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Have this Craftsman mower that was running when someone gave it to me, but I can't get it to start. Watched a bunch of YT videos, cleaned the carb (or I think I did) but still nothing. When I pulled out the spark plug after trying to start, the business end of it was bone dry. So carb still clogged? Something else? TIA!

Remove the carb, take off the bowl, the bowl bolt you remove is the main jet. there are 3 holes in, two going crossways at the base, and one in the top of it, be sure those are clear... spray it out and run a small wire or something in to clear out any crap.
also clean the emulsion tube, which is what the main jet screws into, you'll see the hole that goes up into the venturi of the carburetor.
also be sure that your float level is good, with the float on tip the carb where the float is facing up, and it should be level across the top of the float, and if it is slightly angled down that is fine too.

OK will try this in the next couple of days. Thx!

Might take out the plug, spray in some starting fluid, replace plug and see if it starts and quits. If so probably a carb or fuel supply problem. That red round button on the air cleaner is a primer, push it several times before starting.

I recently had the same engine that wouldn't start. Very likely the problem was that the engine wasn't getting fuel. So I tried cleaning the carb ---several times, then replacing the carb. Replacing the rubber fuel line ---washing out the fuel tank with gasoline to be sure there was no debris that could be fouling the carb.

Nothing helped.

Then I discovered the actual problem. When you mount the carb on the engine, you push the outlet of the carb onto a rubber o ring. The o ring is mounted on a plastic part that conducts the fuel air mixture into the engine, and that plastic part was broken.

This isn't quite obvious by just looking at it ---but I'd check it with some care since it can be the source of your problem.

slomo said:

Might take another cleaning or three.

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I did it only once, so will try again if nothing else helps.

seattlepioneer said:

Then I discovered the actual problem. When you mount the carb on the engine, you push the outlet of the carb onto a rubber o ring. The o ring is mounted on a plastic part that conducts the fuel air mixture into the engine, and that plastic part was broken.

This isn't quite obvious by just looking at it ---but I'd check it with some care since it can be the source of your problem.

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Was your plastic part cracked? Was it simply blocking the mixture flow or redirecting it somewhere? I am assuming you replaced the part? Do you happen to have a URL for a replacement? Or just the name? Thx

<<

Then I discovered the actual problem. When you mount the carb on the engine, you push the outlet of the carb onto a rubber o ring. The o ring is mounted on a plastic part that conducts the fuel air mixture into the engine, and that plastic part was broken.

This isn't quite obvious by just looking at it ---but I'd check it with some care since it can be the source of your problem.

Click to expand...

Was your plastic part cracked? Was it simply blocking the mixture flow or redirecting it somewhere? I am assuming you replaced the part? Do you happen to have a URL for a replacement? Or just the name? Thx >>

This plastic part, which the rubber o ring fits over, was cracked/broken all the way around so that it came away in two parts when I replaced it.

I had another decomissioned engine of the same type, so I simply took that part off the decommissioned engine,

I had spent a LOT of time looking for other reasons the engine wasn't getting fuel. Quite possibly this defect is rare, but after you've tried more common reasons for the engine not getting fuel, I'd look carefully at this part, since I guarantee you it's a possible cause for the engine not to run.

When you have the carb off the engine and you can see the rubber o ring, that's a good time to look carefully for a crack in that part. There was one other part that blocked your view of that part, but that could be removed fairly easily.

I was really quite proud of myself for finding this defect, which no one had suggested.

I'd be interested in finding out how common this problem is. How often is this a cause of an engine not running?

This is on the B&S carburetor part 799868.

The part that was broken was the intake manifold, part 794305

When you take the carburetor off the engine, you can see the rubber o ring that is on the end of the intake manifold.

seattlepioneer said:

This plastic part, which the rubber o ring fits over, was cracked/broken all the way around so that it came away in two parts when I replaced it.

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Thank you much for all the details! Since it cracked, I would expect it to leak fuel -- was it?

Take off your air filter and look into the throat, and then press the primer bulb firmly several times. You should see a pulse of fuel splash up with every button press. The gasket between the air filter base needs to be perfect for this operation to succeed, sometime beefed up with a little smear of sealant on the gasket sides.
If you see the fuel pulse up, and still no start, then your problems are elsewhere.

ilyaz said:

Thank you much for all the details! Since it cracked, I would expect it to leak fuel -- was it?

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No. This part was the intake manifold that conducted fuel/air mixture from the carburetor to the engine valve.

