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Craftsman snowblower problem

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Re: Craftsman snowblower problem

Postby bgsengine » Sun Feb 09, 2014 4:36 pm

1) Pull the fuel line off the carb and do a visual flow test (1 quart in 1 minute would be an average benchmark for a 1/4" ID fuel line and a full tank)
2) Try a new spark plug (Yes, another one)
3) Other than that, it's the carb - as you stated, half choke or adding fuel make sit last a little longer

I doubt you are losing spark, you COULD be losing compression (unlikely but good to check valve clearance) You could have a plugged muffler (Think Banana in the Tailpipe A La Beverly Hills Cop) - engine MAY have a spark arrestor, which if that gets clogged with carbon, will cause the same symptoms.

Now that I think on it, plugged muffler would explain ALL of your symptoms and tests so far. (It would quit even with adding fuel) - OR, your fuel line is bad - Keep in mind they are a multi layer, the inner layer COULD be collapsed causing a restricted fuel flow - or could be routed in such a way that it pinches (but then, adding fuel *should* typically overcome that)

It is unlikely a coil problem, or a valve hanging up, as you say it starts right up after it quits (Which again can point at plugged exhaust) - a coil breaking down from heat would not do that. Likewise a failing coil, unlikely to allow it to start right back up immediately same with fuel line restriction - again everything seems to point at a plugged up exhaust.

Even if there is no spark arrestor, an internal baffle could be loose or broken and clogging up the works..

So I would go with - Exhaust, Spark Plug, Spark Plug resistor cap (plug boot), carburetor, in that order. - Mainly because checking exhaust, a new plug, and a new plug boot are the easiest, fastest, and cheapest to check first.
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Re: Craftsman snowblower problem

Postby frankp » Sun Feb 09, 2014 9:13 pm

what i mean by "how bad is that" is B&S should be ashamed at put engimes so poorly. I have seen leaking head gaskets start and then stop due to loss compression. Start with a quick check of the valves before suspecting head gasket. Just adding my two cents for discussion.
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Re: Craftsman snowblower problem

Postby Tim » Mon Feb 10, 2014 3:13 pm

bgsengine wrote:Me, too. I have never seen a coil do that. from the looks of things, probably gonna have to splurge and get a new carb - Ive seen THAT a lot on these machines - the surging is the clue - even the wondrous ultrasonic really cannot solve the issue because the carburetor itself is simply too lean. MTD actually has updated most of their carburetors (several times) used on these machines (and kits so to speak are NLA if they ever were) so best bet is to plan on getting a new carburetor.

Ive seen coils get hot and fail. But it is unlikely for coil to run for that long before failure, or cause a surge (despite a post earlier today where a shop *claimed* the coil was the problem)

Plugs , yes Ive seen them cause a hunting (but that was actually a lean misfire) and even plug caps (boots) , but never the coil itself, to date, and I'd be very surprised if it was actually the coil. I think the first thing to solve will be the surging problem, which, odds are excellent it will need a new carburetor, and once THAT is solved, the rest of the problems should take care of themselves.. and if not, then you've got 2 separate problems.


Wow..I've never seen coils cause surging either unless there about to fail...kohlers coils are the worse as far as getting less and less run time until they die out..i've replaced MANY and fixed the problem. may not be the case here but its so easy to check with a 3 dollar spark checker and rule it out..i just replaced a briggs coil that would cut out after about 10 minutes of run time only to start back up and repeat it self...been running fine since. i do have to agree with your assesment on the untrasonic cleaners as they arent a fix all as the carb passages get smaller and smaller these days. i've had to replace more carbs in the last five years then the twenty before. still waiting on the results from this thread and actually the coil wasnt my first choice to tackle..just the easiest to rule out as i'm not to old to have been fooled by one or two.
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Re: Craftsman snowblower problem

Postby frankp » Mon Feb 10, 2014 8:53 pm

I sold a snowblower this winter that ran sometime and didn't other times. Problem was mice ate the coil wire. shorted sometime and didn't short other times.
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Re: Craftsman snowblower problem

