a plug chop, but went for a ride around the neigbourhood at least, 117mj was better again than the 115, topped out at 88k/55m at only 9100rpm but it still felt to me like it was lacking a bit of fuel when wound out, the only bigger jets I've got are 119, 120 & 122 so if I get the chance I'll stick the 120mj in tomorrow and go chop the plug!


Oh and the horrible vibration it's always had at high speed is completely gone now, pretty sure adding the spacer to hold the rear wheel in place has solved it lol.

[Lucass2T]

Don't use any sealants near carbs!
Haha you must have cursed at it while pushing it back! XD

[Raizer]

First and last time there will ever be sealant in one of my carbs!
Will hopefully have a correct gasket next week, might try to fix the choke at the same time as it's annoying choking it by hand with the filter freshly oiled.

After the first kilometre I could have sworn someone had hooked a trailer full of rocks to the back of it, swore I'd get rid of the squeak in the rear brake too

['O'Verse]

Now I'm prone to carrying A basic sized O shit kit after any mods. (10mm socket, screwdriver, zip ties, etc.) Last time I thought I needed the kit with me I ran out of gas...

[Raizer]

Interesting day today, went to go and just do a couple plug chops walked out to the car and spotted a parcel in my mail box.

CHT display take 3!

So instead of just going and chopping plugs I decided to wire that in and refit my plastics first.
Hooked the display up on the bench with my scooter battery just to test it and it didn't power up.
Tried a 12Vdc power supply, dead. Ride on mower battery, still won't power up
Came close to throwing it in the bin and giving up on ever knowing my CHT, when I decided to try it one more time.
It powered straight up as soon as I hooked the wires to the battery, then I realized I had just hooked it up backwards!
Turns out the sticker on the display has + and - backwards FFS!

Went from 12 to 35 pretty quick idling for just a few minutes, I take that as a sign its working lol

As I said I figured I'd tidy up the wiring a bit, the factory provided power to the complete DC circuit through a single small gauge wire from the battery and to me that just wasn't good enough!
So first thing I did was add a decent wire directly from the battery's + terminal and ran it to a relay I had sitting around.


Had a moment of "safety first" thinking so went and brought a fuse to so I don't burn the scoot to the ground if I short out my phone charger or anything haha


At the same time I grabbed a strip connector, which I rigged up into a half ass distribution block.

Consider it future proofing, now if I add anything else that needs DC power I can just quickly hook it straight up, made a shorter one for the earth.

Installed the volt meter and ran the wires though the plastics and refitted them, I really like how the bed liner has come out!

Annoyingly the volt meter mount means it's not easy to see the CHT display when actually riding, will have to have a think about mounting the CHT elsewhere.

So tools loaded under the seat, made sure to take more than just the plug socket this time!!


122mj fitted, warmed up and went for a test ride, noticeable 4 stroking from less than 1/4 throttle, WOT wasn't too bad though.
Changed down to a 119mj and took all my jets with me as well so I could swap jets while out and about.
Slight 4 stroking mid throttle wit the 119, less low/mid range than with the 117 yesterday.

Decided to try the 115 again, low-mid felt really good, but WOT wasn't as good.
So back to the 117 which so far has felt best and it was finally time to go do a WOT run to chop.
Temp while cruising to the beach going around the speed limit was between 64-72C or 147-161F.

Got to the beach and pulled the old plug out, nice mocha brown looking plug.
New plug in, fired up and went straight to WOT, held it wide open for over 3.2k (2 miles)


Temp held 68C/154F pretty much the whole run, top speed was lower than expected since I got almost 10k more from the 50cc cylinder, but I had a fairly solid head wind today.
Swapped back to the old plug, went home as as much as it pained me to cut up something that just cost me $6 I chopped it.




Little lean right?
I'm almost thinking I need a slightly bigger main combined with a leaner needle to suit but am open to advice/tips!

[90GTVert]

I think you'll need to get used to what your CHT reads and not compare to stats from others. Yours all sound chilly to me. My CHTs do vary, depending what gauge setup, but your numbers are all idle temps for mine. The plug says the opposite, and is more likely lean.

[Raizer]

I've since tried an A07 needle which I thought should have been leaner at low throttle, richer up high, but it was just too rich right from idle with the 117mj still in.

Going have swapped the A20 needle back in, but have raised the clip one slot from where I had it before to lean it out at low/mid throttle a bit, will see how it goes.
Haven't tested like this yet, rear tyre is dead flat, brought a new tube today just need to fit it.


Have had another idea on what to try too, as it was making decent power until fairly high RPM I'm thinking of changing to slightly heavier rollers to bring the CVT shift point down maybe 500rpm where it was still pulling strong.


Also priced up some decent tyres today when I got the new tube, can get Metzeler ME 1 in 3.50 x10 for $136.50ea or Michelin S1 for $84ea, think I'll grab some S1s at some point, my Cheng Shins aren't that bad but there's room for improvement!

[tsimi]

Raizer

Like Brent said don't mind others CHT temps. I have never seen a 3xxF temps here either.
When the cooling fan is spinning I rarely see anything beyond 180-190F even after a couple short WOT runs.
When the cooling fan stops and I turn off the engine the temps go up high as 240-250F.
Most of the guys here in the forum are tuning cracks and they run racing cranks with mid-race or even race cylinders that might reach temps up to +300F I got other 2 guys here that run sport grade cylinders and none of them has ever seen such high temps. So again check the temps you get with YOUR regular driving and WOT and use those temps as reference to adjust your carb.
If I would suddenly see 250F instead of the 180F with same driving style then I would worry.