Because it was broken/cracked, the vacuum developed by the piston sucked in air from the crack rather than atomized fuel/air mixture from the exit of the carburetor.

So---- no leak, but no fuel/air mixture for the engine to burn either!

Hope that enables you to visualize what was happening. And one other thing to check when the engine wont start.

Fish said:

Take off your air filter and look into the throat, and then press the primer bulb firmly several times. You should see a pulse of fuel splash up with every button press. The gasket between the air filter base needs to be perfect for this operation to succeed, sometime beefed up with a little smear of sealant on the gasket sides.
If you see the fuel pulse up, and still no start, then your problems are elsewhere.

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Trying to figure out where precisely I should be looking. Pressed the bulb but heard/saw nothing. I took a few photos -- anything there seems out of whack?

(In the 1st photo I took off the plate, then put it back on)

seattlepioneer said:

No. This part was the intake manifold that conducted fuel/air mixture from the carburetor to the engine valve.

Because it was broken/cracked, the vacuum developed by the piston sucked in air from the crack rather than atomized fuel/air mixture from the exit of the carburetor.

So---- no leak, but no fuel/air mixture for the engine to burn either!

Hope that enables you to visualize what was happening. And one other thing to check when the engine wont start.

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That'll be my next thing to try.

I think you have the wrong carb, you shouldn't have a Choke and a primer....
I don't think the primer will function on a choke style carb.

Scrubcadet10 said:

I think you have the wrong carb, you shouldn't have a Choke and a primer....
I don't think the primer will function on a choke style carb.

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Are you saying you can install a wrong-type carb and it will fit?

FWIW, the mower did run when the previous owner gave it to me. He said he had to occasionally take of the air filter and spray carb cleaner(?) to be able to start it.

Yes, there were 3 types for that series of engine, one with a choke, or a auto choke, and one with a primer. and I've never seen one of those engines from the factory with a choke and primer. Was there a cable or anything hooked up to that choke valve on top of the carb? the correct part number you need for the primer system is 799868

Choke carb is on the left, primer carb on right... on the primer carb you can see a small hole drilled below the top left bolt hole, that's where the air gets pushed into from the primer. Your choked carburetor doesn;t have that, so it will not prime.

Put a piece of tape on the top that will hold the choke closed, and then try to start. It probably will.
But once it does, it will run very rich, unless you pull the tape off quickly.

Scrubcadet10 said:

Choke carb is on the left, primer carb on right... on the primer carb you can see a small hole drilled below the top left bolt hole, that's where the air gets pushed into from the primer. Your choked carburetor doesn;t have that, so it will not prime.

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So here's another photo. No cable or anything like that, plus a thread for some sort of bolt ("?"), so the whole thing does seem out of place.

Did I reconnect the spring correctly? ("??")

So from the looks of it, are my options:
1. Get a new carb. Would need a primer carb, not a choke one, right?
2. Permanently fix the choke in the closed position.

Fish said:

Put a piece of tape on the top that will hold the choke closed, and then try to start. It probably will.
But once it does, it will run very rich, unless you pull the tape off quickly.

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Will try. But another thing I noticed earlier was that the spark plug was dry when I pulled it out. Do you think closing the choke like this will help with that?

Yes, the choke being shut causes a lot more fuel to get sucked up into the engine, kind of like a shot of gas from the primer...

That threaded hole is only there because you have the wrong carb. thats the mount for the auto choke arm, which you do not have
you have the primer airbox, you need a primer carb. if you permantley close the choke, your mower will never run right.
The choke is only used when cold starting the engine.. just like when you press the primer it shoots extra fuel into the intake for easier starting.
And yes that governor spring is hooked up correctly, though once running you may have to stretch it to increase RPM.

Fish said:

Yes, the choke being shut causes a lot more fuel to get sucked up into the engine, kind of like a shot of gas from the primer...

Click to expand...

Scrubcadet10 said:

That threaded hole is only there because you have the wrong carb. thats the mount for the auto choke arm, which you do not have
you have the primer airbox, you need a primer carb. if you permantley close the choke, your mower will never run right.
The choke is only used when cold starting the engine.. just like when you press the primer it shoots extra fuel into the intake for easier starting.
And yes that governor spring is hooked up correctly, though once running you may have to stretch it to increase RPM.

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OK, so I closed the choke and it started right away. Seemed to be running OK although not perfectly smooth. So it looks like the problem is the wrong carb.

If I keep the choke forced closed like this, will I be burning too much fuel and putting more stress on the engine than needed? I am thinking of keeping it this way for now while looking for a salvage mower with a compatible primer carb to cannibalize. Or should I replace it ASAP?

