Port matching cases on a small frame Vespa. is it worth it?

[harleyracer59]

 High everybody!   Well I came up on a deal again and couldn’t pass it up.  I acquired a barely used mallossi mkh 2 or 3 135cc cylinder a SIP evo 2003 expansion chamber, malossi reed valve intake and a 25mm delorto for 500$ shipped.  
cylinder and piston still look new. Chamber has no carbon build up at all.   
  My question is with the intake mounted on the cylinder,  does anyone think I’d see crazy gains in power by port matching the cases to the cylinder?   About the only thing I can think I’d benefit by opening up the cases is I might get more oil to the bottom end?   
  What are y’all’s thoughts on this?    

[190mech]

Hey Harley,That intake looks to have 2 90degree bends,that's a heck of a restriction right there!I guess you are talking about where it bolts into the case though,,a small step shouldnt cause problems,a few pics would be nice to get a better idea of what needs to be done..

[christopher]

modernvespa.com/forum/forum19

You might try here also, more Vespa people.

[harleyracer59]

Mar 21, 2020 4:45:57 GMT -5 190mech said:

Hey Harley,That intake looks to have 2 90degree bends,that's a heck of a restriction right there!I guess you are talking about where it bolts into the case though,,a small step shouldnt cause problems,a few pics would be nice to get a better idea of what needs to be done..

    that's correct 190mech.  the malossi intake has 2 hard 90*s between carb and reeds.  only reason I can think of is to keep it under the cooling shroud?   I thought this was a performance killer as well.  
  but the port matching I was asking about id between cylinder base and crankcase mounting surfaces.   on a crankcase inducted engine I see the benefit of port matching, but on this cylinder  inducted setup, the mixture goes through the reeds into the cylinder ports and into combustion chamber.  the only purpose the case ports are serving now is to oil the bottom end.  give ne a sec ill post some pics  

[harleyracer59]

heres the pics of the manifold I got with this deal. also a pic of a new and improved version. no 90* bends in the new intake. but its like 3X the price of the old design. and almost half of what I paid for everything. damn...
so I ended up installing the cylinder. thesquish, or lack of is like 2mm from tdc to top of cylinder. not counting the head. so im now looking for a long stroke or stroker crank. other than the low compression, the only other issue im not liking is if I let it idle for mor than a minute or 2, when I give it throttle, itll smoke like Cheech and chong. if I rev it right after it drops back to idle its fine. while riding its fine. sitting and idling for 5+ minutes its fine. but as soon as I open the throttle. itll almost foul the plug. if i feather the throttle i can save it but then the smoke screen appears.
its like at idle the velocity of the mixture is to slow and the 2 stroke oil is falling out and into the crank case.when rpm increases it the rise in velocity now reaches intyo the crankcases and begins to pull this excess oil into the cylinder. and this is on premix. at 40:1 i added some gas to tank to try and get it towards 50:1. issue is still there. with the old cylinder and rotory intake, 40:1 gave no issues.
anyone have a solution to this issue?

[190mech]

Likely the low compression is making it misfire and loading up the crankcase with raw fuel..Did the piston edge line up with the transfer bottoms at BDC?If so,then something needs to be done about getting the compression up,decking the top of the barrel or step cutting the head to sink it into the bore..Perhaps there is another head out there that would work better than the setup now..

[christopher]

Could the loading up at idle be an idle Jet that is to big? How's the adjustment on the idle mixture screw? I usually aim for between 1 and 3 turns when adjusted properly. If that doesn't happen, then I try for the next size up or down idle jet. With the huge squish you have not sure if that will cause idle issues. Maybe it's not providing a clean burn because of the low compression.

[harleyracer59]

the air mixture screw is 2.5ish out. day time it needs 2 kicks to start cold. 1 if you pull the choke. at night it likes the choke to start cold. but once it starts choke can be turned off and it'll idle. it'll idle for 5-10 minutes fine no faulter. if you then rev it, it will smoke screen. but once it clears out, if you let off throttle it returns back to idle with no hanging up and no stumble when it reaches idle. if you rev it again its normal. let it idle for 3+ minutes and itll drop a smoke screen when taking off.
its diffidently isn't burning clean pulled the plug last night it was oily black.
malossi makes a 8mm base spacer and someone I forget who makes a +3 stroker crank with an 105mm con rod (stock is 97). so theres my 8 for the spacer and 1.5 on the stroke. that should put me right about good.
the piston at bdc is maybe 1mm below ex. port and transfers are about the same.
an interesting tread on another forum was talking about ditching the chamber pipe for a polini banana exhaust dropped the power band removing the lag from a stop. I might throw the polini it came with back on tonight and see how it feels. its slower from 0 to 15ish then it revs past the cylinder shift mph. im shifting to second where I used to be shifting to 3rd with old set up. but the gap in gears and powerband sucks now.
another cool lucky upgrade I did a few months back was machine a half inch from the outer edge of the flywheel to lighten it. ive been reading that ignition systems needed to be changed or the bottom 2 fins had to be cut off because the stock 125 flywheel would rub. my lightened one is 1/16" clearance from the fin. I love it when a plan comes together!!!hahaha

[harleyracer59]

so last night I didn't get to swapping the exhaust out. I did mess with the timing and carb. I retarded the timing stock was 24* btdc. malossi recommends 17* btdc. that helped a little on the gearing gaps. it added a little low end power.
I also raise the needle/ lowered the clip. when cruising at 1/2-2/3 throttle if I let off a little it would gain a little power. I cant remember if that's a lean trait or a rich trait. I think its lean. we will see I guess

[harleyracer59]

so these are port timings for the cylinder exhaust seems kinda low compared to what im used to seeing with my honda bbk's.
what could i do to get the power band a little lower?


Exhaust opens at 94.5°
Transfers opens at 118°

Exhaust duration 171°
Transfer duration 124°

Blowdown 23.5°

[190mech]

That jug may be designed for a stroker crank,,a sanity check is to measure from the bore deck to the bottom of the transfer ports,should be very close to your crank stroke...