Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Is there supposed to be a hole in the top of the tower (idle circuit?) on this carb (see arrow). I don't remember seeing it before (but then I don't remember lots of things) and I did drop it.  Also Is this one of those tecumseh carbs that is supposed to rattle when you shake it? I cannot hear a rattle.  The carb kit I ordered for it ($7) came today and I was getting ready to install the seat for the float needle when I noticed this. I've never installed a rebuild kit on a carb. Kinda excited to try it. Model # H-30-35077E Serial # 7107 02456
 

I did stick the old jet back in and it runs the same. 

If the engine is running when the fuel is shut off from the main jet, all the fuel has to be coming through the low speed (idle) jet. That passageway may be the problem.  I could try removing the screw that I used to fill that hole.  I'm not sure how the idle curcuit is supposed to work.  Could there be something wrong with it that its is drawing too much fuel.  With the throttle lever, I can easily get the motor rpms to drop down to a slow idle and then throttle it up to a high rpm.  So I'm not completely out of luck with this motor. Its just really bazzare that it will only run with that high speed jet tighted all the way in.  I'd love to see one of these carbs cut open so I could see what is in there.

 I'm not sure how the idle curcuit is supposed to work.

The low idle circuit gets gas from holes under the welch plug, often three.   The position of the throttle determins if the holes will come into play for gas during idle.  When at high speed the throttle butterfly is away from the throat wall where the holes are so the holes do not get suction from the sweep of the air as it would at low speed when the butterfly is close to the wall.  These generally don't get plugged up.  There are some other holes in the throal which you can prod with a thin wire for air and gas, depending on the carb.  The air hole if there will be close to the base of the shaft holding the butterfly.  The others if there will be on the walls about half way up.  

 

The Welch plug is the round plug next to the idle jet.  Behind that cover is an open space and then the carburetor throat wall.   There are holes inside the Welch area.  One hole goes over to the low idle jet.  The others go through to the carb throat. 

 

Cas can go by the idle jet into the Welch area.  It goes out controlled by suction in the throat of the carb.  

 

The way gas goes out of the Welch area is by suction created in the throat of the carb.  That suction is created by the throttle butterfly and the rush of air created by the intake stroke of the piston. 

 

When the throttle butterfly is at idle speed the butterfly is close to the wall of the throat in the area by the Welch holes.  Because it’s close to the holes it causes the air to rush by the holes sucking gas out of the Welch area.

 

Your low idle circuit is probably fine. 

      I agree with Trouts, you may have the large welshe plug in the bowl leaking fuel into the throat of the carb...  I also believe (Trouts maybe you can check one of your carbs in your spare parts pile) that the tower you put a bolt in is drilled port for fuel emulsion ( Adding air into the main jet draw to mist fuel instead of perculate).   That hole , I think Is drilled at the factory and is capped with a chrome ball bearing (right at the top of the tower where you put the bolt )......The ball bearing is not suppose to come out but maybe it knocked out with the drop  (you said something about a rattle?)..

Anyway, all fuel HAS to come through the main jet on the bottom of the carb,   then it is ported to the low speed jet...  If the jet is in all the way (sealed)....  The engine should not run at any speed...

      Also if you have any Tec or Sears machines laying around you may want to swap the carbs to see what happens,  the carb is very common, you may be able to find something in a junk pile someware and swap just the choke and throttle rods of your original carb to get a good carb.   You maybe able to find a blown motor for near nothing with all the extras...

I show 631921 and 631798A  are replacements.   There may be more...

Good Luck,

Friiy..

Here is a link with a cutout view of the ball/pedistal area.

http://outdoorpowerinfo.com/repairs/...arb_640017.asp

I think there may be carbs with designs which are different.  There may be a pedistal without a ball and some other arrangement to takes its place with no ball.  They probaly make one body carb and drill or bore it differently for different designs.

Trouts2's reply was cut off.

http://outdoorpowerinfo.com/repairs/tecumseh_carb_640017.asp

You may want to check the seal around your screw... the one you installed in the tower to seal that port...  It may be sucking excess full from the bowl bypassing the main jet on the bottom...  (since the engine will still run with the jet all the way in)... Is the the engine only running at idle with the main jet all the way in?  Try to throttle the engine up with the main jet all the way screwed in,  let us know what happens..

Good Luck,

Friiy

Well, its together and running.  I never really solved this problem.  It will idle down just fine and it will rev up to higher rpms.  But it will also try to overspeed and even will surge if the throttle "down" too far (yes down),

I read the referenced links but there seem to be quite a few variations on this carb.  This phrase came closest to the issue:

"Fuel for the low-speed circuit comes through the bowl nut side hole, through this hole, continues past the Welch plug in #10 and on to the progression holes in #17. When this hole is clogged the engine might not run at low speed and may surge at high speed. Shooting carb cleaner into the hole from which the low-speed jet was removed should result in a stream squirting out this hole. "

The engine still only runs if the bottom high speed jet is screwed all the way in.  (even with the rebuild kit and the float adjusted).

IU agree that swapping out another carb would be the best diagnosis.

It's grabbing fuel somewhere... You may just have a damaged carb.. I new carb will make it purr, Maybe you can find a used one that you could throw your kit in.. Friiy