Also, if I do end up buying a new carb, are there cheaper alternatives to SearsPartsDirect where I'm still likely to get the right part which won't fall apart quickly? Saw a bunch of what looked like fitting carbs on Amazon and eBay but don't know if I can trust them.

Thank you much for all the help!

personally i haven't had good luck with the chinesium carbs, engines just a run a bit funky..., also, you may need to stretch the governor spring some to gain RPM, since these carbs dont have an idle circuit that feeds the engine at low rpm, if its running at low RPM, it may run rough.
Just search for briggs and stratton 799868 carb and see what prices you get.
But ultimately its your money, so you do what your finances allow you to.
Oh, did you open the choke after you started it?

Just use the choke to start it only. See if it stays running if you take the tape off and let the choke flapper spring open.
You could rig up a cable or pull to move the choke, so it can easily be opened or closed.

Scrubcadet10 said:

personally i haven't had good luck with the chinesium carbs, engines just a run a bit funky..., also, you may need to stretch the governor spring some to gain RPM, since these carbs dont have an idle circuit that feeds the engine at low rpm, if its running at low RPM, it may run rough.
Just search for briggs and stratton 799868 carb and see what prices you get.
But ultimately its your money, so you do what your finances allow you to.
Oh, did you open the choke after you started it?

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The mower model is 917388521, so on Sears Parts Direct I am seeing part num 498170. Is this the same as 799868 ?

Put up the model numbers off of your engine, the Sears site is not too reliable.

Fish said:

Put up the model numbers off of your engine, the Sears site is not too reliable.

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That's what I did

Snap a pic of the front and sides of the engine, the numbers should be there.

ilyaz said:

The mower model is 917388521, so on Sears Parts Direct I am seeing part num 498170. Is this the same as 799868 ?

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Looks to be, but use the engine model number, it should be stamped above the spark plug or muffler on the metal blower housing.

Fish said:

Snap a pic of the front and sides of the engine, the numbers should be there.

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Crawled all over that thing - nothing. I'll bite the bullet and will go by the mower model number. Thx for all the help!

I see the model numbers in your last pic, above the muffler on that flap. clean it off with a rag.

Look from the top at what I circled in red, looks like they are there.

Hey!!! you stole my idea fish!!! ?

Yeah, It slowed me down!!

Scrubcadet10 said:

I see the model numbers in your last pic, above the muffler on that flap. clean it off with a rag.

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Thanks guys!

It says 123K02-0258-E1 03072559. Not sure if the 2nd number is important but the first one links to 498170 . Any other websites I should check to be 100% sure?

What's the difference between 498170 and 799868

ilyaz said:

Thanks guys!

It says 123K02-0258-E1 03072559. Not sure if the 2nd number is important but the first one links to 498170 . Any other websites I should check to be 100% sure?

What's the difference between 498170 and 799868

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The second one is the type number, and is critical in determining the correct carb.

The third number is the date code. 2003....

This or this are a lot cheaper than this. But are they "you get what you pay for" kind of cheap?

Chinese junk is a roll of the dice. They are not all equal.

Fish said:

Chinese junk is a roll of the dice. They are not all equal.

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Any of those parts ever not Chinese?

Are they made of different metals/alloys? If so, are any better than any other ones?

It's probably all polished pot metal. The Chinese have perfected the art of looks, but not quality.
you might look into an Oregon or stens carburetor. They cost less than the briggs, but quality control is certainly better than Wee Fewl Yu in china.
stens number is 520-966.
Rotary sells them under 14111
oregon sells it under 50-657

Scrubcadet10 said:

Wee Fewl Yu

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Got the new carb in the mail today. Installed. Primed. Started with 2-3 pulls. Then I stopped it and needed a dozen pulls to start again. It ran, then died. Now I can't start it at all. Every 2-3 times I pull, I hear pops like mini explosions. What's my next step?

Flywheel key jacked up? Are you priming to start all the time? Don't overlook anything on a new to you used mower. A good cleaning wouldn't hurt either. Turtle Wax the deck and engine cover. Tire dressing..... That sucker is filthy.

Did you partially crack the fuel cap yet and try to run it? Did I miss the Briggs gas cap trick on one of these pages? Do you have good fuel flow at the line that connects to the car-bu-trator? Take some good pics of your new car-bu-trator setup. Did you get another choke model? Carb linkages all jacked up? Can you open the throttle with your finger and rev the engine while running?

