Hs50 build?

Ok so I’ve been watching you guys build these motors...so I thought I’d try one myself...be kind first time....I purchased all the known parts...arc rod Briggs retainers and keepers and the 18# springs etc....had to hand file the lower retainer cup to fit,as you all know, cut out the ports...had to figure out how to make a manifold for a mikuni style carb....torque tube...and here we go... B791A844-8E3B-4DD0-9593-E2C3FCAFAFCE.jpeg 82D0090B-0D23-4D85-ABC1-7A186BC5475F.jpeg 2E31C04B-1C51-4432-B4D4-D94E5F592A53.jpeg 588ACD8C-E20D-4E2A-9E2A-8D936FEB6E0C.jpeg D1C353D7-921C-4E6A-8F57-4772329367C9.jpeg 749DD1F9-C9F0-4212-8EAD-E62F30C77105.jpeg 4EC34BB2-181C-47DC-AA61-3689F7DA4FBD.jpeg 88006680-EB14-44C0-A798-C8AB4542D7D2.jpeg 30C89D56-E55A-4C8E-8C5E-BC5532680953.jpeg 3AEFC5C2-360B-40C9-ACD3-8472C47EE96D.jpeg First off the piston was put in by guy I bought engine from and he apparently went by the numbers on the shroud and it was wrong...I went by the bore size bought correct piston and .010 over rings....bought a 400 grit flex hone and started....everything went together pretty good those retainer clips are a pistol....so now that it’s all together I’m procrastinating the start....I’ll keep you updated....


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I like the home made lathe on the retainers...hey it works.
up dates will be good to here. what kind of bike is it going on....:scooter:


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sounds like it needed little carb tuning for sure,that should be easy for you..

what was that carb ? same kind of mikuni style 22mm carb they us on a animal?
one thing I have found with the type of mikuni/clone 22mm carb's I have been using is once you got it setup good. it only takes one pull on a cold start with the choke lever on and it will fire right up on high idle until you turn off the choke lever and idle right back down. don't be afraid to let it idle little high 1500+ and if you go only with a clutch. use a 2500-3000 stall spring. 3000 might be better. testing for your app will tell you...
Thanks for the knowledge..yes I somewhat “fine tuned” it in and like you said cold start one pull....I used a cheap 16mm carb...I have a mikuni clamp on carb wanting to use as soon as figure out an intake....I will probably urs a clutch for now, I have a fairly new one already here.......I’m really hoping to put a series 20 on it eventually....I’ve got it set up now So im going to break in slow on the bench, drain the first round of break in oil fill it again and run the snot out of it....just to see what happens....I may go with a 22mm carb...they a lot better?

Ok stupid question....same (22 v 16) intake or make new bigger one?
Depends on the mounting bolt locations on the carb flange, as well as the inside diameter of the intake runner.

If the mounting holes are in the same location, and you can open up the runner to match the bigger carb then I bet it will be fine. Nice job on that intake BTW


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personally think if you switch over to a 22mm mikuni/clone carb it will run much better and what I mean by that is you will be able to change the jets/pilots and get it spot on and gain better performance with the larger carb over a small 16mm carb.


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I have a bunch of HS50 engines (stock other than carb/exhaust) with a variety of carbs. Probably 25 of them, all on bikes. From 16mm china clones to 22mm china clones to Dellortos ranging from 16mm to 22mm. To be honest, there's almost no performance difference between the 16mm up to the 22mm. The big performance gain is just getting away from the stock Tecumseh carb, and getting the jetting right. I also have a bunch of different intake manifolds too. From stock to custom made straight stainless steel using 7/8" material. Again no performance difference (though custom intakes look way cool!)

The big thing is... just get away from the stock Tecumseh carb. Pretty much *anything* with a slide from 16mm to 22mm will be a nice performance increase. The difference in 16mm to 22mm is really minor. But given the cost is nearly the same, 22mm is probably the way to go. That way if you go crazy with a better cam or some other performance thing, you'll be able to feed the motor better. the nice thing about the china 16mm is the jetting is pretty much spot on out of the box, where the 22mm is not.


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other reason you may not experience a big difference in a 16mm to a 22mm might be in the way you rebuild your motor. for example if it's just a rebuilt and no real mod's done to it and you have it on a stock minibike frame and stock gear setup with a stock clutch or torque converter or worst a 30's with 10 percent overdrive. the bike never really gone to spin any good real rpm's or quickly. so yes at low end power your not going to experience any throttle response difference from a 16mm to 22mm or top end because the bike just doesn't rev up high rpm's. now if you build a hs-40 or better yet a hs-50 with little porting,stock cam with animal springs,good header and real good gearing setup with a good amount of stall in you clutch so all this will allow engine to rev much quicker and higher into the 4700-5000 rpm range you will feel a big difference in the type of carb you use.
last year I did help a person with a rupp bike that had some cool mod's done to it and was very impressed. that engine was a hs-40 with the block ported,billet rod,stock cam,16# animal springs and dyno retainers,rupp header,better gearing,the big thing that I was very impressed with it was the 19mm factor dellorto black widow carb with adjustable main jet that was on it. that bike had no problem pulley 4700+ rpm's in 125 ft and this spring it was turning a easy 5000+ on a 1/3 clay circle track.
guess what I am saying it's a whole combination of things that need to be done to achieve noticeable difference in carb size.


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I would say you're pretty correct. I do run pretty much stock Tecumseh HS50 engines. Here's what i do...

1. remove the governor
2. use a straight exhaust (usually custom made).
3. often (but not always) an Arc billet connecting rod.
4. lap the valves.
5. check the ring gap... hone and re-ring if needed
6. use a 16mm to 22mm slide carb and custom or modified intake (sometimes china made, sometimes dellorto. rupps get dellortos)
7. run a torque converter (series20 or series30, bike dependant).
8. run stock gearing (usually 11t on the jackshaft, 54t or sometimes 60t on the wheel.)
9. all bikes are 10" or 12" or 14" spoke wheel varieties (like a rupp or speedway or fox)

i'm not sure that is considered 'stock', but i guess it leans that way.

Recently i have started playing with cams. made my own cam grinder/duplicator, and have a dynocam 245 and 255 to use as the reference cams. I have built one HS50 with the 245 and a 22mm carb and arc rod, on a Fox 14" wheel bike with a series 30 torque converter. i wouldn't say it spins that fast. But the torque converter may be the sort of governor to hinder high rpm.

i think if you want high rpms you really need to use a centrifugal clutch... but i never use those.
So I’ve been playing a little thus weekend.....here’s what I started with.... F8F2C4F3-F0AD-4615-B570-D69978B5A047.jpeg did a little sanding and painting...reworked the front end....used all allen/cap heads on build.... AAF029BC-7062-4317-B372-FFBF59D7989C.jpeg 17207651-2D39-4E17-8AF6-2E2A1ED457B8.jpeg AE3DF0EA-2D09-4F41-A0A5-FD5369CD44F1.jpeg 60B990F6-4077-4727-BD08-8E253507B81D.jpeg 5DB7E2EA-814D-4F73-B380-694812859712.jpeg i have a 12 tooth green spring max torque on front and a 60 tooth on rear...I’ll get a tank mounted today and take it for a spin....