[Raizer]

Took it for a test ride with the lowered A20 needle and 117mj, went OK, sounded slightly lean without bogging, temp got up to 78C/172F just around town with a couple short WOT runs and was lacking a good bit of power right through the rev range.
119mj helped a little, but still wasn't great, so plan now is to go back to the 117mj, A20 needle on the center clip and to order some 4.0g and 4.5g rollers to play with as the engine is pulling hard until about 8800rpm and my CVT holds it at 9100rpm so I'm fairly confident I'm trying to run it above peak power.
Am kind of surprised at how low the peak power is being made, wonder what it will do with the Po Rep lol.


tsimi I'm going to try to borrow a mates fluke ir thermometer and do some comparisons, our Procon CHT set ups might even be consistently low?
Looking in the instructions that came with the display they are calibratable too so might be able to be tweaked to suit/my low temps in the morning before starting the engine seem about right, just below outdoor ambient temp.

[tsimi]

I have compared my CHT with a room temp gauge and a cooking temp gauge and it was maybe 1-2 degrees off but otherwise same.
Like I said some of those guys here run heavy setups with overrange stuff and high rpm pipes you cannot compare such a setup to our tiny sport grade.
I hope I can get my mid-race engine together asap and then I can say more.

[90GTVert]

My bone stock 49cc ran well hotter than what you guys are seeing. Literally you're seeing a little above idle temps for me. Most of mine, regardless of cc and porting, run within a similar range that's at least near 300F if not over. I can't see how you'd have 170F max with efficient combustion if the gauge is correct. When mine dip well into the 200s, they're so rich and cold that they're running poorly. Even when I rode in the teens and twenties I run hotter than that on a scoot with no fairing to block any air around the engine.

As long as you learn what range that it runs in when in tune at various throttle positions, I don't know that it matters. Just saying, I don't think it's solely because of a mild setup.

[Raizer]

Pulled my rear tyre off today, was originally just going to lever off one side and swap the tube out, but all the flakes of rust and little shards of metal (looked like grinding dust) that came out of the tyre killed that idea!


That's after it got cleaned up by the soapy water I used to lube the tyre!
Tube was badly stuck to the rust in a few spots, don't know how it lasted this long TBH.

I had a prefect condition rim sitting on the shelf so I swapped the tyre onto it instead.

Sorted! Didn't even pinch the tube with my lever lol


Set the A20 needle back to the centre clip and it's running really well again, just need to go up a little in roller weight to bring the RPM down a touch now.
While riding around town for 30+ minutes inc a few WOT pulls I never once saw over 72C/161F on the CHT gauge.
This is after getting home and letting it idle for 5 minutes while I tweaked the air screw a touch

If I turn the engine off it gets up to somewhere around 90C/194F pretty quickly.

[Raizer]

Just been riding it tonight, didn't see over 63C/145F that's with an ambient temp of 8C/46F.
Going damn well though in my opinion!!

My ass dyno is telling me my cylinder/pipe combo is peaking just after 8600rpm and dropping power fairly hard after that, so yeah heavier rollers are on the way to bring the CVT down from 9100.

Also finally got to try out my LED lightbar in the the dark

Stock high beam


With LED on


It's brighter when the RPM is higher too!

[Raizer]

Gave the SJ50QT CVT set up a birthday today, had low acceleration and was super slow to shift so figured I might as well clean it and evaluate the condition of the rollers etc.

Found the rollers were gummed up with crap and the variator was sticking to the boss just like mine does!
Belt was also super thin, and there a grove worn around the outside face of the variator from the belt and it was clear the belt wasn't reaching the outside of the variator.
Mounted the variator in my drill with a big bolt and used a file and sandpaper to reface it, pulled the belt out of the Let's 4 stroke engine I've been raiding for my Let's II, was happy to find Suzuki used the same belt in it and that it was a like new Bando!!


The rollers are in perfect condition, 16x12mm 6.5g.
Cleaned up the clutch (same decent stock 3 shoe I run in my Let's) while I was in there and fitted the 1000RPM contra from the kit I got for my Let's.

Spun the fixed face of the variator and cleaned all the remains of old belt off it and reassembled it the kick starter assembly.




Belt is a bit short right??
It reaches the outside of the variator but is sitting pretty low in the clutch right?


Also it's been 4 stroking pretty made mid-3/4 throttle and was a touch rich at WOT, so I dropped the needle one clip (I had raised it one when we first got the scooter) and discovered that the Mikuni takes the same 6mm jets as my Dellorto rather than the 5mm jets I was going order, so out came the "about 75" drilled jet, in went a 74 (stock was a rather lean 68)

Sorted the 4 stroking.

It's a lot nicer to ride now, CVT shifts smoothly.
BUT there is NO power down low, clutch engages and it almost feels like there is slippage as it really struggles to get moving, once over say 15k it's fine.
I'm thinking lighter rollers, longer belt and maybe the springs out of my clutch once I get a new one.

Might get a video of it soon to try show the lack of pull.


Ooh and I made the mistake of letting the wife ride my Let's while I test rode this thing, she really didn't want to give it back haha

[niz76]

Raizer, that belt does look really low in the rear pulley. How deep is it sitting up front on the drive boss of the variator? It almost looks like it's not getting down very deep up front which would be like "taking off in second gear". Can you add shims to the drive boss to give more room between the faces of the variator for the belt? I often find there's not enough room on the crankshaft splines for many spacers but if you can get the belt deeper down up front and higher in the rear pulley it should really improve takeoff..