Re: Derbi porting

are you using the decomp head? I ran a derbi head forever with a lapped decomp that never passed like 370, but ditched it and temps dropped a good 20-30 degrees.

Re: Derbi porting

I am running a decomp, it is also lapped and I’d honestly run 370 all day long I call my redline at 400. That’s an interesting thing though I figure no decomp would actually raise temps since there is less room in the combustion chamber since if I remember correctly where the valve sits is recessed a little.

Also Eric, I have a weird new idea and understanding of needles and I now am under the assumption that a longer taper actually fattens up your mid and lower range pull before wot were your main jet fully takes over. If that’s true the w9 would actually richen my mids, I think my goal is to lean my mids more so I can run a larger main jet,

However the better solution might be smaller main and more aggressive taper? From what I experienced outlined in my new needle post, a longer taper does not do what I thought it did.

Re: Derbi porting

This thing is still being a pain. Still getting that 49/49, but I’m struggling to keep my temps under 400.

Ya know when you’re getting a little spicy and you just back off to 3/4 and let it do it’s thing? The derbi don’t slow down at all just gets hotter quicker. Thinking about maybe a longer taper on the needle to make sure I’m getting sufficient gas flow at that 3/4 position. Hmmmmm lots of things left to try including a colder plug and retarding the timing a smidge. Hopefully that last one don’t kill my top end speed much.

Re: Derbi porting

What weights / gears are you running?

Maybe is you back off the RPMs a smidge you'll cool off

Re: Derbi porting

3.5g Polini in all 6 slots all together they weight about 21g any lighter and it won’t variate all the way. Stock gearing never really paid mind to it however that’s not a bad idea. I’ll honestly think the timing will do it good to help it cool off if I can’t find jetting that fixes it.

Pushing a 49 bike to 49 I understand is a lot for the little engine so I should bet expect it to be easy and just run flawless

Re: Derbi porting

Now that I think about it, I may be able to go lighter in the weights, my carb was way less dialed in than it is now so it may variate all the way with my 3g dr pulley sliders

Re: Derbi porting

That seems like a lot of weight. I had 12g polini weights in with my ported head + zen + 19 phbg. I didn't variate allll the way but it deffo hit 50 no problemo. I do have a lightened clutch bell and variation though so I dunno.

Did you lap the decomp?

A leaky decomp could be the extra 20° of temp you could shrug off.

What plug too?

> Wolf Wizard wrote:

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

> Now that I think about it, I may be able to go lighter in the weights,

> my carb was way less dialed in than it is now so it may variate all the

> way with my 3g dr pulley sliders

Re: Derbi porting

Decomp is lapped and I’ve hit it with carb clean many times but may try the air compressor test too, apparently if you take a spray nozzle for an air compressor and spray around the engine while it idles that’s even better than carb clean. I though 21 seemed like a lot too, everyone else seems to be around 15-18. Like I said maybe my carb was a bit wonky last time I tried less. 3g sliders were about 18 g total sometimes 19g my scale is not the best I just was told make sure you weigh them all at the same time.

I’m running a b5hs which apparently sucks at dissipating heat I’ve read. Was reading some other two stroke forums tonight and was reading about how bikes that run WOT a lot of the time do best with cooler plugs like a b8hs because they dissipate heat better to the head. Something with the length of the electrode being different. Also thinking about the Parma box, seems they run fantastic in derbis with their wicked top end curve

Re: Derbi porting

Oh wow 5 is hot

I don't think I've ever run below an ngk 8. If you went to an 8 I bet you'd drop 50°

Re: Derbi porting

All my bikes normally run a 6, my local place was out but had 5s. I’m ganna call around and see if I can’t track down an 8 tomorrow since it would be the quickest easiest option for sure at this point

Re: Derbi porting

Does the stock derbi head use the short hs plug? The derbi head I’m using on the hobbit needs the longer threaded es plug.

Re: Derbi porting

Woah I didn't know they even made a 15 PHBG

Re: Derbi porting

All my derbis run the longer es ngk plug

Also yeah I’ll run a 6 on a stock bike but always 7 or 8 for kitted setups to help run cool

Re: Derbi porting

So my head does take an hs plug. Popped an es in and it hits and won’t turn over haha.

Bad news, it actually already had a b7hs in it :( still going to try an 8 or 9 if I can find it for good measure but I just retarded the timing a smidge and will see what that does as well.

Edited out a part about how I may try an Ali express cdi box that was recommended on moped army a while ago, but it’s out of stock (edited)

Re: Derbi porting

I just realized, a colder plug does a better job at transferring heat to the head, so in fact won’t the make my head temps read higher? But in theory the temp in my cylinder should be effectively lower?

Re: Derbi porting

Maybeeeeeeee the b8hs is tooooo cold? 79 main jet, 42 idle. 8 miles of riding 4 there 4 back blasting full beans for about half of it.

309FE9FB-4EBD-4A1B-A848-09348C0B6093.jpeg

Re: Derbi porting

Heat range looks right, looks like rich idle lean wot, not sure if those deposits r oil or insulator.

