Tecumseh Idle Mixture Restrictor Screw P/N - 5 HP HSSK50 - Snowblower Forum : Snow Blower Forums
 
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post #1 of 9 Old 11-29-2015, 02:24 PM Thread Starter
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Tecumseh Idle Mixture Restrictor Screw P/N - 5 HP HSSK50

Further examination of the Tecumseh 5HP HSSK50 #67340N
engine discussed in a previous thread reveals a damaged idle
mixture screw.

The screw is missing its tapered needle tip. The broken end shows
signs of 'necking' at the break, suggesting a tensile-type failure.
Research of on-line engine parts catalogs indicates this engine
is fitted with Carburetor #632107A. Research of carburetor
parts catalogs indicates that this carburetor is fitted with
Idle Mixture Screw #631838.

A vendor image below of IMS #631838 show a screw that appears
to be similar to the broken OEM IMS.
Img Courtesy: Randy's Lawn Mower Repair in Greenfield, IN
However. A question arises due to a number stamped on the
mounting flange of the actual carburator: 142864A (or possibly
1428G4A).

Is #142864A as stamped on the carb body relevant to determining
replacement parts for the OEM carb? Or as revealed by the catalogs,
is IMS #631838 for carb #632107A the correct item required to
replace the broken part?

Also, is there a kit that includes the #631838 idle mixture screw
along with fresh screw seals, bowl gaskets & ect?.

.
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post #2 of 9 Old 11-29-2015, 03:47 PM
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I would normally say the number on the carb is what I'd go by but that number (both of them) pull up no results for anything Tecumseh or Carburetor related. That I can find.

Overhaul kit with adjustment needle $12 Genuine Tecumseh 31840 Carburetor Overhaul Kit

BUT it looks like you can get a whole new adjustable carb for $20 Adjustable Carburetor Tecumseh 640084 640084A 640084B 632107 632107A Carb | eBay

and a non-adjustable one for $12 New Carburetor for Lawn Mower Tecumseh 632107 632107A Toro Durable Carb | eBay

.
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post #3 of 9 Old 12-01-2015, 12:16 PM Thread Starter
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Kiss4aFrog. Thank you for going to the trouble to not only
research the body stamping, but also track down the carb
kit P/N and two suitable replacement carburetors.

Like you, I drew a blank searching on the number stamped in
the mounting flange. I also scoured catalogs on the unlikely
possibility the number might be a P/N for the body itself, but
came up with nothing.

No luck sourcing a Overhaul Kit #3I840 locally, but I did find an
IMS #631838 . It is a very near match to what remains of the
OEM, but is not an exact duplicate. The image below shows
a comparison:


(The tip failure seems unusual.

Earlier, I speculated that the screw tip had somehow become
seized/welded to the seat or bound up by varnish and then
separated by tensile failure when the screw was removed.

Not so plausible now. How could the very end of the screw
be held so firmly as to be pulled off when the screw was
removed? The engine appears virgin: seemingly unserviced
and few hours. Presumably the needle was adjusted for the
usual 1-1/4 turns, leaving a gap between needle and seat.
There is very little surface area to the missing part of the
tip. The screw is steel, the seat and body are non-ferrous. )
Despite the Idle Mixture Screw bore & seat appearing to be clear
when viewed w/ mirror and a borescope, the threads of the new
screw did not engage with those in the carb body during a short
work session last night.

Unless there is a thread mis-match, I expect to find that the tip
is still in the body when I get back to examining the carb. I have
already applied compressed air at the air bleed in the throat just
downstream from the choke without result. Removal of the choke
may make it possible to probe through the air bleed in an effort
to dislodge the tip. The IMS screw hole seems to be blind with
no access from the opposite side. If it might do any good and
there are no obstructions, perhaps an opposing access hole can
be drilled and later resealed (lead shot, epoxy ...).

I am not sure how it is possible to produce a functioning aftermarket
carb for $20, it is comforting to know one is available as a contingency
if other efforts fail. Thanks again for the tip

.
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post #4 of 9 Old 12-01-2015, 12:37 PM
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The tip snaps off when you over tighten the idle screw, I have had it happen to me. I was lucky, in that the tip came out with some light tapping of the carb on the work bench. Took me a while to find the right idle screw, but looks like you already have one. It may fall out on its own, pull the carb and see if a few taps on the body will get the tip to drop out.

