Tired of Tecumseh Carbs

Howdy y'all. I'm new here and was hoping to get some advice on carbs on Tecs.

I have a love hate relationship with tecumseh engines, I rescued a couple old ones being thrown out at my high school a couple years ago. Every single one had a messed up carby, but the engines themselves (snowblower engines, mind you.) were in perfect shape with the factory cross hatching and everything. Even snagged a brand new one that was disassembled by the autoshop class and tossed away.

So on to my main issue. I've re-purposed many of the engines I rescued, two of them are on mountain bikes (HS40, AH600), another is powering a makeshift arc welder (HM80). One of them is on a snowblower I rescued from my school (HSK50).

and all of them take 20 pulls to start
It doesnt help that the recoils break every 5 pulls, ESPECIALLY THE OLD STYLE ONES!

All their carbs have been thoroughly cleaned and 2 of the engines have brand new carbs!
Priming the engines just causes them to fire and sputter to a stop, Rinse and repeat until it warms up enough to stay running. They ARE stored with gas in them, but the engines are used year round and there's NO way the gas is getting stale in there. It just seems after a week or so they just dont wanna start up easily.

I have a Briggs quantum lawnmower and it gets stored with gas in it for the entire winter. And when its time to pull it out 6 months later. Prime 3 times and one pull. Without even refueling. HOW CAN IT DO THIS? WHAT MAKES IT SO MUCH MORE RELIABLE?! THE CARB DESIGN IS EXTREMELY SIMILAR TO THE TEC CARBS yet it doesnt clog up or give the slightest bit of trouble for the past 15 years/ Meanwhile a tecumseh with 5 hours total on it wont start up even when its already warm

I stored my AH600 indoors for 6 months with the gas fully drained from the bowl and tank. The result? It rusted to crap and the float had a hole in it. upon trying to replace the float, the float pin holder thing snapped off the carb body, the jets were clogged with rusticles.

Guys I can't do this anymore, There must be a better solution. Has anyone ever replaced the carb on a tec with a Briggs carby or walbro or SOMETHING that can turn my engines into one pull wonders, or even 3 pull starts??

I don’t know what you might be doing wrong, but Tecumseh carbs are the simplest carb to clean, rebuild and adjust. I rebuild about 75-100 each year and my preseason order on the needle seat part 631021B is 50 parts. After a good cleaning and replacing the float needle, seat and two gaskets, I would say I have over a 90% success rate. I may replace one or two carbs a year. I use an ultrasound cleaner, but have cleaned them in the field with a can of carb cleaner. Two big mistakes I have seen by novices is not setting the float level properly and failure to clean the idle and high speed jets. This is the procedure which I follow, and it may help you out. If you have any carbs with both high speed and idle mixture screws, initial setting is 1-1/2 turns out on high speed and 1-1/4 turns out on idle. Set your high speed mixture first, then set your idle mixture and speed second. If you have any specific questions please post them.

[FONT=&quot][FONT=&quot]Needle and seat replacement.[/FONT][/FONT]
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[FONT=&quot][FONT=&quot]Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.[/FONT][/FONT]
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[FONT=&quot][FONT=&quot]I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.[/FONT][/FONT]
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[FONT=&quot][FONT=&quot]With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. Next check to make sure that the float does not have any liquid in it. If it does, replace. If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.[/FONT][/FONT]
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[FONT=&quot][FONT=&quot]PS: On the side of some Tecumseh carbs you will find a plastic cover. Under this cover will be an idle jet. Remove it and check to see that the jet is open both horizontally and vertically. You should be able to push the old float needle wire through the vertical opening.

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Adjusting a carb
This is the procedure I always taught my students to adjust a carb with two fuel controlling needles.
1. Start the engine and move the throttle control to top speed.
2. Adjust the high speed needle (this is the one under the float bowl) clockwise very slowly until the engine starts
to bog down.
3. Back the needle out 1/8 turn, the engine should now run smoothly.
4. Now move the throttle control down to idle. If the engine stalls out turn the idle speed screw in one full turn,
restart the engine and bring the throttle control down to idle. If the engine is running to fast, turn the speed
screw slowly out until the engine seem to want to die and then in 1/8 turn.
5. Now with the engine running, adjust the idle needle out until the either gains in RPM's or starts to bog down. If
the engine gains in RPM's, continue to adjust out until the engine starts to bog down. At this time turn the
screw in 1/4 turn. Now the engine may be running to fast, so turn the idle speed screw out until you get an
RPM you like.
6. Now you must repeat step 5. If the engine bogs down right away turn idle needle back in to your starting point
and go to step 7. If it speeds up, repeat step 5 again.
7. Turn idle needle in until the engine bogs down and then out 1/8 turn.
8. Now the engine should run smoothly at all speeds.
9. To check, set the engine to idle, then quickly push the throttle control tohigh speed. If it dogs and does not
come to speed, open the idle needle 1/8 turn and repeat.
10. Set to go.


There are 2 reasons I have it done this way is, first the high speed needle controls the fuel going to the low speed circuit and second is that the idle needle controls how much fuel is used when going from idle to high speed. You should also review the section in the manual I posted before starting this procedure.

Fuel can go stale in as little as 2 weeks.
It all depends upon what blend you get locally and your local weather.

My landlord is 450 yards from my workshop.
Mowers in my shop will have their fuel go bad in about 6 weeks but his will go bad in 2 weeks ( during summer ).

Some engines are more sensitive to fuel quality than others.
If your start rope is breaking that quickly you need to use better quality cord and cut it longer.
The limit of chord is when it starts to foul on the housing when fully retracted.
Everything I fit here is at least 1' longer then specification.
Nearly all of the chord on the web is trash.

