HS40 cam upgrade

#1
Looking at putting a 245 cam in a HS40 I'm rebuilding. The reading I have done says its a drop in cam, I can still utilize the stock springs and keepers. Is the cam worth the upgraded throttle response, or am I just wasting money with it?
 
#2
It’s not a drop in…I have had to remove the governor rod, drill and tap the hole….then go to dyno cams, and order the retainers springs and clips….can’t remember the numbers right off but there is several post on this subject…

the mikuni you’ll need to add will give you the throttle response you seek….and yes you are probably wasting money but it’s a damn fun way to waste it!

you’ll need an ARC billet rod too for safety reasons…
 

markus

Well-Known Member
#3
You going to have dyno grind one for you? I have a box of cams was thinking about sending some in.

I have the Tecumseh motorsports single spring retainers if you’re looking for a little more durability. They are $30 plus the ride in the lower 48 FEA7BE95-8DF8-4F56-A159-469DFF4C880C.jpeg
 

cfh

Well-Known Member
#4
i had dynocam do about 15 cams for me last fall, the HS40/HS50 dynocam 255 (which is just a tad more aggressive than the 245.) had to send in the stock cams, and then they weld and grind them. took about 2 or 3 weeks. BUT there are *three* different 255 grinds. I had to send all the cams back and have them re-do them again, because they ground the "whimpy" 255 version. the best 255 grind was the one they were using from about 10 years ago. had to send one of those too, so they could re-grind my cams correctly as i wanted, the second time.

as to new valve retainers and springs. that is optional, not required. i run the 255 all the time with stock valve springs and retainers. it just depends how you are using the motor. i run off-road, on varying terrain. if you run on the open road, wide open for lengths of time, then you will need heavier springs. but for what i do, with minimal time spent with the throttle WFO, bigger springs don't change anything.

and also yes you should remove the governor if you're using any non-stock cam, otherwise you are hog tying the motor. and probably put in a billet connecting rod too. though to be honest, i don't do the billet rod all the time. again, depends on how you're riding. if you're on the open road going WFO for anything more than probably 5 seconds, you need better valve springs and a billet rod. otherwise you can just modify the stock rod and that will work dandy. that's what i have done on bunches of motors, without a single rod failure. but i *know* what will kill a tecumseh rod, and i stay away from running the motor for any length of time at WFO.
 
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cfh

Well-Known Member
#6
i would agree the 245 or 255 dynocam is worth it. that and a slide carb and open exhaust are the things that make an HS50 really kick. the problem is getting the dynocam. they are not readily available. and as i found out, sending a stock cam(s) to dynocam for re-grind does *not* always work as planned. (I sent my cams in and got 255 whimp version1. sent them back and got 255 less whimp version2. but really wanted 255 kickass version3.) that's why i made a machine to grind my own cams. i've done that probably 30 times and love the results. but it's time consuming to do.
 

delray

Well-Known Member
#7
hoy1967, here is my link to hs-40 build. you could say i started this crazy hs-builds with this motor showing the guys what aftermarket stuff will work with valve train etc... Hs-40 build | OldMiniBikes.com
don't have to go crazy like i did, but i do show what parts will work with the mods that you will be doing. the only aftermarket retainers that will work with 18 animal springs are from dyno cams for a flathead Briggs that will need little machine done. the Tecumseh retainers will have a different off set and even the factory animal retainers will too..not good. some guys have use the stock stuff and it will run, but anytime you start to reeling rev that little guy to 6000+ the valves will float and you always risk popping the stock retainers off or breaking them. buy the retainers cheap insurance...lol
The 245 cam is rated right around 6800-7000 and the 255 is right around 7500
 

delray

Well-Known Member
#8
i would agree the 245 or 255 dynocam is worth it. that and a slide carb and open exhaust are the things that make an HS50 really kick. the problem is getting the dynocam. they are not readily available. and as i found out, sending a stock cam(s) to dynocam for re-grind does *not* always work as planned. (I sent my cams in and got 255 whimp version1. sent them back and got 255 less whimp version2. but really wanted 255 kickass version3.) that's why i made a machine to grind my own cams. i've done that probably 30 times and love the results. but it's time consuming to do.
I believe you will want to asking dyno for the 255 OHV 5.5HP TECUMSEH GRIND
tecumseh dyno cams.jpg
 

cfh

Well-Known Member
#9
the guy i talked to, Randy, he was shocked when i sent him my 10 year old 255 cam. he didn't think that grind even existed. which i thought was weird. but yea maybe that is the trick, use the 255 OHV 5.5hp nomenclature...
 
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#10
Thanks for all the great help, I purchased the 245 cam and I already had the billet rod. Just going .20 over so I have a fresh and square bore. Im wanting to keep the stock appearance on the carb, any suggestions there?
 
#11
Thanks for all the great help, I purchased the 245 cam and I already had the billet rod. Just going .20 over so I have a fresh and square bore. Im wanting to keep the stock appearance on the carb, any suggestions there?
My honest opinion-
If you are serious about performance and drivability (or rideability) then i would use a slide carb. Lawn mower carbs are fine and can work really well but they are kind of on/off if that makes any sense. On a governed engine that is stock, running stock bore, stock cam and stock RPMs the stock carb works great once it is tuned correctly.
I ran a stock Hs50 carb and it worked great but once i upgraded the engine with billet rod, flywheel, cam and valve spring mods, the stock carb couldn't really get the job done for my style of riding.
The slide carb gives a lot more "part throttle" response, and can be jetted to better suit the mods.
This is just my experience and my opinion.

