Mower won't start

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I have a Scotts 229630x8A mower with OVRM 120 engine.
Bought it used, so unknown history. Was difficult to start first season, but worked.
Now, it's extremely difficult to start, but runs fine if you get it started. If I shoot it with starting fluid, it fires once or twice. Does backfire thru the carb a little, that's why I checked for the sheared key.
If I can get to the priming pump fast enough, I can sometimes get it to run. Runs fine afterward. Starts first pull when hot. Back to not starting when cold.
Symptoms point to not getting enough gas.
Has spark. New plug. Fresh gas. New air filter. I've rebuilt the series 8 carburetor twice. Yes, I put in the float valve seat the right way. Checked valve adjustment. Took off the flywheel nut to verify the key is not sheared.
I haven't checked compression...this is the first OHV lawnmower engine I've tried to fix. The compression release probably affects the compression measurement anyway???? I don't know what to expect.
I like this mower because it mulches the grass very well. I'd like to make it run.
Suggestions?
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On Sunday, May 10, 2015 at 5:51:00 PM UTC-5, mike wrote:

It is fairly common to have the wrong key..."Scotts" doesn't tell us the motor brand? There is one on Youtube and it's a Tecumshit motor...you might have to get the model and serial and make sure you have the right key for the fly.
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mike wrote:

I just plug up the spark plug hole with chewed up paper ball and if it pops when I pull the cord. That is good for me for compression. I have an old John Deere mower, first start at the start of season it takes about 10 pulls to start. after that 3,4 pull starts it always. To store it at the end of season I run the engine until fuel tank goes empty.
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wrote:

plug. Run a tank full of fuel with heavy dose of sea foam.
If at all possible run ethanol free (here in Canada shell premium is ethanol free)
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On 5/10/2015 6:50 PM, mike wrote:

My first two thoughts are leaky intake valve, and bad carb to engine gasket. Possibly also choke not closing. Well, that makes three.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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On Sunday, May 10, 2015 at 7:02:07 PM UTC-5, Stormin Mormon wrote:

It doesn't have a choke, it has a primer...and you always say a leaky cab gasket. I've never seen that...I'm sure it does happen, but not as often as you think. Tecumseh Engine Model: OVRM120 FAMILY: YTPXS.1951AA Displacment: 195
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On Sunday, May 10, 2015 at 8:15:06 PM UTC-4, bob_villa wrote:

Does the priming bulb inject fuel into the carb throat when it's pushed?
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On 5/10/2015 8:17 PM, trader_4 wrote:

Hope so. I've also seen more than one or two cases of bad carb to engine gasket. The choke closes, but there is so much blow by air, not enough gas mix gets in.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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On 5/10/15 8:17 PM, trader_4 wrote:

the manual said to press the primer 3 times. I had to press it a lot more. Then I learned that each time you press it, you're supposed to hold it. I don't know how many seconds is recommended. I think that's true of the OVRM120, too.
It still took more than 3 presses. I couldn't get the primer apart. In the last year, after several years, it has improved. Maybe at some point I put a little Sea Foam in the tank, and that cleaned it up. I don't remember.
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On 5/10/2015 5:17 PM, trader_4 wrote:

That's how I get it running. Prime it Shot of starting fluid Pull the cord a lot If it kicks over, it will die quickly. If I can run to the side and start pumping the priming bulb, I can keep it running long enough to warm up...starts easy after that.
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On 5/10/2015 10:03 PM, mike wrote:

How about crap in the gas tank. Not enough crud to block the fuel flow completely, just enough sitting there to prevent the engine to run on its own until your screwing around trying to start it dislodges enough to get going.
Had that problem recently with a large mower. Would start up and then die under load. Filter looked okay but only partially filled with gasoline. Removed the intake to the fuel pump and there was just a trickle of gas. Blew back into the line, heard it gurgle in one the tank and then gas flowed freely. Worked fine after that due, I suspect, to it bouncing along as I mowed.
As it's a Zero-Turn Bobcat, I'm not looking to pulling out the fuel system from two saddle tanks but suspect that's what it'll take before long.<g>
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On 5/10/15 11:03 PM, mike wrote:

Each time you press the bulb, do you hold it several seconds?
Have you taken the primer apart?
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On 5/10/2015 8:28 PM, J Burns wrote:

I've tried every combination of number and speed and force that I can think of. Bulb appears to squirt gas out to the input side of the carburetor.

the rubber part.
The primer seems to be what keeps it running early in the start process.
I didn't mention that I popped the cover and took out the idle jet and cleaned all that stuff too.
This is all very frustrating because I can't come up with a rational cause that fits the symptoms.
Only thing I haven't tried is to look at the valves.
If I stuck a compression gauge on it, what should I see at speeds I can muster with the pull starter? The compression release is a wild card with which I have zero experience.
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On 5/11/15 6:33 AM, mike wrote:

but the family is YTPXS.1951BA. That sounds pretty close to yours.
A decal on the engine simply says to press the bulb 3 times. I found that even pressing it 10 times didn't do much. Then I read online that I should hold it down. Now sometimes 3 is enough.

I shined a light in my carburetor but didn't see any gas squirt. This manual seems to say they all work about the same way. Online, I read that the bulb pumps air, which picks up gas by venturi effect.
http://www.barrettsmallengine.com/manual/tecumsehcarburetormanual.pdf

Mine usually stalls in a few seconds. I press the bulb one more time, holding it about 3 seconds. Then the engine will start and keep running.
The manual says if I remove the bulb, there are air passages I could clean. Removing the bulb would destroy it. Sears' price is $9.75.
I guess my primer system doesn't work very well. Maybe it was designed as a theft deterrent. If they see me trying to start my mower, they won't steal it.
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On 5/11/2015 6:16 AM, J Burns wrote:

Looks like the carb is series 11 bridged. Looks like I've cleaned all the passages except the ones under the welch plug. But I can get carb cleaner thru that area.
I'll try the compression test tomorrow.
I really don't want to dump a lot of money into this thing. I can buy a whole new carb on ebay for $17.50. I'd do it in an instant if I was sure it would fix the thing.
One thing I noticed about the ebay carbs is that there's a plastic tube that fits in the hole near the primer and pokes out the throaat into the air filter. Mine doesn't have that tube. Something else to try.
Thanks for all the inputs. mike
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On 5/11/15 9:44 PM, mike wrote:

Mine has that tube. Maybe that's the air inlet, and maybe your inlet is a hole in the middle of the bulb.
My priming was weak, not much gas. I discovered that the float-bowl gasket was cruddy. A little grease on the gasket gave me a lot more gas when I pushed the bulb. So my float bowl has to hold air to prime. I've ordered a gasket, $1.99.
A little grease on the gasket might improve your priming, too.
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On Monday, May 11, 2015 at 5:34:00 AM UTC-5, mike wrote:

If it has a fly-key like this:
http://thumbs1.picclick.com/d/l400/pict/300928013580_/Flywheel-Key-Fits-Aspera-Tecumseh-Engines.jpg I would change it as a matter of course...it's not expensive.
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more likely to be a pony or a horse - possibly an ox.
Pony or horse would be blocked carb or bad gas - Ox would be poor ignition (bad plug?) or a loose carb (leaking base gasket). Bad ring or other mechanical problem is at least a zebra - possibly aproaching a Unicorn.
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J Burns wrote:

Would the local auto parts store have some gasket material that you could cut your own seal from?
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On 5/11/15 9:03 PM, Dean Hoffman wrote:

it turns out I have the wrong carburetor, I'll buy a carburetor to fit the gasket!
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