Craftsman Briggs & Stratton Snow 8hp backfires and wont start- please help!

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  #1  
Old 01-15-11, 02:15 PM
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Craftsman Briggs & Stratton Snow 8hp backfires and wont start- please help!

Hello,

I have a Craftsman snowthrower with a Briggs 8 HP engine. The Craftsman model is 536.881800.

It has an electric start on the unit. I cannot get it to start. Sometimes, the electric start will spin idle and not turn the flywheel, other times it will catch and will spin the fly/crank but the engine will not start. Sometimes it backfires. I can verify that the carb is getting fuel, and here is a list of the other things I have done to troubleshoot.

1- new spark plug
2-new fuel line
3- replace one/off switch wiring, and verified that safety key is in place
4- removed flywheel and changed flywheel key which keeps timing proper (I really thought that it was a broken key and the timing was off, since I had almost the exact same thing happen with a mower, however the flywheel key was in tact, and this was not it)

5- Verified that I have good compression- appr 120

6- drain and refill fuel tank
7-sprayed the inside of the carb/choke with starting fluid
8- remove carb bowl, cleaned and reinstalled


Any idea? Could I have a valve problem?

I can pull the pull start recoil, and the flywheel will spin freely. I do feel the compression when it gets around to a certain point. Sometimes, the recoil does not act quite right though, becoming harder to pull, or easier to pull, or snapping back fiercely.


Any thoughts at all? The unit is about 5 years old, but is in great shape (so I thought). I use it annually, but only a couple of times each year. I usually put Sat-Bil in the fuel tank and store it indoors over the summers.

Please help with any ideas.

Thanks
 
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  #2  
Old 01-15-11, 02:33 PM
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COuld it possibly be the starter? It will turn the engine over sometimes, other times it will not. I just hear the electricity trying, but nothing is budging. And it will smoke a bit and smell like electricity if I try to let it go too long without it turning the flywheel.

Thoughts?
 
  #3  
Old 01-15-11, 05:05 PM
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I think there are other posts on here that refer to problems with the ignition system with this model.... Do you have a good solid blue spark @ all times??....Roger
 
  #4  
Old 01-15-11, 08:25 PM
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Well, I put a brand new plug in. Could you let me know how to tell if it has a solid blue spark? Should I hold the wire with the plug attached near the threaded hole and crank it over and just watch?

Also- could you be more specific about "ignition problems" - would this rule the stater out? Should I just do a search with the model number included to find them?

Thanks for your help
 
  #5  
Old 01-16-11, 12:19 AM
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I would use an air gap spark tester that allows you to visuall watch the spark as the engine runs. Only 5~6 bucks @ any auto parts store.. Here's the link http://forum.doityourself.com/outdoo...wer-dying.html
Roger
 
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Old 01-16-11, 05:37 AM
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Thanks for the reply Hopkins. I read the entire thread there, and there are a few things I will try. I will try the cap off, although I am not sure that it is. I will also disconnect the ground wire on the safety switch.

What makes most of those situations different from mine is that I have not even been able to get it started. It is not a case of it running for 15 minutes, then dying out, so it is not a heat related issue.

I will get the air gap spark tester to see if I have a good spark. When I replaced the plug, the old one that came out was black, and oily.

If I am not getting a good spark would that be the coil that needs replacing? I am guessing that is the half-moon cutout shaped electrical module which is adjusted to fit around a portion of the flywheel. It has some magnetic looking contacts, and some wires leading out of it. I did have to remove it when I took the flywheel off, and it looks like it is adjustable as to the distance that it sits from the flywheel. I believe I put it back just as it was taken off (there is a mark in the module where the screws held it in place). Anyway- does no spark mean a bad coil?

Thank you
 
  #7  
Old 01-16-11, 07:03 AM
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On an engine produced after '86 (no points), if you disconnect the kill wire at the ignition module (right at the flywheel to rule out any possible grounding of the wire enroute to the kill switch, and you have the module grounded to the engine and gapped at .010-.012, you should have a strong blue spark at a good, well grounded plug.

If you had a running engine when you parked it in the spring the most common problem starting is the fuel/carburetor. This is where you can't get it to fire at all.

Often an engine won't fire right off because of the residual fuel left over from the previous year. The igniting vapor of gasoline is one thing which evaporates, while the remaining additives reside on the spark plug and inside the carburetor as varnish and a light powdery substance. Those make for a difficult starting and we never know when to choke or stop choking the engine which doesn't work quite as well as before. After it's started the first time, we're in business for the rest of the season.

It sounds like you have a flooded engine. Take out the spark plug, shut off the fuel, hold the throttle at full on and choke off. Then spin it over about fifteen times or so.

Then put a teaspoon of fresh gas down the the plug hole, new spark plug, half throttle, no choke with fuel turned off to the carb and see if you can't get a fire. It takes about four or five pull to get something.

If it tries to start, turn the fuel back on, half throttle, half choke and see if it goes for you. Usually it will.
 
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Old 01-16-11, 07:58 AM
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Thank you, I will try.

For the record, I have ruled out the gas cap and also simply ungrounding the kill switch. I will remove the ground wire right at the flywheel though.


I will post back
 
  #9  
Old 01-16-11, 05:40 PM
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I bought the air gap spark tester- and I do see a blue spark shooting between the connections. So- I guess that rules out the coil right? I would not get the spark if I had a bad coil correct? If I am right on that...then I guess the only other issue could be fuel. So, I will go ahead and run through the procedure that marbobj outlined in the earlier post. Hopefully I just need to get it going and clean it out from the storage period last summer.

Would starter fluid do me any good in this instance? Or can that still keep it flooded out. I did spray some in the choke area of the carb, but still no luck. Seems like I am usually able to get flooded small engine (or large engines) going after a while, but I will go through the full procedure in the morning. Any other thoughts would certainly be welcome. Thanks to all who have chimed in.
 
  #10  
Old 01-17-11, 10:11 AM
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Well, I performed the procedure suggested- I removed the plug and spun the engine over. I did notice that the engine spun over very easily without the plug in (no compression), so I guess that means that the electric start is just fine.

Next, I poured a bit of gas into the spark plug hole, replaced the plug and turned it again. It was noticeably more difficult to turn over ( I guess that means good compression), but I could not get it to fire, or even start to fire.

So does this mean that I need a better spark? I did use the air gap spark tester, and did see a blue spark. How big was the spark- I guess I am not sure. It was about the size of a .5 pencil lead I would estimate. Is that strong enough?

Also- just to clarify. I do have the wires reconnected again (both at the kill switch and at the coil near the flywheel). Should I have these connected? Or have them disconnected? Can I start this engine with out any of the wires connected? At the flywheel- there are two wired that enter one connection on the coil. Should I pull the combo of both? One leads to the ground wire on the safety kill switch.

Also- there is a medium gauge single red wire, with a plastic wire connection tip (round) that comes out near the electric start. Is this for anything? It has never been hooked up to anything. I guess I thought it was for diagnostics, or something. Any idea?

Also, to clarify- I do have a brand new clean plug in. If it is firing, but not strong enough to ignite- where do I turn next?

Any help would be appreciated. We are supposed to get dumped on tonight.

Thanks very much
 
  #11  
Old 01-14-12, 06:24 AM
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Check Spark Plug

I know this thread is old but just in case anyone reads this it could be the actually spark plug. I have the same model snowblower and the spark plug that is recommended in the manual is "Champion RJ19LM" when the correct spark plug is either "B&S 491055 HAB" or RC12YC." The information in the manual is incorrect.
 
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