HM100 tecumseh engine swap

Nesster

New Member
#1
Hi, new comer to the mini bikes world here.

I just was fortunate enough to pick up a Super Bronc 2 VT-1040 lately. Played with it a bit and not sure I'll keep the tecumseh (HM100) around for long. Ideally I'd go for a used honda engine, if I can find one, but I heard there are some good Chinese honda replicas (predator?). My 1040 doesn't have the electric starter anymore, and don't really want it, so I'm looking for the best bolt-on replacement if any, for motor position and cables. Any pointers for:
1) honda engines models ?
2) other brands / Chinese ?

Also, my brake master cylinder is busted, oil leaking from the assembly if I put oil in it. Any good universal model known here ?

Thanks a lot guys
 

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DaddyJohn

Well-Known Member
#2
You'd be far better off keeping the current engine, for a couple of reasons:

Firstly, you'd kill the (not insubstantial) value of your Bronc by doing such a modification.
Many would consider the word "ruining" not too strong a term.:(

Secondly, it would be a holy nightmare to try and adapt a GX200/clone engine your chassis and retain any of the original power transmission architecture, covers, etc. Lots of re-engineering and fabrication work would be involved. Probably more money in associated parts than it would take to freshen your original engine (which is a great unit btw).

Anyway, welcome to the forum, and best of luck getting the Bronc going!
 

Nesster

New Member
#3
Hi, thank you John for the response. (sick avatar btw lol)

I really like your input on the qualification of the engine, to be a "great unit". I always thought that tecumseh engines were good units, but since I found the bronc, I've heard and read some contradictory arguments. I'd way better like to keep the original engine, to retain the original measurements and such, but I was afraid I couldn't get the engine to "just work" in any condition (read: like honda engineering).

Maybe that's just a carburator thing though, I've seen prople using (mikuni 22mm I think ?) on those engines. Would that be a good approch to have a reliable and more stable engine ? Or is it possible to achieve this with the stock carb ? Are the cheapo 20$ replacement carbs worth it or should I go with the 100$ official replacement, if I decide to replace it ?

I'm going to take the carb apart today. It's supposed to have been recently cleaned by the last owner but I highly doubt it. I have to open the main jet screw almost all the way to get a proper idle, not a normal thing. And the spark plug confirmed this, took it out yesterday and I've never seen so much carbon on a spark plug, was way too rich.

Anyhow, thank you for your input, and to those who may respond to my (most probably other questions :p). We are lucky to have this community for information on those bikes. And I promise I'll do my best to keep the super rare bronc as close as possible to it's original nature ;)
 

chrisr

Active Member
#4
The HM100 are great motors and with the lighted coil they are good for the eclectic start and powering lights. If the original carb can be cleaned is the best bet, usually just need to clean the jet. I also echo DaddyJohn in the value of your Bronc is with the HM100 and once tuned will last a long time.
 

45t

Well-Known Member
#5
Welcome to the hobby (and addiction) ;). I saw your post yesterday and i hesitated to respond because I didn’t want to come across as telling anyone what to do with their bike or build. Your bike Is so beautiful/original looking and you can do what you want with it. I’ve never had an original bike but I’ve always appreciated that they are only original once.

Since Most of us on OldMiniBikes And in the hobby can never just stop with owning one bike anyway, I recommend finding a project bike to build and modify. I’ve found that I enjoy the build more that anything, but I understand that may not be the case with everyone.
Just my 2cents and I hope that I didn’t offend you.
 

Nesster

New Member
#6
Welcome to the hobby (and addiction) ;). I saw your post yesterday and i hesitated to respond because I didn’t want to come across as telling anyone what to do with their bike or build. Your bike Is so beautiful/original looking and you can do what you want with it. I’ve never had an original bike but I’ve always appreciated that they are only original once.

Since Most of us on OldMiniBikes And in the hobby can never just stop with owning one bike anyway, I recommend finding a project bike to build and modify. I’ve found that I enjoy the build more that anything, but I understand that may not be the case with everyone.
Just my 2cents and I hope that I didn’t offend you.
Hey 45t, thanks for the concern. I actually thought about writing something about not wanting to offend anyone, as I understand the religion of originals ;) And about enjoying the build, I know, I'm more of a computer guy and I'd build a nice gaming rig everyday over actually gaming with it I think.

In all honesty, what I'd really like to do with the bike is restore it to some very nice state if I ever have the time (and I setup a proper workshop). But with work and other hobbies (addictions), I'm just not sure if/when that'll happen. Maybe a winter project for next year. I've tinkered with bikes before, just not minibikes. And to reassure you a bit, I'm not the kind that butchers first and fix with wire later, I like to keep things where they belong, doing what it was meant for.

