Help! Mower won't start

[gocards1177]

I need some small engine expert help. We've been using a 30 year old Snapper RER from my wife's childhood to keep a "lawn" mowed at our land weekly this summer. When my father in-law let us have it this Spring I was skeptical, but it's turned out to be quite dependable. Until this past weekend ran smooth and started easily.

On Sunday, I started to mow with it, and after mowing about 2 minutes it just lost power and died. Kind of like the Millenium Falcon coming out of hyperdrive. Wouldn't restart. Yesterday I brought it home to take a closer look. First thing I tried was a new spark plug. The old one was way corroded and I got a spark to ground when I put a screwdriver in the socket wire. That didn't work. I tried changing the gap on the plug, but no effect. It has good compression using a "finger test". I tried spraying starter fluid in the chamber, no fire. I sprayed starter fluid into the intake while trying to start and on one occasion I got a fairly impressive flash of fire coming back through the carb, but otherwise nothing. I also took an identical plug off of a working engine and swapped it in, but it still wouldn't fire.

I took it by the local small engine repair place, but they have a 2 week waiting period. So I told them I would try to fix it while I waited. I'm at a loss for what to try next. I fear something catastrophic. I seem to have compression, spark, and fuel. What else can I try? By the way, this thing has all of it's safety switches removed.

 

[eddie48]

I can think of a couple of possibilities; Water in the fuel and, if it is a Briggs engine, a valve spring keeper that came loose. Start by loosening or removing the nut on the bottom of the carb bowl catching the liquid (gasoline, hopefully) that comes out. If it is water, drain it off, refill the tank and go mow. If you get only gasoline coming out, retighten the nut. Then I would remove the valve spring cover and check that both springs are attached firmly to the valves and that the valves open and close when you turn the engine over. Try that and report.

 

[kencunningham]

You post is a little confusing. If you are not getting spark at the plug but it will give a spark when using a screwdriver, then i would be the end of the plug wire has come loose. Of course this is if you have a known good plug. Please clarify, because trying to point you in the right direction will depend on if you have fire or not.

If you are not getting any fire to the plug electrode or the coil wire end, i would take the flywheel cover off and remove the rust on the outside of the flywheel and ends of the coil. Use a index card between the flywheel and the coil when putting it back on to insure proper air gap. If your engine uses points, then you will need to remove the flywheel to check them. If you dont know how to do that, you would probably be better off finding someone who can do it for you. Good luck

 

[gocards1177]

I can think of a couple of possibilities; Water in the fuel and, if it is a Briggs engine, a valve spring keeper that came loose. Start by loosening or removing the nut on the bottom of the carb bowl catching the liquid (gasoline, hopefully) that comes out. If it is water, drain it off, refill the tank and go mow. If you get only gasoline coming out, retighten the nut. Then I would remove the valve spring cover and check that both springs are attached firmly to the valves and that the valves open and close when you turn the engine over. Try that and report.

I had thought of water in the fuel as well. I typically put Sta-bil in the fuel, but I went ahead replaced the fuel with fresh anyway. I tried the starter fluid after that and the lack of ignition made me think it wasn't the fuel. I'll try the valve spring when I get home from work if I can. Thanks!

 

[gocards1177]

You post is a little confusing. If you are not getting spark at the plug but it will give a spark when using a screwdriver, then i would be the end of the plug wire has come loose. Of course this is if you have a known good plug. Please clarify, because trying to point you in the right direction will depend on if you have fire or not.

If you are not getting any fire to the plug electrode or the coil wire end, i would take the flywheel cover off and remove the rust on the outside of the flywheel and ends of the coil. Use a index card between the flywheel and the coil when putting it back on to insure proper air gap. If your engine uses points, then you will need to remove the flywheel to check them. If you dont know how to do that, you would probably be better off finding someone who can do it for you. Good luck

Sorry my post is confusing. I agree the situation is confusing. I made sure the spark plug socket is making good contact. I get spark with a scredriver. I get spark with a sparkplug in the socket and if I ground out the little central post. But I don't get a spark if I just ground the threaded part of the plug. Is that normal? It does the same no matter if I use the old, new, or donor/working plug. Is it possible for a spark to be "too weak"? I called the farm&home where I bough the plug from and they suggested dipping the plug in gas. That didn't work either.

