hs-50 d shaped intake port.

#21
I built a HS50 to look like a period correct hs3.5 for a early rupp used a tillotson instead of the tec carb as it had a much bigger venturi also used a 245 dyno. Not exactly stock looking but unless you look close it could pass for stock. Runs good but its tough to start because of no compression release.
 

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delray

Well-Known Member
#22
really killing the motor when going with a stock intake and carb look. I did play around little with a 8-10hp big block carb and modified the factory slant intake so it would flow better. it seem to work real good. but not quite as good as the 22mm mikuni carb did. never got the big block carb dialed in good on the low circuit end. I just quit playing with it because the class I race my flathead had change the rules and no longer had to use a stock appearance carb and so now I went with a real carb and that was a no brainer for me.
something I did find out when I was running the big block carb was that Tecumseh must of modified the carbs that went on the ohh motorsports engines and others too and work good and the type of carb's they where using,big blocks carbs with the big bore.
here was a dead giveaway it was a big block carb they use. the two small holes on the side where used only on a big black 8-10hp carbs.
both pictures are from motorsport engines



in the one picture you can see how large the bore is and it is Big.....



pull the choke stuff off and epoxy the choke shaft close. if can open your stock intake and figure out the low circuit on how to make it work spot on you might have your self a sleeper.
 
#23
its like you guys are reading my mined. im siting here thinking if this was a full size motor whats next. a port matched intake and the proper sized carb. my next thought. any time i changed the cam in a car or a bike it always wanted other than factory ignition timing. which leads me to ask dose the 245 want more timing and if it dose can you start it without loosing an arm. looking at oli4 nice fat port last night got me to thinking about the little carb as soon as i finish my coffee i will look at the manifold and see how much it can be opened up. ind i guess that will dictate the carb size. looking at the picture of the big block carb next to the small block carb. theres a huge difference. it looks like the big carb can swallow the manifold. time to go in the garage an ponder. more good info thanks. anthony
 

cfh

Well-Known Member
#24
don't want to be a buzz kill, but i've done a lot of experimenting with intake manifolds on the HS50. various configurations. make my own intake manifold, but mostly for the look and convenience. i always use a slide carb (16mm to 22mm, just depends)... On the intake manifold, from stock to straight (custom), really hasn't changed anything in performance.

for example just re-did the intakes on a couple speedway 10" wheel bikes. kept the same (slide) carb, just changed the intake from stock to straight 7/8" stainless (with custom manifold plates for the HS50 port and slide carb.) These are stock HS50 engines with open exhaust, slide carb, stock cam, no governor (sometimes a billet rod). Was there a performance difference? absolutely none that i could tell. but it sure looks a lot cooler! It also makes doing a custom straight pipe exhaust a lot easier with a straight intake manifold (another good reason i make custom intakes.)
 
#25
i think delray is on the right path. to keep the the stock look that i love and get some kind of performance gain out of the 245 cam i need to go with a bigger Tecumseh carb.i measured the intake to carb flange 0.819 the carb flange to manifold 0.817 there is room to open up the manifold. i can also open up and slightly reshape the d port on the block and intake manifold. now i need to know factory carb sizes from 0.817 up. and have no idea where to start looking. thanks for the reply. anthony.
 

delray

Well-Known Member
#26
when I initially fire up my hs-40 build it was on a small carb and the response was good, for top end it just seem to rev high and the power just flattened out. it was kind of like running a restrickor plate. then I got into modifying the intake inside it all they way though and not just the end where it match the block. so the whole thing got open up to a 22-23mm size(BIG) and I found a new big block 10hp carb for a snow blower engine. why I pick a snow blower carb. I wanted to eliminate the factory choke parts but still have the primer button hook up so I could get it to still start.
as I stated earlier I never finish really dialing in this carb when it came to the low circuit because I had change it over to a 22mm mikuni.
when I did install the big carb with the the mod intake. WOW what a big difference and where I found the big gains was in the upper mid range to top end. for most people that just play around with stock or re-ring motors are never really going to see this gain of power because they are not spinning the rpm's that I am talking about. when I say mid to top end gains this is in the 5000 to 7000 rpm's and is done with a engine that has all the major modifications done to it.
so when it came to mid range to top end from a big block carb to a 22mm carb it was kind of hard to tell the difference between the two.
also remember the big block carb bore size mic's out at .936 so that would be about 23.77mm you could safely say that's a big carb...lol
big thing is to figure out how the low circuit works in these carb's. sorry I just don't play with them anymore. not when I can run a mikuni.
markus as been playing around with some of the factory carb's. not sure if he as had any good luck in getting the low circuit system to run right on a small block engine or knows how to maybe get it to work better for something like your project.
 
