Looking for 1 more HP !!

#1
Got a 80’s hs40 that runs good, measured 100 psi on compression test. Installed a pz16 carb which seems great! Haven’t rode the bike yet still a work in progress, can follow along on the project forum under manco chopper. Anyway it runs good, is it worth the time to port the I/E bowls and ports ? And for exhaust I’m thinking of using bicycle frame 7/8” and making an exhaust pipe but what decent hi flow muffler can I use ? Is 93 octain the fuel to use or 87?
Intake has been blended BEBC7600-F5F2-48D2-9E50-5B5D9C9A4915.jpeg BEBC7600-F5F2-48D2-9E50-5B5D9C9A4915.jpeg B1895391-3719-4F32-A89E-0B61E06A066C.jpeg
 

mustangfrank

Well-Known Member
#2
Got a 80’s hs40 that runs good, measured 100 psi on compression test. Installed a pz16 carb which seems great! Haven’t rode the bike yet still a work in progress, can follow along on the project forum under manco chopper. Anyway it runs good, is it worth the time to port the I/E bowls and ports ? And for exhaust I’m thinking of using bicycle frame 7/8” and making an exhaust pipe but what decent hi flow muffler can I use ? Is 93 octain the fuel to use or 87?
Intake has been blended View attachment 279828 View attachment 279828 View attachment 279829
Got a 80’s hs40 that runs good, measured 100 psi on compression test. Installed a pz16 carb which seems great! Haven’t rode the bike yet still a work in progress, can follow along on the project forum under manco chopper. Anyway it runs good, is it worth the time to port the I/E bowls and ports ? And for exhaust I’m thinking of using bicycle frame 7/8” and making an exhaust pipe but what decent hi flow muffler can I use ? Is 93 octain the fuel to use or 87?
Intake has been blended View attachment 279828 View attachment 279828 View attachment 279829
With stock compression, cam and timing you won't benefit from running higher octane. Most advice I've read on porting the flatties is to clean up casting flash and not go hog wild.

You'll definitely benefit from a better flowing exhaust, I'm no exhaust designer/fabricator but I've heard more than a few recommendations for a "stepped" up straight pipe design for power or Rupp Black Widow style with the turnout to quiet it down some. Black Widow Motorsports has a short straight pipe design with a threaded end for a "hotdog" muffler I ordered but I'm using it for neighborhood duty, probably at a little giveaway of power...still better than an old Taylor with a clogged spark arrestor though.

Throw a billet rod in it and rev it up a little more.
 

I74

Well-Known Member
#3
Got a 80’s hs40 that runs good, measured 100 psi on compression test. Installed a pz16 carb which seems great! Haven’t rode the bike yet still a work in progress, can follow along on the project forum under manco chopper. Anyway it runs good, is it worth the time to port the I/E bowls and ports ? And for exhaust I’m thinking of using bicycle frame 7/8” and making an exhaust pipe but what decent hi flow muffler can I use ? Is 93 octain the fuel to use or 87?
Intake has been blended View attachment 279828 View attachment 279828 View attachment 279829
It's good to leave the intake ports a bit rough,, helps '' a lot'' in atomizing the air/ fuel mixture.
Exhaust ports,, as smooth & unrestricted as you can get them with out going to excessive. . ;)
Like mustangfrank said,, just don't go hog wild..

Also putting an ''inside'' chamfer ''taper'' on the flange ''inlet'' end of the pipe,, helps smooth the flow out.
 
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cfh

Well-Known Member
#4
if you're running a slide carb, you won't get the full benefit unless you run an open exhaust too. i use 7/8" stainless tube .065 wall from Zoro.com. keep bends to a minimum. i do light porting. but it's not a huge difference in the big picture. a cam really is the next thing. but you will need a better rod (or a modified rod at minimum), and of course no governor. but if you really wanted 1 more horsey, you should have started with an HS50... if you really need that HS40 1968-1972 "look", use an HS50 a,b,c series engine with a 32517 alloy flywheel and rounded blower housing. that will really get you there!

frankly i don't understand why people bother with an HS40. it's the same work to rebuild an HS50, and they are easier to get and cheaper. and they look identical to a 1973-1988 HS40. we're all fat old men now... we need an hs50 !!
 
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