Cheers,
 

45t

Well-Known Member
#7
Hey 45t, thanks for the concern. I actually thought about writing something about not wanting to offend anyone, as I understand the religion of originals ;) And about enjoying the build, I know, I'm more of a computer guy and I'd build a nice gaming rig everyday over actually gaming with it I think.

In all honesty, what I'd really like to do with the bike is restore it to some very nice state if I ever have the time (and I setup a proper workshop). But with work and other hobbies (addictions), I'm just not sure if/when that'll happen. Maybe a winter project for next year. I've tinkered with bikes before, just not minibikes. And to reassure you a bit, I'm not the kind that butchers first and fix with wire later, I like to keep things where they belong, doing what it was meant for.

Cheers,
you got a good head on your shoulders and are thoughtful in your response. I look forward to seeing future posts from you. Again, welcome to the mini Bike culture And the site. There are some good folks here that can help if you have any questions. :scooter:
 

Nesster

New Member
#8
Ok, so took the carb out yesterday, here are the pictures. BTW, if this is not the right forum section to ask for advice please let me know and I'll post accordingly.

Not sure the carb is still in working order, some corrosion in the main jet socket. I cleaned the best I could with carb cleaner. The needle was so gummed up I had to use sanding paper to take it all out (may still not be optimal). Cleaned the main jet very well I think (the mini hole too). After putting it back in, at first it seemed like I could achieve a good idle and throttle response seemed all right, but then when I started it again a few minutes later it started, revved to good idle then slowly died again :p
Needle before/after:
IMG_20200407_132606.jpg IMG_20200407_170928.jpg

Some questions I have for this particular carb:
1) is the float assembly complete ? On some other carbs there's a small spring to "push down" the float. In here there's none.
IMG_20200407_132731.jpg IMG_20200407_133044.jpg IMG_20200407_133055.jpg IMG_20200407_133119.jpg

2) What's this lever for ? it's activated by the throttle wire. When the engine runs it goes back to it's original position but not if the engine's off (bad spring ?)
IMG_20200407_131413.jpg

3) The stock carb seems pretty fragile to the bike position (up right vs on the kick stand for example). I'm considering a mikuni 22mm, how would that impact the other "lever" that's activated with the throttle (see previous picture). I guess that's what I'd need:
https://www.gopowersports.com/22mm-mikuni-carburetor-performance-kit/


Other parts:
a) I will need a new air filter. I only have the filter (in really bad shape), and the end part (no boot to fix to the carb). If I buy the mikuni kit this is fixed.
IMG_20200407_143940.jpg IMG_20200407_143951.jpg IMG_20200407_143935.jpg

b) Belt. What belt do you guys recommend for the 40 series ?
IMG_20200407_152958.jpg

c) I'll also need another handle brake / master cylinder (unless I can by the parts inside to repair it, not sure, never done that). Mine's leaking crazy if I put oil in it (leaks by the handle I think).


And finally, a bit of a look into the engine. Seems pretty rough to me but I'm no expert on engines :p
IMG_20200407_134617.jpg IMG_20200407_134719.jpg
What is this hose and why should it be plugged like that ?
IMG_20200407_131553.jpg

Thank you for any input !
 

chrisr

Active Member
#9
The hose that is plugged would be used with a fuel pump which seemed that model used, however, looks like you had some blowby possibly the rings and accounting for the oil around the open hose (crankcase breather) and the air filter is pretty bad. The rod you have circled is for the governor and the enclosed link describes how to adjust. Did you run a small wire up where the main jet lives to insure the passage is clear? Not sure if that carb is original, may still work ok.

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh_horizontal_shaft/lh318-358-owners.pdf
 
#10
Ok, so the engine IS due for a rebuild, good to know.

I think I cleaned the main jet housing, actually I'm sure I did, but maybe not far enough, I'll have another look. Thanks
 
#11
Well, I'm happy to report that the bike is now running pretty well, with the original engine and a good idle (although it's kind of eager to go ride when it's still on choke as the engine warms up, as I have to keep the RPM a little high to keep it idling well :p). I was able to find a good, retired, mechanic that enjoys the challenges. He verified the points and all ignition elements and I actually had brand new points. He adjusted them to the specs too. The carburator was changed for a used one he had in his shop, looks like an original too.

One key thing that helped was replacing the brand new NGK spark plug with a Champion one. I had looked what spark was needed for the HM100 engine and went with NGK because, well, I've always bought NGK. The Champion he put in was an old one lying on his workbench. He suggested to go with the Champion RJ17LM when I change it. Feel free to comment on that choice if you have different experiences.

Thank you all for your inputs. I'm glad I was able to retain the original engine and not screw around trying to fit a honda clone in there. Will report on more adventures if they come along.

Happy trails,
Nesster
 
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