Ray
1962 Ariens 10ML60
1979 Toro 524
1975 MTD Snowflite 4/22
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post #5 of 9 Old 01-15-2017, 01:49 AM Thread Starter
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Quote:
Originally Posted by Ray 1962 10ML60 View Post
The tip snaps off when you over tighten the idle screw, ...
A follow up:

There may be more to breaking off the tip than just over-tightening the IMS.

Subsequent reading back in Dec'15 led to information that stated there is a loose/floating metal pin in the vertical idle mixture passage from the float chamber of carbs like this one. I do not know what purpose it would serve, besides displacing volume. Apparently, if the idle mixture screw has been removed and the carb is inverted, the pin can travel up into a pocket in the body behind the seat for the IMS - if the pin is in this position and an attempt is made to install the IMS, the tip of the idle mixture screw can be damaged and the pin may be wedged in the 'up' position.

The foregoing seemed to describe the situation with this carb. Something beyond the seat was obstructing the tip of the IMS - with the limited view and 'feel' available through the IMS hole, it seemed that the object was larger than the missing IMS tip, cylindrical in shape and oriented vertically. Despite efforts to dislodge it downward, the object continued to be an obstruction.

What I chose to do next was NOT a complete success because it compromised the ability to adjust the low speed mixture. With what I learned, I would take a different approach next time. That said, the end result is that the carb was reinstalled and has worked to the satisfaction of the owner.

Continued next post ...
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post #6 of 9 Old 01-15-2017, 02:04 AM Thread Starter
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Quote:
Originally Posted by EddyCurr View Post
What I chose to do next was NOT a complete success because it compromised the ability to adjust the low speed mixture. With what I learned, I would take a different approach next time. That said, the end result is that the carb was reinstalled and has worked to the satisfaction of the owner.
After studying the casting of the carb body, I elected to cut an opening in from the opposite side of the body for access to the top of the pin rising out of the idle mixture tube

Milling a flat face to work from.


Drilling to reach pocket behind needle seat and above top of mixture tube.


After clearing passage and tapping threads for a SHCS to seal opening.


.
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post #7 of 9 Old 01-15-2017, 02:27 AM Thread Starter
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While I was successful at getting access to the top of the pin and dislodged it so that it dropped back down the idle mixture tube, I managed to damage the needle seat. As a result, the engine can not be throttled down to a slow idle.

However, it CAN be operated slower than it could when the passage behind the seat was obstructed and the tip of the needle was missing. The owner's perspective was that the snowblower ran like it did when he first got it and he was tickled to have the machine back in operation.

We put stabilizer in the tank at the end of the season and the owner fired the machine up without trouble when needed this season.

What I would do differently next time is consider entering from above, instead of from the side. This will mean cutting through the body into the throat and then through the throat into the chamber behind the needle seat - obviously, leaving two holes to close afterwards where the material closing the holes could enter the combustion chamber if it came out of position.

Or take a chance on an import carburetor. I read unfavorable reviews and there was some other, now forgotten, obstacle to going with an aftermarket carb.

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post #8 of 9 Old 01-15-2017, 11:06 AM
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I've had great luck with the Chinese carbs......bought four last week and they showed up at my door in four days for $14 each shipping included. With the Techumseh carbs, I can usually get them cleaned and working, but it sometimes takes me several tries. The Chinese carbs I've tried come pre adjusted and work perfect right out of the box.
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post #9 of 9 Old 01-15-2017, 12:04 PM Thread Starter
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Quote:
Originally Posted by cranman View Post
I've had great luck with the Chinese carbs...... The Chinese carbs I've tried come pre adjusted and work perfect right out of the box.
Any and all of them? Or do you have a preference?

If memory serves, there was uncertainty because of the variety of vendors, carbs, adjustable vs non-adjustable versions, and some less-than-glowing reviews. An additional consideration was the need to import, with all the drawbacks that entails when something is unsatisfactory.

Plus, although you could not meet a nicer person, the owner is utterly non-mechanical and is loath to inconvenience someone in any way. All along the journey, he was urging me not to waste my (no charge to him) time and saying that he would just buy another machine to replace this essentially shiney new one! A too-common and discouraging trait in people around me.

Anyway. With the option of taking a chance on an import carb as a first contingency and the owner not having faith that anything short of spending many hundreds on a new machine, I was free to operate on the OEM unit.

Time well spent.

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