As for carbs, any carb can be fitted to any engine.
It is nothing more than a device for vapourising fuel and controlling the volume.
Hooking up the governor so it works is the problem.
Any carb with the same choke size will be fine.
Carbs with a bigger choke size will also be fine but they will use more fuel and tend to surge a bit under acceleration.

I've always been following the service manual for adjusting these carbs, All my engines aside from the non adjustable ones run fine once warm, they are just all a pain to start. Priming it usually results in the engine firing and then stalling right away, rinse and repeat until the engine warms up enough to keep running. Choke will usually just keep it running for a second or two longer before it stalls.

Gasoline here takes a long time to go bad. My briggs engines start up 1 pull with 5-6 month old gas and runs fine

Lemme be more clear on the pull starters breaking. The ropes are never what break, its the mechanism. The older single pawl design, the pawl always gets ripped out on the various engines I have, and I'm quite gentle with the way I start my engines too. Pulling over slowly until I feel a compression stroke and giving a sharp forceful pull. The engines have A ton of compression and dont have a comp release.

I know just about any carby can be fitted, but is there a carb out there which is fully adjustable like the tecumseh carbs, but is not actually made by or for a tecumseh. I know honda and briggs carbs dont typically have both high and low jets adjustable.

I have tried the following with not much success on a 2 stroke AH600:
Briggs vaccujet: poor idle, great mid range, not great on the top end.
Briggs quantum (non-adjustable): Didnt even fire
Rebuilt Tecumseh carb from an HS40: rough idle with choke on, stalls when throttle opened, No idle with choke off, great top end power. Leaked gas when engine was off, float was adjusted to spec prior. Went runaway once and even choking it couldnt stop it. That was weird but why am I surprised?
Original carb rebuilt: this carb has no idle circuit which is the whole reason I was replacing it, Great high end power. Also leaked the entire time goddammit screw this crap

I have not been able to find any suitable sized diaphragm carbs, which is a shame because I find those to be much better for my applications.

AFAIK, all small single cylinder engines have an ACR, either as an add on or as a funny grind on the cam.
If there is no AC on the engines your are using that would explain the broken starters.
If it is a big problem you could always just fit a notched pulley and use a rope.
By going that way you can fit a bigger pulley and get more mechanical advantage over the engine.

Also the starting technique need modification.
If you have no ACR then the correct procedure is to slowly pull just over TDC compression stroke then pull the chord.
That gives the engine 2 full cycles to build up momentum to overcome compression.
When repurposing engines you need to be a little careful as many setups use the momentum stored in the impliment to help starting.
Your scenario is exactly what happens when you take the blade off a push mower.
It fires a few times but does not have enough energy to carry on to full engine speed..
Remember all these engines run basically static timing so at cranking speeds the spark is way too far advanced.

I run a lot of Vintage motorcycles.
You can get them to run as slow as 300 rpm with the spark fully retarded, but to start them the spark needs to be 1/4 to 1/3 advanced or they fire a few times & stop.
At 1/2 advance they will pop but not run and at full advance the engine kicks back throwing you into low earth orbit.

All of my Tecs are horizontal shaft engines from snowblowers, and the 2 stroke engine doesn't have a compression release. My HS40 is from the mid 70's and it just has a simple camshaft with no fancy cams lobes or compression release. The compression is quite high and it broke the starter every second pull and it had to be taken off and the pawl had to be snapped back in place. The two stroke engine I had did the same thing. The old starter IMO was a bad design, one single pawl vs all that compression just wasn't a good idea. I got some $20 Chinese starter from ebay with 3 pawls, and so far it seems to be better, I dont know how it'll last.

As for re purposing the engines, All my tecumseh engines came from snowblowers, and are designed to run with 0 load on them as they have the simple belt clutches. The have the heavy flywheel, and they dont run rough once they finally catch and stay running. I've run lawnmowers before without their blades and I am certain this is not the problem with my tecumseh engines. I have actually made an adapter to put a briggs vaccujet carb onto my tecumsehs, and found that with every engine I put it on, It would always start and run on the first pull, but it wouldnt run very well because of the jetting. My issue is their stupid
Tecumseh carburetors. I once had my HS40 on a bicycle. Going up steep hills, the float would act funny and cause the engine to run rough, every bump would cause it to run rough. On flat roads that thing was just zipping around and was awesome. Starting it was a nightmare and the compression and starter pawl really did not help. My comparable briggs with a float carburetor did not do this under the same conditions.

bertsmobile1 said:

AFAIK, all small single cylinder engines have an ACR, either as an add on or as a funny grind on the cam.
If there is no AC on the engines your are using that would explain the broken starters.
If it is a big problem you could always just fit a notched pulley and use a rope.
By going that way you can fit a bigger pulley and get more mechanical advantage over the engine.

Also the starting technique need modification.
If you have no ACR then the correct procedure is to slowly pull just over TDC compression stroke then pull the chord.
That gives the engine 2 full cycles to build up momentum to overcome compression.
When repurposing engines you need to be a little careful as many setups use the momentum stored in the impliment to help starting.
Your scenario is exactly what happens when you take the blade off a push mower.
It fires a few times but does not have enough energy to carry on to full engine speed..
Remember all these engines run basically static timing so at cranking speeds the spark is way too far advanced.

I run a lot of Vintage motorcycles.
You can get them to run as slow as 300 rpm with the spark fully retarded, but to start them the spark needs to be 1/4 to 1/3 advanced or they fire a few times & stop.
At 1/2 advance they will pop but not run and at full advance the engine kicks back throwing you into low earth orbit.

Click to expand...

I have one that did that. It turned out that the primer bulb was not seated and was leaking air. Once I replaced it with a new one and seated it, the engine started like it did when new. I've also had it where the fuel pump diaphragm went bad. On mine that is part of the carb base.