New Tecumseh HS40 carb(s)

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cfh

Well-Known Member
#1
#1
I have a 1971 Fox Scrambler and i've been messing with the carb on this thing. Just can't get it to work consistently, seems like i'm chasing my tail on it.

foxscrambler.jpg

So decided to get a new carb, since they're like $15 each (including shipping!) In another thread there were some suggestions. I thought i would report here how the new carb(s) worked.

First one i bought was from ROP (rugged outdoor products, Bluffton IN). It's part number NJJ-631921, and it replaces the stock Tecumseh 631921 carb. I'm not sure that's the exact correct carb for an HS40, but it was what someone suggested, so I bought one. I got it off ebay and here was the link:
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=251086321740
With 961 sold to date, it seems to be a popular model.

carb_rop.jpg

It looks identical to the original HS40 carburetor, with a couple small exceptions. The choke lever is slightly different, but with some small bends, that was easy to fix. The choke lever now looks and positions the same as the original. The gas intake port was slightly different. No big deal, slight turn and it was positioned in the proper place. And last, the float bowl didn't have a sprung drain plug. So i used the original carb's float bowl on the new carb, because I like that feature. Also the float itself is plastic, opposed to metal in the original unit.

Hooked it up, and the bike started and ran great! just a couple small tweaks of the three carb adjustment screws, and the bike runs strong! Well worth the $15 total price for this unit.

I bought new carbs from two other sources also. I will report back with those when i get them and have a chance to install.
 
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Harquebus

Harquebus

Well-Known Member
#3
#3
Those carbs can be had for as low as $9.40 on the same site... Any particular reason you chose to pay $15?

I guess it is safe to say these carbs are all made in China.

I bought a Chinese Briggs diaphragm carb off eBay as well and it worked flawlessly, so...:shrug:
 
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capguncowboy

capguncowboy

Well-Known Member
#6
#6
I also suggest the ROP brand on a regular basis. I have bought a dozen or so and haven't had a single issue. The extra $5-6 is insurance well spent.
 
Harquebus

Harquebus

Well-Known Member
#7
#7
I understand your reasoning perfectly. Many thanks for sharing the intel. :bowdown:

Also, when it’s a US-based seller you’re supporting a “brother” plus it generally arrives faster than the $9.40 price leader which comes directly from mainland China, whether by slow boat or fast jet airplane...
 
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C

cfh

Well-Known Member
#9
#9
Next up was the 1972 Rupp Hustler i bought recently. The carb float bowl was leaking, and i feared that the carb would be a disaster. So when i ordered from ROP (rugged outdoor products) via ebay, i ordered *two* of the tecumseh replacement carburetors.
CARBURETOR for Tecumseh 631921 632284 631070A fits many H25 H30 H35 H40 Engines | eBay

The Rupp also had a 1971 Tecumseh HS40 motor. With the stock carb, it ran OK. Through the power band there were definitely flat spots. Also it would start inconsistently, and through the warm up, do weird stuff and generally be pretty picky about the choke position (it was 40 degrees outside today.)

hustler.jpg

So installed the new ROP carb #631921. The only issue was the choke lever, which was set up for the left side of the carb. On the Rupp, it needed on the right side of the motor. It took some bending, but in the end, that worked out OK.

carb_rop2.jpg

So how did the new ROP carb run? Pretty darn good! The power band smoothed out, and starting the Rupp in the cold and through the warm up period was much 'easier' and consistent. Again well worth the $15. Only a couple small adjustments needed to the high speed jet adjustment (at the bottom of the float bowl).

Next up, a Tecumseh H30 motor and some carbs from Amazon! (again suggested by someone in another thread.)
 
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C

cfh

Well-Known Member
#10
#10
Got the carb in from Amazon today. As pointed out before, it's probably not a good choice:
https://www.amazon.com/gp/product/B077M7NYB6/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Though it has the desirable float bowl with the spring loaded drain, it also has a "funky" choke. But probably the biggest issues is the port for a primer bulb.

carb_amazon1.jpg

carb_amazon2.jpg

The choke is particularly an issue as it will interfere with the standard Tecumseh air filter. I believe it will prevent the choke from being fully "off". I can probably bend it, but it certainly isn't as nice as the ROP shop replacement tecumseh carb.

And of course the next issue is the port for the bulb primer. Can i just plug that? hmm....
 
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markus

markus

Well-Known Member
#11
#11
cfh said:
Got the carb in from Amazon today. As pointed out before, it's probably not a good choice:
https://www.amazon.com/gp/product/B077M7NYB6/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Though it has the desirable float bowl with the spring loaded drain, it also has a "funky" choke. But probably the biggest issues is the port for a primer bulb.