If stock appearance is of the utmost importance, then i know people have run bigger tecumseh carbs on smaller engines, but i have no experience with that. Someone here will definitely know.
 
#12
This has been an interesting and educational thread. The "take away" for me is that it seems like it is not really worth upgrading with a performance cam on a Tecumseh unless you are also upgrading with a performance carb as well. Is that correct?
Michael
 

delray

Well-Known Member
#13
This has been an interesting and educational thread. The "take away" for me is that it seems like it is not really worth upgrading with a performance cam on a Tecumseh unless you are also upgrading with a performance carb as well. Is that correct?
Michael
correct, really need the whole package, carb, good header...etc..
 

cfh

Well-Known Member
#14
the chain is only as strong as the weakest link. so if you put in a hot cam but run a stock carb, the cam really is not doing much of anything. also as Mass said, you can't really tune a stock carb with different jets. also stock exhaust will hog tie the set up too... an open exhaust would be ideal to let the whole system "breathe".

now as a compromise, you could run a Dellorto. that would be "period correct", opposed to say a 22mm xr75 style pz22 slide carb (which is what the majority of the people here are using.) The Dellorto is awesome, probably better in some respect to the pz22 carb. but the down side is cost. now you don't need a Ua19 dellorto (as used on Rupp Black Widows)... in fact i would not recommend that carb as it's really expensive. but you can get 16mm to 22mm dellortos on ebay often for cheap. parts are a bit of an issue but for the most part BlackWidowMotorSports.net sell everything you would need. I have used all the dellorto sizes from 16mm and up, and they all work great. like *way* better than any stock tecumseh carb. even a 16mm dellorto works great, though 18mm to 22mm is ideal. in fact i have NO motors with a stock tecumseh carb... those butterfly carbs are a joke...

now if money is a factor, the pz22 carbs made in china and available on ebay are pretty awesome, for all of about $20, and often even come with an air filter! you can't beat it. and often they are jetted correctly right out of the box (not always, but often.) i would buy a set of M4 jets (#85 to #95) just to have, they are cheap on ebay. you do need an intake manifold. but again if you are on a budget, you can mod the carb a bit to fit on a stock tecumseh intake manifold. not the best way to go, but it works. and if you don't like the result, all your out is a $20 carb and a $12 db30 style throttle (yes you will need a new throttle assembly with the slide carb, as your stock cherry assembly won't work.)

if you want to read more about this stuff, including Dellorto carbs, check out this link:
http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2
 
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#15
Hopefully the OP (hoyt) is reading the replies above. It sounds like he is wasting his $$ on the cam if he does not do a performance carb upgrade as well...
Michael
 
#16
My honest opinion-
If you are serious about performance and drivability (or rideability) then i would use a slide carb. Lawn mower carbs are fine and can work really well but they are kind of on/off if that makes any sense. On a governed engine that is stock, running stock bore, stock cam and stock RPMs the stock carb works great once it is tuned correctly.
I ran a stock Hs50 carb and it worked great but once i upgraded the engine with billet rod, flywheel, cam and valve spring mods, the stock carb couldn't really get the job done for my style of riding.
The slide carb gives a lot more "part throttle" response, and can be jetted to better suit the mods.
This is just my experience and my opinion.

If stock appearance is of the utmost importance, then i know people have run bigger tecumseh carbs on smaller engines, but i have no experience with that. Someone here will definitely know.
This makes sense, I guess I know better to expect better performance from the stock carb. What slide carb is best suited for the HS50?
 
#17
the chain is only as strong as the weakest link. so if you put in a hot cam but run a stock carb, the cam really is not doing much of anything. also as Mass said, you can't really tune a stock carb with different jets. also stock exhaust will hog tie the set up too... an open exhaust would be ideal to let the whole system "breathe".

now as a compromise, you could run a Dellorto. that would be "period correct", opposed to say a 22mm xr75 style pz22 slide carb (which is what the majority of the people here are using.) The Dellorto is awesome, probably better in some respect to the pz22 carb. but the down side is cost. now you don't need a Ua19 dellorto (as used on Rupp Black Widows)... in fact i would not recommend that carb as it's really expensive. but you can get 16mm to 22mm dellortos on ebay often for cheap. parts are a bit of an issue but for the most part BlackWidowMotorSports.net sell everything you would need. I have used all the dellorto sizes from 16mm and up, and they all work great. like *way* better than any stock tecumseh carb. even a 16mm dellorto works great, though 18mm to 22mm is ideal. in fact i have NO motors with a stock tecumseh carb... those butterfly carbs are a joke...

now if money is a factor, the pz22 carbs made in china and available on ebay are pretty awesome, for all of about $20, and often even come with an air filter! you can't beat it. and often they are jetted correctly right out of the box (not always, but often.) i would buy a set of M4 jets (#85 to #95) just to have, they are cheap on ebay. you do need an intake manifold. but again if you are on a budget, you can mod the carb a bit to fit on a stock tecumseh intake manifold. not the best way to go, but it works. and if you don't like the result, all your out is a $20 carb and a $12 db30 style throttle (yes you will need a new throttle assembly with the slide carb, as your stock cherry assembly won't work.)

if you want to read more about this stuff, including Dellorto carbs, check out this link:
http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2
Great info! TY
 
#19
I forgot all about the Dellorto carbs. I've never messed with them, but many have and they seem to perform really well.

I'm running the pz22 style "chikuni" carb with bigger jets. Night and day difference. It was cfm and del ray that put me on to those carbs. I ended up making custom intakes to fit the slide carbs.
 
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