Derbi porting

I raised the exhaust a little so far, and cut down the transfer walls a little.

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I still need to knife the walls a little more.

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But has anyone done this on a stock boy? Not sure if I should cut too much away.

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(edited)

Re: Derbi porting

I raised the exhaust to 66°(170° duration) I think that might be the before measurements and widened .5mm on either side.

It ripped super fucking hard. No head gasket.

This is the piston and intake cut away

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Re: Derbi porting

EH 📣FCC of the QCB /

I have and I would again.

Re: Derbi porting

NIF edge.

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Going to cut it all out tomorrow.

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Was going to keep this end but and ramp it like this opening it wider, but without doing it in the case as well I feel it’s kind of a waste

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Re: Derbi porting

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)

Re: Derbi porting

I think I’m going to copy that photo above your comment but also knife the top edge to the port some for smoother transfer of flow.

Re: Derbi porting

> Wolf Wizard Wrote:

> -------------------------------------------------------

> 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?

Yep widened it as well, never touched the transfers

Re: Derbi porting

Okay done now. All transfers are ramped nice and sharp, and raised the exhaust just a tad more

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Re: Derbi porting

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

Re: Derbi porting

Also to address the scratches on the piston before anyone asks, I must have missed a burr when I cut out the top window piece on the cylinder skirt itself, that happened when I put the piston in to trace the opening to cut the window, I lightly hand sanded the scratches with 400 and they can no longer be felt, luckily the the rings were unhurt (they were in at the time but no marking on them, and that’s why I took em off, made sure to label which one was on top.)

Here’s the ramp angle from the side, I did my best to make a nice smooth slope to help the charge flow as smooth as possible, it’s still rough like 120 grit, so it should not be smooth enough to bead up on the ramps. I know a little texture is good in the ports to help atomize the fuel.

image.jpg
image.jpg

Re: Derbi porting

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

Re: Derbi porting

Arnt those skinny legs a recipe for diaster? Update picts in a bit.

Re: Derbi porting

> pat splat Wrote:

> -------------------------------------------------------

> Arnt those skinny legs a recipe for diaster? Update picts in a bit.

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

Re: Derbi porting

Alan Jackson /

what derbi model is it and what is the stroke and bolt spacing?

i would appreciate an answer because im looking for a cylinder to use my 43mm stroke crank with plus yours has the same transfer feeds that i need.

Re: Derbi porting

> Alan Jackson Wrote:

> -------------------------------------------------------

> what derbi model is it and what is the stroke and bolt spacing?

>

> i would appreciate an answer because im looking for a cylinder to use

> my 43mm stroke crank with plus yours has the same transfer feeds that i

> need.

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!

B3E03D24-E443-4C8C-8443-256667B42173.jpeg

(edited)

Re: Derbi porting

> Alan Jackson Wrote:

> -------------------------------------------------------

> what derbi model is it and what is the stroke and bolt spacing?

>

> i would appreciate an answer because im looking for a cylinder to use

> my 43mm stroke crank with plus yours has the same transfer feeds that i

> need.

40mm stroke

And 65mm studs

That's just what I found from a Google search don't know the veracity of it though

Re: Derbi porting

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

Re: Derbi porting

Alan Jackson /

my moby cylinders are 41.8 stroke. and i cant get them to run with the longer stroke crank

unless i could stretch the cylinder.

if i jack up the cylinder to get deck height correct the ports are all too high.

peak rpm at 12k which isnt what i want. i was hoping your derboi was 43mm stroke.

i know puchs are 43 mm stroke but stud spacing is way out. studs are outside the barrel. i might have to get creative and weld some alloy tubes etc

Re: Derbi porting

686F9229-6E6F-46E5-9419-25749C67D596.jpeg

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

Re: Derbi porting

EH 📣FCC of the QCB /

Hell ya dude! That’s what’s up.

Re: Derbi porting

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?

Re: Derbi porting

Re: Derbi porting

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

Re: Derbi porting

EH 📣FCC of the QCB /

> * wormdirt * Wrote:

> -------------------------------------------------------

> http://outofcontrolmopeds.blogspot.com/2012/03/dellorto-sha-boring.html?m=1

This is what I do to every SHA slide I mess with. Works perfect. Should fix the condition your describing. The angle definitely affects it. (edited)

Re: Derbi porting

> EH FCC of the QCB Wrote:

> -------------------------------------------------------

> > * wormdirt * Wrote:

>

> > -------------------------------------------------------

>

> >

> http://outofcontrolmopeds.blogspot.com/2012/03/dellorto-sha-boring.html?m=1

>

> This is what I do to every SHA slide I mess with. Works perfect.

> Should fix the condition your describing. The angle definitely affects

> it.

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

Re: Derbi porting

EH 📣FCC of the QCB /

Yes and it works surprisingly well.

Re: Derbi porting

Emil Kniemel /

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

Re: Derbi porting

Dirty30 Dillon /

> Alan Jackson Wrote:

> -------------------------------------------------------

> my moby cylinders are 41.8 stroke. and i cant get them to run with the

> longer stroke crank

>

> unless i could stretch the cylinder.

>

> if i jack up the cylinder to get deck height correct the ports are all

> too high.

>

> peak rpm at 12k which isnt what i want. i was hoping your derboi was

> 43mm stroke.

>

> i know puchs are 43 mm stroke but stud spacing is way out. studs are

> outside the barrel. i might have to get creative and weld some alloy

> tubes etc

Yeah, Moby's aren't very simple for a swap. Although if you're already at 43mm (why, I guess we'll never know), there are a plethora of different cylinders that work great with that stroke in the scoot world. You'd be better off switching to an AV10, honestly.

That said, Derbi PP/PR motors are all 43mm stroke, hence why they fit Puch cylinders on them no problem. Although this doesn't really answer your stud spacing (Moby's have a rectangle, vs. a square pattern).

If you had your stock crank you could try to find yourself one of these or one of these top ends. They are the same stud spacing and stroke. In the end, you still need to figure out how to make the motor swing on the head, with either option.

Re: Derbi porting

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)

Re: Derbi porting

EH 📣FCC of the QCB /

Sick! I love it.

Forever and always w9…

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