MOPED ARMY

I have and I would again.

Ohh I see I see, you only cut away the outer lip, then marked the piston and matched the window? Did you also cut always the side transfers? (edited)

Yep widened it as well, never touched the transfers

Can you post a picture of the transfers from more of a side angle?

Fuck yeah thanks dude, I'm going to cut mine up this weekend

I've put maybe 10 hours on one like that, no problems

So this is my first Derbi I’m not familiar will all the specs off hand, however for some basic info, it’s a variant sport: world champion with a flatreed engine. My calipers just crapped their pants and I’m ordering some new decent ones now, so I can’t get the stud spacing this moment, maybe someone else can? However for the crank stroke length, I think you can find the stock stroke on the Wiki under scooter and moped crank strokes.

Good luck!

(edited)

So since the stroke is 3mm longer you could try to use a base spacer, but you have to check that all your ports still open, and you hit too dead center at the top. Maybe a little base spacer and some milling off the top of the cylinder

15 SHA (not tuned yet litterally just ripped it up and down the road with the stock jet and hit 405* haha) zen 50cc, new reeds and this porting, still also have to tune the vario for sure. And get the sha MAGIC slide to sit correct I got that high ass idle for no reason

I can’t get the cracking/ 4 stroking/ cutting on the bottom end to stop with this SHA.

Stock get was a 68. Cracked a little on the bottom end but hit almost 48 mph BUT also got way too hot. Screams lean on the top end, I am running the air filter and little stock pod box.

Upjet to 71, temps get a little more under controll, but the bottom end gets worse, i have to like blip it multiple times and give her WOT until she hits the pipe the. She’s golden.

I tried the magic slide from treats, did not seem to do anything for it other than the notorious high idle issue

Is there a way I can modify my own slide to try and get more air in here at the bottom end? I don’t know slide science well and how all that works on a reed motor (any motor really) I know the angle on the bottom and change air velocity? Or some are notched?

My brain just says “throw a 15 phbg on it and call it a day” because I love them and run them on everything and have become pretty good at tuning them. (See my wtb thread if you have one, treats has them but I try to buy used if I can)

I’d like to take this obstacle as a way to learn slide tuning if I can.

Or is there something else y’all have seen before that can cause this?

Oh man I remember this article! So if I’m reading correct, place to start, would be a steep angle on a slide? I have like 10 junk slides I can play around with, and possibly enlarging the top hole on the brass tube a little to try and make the bottom end as lean as I can and the top as far as I can.

I’m not sure if the steepness of the angle plays directly into how lean the bottom gets but I can try, maybe I’ll make 3 or so and then test them all with different angles of steepness, most of mine are the flat bottom ones. I have a few stock angle ones with no cut out. Hmmmmmm it seems like I’m my peak I’ll need around a 72 or 73 main. So a steeper angle creating lower pressure and thus less suction out the tube might help. I also might try just running no air filter to help lean it. Or like remove the mesh or the pod box thing.

So many things to try

Is that actually correct though, the stronger I make that angle. The leaner it will get down low?

If your SHA slide mods dont work and you dont want a PHBG, 15mm AMAL is what the spain boys use (i think).

i have one, and i love it. YMMV. Direct fit onto my derbi intake. Hopefully it comes with the 15 idle jet but you can buy them on ebay for cheap.

https://www.treatland.tv/amal-15mm-carburetor-p/amal-carburetor-15mm.htm

So I did eek out the last few mph and she’s 49/49 with awesome low end,

Green polini springs

19 metra phbg intake

15 phbg

81 main, 38 idle, w7 needle clip on the top***

Zen 50cc exhaust

Stock 6 roller

Staggered weights, 3.5g and 4g every other

New 3.5mm reeds

One way bearing in the clutch.

*** still tuning a bit holding WOT for 5ish miles and I hit 400*. I understand I’m making a bike do double the speed it used to without changing displacement so my temps may continue to be a bit of an issue.

However, I think I’ve been tuning my needles wrong. I’m making a new thread about it after I post this. So will report back after I continue to figure some of that out maybe I’ll get the temps to even out! (edited)