HS40 Carburetor Finally found that annoying rattle.

#3
Hello @f4radar

To my knowledge, that "rattle" is a sign of health for the 'venturi'. If it does not rattle, then the part in the tube is unable to move, and won't function properly. So make sure it still rattles once you seal it back up.

This is not a very technical description, and I don't understand the complete function of the venturi.

@markus This will send an alert to our member markus, I believe he understands the 'function' of the venturi, and can perhaps explain it to us, as well as let me know if I am completely off base...lol.

Markus, thank you in advance for your advice.
 

markus

Well-Known Member
#6
:) you found the ones with the Ball bearing type port plug dont like to be drilled too!!! You can do the ones with the brass plug pretty easy though.
that rod does need to be in there though, depending on what Tecumseh book or service info you look at they call it a metering, and sometimes a restriction rod. Its there to choke down that passage so fuel can be pulled a proper rate. There are some other versions I found when drilling them that have a pressed in jet style as well. They dont rattle, I thought I had another stuck one and turns out there is a section of brass tubing with a really small hole drilled thorough for the fuel draw.

This pic and info is an older post of mine showing the first one I drilled out to unstick the rod and clean the idle circuit out real good.

(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:

 
#7
:) you found the ones with the Ball bearing type port plug dont like to be drilled too!!! You can do the ones with the brass plug pretty easy though.
that rod does need to be in there though, depending on what Tecumseh book or service info you look at they call it a metering, and sometimes a restriction rod. Its there to choke down that passage so fuel can be pulled a proper rate. There are some other versions I found when drilling them that have a pressed in jet style as well. They dont rattle, I thought I had another stuck one and turns out there is a section of brass tubing with a really small hole drilled thorough for the fuel draw.

This pic and info is an older post of mine showing the first one I drilled out to unstick the rod and clean the idle circuit out real good.
I'm thinking of drilling that chamber larger and inserting an aluminum tube to house a new metering rod or
 

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