Fix my setup

Tracy Meade /

Hello moped nerds out there, hoping to get some input on this build:


new style aluminum metra65, mild -- exhaust widening.

mlm people's pipe sidebleed

19 del @ 82 main

treatland cheapo cdi with pietcard box

16x42 gearing

really really old "70cc" head from like 2006 without a super defined squish, but has a bit of a slope and a medium sized chamber.

Out of the box, I used aluminum spacers and some paper to boost the cylinder to clear the exhaust. Measured up, looks like it is running about 131deg trans and 170deg exhaust.

Did some riding and break in, ended out with

jet about 82

timing retarding about 21->16

compression tested showed an abysmal 90psi (probably from boosting cylinder 2mm)

Goes about 45-49ish so maybe creeping up to 9.5k-10k? no tach.

Still runs pretty dang hot for such little compression -- gets up to 390 or so after a 2-3 miles of WOT with some up and down.

The main issue here is that it feels lean up top, surges a bit at top speed. If I bump the jetting any higher, then it sputters and 4 strokes a lot mid range on WOT from a stop --> so upping the main makes riding crappy and unfun.

I'm not really trying to go any faster, this is supposed to be a dumb easy around town bike, just trying to shake out this annoying problem.

So, how would you approach this:

Could be a port timing problem? -- seems like a lot of transfer duration for that ex timing.

Could this be because my compression is all low? -- I don't really seem to have the thermal credits to go bumping it, although maybe getting a tighter squish could help with temps.

Would you address this as a carb problem? -- Maybe some airbox or some air passage drilling would help even this out -- although never really had to go ham on a dellorto carb before.

thanks in advance smarty pantses (edited)

Re: Fix my setup

i can't help, haven't built the new mk65 but how do you like it otherwise?

82 seems kind of on the big side, do you have the au262 atomizer and bushing?

i've been scared to try one until i hear firsthand how the new piston works in there. i loved the old ones but i'm not sold the copy is as good as the OG. that really nice meteor piston they shipped with was a pretty big part of the special sauce

Re: Fix my setup

Tracy Meade /

I have some primary type atomizer/needle orface, but at this point I can't remember which one. I would bet I would have done 262? I don't remember.

I guess I can't really say, I haven't run the old style in quite a few years, and I have never run this mlm pipe with it -- I will have more to say once I dial this in.

In the mean time, casting and everything looked good, so no complaints yet. It isn't rocking my boots, but has pretty strong mid-hi when paired with with this pipe, but not quite the low end that my old estoril setup had with the iron jug, as I recall. Feels a bit less peaky than TCCD's, but I suppose that is expected.

The jetting did seem high for metra65, but it seems to want it up top, but hate it mid rev range, which is kinda the pickle I'm trying to work out. (edited)

Re: Fix my setup

yeah, i've heard less than stellar things from the people's pipe but its always the case when people cut corners on a cheaper pipe they tend to cut corners on the tuning. some of the comments i've heard are that it has that 'boss' style hole in the midrange... makes sense with a big header and sorta similar chamber.

the old mk65 with a estoril or proma was a midrange monster, from like 5k to 8k it would stomp... pretty much all done by 9,5k with stock porting. even with a biturbo it held its own in the mids. if the port map is the same i'd be suspicious of the atomizer/needle/pilot jet combo. those damn phbg's don't really four stroke to tell you what they are doing.

or just push the 'easy' button and throw a VM18/ 20/22 on there haha

oh wait I forgot you're pretty much committed to the dellorto haha

Re: Fix my setup

Tracy Meade /

heh, yeah.

I actually like VM's a lot, run them on the CB350 and RD400. Never ran one on a moped tho.

I ran a flatslide once, and it kinda blew my mind. It didn't really care what jet I put in it, it just ran good even if I switched 50 jet sizes. Like WTF is happening.

Re: Fix my setup

Tracy Meade /

hmm maybe it's worth changing the pipe here back to estoril for retro setup

Re: Fix my setup

Tracy Meade /

I don't have a boss around, but it seems pretty similarly shaped, similar divergent cone size, but peoples has a few inches of straight section before the back convergent cone.

Re: Fix my setup

Tracy Meade /

I tried porting the kit a few more degrees up to about 175 to test theory #1

No real change vs my problem, but did seem to run a little smoother.

Image from iOS (4).jpg

Re: Fix my setup

Tracy Meade /

But this is interesting, I went to inspect the carb air bleed holes to test theory #3 and this is what I found:

The brass jet for the air inlet is completely gone! Hope it isn't in the engine somewhere. (edited)

Image from iOS (2).jpg

Re: Fix my setup

Tracy Meade /

Compare with 17.5 and 19.5 del's I had laying around:

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