small frame H tecumesh in the works

old shed finds

Well-Known Member
#2
this one has been unfinished for quite awhile up on my bench, I finally got around to modifying a carb to try out and see what happens, so far so good! Now to figure how to set it up so I can paint it!


Tecumseh H25-H35 custom build for mini bike ShareEmbedEmail


Heres the internals of the short block:

View attachment 251226 View attachment 251227 View attachment 251228 View attachment 251229 View attachment 251230
That one is going to be sweet first thing I notice is its bearing PTO cover...
 

delray

Well-Known Member
#4
little guy sounds like it rev's to the moon. was that the Tecumseh camshaft 32197A . I been looking into using one of them and sending it off to dyno.
It also appears you wouldn't have modify anything to install it? I have not look into lifters. does it take the older flathead lifters or is the cam lobe base circle just little different in size? like the ohh camshafts with there compression relief.
 

markus

Well-Known Member
#5
little guy sounds like it rev's to the moon. was that the Tecumseh camshaft 32197A . I been looking into using one of them and sending it off to dyno.
It also appears you wouldn't have modify anything to install it? I have not look into lifters. does it take the older flathead lifters or is the cam lobe base circle just little different in size? like the ohh camshafts with there compression relief.
Yea it will wind right up, hopefully it will still make power from a pull though as thats where its needed the most. I had my doubts that the carb was going to work, After having a few carb bodies apart I noticed that they deviated a lot on air passages in the idle/low speed circuit depending on bore size so the H, HS40, and even HS50 specific carbs have totally different. I started to think upsizing the bore was going to create an issue with transitioning off idle, but it actually seems really smooth and and the adjustment of low speed needle so far does not seem finicky.

Yes that is the 32197a, The late model engines that used them called for the same lifters as the earlier engines used. IIRC though the overall lobe measurement came in just slightly different between the cams. Cant remember which way as its been awhile since I have measured but with new valves having to be trimmed to fit no matter what it was an irrelevant difference. And yes all the release parts are built in and on the inside, like the early HS cams were done.
 

delray

Well-Known Member
#6
maybe something to try out markus when you install it on a bike is to go with a true header pipe and if your running a clutch only set up . go with a least a 2500 stall spring and if you don't have a jackshaft on that bike? go with the biggest rear sprocket you can fit safely on. that all should make it pull hard right up to 4700+ rpm's without any problems. just watch for valve float with the stock springs. to bad you can't get a billet rod to fit in the H blocks without modifying them. I do have one motor that is running a newer stock ohh rod that is only ground and polish and that's been holding up to 5000 rpm's for couple years now. also big plus you are running that aluminum flywheel and bearing crank. makes it much easier to spin to the moon....
 

markus

Well-Known Member
#7
just watch for valve float with the stock springs. to bad you can't get a billet rod to fit in the H blocks without modifying them. I do have one motor that is running a newer stock ohh rod that is only ground and polish and that's been holding up to 5000 rpm's for couple years now. also big plus you are running that aluminum flywheel and bearing crank. makes it much easier to spin to the moon....

I modified an old set of upper spring retainers and pressed them together with the new set to double them up for a little more spring tension.....I'm so ghetto! :D
 
#8
Nice work as alwaysHow about a little tutorial on the carburetor idle circuit modifications.

As I recently stated in another post, knock off carbs can be used for expediency but I prefer original tecumseh carbs if possible .

There are three carb killers in my experience, corrosion due to water damage, broken float pivot posts and poor/no idle due to stuck check valves. The first two are "fatal" faults whereby the carbs are junk. The third, check valve problems, are occasionally corrected by soaking, tapping and boiling. But these methods do not always work.

I would be interested in seeing your method as the likelyhood of success is much greater.

Your contribution to the craft is immense, highly respected and greatly appreciated.
 

markus

Well-Known Member
#10
Nice work as alwaysHow about a little tutorial on the carburetor idle circuit modifications.

As I recently stated in another post, knock off carbs can be used for expediency but I prefer original tecumseh carbs if possible .

There are three carb killers in my experience, corrosion due to water damage, broken float pivot posts and poor/no idle due to stuck check valves. The first two are "fatal" faults whereby the carbs are junk. The third, check valve problems, are occasionally corrected by soaking, tapping and boiling. But these methods do not always work.

I would be interested in seeing your method as the likelyhood of success is much greater.

