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Discussion Starter #1
When I picked up my Tec. HS50 (70's Arien's blower) I immediately noticed the lack of a primer bulb/line and was told it was a 'self-priming carb'.

Almost every carb I see mentioned on this site or on the repair videos all have primer lines/bulbs.

How does a carb 'self-prime' and why don't all carbs use this feature/why the discrepancy between designs?
 

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Here's my guess.

Usually engines that operate in colder weather need a richer air/fuel mixture to start. That's why on some of the really old Tecumsehs there's a push plate that's a cold weather choke, it has smaller holes than the choke plate does and allows for additional choking when the temps get below 0F.

A bulb primer probably eliminates the need for different diameter holes in the choke plate and allows the engines to be more easily used across a wider range of both summer and winter applications with no changes in carb design whatsoever.

Or maybe the engineers found that the engines start easier that way, who knows :)
 

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Did you check the carb numbers to see if it is the right carb for that engine and blower and not replaced with something off a mower or tiller or something ??
 

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Discussion Starter #6
This is the best I can read the numbers off the carb, the second set is what puzzles me:

568 8J22
 

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This is the best I can read the numbers off the carb, the second set is what puzzles me:

568 8J22
The carb numbers indicate 568 is Tecumseh carb number 631914.
The 8 indicates year (68 or 78) Probably 78.
The J indicates month (Jan,June,July)
The 22 is the day of the month.

From Here-
Tecumseh Carburetor Manufacturing Numbers
 

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Discussion Starter #8
Cool, thanks for that. I thought I was supposed to have only 3 characters in the second bit. So '78 makes sense because it is the year of the blower. The engine is HS50-67008B with the a 1978 serial number and carb #631914 matches this as far as I can tell.

Also, there is no push-plate on this machine.
 

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In looking up that carb it doesn't have anything other than just the choke. It might be that it was jetted rich enough it started just fine with just having the choke on.
 

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Carbs

I may be a heretic here but I've had a couple of machines without a primer and those air-doors and I just could not work them so I replaced the carb.
This is what I'm talking about

I swapped a carb for a comparable size engine with the same throttle setup, different style choke and provisions for a primer bulb.
The choke linkage fit through the hole where the button for that air door went.
On one I bent up a piece of tin like the originals have with the primer on the flywheel cover and spotwelded it in the inside of the flywheel cover and drilled the holes to mount the primer bulb on the flywheel cover (I think the tin is to keep the hose from catching on the vanes of the flywheel when running). On the other one I made a little tab to mount it onto the bottom of the carb cover and poprivoted it in place.
Both methods worked fine for me.
All the primer bulb does is pressurize the fuel blow so a little gas is pushed into the throat of the carb to aid in starting.
In fact, one is on a Ariens I still have and at least now I can start it up where before I couldn't.
 

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I just got rid of that old Hahn and it had the carb w/o the primer and had the air door. Kind of a poor setup. In theory it should work but the primer is really nice. If your machine is in halfway decent running order it'll work every time.
 

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That's why on some of the really old Tecumsehs there's a push plate that's a cold weather choke, it has smaller holes than the choke plate does and allows for additional choking when the temps get below 0F.
Those air doors aren't used for normal starting. I've never had to use one, honestly. They're a garbage setup IMO, but then again they're not something that's used regularly.
 

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My Eska 5hp has one and when it's really cold it's the easy way to start it. When it's well below zero it helps the engine pull in more fuel.
 
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