Remove the top engine cover. Clean all the dirt, oil, grass and bugs from the cylinder block cooling fins yearly. It's in the manual for ALL small engines.

slomo

slomo said:

Flywheel key jacked up? Are you priming to start all the time?

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I primed a couple of times, then took the filter off and sprayed carb cleaner into into the carb. Not sure if it helped at all.

slomo said:

Did I miss the Briggs gas cap trick on one of these pages?

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Don't remember seeing it here. What's the trick?

slomo said:

Did you get another choke model?

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No, I got the primer model. I am curious if there was a reason why the previous owner put the wrong carb on it other than a mistake or using what was imemdiately available.

slomo said:

Remove the top engine cover. Clean all the dirt, oil, grass and bugs from the cylinder block cooling fins yearly. It's in the manual for ALL small engines.

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Will do. Would a motor be overheating if the cooling fins are too dirty? Although wouldn't it happen after the motor was running for some time, not for 30 seconds, no?

Crack open your gas cap. See if it makes the engine run proper after say 1-2 minutes. After 1-2, the fuel bowl will get low and make the engine stumble. If your vent in the cap is bad, it will cause this.It stops the fuel flow to the carb.

Bet someone just threw on some carb they had sitting in the garage just to try it out??

If the engine has a small oil leak or someone misses the funnel when changing the oil, some how oil will find its way to the top of the engine block. Then when you dirt mow, makes a dirt/oil/grass/bugs dam on top of the cooling fins. I've seen birds and mice nests and of course there's always a ton of oil up there. If you neglect this step, you will get valve seats popping out and such. Burning oil from the bore getting out of round and so on. Internal engine issues from improper/lack of maintenance.

Air cooled engines like these got hot in less than one minute or shortly after. Not like a car engine with water that takes minutes to heat up. Surface dirt like you see on your mower shouldn't cause an over heat. Unless you get oil and grass up there with it. Keep the sucker clean. Use a blower after every mow and a dusting paint brush. Clean the air filter after every mow with your paint brush,.especially when you dirt mow. Put a small trail of grease around the air filter sealing gasket. Helps stop the dirt from getting inside the engine.

slomo

ilyaz said:

Got the new carb in the mail today. Installed. Primed. Started with 2-3 pulls. Then I stopped it and needed a dozen pulls to start again. It ran, then died. Now I can't start it at all. Every 2-3 times I pull, I hear pops like mini explosions. What's my next step?

Click to expand...

Try the gas cap trick.

slomo

Well, tried it.

Also cleaned the mower a bit -- it was pretty clean to begin with, no oil leaks combined with grass/dirt.

Things seem to be getting worse: now after about a dozen pulls all I get is a loud pop and that's it. Will be looking at the flywheel.

How old is the fuel? Are you running E10?

slomo

slomo said:

How old is the fuel? Are you running E10?

slomo

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I got it from the nearest gas station 1-2 weeks ago

Remove and clean the fuel tank out. Make sure you have good fuel flow to the carb inlet pipe.

Get an inline spark tester. 5 bucks at Harbor Freight.

slomo

ilyaz said:

Well, tried it.

Also cleaned the mower a bit -- it was pretty clean to begin with, no oil leaks combined with grass/dirt.

Things seem to be getting worse: now after about a dozen pulls all I get is a loud pop and that's it. Will be looking at the flywheel.

Click to expand...

You either need glasses or something. Those pictures you posted up showed a filthy mower. Look at the air filter box. It has a ton of sand/dirt inside past the air filter. Go to a mower shop and look at a NEW mower. Those are clean. Like Bertsmobile1 said there's clean then there's CLEAN. Think hospital clean.

Did you remove the top engine cover? Did you inspect the cylinder block cooling fins?

Go to Harbor Freight and get an inline spark tester. Air, fuel, spark and compression.

slomo

I like this type for pull start engines.... easier to see.. https://www.amazon.com/Lisle-20610-...TDZ3CP8B36V&psc=1&refRID=V2PTDHJD3TDZ3CP8B36V

i also have this one https://www.amazon.com/Oregon-42-08...ark+tester&qid=1595252608&s=automotive&sr=1-4
they're life/time savers and worth every penny.

$4.99 at HF.

LIKE MOST OF WHAT hf sells it is designed to be as cheap as possible, not to be easy to use.
A white globe iin a spark tester is no easier to see than a spark in a B & S 3 point tester.
The Oregon one has a red globe in it so it can be used in places other then the bottom of a coal mine.

Could be a stuck intake valve.
How is the compression when you pull the rope?