The coil appears gapped correctly, which I didn't question since I was getting spark (even though it wasn't in the place/circumstances I would expect.) As to comfort level, I'm pretty mechanically inclined. It is a Briggs, and I have rebuilt 2 small engines in shop in high school, but that was 20 years ago. I wasn't planning on having to change the points, because I was getting some spark. But if I have to remove the flywheel that would give me an excuse to buy a new tool...

 

[eddie48]

any project worth doing is worth buying a new tool for.

 

[kirkawilson]

I would think a 30 year old Briggs has ignition points and condenser that probably need replacing.

 

[gocards1177]

I would think a 30 year old Briggs has ignition points and condenser that probably need replacing.

Just called my FIL. He says he replaced the points once but doesn't remember when. Can points be "partially bad". What I'd like to know before I go to the trouble of removing the flywheel is can bad points and condenser cause no starting and "weak spark"? Could that cause it to run for a while then die like it did? Or are bad/worn points all-or-nothing?

 

[BukitCase]

I didn't know briggs even HAD points, at least not the smaller ones - everything I've worked on had a magneto, which needs to be "gapped" (a match book cover works OK) -

you didn't mention this, but did you by any chance hit a rock or something during mowing? Reason I ask is because I've had a couple small engines "lose" the woodruff key that keeps the flywheel/magnet locked to the crank - so even tho you get spark, it's at the WRONG TIME and won't do you any good.

If you have the complete "combustion triangle", air, fuel, spark - about all that's left is timing... Steve

 

[gocards1177]

I didn't know briggs even HAD points, at least not the smaller ones - everything I've worked on had a magneto, which needs to be "gapped" (a match book cover works OK) -

you didn't mention this, but did you by any chance hit a rock or something during mowing? Reason I ask is because I've had a couple small engines "lose" the woodruff key that keeps the flywheel/magnet locked to the crank - so even tho you get spark, it's at the WRONG TIME and won't do you any good.

If you have the complete "combustion triangle", air, fuel, spark - about all that's left is timing... Steve

No points huh? Great. No I unfortunately didn't hit a rock. Mowing fine one moment then died.

 

[kirkawilson]

Yes. Points and condenser can cause the problems you describe. Best to just pull the flywheel (might need some coaxing if you don't have a puller), check the sheer pin (Woodruff key) and replace it even if its just barely offset (the timing must be exact), replace points and condenser located in round aluminum casing directly under the flywheel. If there are no points and condenser (magneto fired), then your problem is likely the sheer pin (timing).

 

[alchemysa]

I've had 2 instances in the last month of spark plugs appearing to spark (albeit weakly) when grounded but failing to fire correctly in the cylinder. So firstly, buy a new plug to eliminate the possibility of a faulty plug. And make sure the connection to the plug is very good. Sometimes the action of bending the plug lead into an 'unnatural position' to create a ground can create a good connection within the lead that disappears when the lead is pushed back into its correct position. (The fault is usually at the ends of the lead.)

If you have compression, and a strong spark from the screwdriver, but the engine still won't even briefly fire when you spray starter fluid into the carby then it almost has to be the spark plug or the lead. (If it fires but still wont run then you can move on to other possible problems.)

By the way, a simple way to get a good ground to a plug for testing is to use a car jumper lead. Just attach one clamp to the spark plug, and the other clamp to an earth on the mower engine. That way you'll get a good earth and should see a good strong spark if the plug and the associated electrics are OK.

And make sure you can feel 'sucking' at the carby air intake when turning it over with the plug fitted. If the intake valve is stuck shut for some reason (e.g. a broken rocker or pushrod) you won't be getting any fuel or starter fluid into the cylinder.

 

[gocards1177]

Thanks all for the suggestions. I knew i'd get some help here. Looks like I've got some things to try tomorrow...

 

[Don87]

Thanks all for the suggestions. I knew i'd get some help here. Looks like I've got some things to try tomorrow...