Postby Josef » Thu Feb 13, 2014 11:17 am

Bgsengine – Just to update things: Checked the valve clearances and they were about double spec, but fixing that only had a marginal effect. It would run just maybe 15 or so seconds longer than it had been running. The snowblower is 10 years old, but has relatively little run time and has always been garage kept, so nothing (muffler included) is rusted at all, and the exhaust blows out with vigor, so that didn’t seem likely to be a problem (although I agree a constricted exhaust could fit the symptoms). Getting a replacement carb proved challenging – they are apparently on backorder nationally, which may imply that there are a lot of issues with these B&S carbs. I finally found one locally (if you call a 2 hour drive local, but with a major snowstorm coming and a 200 yard driveway I bit the bullet and hit the road). Putting the new carb in did appear to fix it. With the replacement carb it ran without stalling for more than 5 minutes (although it didn’t sound completely smooth). At that point, I needed to switch to working on my generator (fuel leak) in case we might lose power in the storm (I'm on a well, so no power means no water in addition to no heat). I’ll be getting outside to work on the snow shortly and hopefully the snowblower will hold up for a few hours under load – we have about a foot of heavy snow on the ground. I’ll update you on that later.

I’m still puzzled about what was going on with the old carb. It’s not clear to me whether there was too much or too little fuel getting in or why it would start ok each time (1-3 pulls both for the initial start and for restarts immediately after it quit) but not keep running. Too much fuel and you wouldn’t expect adding choke to make it run longer. Too little fuel and squirting some in the carb should have made it run longer. Either too much or too little and you wouldn’t think it would restart easily immediately after quitting.

frankp – Compression was good cold (55-60 psi), but I’m not sure how I would check it hot without risking damage to the o-ring on the compression tester (and there's no way to pull the plug fast enough for it to still be fully hot anyway). And since it restarts right away, I don’t think it could cool and restore compression lost due to heat in literally a few seconds. As for the valves, other than the clearances everything looked fine under the valve cover, and to the extent I could see the intake valve with the carb off, the only thing that seemed unusual (to me) was the aforementioned blueing. No way to see the exhaust valve, but with ok compression my guess is that it is ok.

“Problem was mice ate the coil wire.” Pretty sure I don’t have that problem on the snowblower, but there was a time about 15 years ago when my A/C went out. I diagnosed that as bad module in the furnace and replaced that part. The new part immediately failed as well ($25 trashed), and then I found where the mice had chewed wires as they left the foundation heading for the A/C unit (leaving them shorted in a way that killed the part). Aggravating little critters.

Tim – I agree that the coil/spark seems unlikely to be a factor (although I never did get around to using my timing light to try to make sure the spark wasn’t fading as it quit).

Thanks all, I’m headed out to hopefully move some snow. Update you later.

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Re: Craftsman snowblower problem

Postby Josef » Thu Feb 13, 2014 5:10 pm

Update: Good news. It kept running for about 3 hours of moving heavy wet snow, so the new carb has mostly taken care of things. I still need to figure out how to adjust the governor a bit because the rpm was staying a bit lower than it should – the engine was often lugging and laboring with the heavy snow (and even occasionally popped a mild backfire), and of course running slower means it doesn’t toss the snow as far.

A couple of more inches of snow are forecast to come tonight and more still Friday night (the weather folks aren’t predicting an amount yet for that other than 'less than today'). Heck of a winter so far.

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Re: Craftsman snowblower problem

Postby KE4AVB » Fri Feb 14, 2014 2:31 pm

Josef wrote:Update: Good news. It kept running for about 3 hours of moving heavy wet snow, so the new carb has mostly taken care of things. I still need to figure out how to adjust the governor a bit because the rpm was staying a bit lower than it should – the engine was often lugging and laboring with the heavy snow (and even occasionally popped a mild backfire), and of course running slower means it doesn’t toss the snow as far.

A couple of more inches of snow are forecast to come tonight and more still Friday night (the weather folks aren’t predicting an amount yet for that other than 'less than today'). Heck of a winter so far.

Joe


Tnx for letting us know you got it running; although, like you I am wondering is wrong the old carburetor. The problem just does fit what I normally see here when one is giving problems. If you happen to find out what I would be interest in the results.

Yep it seems to a winter that just keeps giving; I am surprise that I haven't heard of any Wooly Mammoths sightings yet. :lol:
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