#27
delray. im kind of having the same thoughts on this. i was thinking cut the intake manifold right in the middle to open it up right thru the entire manifold. then tig it back together. the small carb and manifold will keep the charge velocity hight witch would give good throttle response and low end torque but fall flat on its face at higher rpms. its the same old compromise you face building an old school hot rod. theres always a trade off. to ride this thing between 5000 and 7000 rpm is a scary thought basically unusable power. i'm wondering if theres a cam between stock and the 245. iv ben getting very useful info from several people. thanks for the response. anthony
 

delray

Well-Known Member
#28
that's what I like about the 22mm mikuni/clone carb on my hs-40 build. in a round about way it compensates for that low end problem you normally get with a standard carburetor and gives you that great response throughout all rpm's. you got idle adjustment/pilot adjustment,main jet,metering rod. all these things are adjustable and way the throttle plate works or I should say round throttle tube works. i think the 245 is a great cam when you get all the right stuff together. i am no means a expert at telling you whats the best thing . just a gear head....lol i think for porting i would try to keep the porting at about 22+mm and no more. thats on the intake and the entry into the intake port/bowl area. i dont think it would make any sense to make it any bigger when you carb for example is only 22mm bore diameter.
another get setup that would be below the 245 cam build. would be using a stock cam with the mechanical relief compression arm,animal 16 springs and dyno retainers,advance timing(points engine)hot coil for electronic ignition. a factory 19mm rupp dellorto carb or maybe a 22mm mikuni/clone carb,porting still done and good intake and header and good gearing of course. friend had this setup with the dellorto rupp carb and it pulled easy 4700 rpms. strong little motor for just being a stock cam.
you can see in this video my bike/engine going right around him on this dirt track,but you can clearly see him moving pretty fast too for a mild built hs-40 on a rupp bike. he didn't have a tach on his bike that day but that thing must of been pulling 5000+ on that wide open track and still didn't seem to flatten out on him.
 
#29
delray. remember my engine is a 1972 points. big valve. fat ring piston. hs-45 with no compression release. is there a hotter coil for this engine and how for can i advance the timing with no compression release. when i was 16 just before i stopped playing with minibikes and carts i traded an hs50 big block for a mint condition black rupp roadster hs40 no lighting. it was missing a pully and belt. i never fixed it. instead i sold my two cart frames and five minibike frames and all my engines and built my first car 1966 mustang. anyway i watched your video witch reminded me of the rupp. you were buzzing around that track pretty good. my hs 40 just came. its got good compression but no spark. i'm gonna go in the garage and pull the blower cover off and see my new flywheel. i hope the lighting coil is good. i might thro my lighted steel flywheel and square blower cover on it and sell it. off to the garage. anthony.
 
#34
ok went to pull the blower cover off and looked more closely at the rupp engine. it has really good compression but zero spark. its the original grey paint, there is a coller on the shaft right by the oil seal. i guess for the torque converter. none of the bolts have paint chips from a wrench or socket. so i don't know how much wear it has but i like that it hasn't ben messed with. for a fifty year old engine it looks good. it has a diafram carb and straight manifold so it wasn't on a slant frame. i was hesitant to take it apart before admiring it. i feel like a child not a 60 year old. in the morning i will get to work on it. anthony.
 
#35
Nice
Diaphragm carb may give performance, plus look original
Sounds like a win/win to me
Also if I remember right I think diaphragm carbs can be mounted at an angle so it could have been previously mounted at an angle before.
 
#36
No spark could be just incorrect gap, or just need a cleaning. Make sure flywheel key is not sheared.
Nice to see other TIG welders on here
Pretty easy to fab up an intake
 
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#37
rupp hs40 i bought for the flywheel is not to bad. bore has no groves but has a heavy glaze but i measures. 2.625. probably just hone and re ring. valves are another story. intake has a little slop exhaust guide just as bad as my hs50. they have the same valves so i will buy a another set. had no spark put in points and condenser getting intermitting spark. the kill wire is disconnected and i pulled the coil off no frayed or shorted wires. clean every ground piont and wire lug still intermitting spark. bad coil im sure of it. spun it over with my drill and both legs of the lighting coil are fine. im very satisfied with it. theres a picture of new flywheel next to the big steal beast. anthony
 

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markus

Well-Known Member
#38
your HS50 flywheel in that picture is actually cast aluminum ;) the first almost 2 years they did them in cast AL. Then they transitioned into the steel ones.
 
#39
markus. your right. i just took a magnet to it. cast aluminum. it was painted black when i bought it and its real heavy. i assumed it was steal. one should never assume. anthony.
 
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