The thing that bothers me the most from what you've described is exactly what alchemysa said, and what I've experienced.

If you can't get spark on the plug, between the center electrode, and the curled metal part by touching the threads to the ground, you have a bad plug (ceramic broken).

If you hold the plug at the correct angle so you can see it good, then hold the threads against a good ground, you will probably see the spark going 'sideways' from the ceramic to the outside of the plug(just inside the threads). It will never, ever run that way. And I have had on occasion, where a new plug will do this.........possibly from being dropped at some point I think.

 

[sd455dan]

Yes. Points and condenser can cause the problems you describe. Best to just pull the flywheel (might need some coaxing if you don't have a puller), check the sheer pin (Woodruff key) and replace it even if its just barely offset (the timing must be exact), replace points and condenser located in round aluminum casing directly under the flywheel. If there are no points and condenser (magneto fired), then your problem is likely the sheer pin (timing).

The magnetos coil can also go bad .. and spark plugs can foul do to (glazing of the ceramic insulator ) usually from cracked or old varnished fuel- u would normally be able to smell the bad fuel tho

 

[sox3]

If you have a wire from the coil going under the flywheel, you have points and condenser. If you do, I would cut the wire and replace with newer electronic coil. Either new or used. You could also have a valve stuck partially open
which you can check by turning the motor by hand. If it can be turned past the compression stroke easily,
then valve(s) may be passing enough to hamper starting. A lot of those older units had a problem with the exhaust valve seat coming loose from the block. Usually due to clogged air passages creating overheating. they would run until hot, seat moves or comes out, and it dies. You said it popped through the carb when trying to start once. that sounds like a leaking intake valve.

 

[The kid]

Just a thought here. Magneto and coils. Two items easily overlooks. When I set the gap on my coil. I simply take a piece of printer paper, fold it and place between the magneto and coil. Tighten the coil and rotate the the flywheel to make sure it's clear.

My son left my riding mower outside once for several days. It rained a few times. Although these engines are made to endure weather. Weather can damage them. The mower wouldn't start. Had spark. No start. Pulled the cover and found a bit of rust on the magnetic part of the flywheel. Particles where also magnetized on the coil. Removed the coil. Cleans all debris from it. Sanded the flywheel. Reset the gap with paper as mentioned. Tightened and secured coil. Reassembled and it fired right up. Seems the spark was weak and would cause a weak attempted start. Not saying that this is the problem, but take a look see. Eyeballing something is not always science. -kid

 

[gocards1177]

The thing that bothers me the most from what you've described is exactly what alchemysa said, and what I've experienced.

If you can't get spark on the plug, between the center electrode, and the curled metal part by touching the threads to the ground, you have a bad plug (ceramic broken).

If you hold the plug at the correct angle so you can see it good, then hold the threads against a good ground, you will probably see the spark going 'sideways' from the ceramic to the outside of the plug(just inside the threads). It will never, ever run that way. And I have had on occasion, where a new plug will do this.........possibly from being dropped at some point I think.

I'm pretty sure it's not the plug. I put the plug in question in a different mower and it fires right up.

 

[gocards1177]

If you have a wire from the coil going under the flywheel, you have points and condenser. If you do, I would cut the wire and replace with newer electronic coil. Either new or used. You could also have a valve stuck partially open
which you can check by turning the motor by hand. If it can be turned past the compression stroke easily,
then valve(s) may be passing enough to hamper starting. A lot of those older units had a problem with the exhaust valve seat coming loose from the block. Usually due to clogged air passages creating overheating. they would run until hot, seat moves or comes out, and it dies. You said it popped through the carb when trying to start once. that sounds like a leaking intake valve.

It doesn't spin very easily through the compression. It spins with effort but its not freely spinning.

I have points. Replacing the coil is tempting but given the machine if go used so that may be hard to find here on a Saturday. I'm going to try to get the flywheel off and check/replace the points and condenser.

 

[gocards1177]

Getting ready take flywheel off. But I thought I'd give another update that the shear pin looks partially sheared.