Your contribution to the craft is immense, highly respected and greatly appreciated.
The ones with what looks like a tiny freeze plug on the bottom of the Idle port you can drill out, the ones that have a ball bearing pressed in to plug the hole wont drill out. Some of these actually DO NOT have the "rattle rod" in them, they have a tube pressed in that is drilled to reduce the size. So some of these carbs that dont rattle may not always have a plugged or stuck rod inside. For instance the one I built for this motor above was that way and I installed a rattle rod instead when I put it back together. This info below from the first one I drilled out may help:

Here you go ;) https://oldminibikes.com/forum/inde...t-find-help-needed.160675/page-2#post-1185772

And to go along with that info that I posted about the idle circuit in that thread, I had actually drilled out the plug on one since that posting and pulled the rod out. (not a great pic was trying to focus on the corrsion buildup on the rod, this one did not rattle and barely passed any air or liquid through the passage):



gotta figure an easy and reliable way to plug the hole back up still... don't want to risk any type of adhesive plugging the very tiny drilled inlet in the main port though, a lot of times the plug actually looks like a tiny freeze plug, but I have not really tried to do any searching as of yet...I was thinking of pressing in a piece of solid AL rod or something. Hopefully I can find a solution for that and get some more of these saved that I cant get freed up and degunked.

Page 10 of the Tecumseh service manual shows a cutaway drawing showing the rod, and the warning that I gave in the info I posted in the above linked thread about needle installation as well. I have to say after actually drilling one out and pulling the rod, I believe that the rod is actually nothing more than reducing the passage in size and not actually serving any other purpose, hence why its important to make sure you hear it rattle, If not it plugged or restricted even more than it already is. I always thought it opened a closed a passage as you came on and off the throttle but that does not seem to be correct. And a "fun fact", the rod is actually the same diameter/material as the float pin, only not as long. It is about 3/32" dia where the carb passage is 1/8".

o_O Double Bonus Fun Fact, in the pic below the assembly in the upper left is the high speed needle for a Dellorto UA19 (black widow carb). the Tecumseh float pin is also the pefect size for pin (makes the T) so you can make adjustments.....for some reason this carb assembly was missing it, it was an NOS out of box unit so maybe it was never installed or something, never the less I will be using a Float pin for it :cool:

 

markus

Well-Known Member
#11
heres what I have been doing to the exhausts on these earlier style builds that use the street elbow and 7 hole muffler since they are so restrictive: a big step drill bit will hog them out pretty good on its own, a little shaping with a Dremel can get them a little more as well. A bolt on header of course will really open things up, but when your trying to keep an original look you get kinda limited to what they used at the time.

This engine above got as much carving as I dared to go, and it will get a muff thats transitioned like on the right as well


Some HS40's I did with this mod previously, they sounded pretty good still, and liked the more open flow!
 

delray

Well-Known Member
#14
I notes you set the timing little different with the H blocks at 65 and the HS blocks at 35. have you ever notes a difference in how they pull over when using only a bump cam decompression relief setup only or even the newer cams and have you ever hook up a timing light to see the difference in timing would be. if not I think it would be interesting to play around with and maybe see.
 

markus

Well-Known Member
#15
I notes you set the timing little different with the H blocks at 65 and the HS blocks at 35. have you ever notes a difference in how they pull over when using only a bump cam decompression relief setup only or even the newer cams and have you ever hook up a timing light to see the difference in timing would be. if not I think it would be interesting to play around with and maybe see.
Not really much of a difference, some of the ones where I deleted the compression bump out of were not even that bad to pull compared to an HS with modded cam. This one is actually a little stiffer than I thought it would be (not kickback stiff though), but I have only used this style cam before in a 2000 H35 which has small valve and 2lb heavier flywheel on it. Never messed with timing other than setting to factory.
 
#18
heres what I have been doing to the exhausts on these earlier style builds that use the street elbow and 7 hole muffler since they are so restrictive: a big step drill bit will hog them out pretty good on its own, a little shaping with a Dremel can get them a little more as well. A bolt on header of course will really open things up, but when your trying to keep an original look you get kinda limited to what they used at the time.

This engine above got as much carving as I dared to go, and it will get a muff thats transitioned like on the right as well


Some HS40's I did with this mod previously, they sounded pretty good still, and liked the more open flow!
I know this is an older post but I’m building a 1968 snow blower HS40 for my 1970 Lil Indian and I’ve search for these mufflers til I’m blue in the face. Is there any chance you would share any more info for a copycat like me?
 

markus

Well-Known Member
#19
I know this is an older post but I’m building a 1968 snow blower HS40 for my 1970 Lil Indian and I’ve search for these mufflers til I’m blue in the face. Is there any chance you would share any more info for a copycat like me?

They are available, problem is right now everyone jumped the prices up to $85 or more for them. They were selling on average 40-50 on a good day (for the seller) before. I have been trying to find one for a customers engine for a reasonable price because my supply of them has run down to what I have for pre 1970 engines that I have saved to build. But I am going to have to sell him one of mine cause as of this morning the tank sealer is cured and the engine is ready for paint, I'll just nix a build off my list.

Good luck with your build!
 
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