Re: Derbi porting

What’s leading you to day that? The black ring around the top of the threads? And the white electrode? I was up till like 2am reading about plug reading again haha.

From what I understand the white ceramic should tell me about the wot range. What is pointing to a rich idle to you? Also why the whitish chalky spot on the top of the metal electrode?

Re: Derbi porting

The plug heat transfer thing is all about pre ignition, if you are getting pre-ignition or detonation (unlikely with stock) your temps will spike up, usually under high load. The electrode gets hot and either totally lights off the fuel or just makes it burn faster. That's what's kinda crazy about the whole heart range thing, it will actually speed up the rate that the fuel burns in the chamber in effect advancing your timing. In order for the fuel to burn it's got to absorb the latent heat of combustion so anytime you increase that heat you make it burn faster which has the same affect as advancing timing.

I haven't fucked with derbi much but when we were designing the derbi heads on the hobbit, we found those head shed heat really well. Seeing cht over 400 is pretty high for a derbi. But at the end of the day, cht really doesn't matter, look for scorching on the back side of your piston to know if you piston temps are actually too high. When we were messing with hobbit heads they could be 450+ cht and still happy clean piston just because the head sucks at getting rid of heat.

If everything else is perfectly tuned and you are just seriously making that much heat and power, you can switch to redline or maxima 927 or klotz beanol, those seem to have the highest temp stability. Anything with castor, and whatever crazy magic is happening with redline.

Re: Derbi porting

This is a really good point.

It just occurred to me just how much richer the top end itself gets with the needle in the bottom clip vs the top. I put my needle on the top, opened the slide with my finger and made a sharpie mark at their bottom of what I could see if the needle, and just as you may guess and as I overlooked, when you put the clip on the bottom, viola the needle goes up much higher and because the needle is tapered, less of that atomizer whole is covered. Man I may just try a super skinny needle and down jet a bunch haha

Re: Derbi porting

> Wolf Wizard wrote:

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

> What’s leading you to day that? The black ring around the top of the

> threads? And the white electrode? I was up till like 2am reading about

> plug reading again haha.

>

> From what I understand the white ceramic should tell me about the wot

> range. What is pointing to a rich idle to you? Also why the whitish

> chalky spot on the top of the metal electrode?

No plug expert but yes black ring idle and electrode being white wot. Thinking heat range is good cuz the burn is halfway up the electrode n halfway on the point.

The deposits not sure of is it ashy or hard? Ashy oil hard porcelin.

I run my bikes rich.

Needle clip position is important.

Re: Derbi porting

> MPB Andyrew wrote:

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

> Woah I didn't know they even made a 15 PHBG

They make a 12 PHBG too.

Re: Derbi porting

So my parmakit box is advancing my timing not retarding it. Cool. Reached out to treats, is this something wrong in my end?

I have the stator at full advance and it’s firing somewhere like 1.3mm before tdc and stock is 1.8-2mm moves towards my 1.8 mark as I rev. Does the stock Motoplat 402 box and coil unit have a curve or is it static? Just got my light today and did not test the stock one before I took it off. My bike is stock 12v motoplat

Re: Derbi porting

So I realize these could be different on every box if they are like a manufacture date but I don’t have any codes part numbers anywhere else on the box coil combo. So ¯\_(ツ)_/¯. Can anyone confirm if they match either?

B3143322-82D1-46E0-9A9C-FE3D8D9D6461.jpeg

The treats photo seems to read 82 06/14 you really gatta squint. Seems like it could be date. However mine says 66 25/21 which does not seem like a date. Anyone’s match either of these?

Re: Derbi porting

Totally normal JBOT /

You should do underpiston smoothing.

It’s helpful I swear.

Just put piston at bdc and then smooth around the wrist pin leading into the 3 transfers.

So much mix is under the piston so by smoothing the transitions it just wants to flow like mad.

Also throw a big carb on it. I’m running a 21 on my stock cyl reed conversion. Runs cold and very fast.

I also love the high comp derb 50cc head. So much squish! Runs cool as well.

863C5CBC-E6EB-4E5D-8ECA-C6FA2B32B862.jpeg

Re: Derbi porting

Hey j! You talking about this edge right here?

72F1EEAD-19D5-49E7-8632-191CFEE7BAAD.jpeg

Honestly I may just try a larger carb.

Does a larger carb mean more vaccume therefore more gas from the same jet?

Or am I thinking backwards a smaller carb has less open area so it would speed up the air as it travels down the Venturi?

Re: Derbi porting

Totally normal JBOT /

Large carb can always be used at low throttle.

If you’re setup to flow you gotta have mix to flow out.

Yes of course that’s the area

I put the piston at bdc then make a clean transition into the transfers from under the piston

Re: Derbi porting

Totally normal JBOT /

But I don’t just fuck with that edge, I go from the inside of the piston and smooth everything near a transfer from inside to outside.

The area under the piston is one key to easy fast flow

Re: Derbi porting

I don’t know what you mean to not fuck with the edge

Re: Derbi porting

Totally normal JBOT /

I mean I don’t just smooth the piston edge, I try to smooth the entire path from inside the piston to outside so it’s buttery

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