View attachment 104140

View attachment 104141

The choke is particularly an issue as it will interfere with the standard Tecumseh air filter. I believe it will prevent the choke from being fully "off". I can probably bend it, but it certainly isn't as nice as the ROP shop replacement tecumseh carb.

And of course the next issue is the port for the bulb primer. Can i just plug that? hmm....
Click to expand...
If the Chinese followed Tecumseh specs in thoery its a better carb to use on the HS as the originals had a larger bore than the other type you bought. They increased the bore size on the HS50 carbs to rougly 14.5mm over the 12.5mm that is found on the 2.5-4hp. I have never bought one of the china ones though, only modified and retrofitted original carb bodies to HS recreational configuration so I dont know if they upped the bore size or not on them.

This thread linked below I did talks about the vent/primer line inlet. What I have been doing on retrofits when its gotta look right is pulling the bung out and filling the hole with JB so it looks more "correct", and drilling the atmospheric vent to the larger size, but they make vacuum line caps in that size as well and its a quick and easy way to plug the line since you dont have to wait for the JB to set up etc, still drilling the vent larger of course!

https://www.oldminibikes.com/forum/tecumseh/111055-tecumseh-carbs-primer-bulb-vs-primer.html


Most of the orginals I have retrofitted also had correct hole drilled for the choke detent spring as well.....the chinese kinda screwed us on that by not offering the 2 different detent positions so you get stuck with the incorrect choke levers.....First thing that sticks out like sore thumb.....and usually ends up giving you a burned thumb when you hit that cobbled up mess of a lever trying to clear the air filter and exhaust :laugh:
 
C

cfh

Well-Known Member
#14
#14
and what does opening that hole to 1/16" do?

on other issues, i compared the openings of the Amazon carb and a stock H30 tecumseh carborator. on the choke and output side, the openings are the same.

carb_amazon4.jpg

The other issue is the choke. But you can take the choke off an original carb (black carb on right) and transplant it to the Amazon carb (top left carb). I did that in the picture below. The position spring needed to be slightly bent though, which you can see in the picture below.

carb_amazon5.jpg

I will try this modified Amazon carb in a tecumseh H30 engine and report back...
 
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markus

markus

Well-Known Member
#15
#15
cfh said:
and what does opening that hole to 1/16" do?

on other issues, i compared the openings of the Amazon carb and a stock H30 tecumseh carborator. on the choke and output side, the openings are the same.

View attachment 104155

The other issue is the choke. But you can take the choke off an original carb (black carb on right) and transplant it to the Amazon carb (top left carb). I did that in the picture below. The position spring needed to be slightly bent though, which you can see in the picture below.

View attachment 104156

I will try this modified Amazon carb in a tecumseh H30 engine and report back...
Click to expand...
the bore chokes down in the center of the carb, thats were the measurement would be taken for the bore size.

Opening the hole allows the fuel bowl to breath, the hole is reduced on the primer version so when you push on the bulb the rush of air you are creating does not just blow out of the vent but instead goes down in the bowl, disturbs the float, and draws fuel up into the intake. It can be reduced on the primer style because the primer bulb assembly itself is vented as well so it evens out when not being used to prime.
 
C

cfh

Well-Known Member
#16
#16
per your suggestion I opened up that hole with a 1/16” drill bit. Which really easy only took a couple turns of the drill and that was accomplished, no sweat.

Instead of doing JB Weld to plug the hole for the plunger bulb, i pulled the brass insert out and tapped the hole with a 6-32 tap, and used a 6-32 short screw to block the hole

D009FC59-3C80-450B-B97C-56CD486FBD1C.jpeg

So now the test. I put the modified carb in the H30 tecumseh motor. Fired it up, and it runs great. The old carb was sluggish with a lot of dead spots Through out the band. This thing is solid through the entire power band, and just wants to light up really nice.

though this carburetor required some extra effort compared to the ROP carb, it does seem to work just as well. Heck maybe even better. It’s hard to say for sure because I didn’t use one single engine and change all the carbs between it. But I still think this is a good solid carburetor for these motors.

965B836E-0F4F-4CC9-A145-E09E58CE648E.jpeg
 
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C

cfh

Well-Known Member
#20
#20
Tried out the last carb from ebay. This Tecumseh #631918, about $15:
https://www.ebay.com/itm/Carburetor-...72.m2749.l2649

Put this on a 1978 Tecumseh HS50 five horse power. Again, no issues, runs very well. Since it's not actually in a bike, hard to comment much past that. But it did work very well.

A couple comments on this particular carb... no spring loaded drain on the float bowl. Also the gas line-in spout is not right angled. This may present a problem with hose lengths on engines with a mounted gas tank. The choke lever is obnoxious long and on the wrong side, much like the ROP replacement carb. Not that this is bad... but the lever is pointed to the left (instead of the more common mini-bike standard of choke on the right.) Note a huge deal, can just bend the lever to the desired position.
 
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