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post #1 of 4 Old 07-01-2019, 08:36 PM Thread Starter
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JS38 Mowmentum carb question

I know this is primarily a tractor group (which has been exceedingly helpful in the past!), but I'm hoping some of the gurus can still help with a small push engine question. Engine just coughed and quit one day and would not re-start. Went ahead and changed oil, air filter, and spark plug just to be safe. Cleaned everything visible as much as possible with shop air compressor. Checked carb bowl and pin stopper for cleanliness and smooth operation and also verified clean fuel flow. All pristine. Finally narrowed down to carb (valve?) just behind air filter.

It's connected to a rod/bracket that moves it open and closed, but that rod isn't attached to anything except return spring that CLOSES it. Exactly what actuates that flapper open? I don't see anything hanging loose, but has a linkage come loose? Wondering if it's somehow supposed to mechanically connect to the "kill switch" handlebar. Used my engineering prowess and zip tied the arm in full open position and engine ran like an absolute top. Mowed all day including several full start stop cycles with no problem. Sure doesn't feel like the proper solution, though, so I'm hoping someone knows correct fix for this!

Thanks in advance.
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post #2 of 4 Old 07-02-2019, 11:41 AM
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Re: JS38 Mowmentum carb question

Pictures would help, but I assume like most small engines it probably has a governor. A vane governor flywheel turning speed controls how far throttle opens.
I would blow it out good, leaf blower or shop air blow gun, then hose wash. Either grass, debris causing lever(s) bind, or clean you can see if one came off.
Online there are exploded views.

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post #3 of 4 Old 07-13-2019, 03:39 PM Thread Starter
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Re: JS38 Mowmentum carb question

Sorry for delay. Finally have time to mess with it again! Took a couple of pics.

Pic 1 is the bar I'm talking about. There's a spring next to my finger that's fairly shot, but it pulls carb CLOSED. It's the open direction giving me problems. This is bar I temporarily zip tied open & it ran fine.

Pic 2 is opposite side of same bar. It's not attached to anything but there's also the little aluminum piece by my finger on this one. I can push it forward towards the bar in question and the aluminum springs back towards where my finger is when released. The 2 are eerily close to each other. Are they supposed to be mechanically connected?

Tinkering today, engine seized on starting & caused starter rope to break. Following internet guides, drained all oil and put penetrating lubes in spark plug hole. Let it sit for an hour and blade turns pretty smooth by hand. Headed to store now to buy a new push mower AND starter rope.

Re-assembly results of Deere determines which one I keep. Unless anyone here has other ideas of what I'm missing. FYI, have my eye on vertical storage Toro recycler series mower. In my budget (400ish) and gets really good reviews......
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~Vol
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post #4 of 4 Old 07-13-2019, 10:20 PM
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Re: JS38 Mowmentum carb question

Quote:
Originally Posted by Vol4Ever View Post
Sorry for delay. Finally have time to mess with it again! Took a couple of pics.

Pic 1 is the bar I'm talking about. There's a spring next to my finger that's fairly shot, but it pulls carb CLOSED. It's the open direction giving me problems. This is bar I temporarily zip tied open & it ran fine.

Pic 2 is opposite side of same bar. It's not attached to anything but there's also the little aluminum piece by my finger on this one. I can push it forward towards the bar in question and the aluminum springs back towards where my finger is when released. The 2 are eerily close to each other. Are they supposed to be mechanically connected?

Tinkering today, engine seized on starting & caused starter rope to break. Following internet guides, drained all oil and put penetrating lubes in spark plug hole. Let it sit for an hour and blade turns pretty smooth by hand. Headed to store now to buy a new push mower AND starter rope.

Re-assembly results of Deere determines which one I keep. Unless anyone here has other ideas of what I'm missing. FYI, have my eye on vertical storage Toro recycler series mower. In my budget (400ish) and gets really good reviews......

That's the ready start auto choke system.

In stopped position when cold or cool engine, the plastic choke arm, or air vane is pulled in by small fairly weak spring to close the choke.
As soon as engine starts the air from flywheel vanes blows the arm out to open choke.

All is well UNTIL you need to start a hot engine that doesn't need choke as it will flood and not start with full choke...ENTER the heat riser spring loaded muffler auto choke thermostat.

In just a couple of minutes of running the exhaust heats this up and the inside (bimetal I assume) spring moves the arm forward and keeps the choke open. So when you turn it off and the airflow is gone...the plastic choke arm stays held open.

The end is adjustable and usually adjusted poorly. A lot of hot start issues if you wait too long to restart hot engine. Usually you are good up to 8-9 minutes but if you wait 12-15 (each engine is different) the arm will shut due to muffler being thin steel and cooling quickly, wile the engine is a giant aluminum heatsink and very hot and needs NO choke.

Open the end to it farthest position and it will be best overall from what I've found.
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