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Old 01-16-2011, 01:52 PM   #1
scipper77
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Default Craftsman snow blower not running well.

I have a 2005 8.5 HP Craftsman model 536.881851 (Briggs)

This season I noticed a surge at idle. Now after a half dozen uses it is really hard to start. I have never used the electric start before, now it's the only way I can start it. After starting it seems to run pretty good but in my opinion it bogs down "a little" easier than it should.

I have checked compression and several turns of the engine with the electric start brings the reading to 75 lb's. From what I understand this number doesn't mean much because there is a pressure relief mechanism for ease of starting.

In the interest of full disclosure I think the original owner replaced the shear pins with regular bolts. I have bogged the engine pretty good on occasion so I'm at piece with the possibility of needing a major repair.

There is a spot on the heat shield (front side of motor) that looks like someone has held a torch to it (discolored).

Now that I have the lengthy description out of the way I'll tell you what I'm thinking and then hopefully someone here will ignore my opinion and tell me what I need to do to determine the issue.

From the idle surge I thought the carb was the issue. Now with the very sudden change in starting performance and the hot spot on the front heat shield I'm thinking there is a leak in the head gasket. That leak would cause a lack of compression making it hard to start. Carb may also be an issue.

What do you guys think??

(Mods, I think this thread may be more appropriate for the small engine forum. Please move it if you think I'll get more help over there)
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Old 01-16-2011, 02:04 PM   #2
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Default Re: Craftsman snow blower not running well.

Most likely, you need a carb rebuild. If its hunting at idle its running lean and the govenor is trying to keep the engine from stalling. I would also get the correct shear pin bolts. Sears stores carry some of them in the stores.
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Old 01-16-2011, 02:54 PM   #3
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Default Re: Craftsman snow blower not running well.

I agree that you have a carb problem. I would first try some SeaFoam and see if that makes it better. If not, then a carb disassembly & cleaning is needed.
And make sure you buy the correct shear pins for it. $8.00 for shear pins versus $50 for an auger gear and more if the gear breaks the housing plus the down time and aggrevation of repairing it.
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Old 01-16-2011, 03:11 PM   #4
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Default Re: Craftsman snow blower not running well.

Make sure the carb-to-engine bolts/screws are tight. Check for gasket leaks in that area, too. I agree that it's running lean, and you probably have to disassemble the carb and give it a thorough cleaning. But, start with the easy stuff.
I'd like to add stress to installing the proper shear pins - that could save you from a mechanical disaster.
The hot spot could well be caused by running lean, and the extra heat is not doing your engine and the exhaust valve any good.
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Old 01-17-2011, 05:01 PM   #5
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Default Re: Craftsman snow blower not running well.

I hope you guys are right.

Before I posted here I had added a fuel cleaner to the gas and cleared the driveway.

Yesterday I used it. I primed it set the choke and pull started it (it would not start.)
then I plugged it in and pressed the starter button. It backfired, I could see a flame come out of the carb, but did start without too much trouble.

I think I will pull the main jet and see if I can clean that. With it "running" I really don't want to pull the whole carb off to clean until the season is over.

My biggest concern is that I may cause severe damage if I run it when I know there is something wrong.

At the end of running yesterday the unit was holding a steady idle.

Also, is it possible to reuse the gasket for the main jet or do I need to get a new gasket before I even begin?? It's so easy to pull the main jet that a trip the store is 10 times more effort than checking the jet.
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Old 01-18-2011, 06:10 AM   #6
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Default Re: Craftsman snow blower not running well.

Sometimes you can reuse the gaskets and sometimes you can't. It depends on how old and brittle they are.
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Old 01-18-2011, 09:34 AM   #7
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Default Re: Craftsman snow blower not running well.

Quote:
Originally Posted by scipper77 View Post
I hope you guys are right.

Before I posted here I had added a fuel cleaner to the gas and cleared the driveway.

Yesterday I used it. I primed it set the choke and pull started it (it would not start.)
then I plugged it in and pressed the starter button. It backfired, I could see a flame come out of the carb, but did start without too much trouble.

I think I will pull the main jet and see if I can clean that. With it "running" I really don't want to pull the whole carb off to clean until the season is over.

My biggest concern is that I may cause severe damage if I run it when I know there is something wrong.

At the end of running yesterday the unit was holding a steady idle.

Also, is it possible to reuse the gasket for the main jet or do I need to get a new gasket before I even begin?? It's so easy to pull the main jet that a trip the store is 10 times more effort than checking the jet.
CORRECTION: I said I saw a flame come from the carb, I meant from the muffler. If a flame comes from the carb I'm in a world of hurt!!!
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Old 01-23-2011, 03:04 PM   #8
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Default Re: Craftsman snow blower not running well.

I'm convinced it's a head gasket or something like this. Today I tried to start it but forgot to turn the toggle switch to on. When I remembered and turned the switch it started but smoke came out from behind the heat shield. Attached are some pics as I know we all love pics.

I have trouble believing this is from the carb...




I'm likely going to tear into it this summer if it's not that complicated.

Can someone tell me how hard it is to replace a head gasket on a small engine like this?

Please any comments on my problem are appreciated even if they are things like your screwed... At least that bumps this thread so others might see it.
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Old 01-23-2011, 03:56 PM   #9
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Default Re: Craftsman snow blower not running well.

Head gaskets are not difficult to change. Flathead engines are very easy, overhead valve engines are still pretty easy. You will get plenty of help and encouragement here, so no big problem even if you haven't done one.
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Old 01-23-2011, 06:00 PM   #10
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Default Re: Craftsman snow blower not running well.

Take the shield off and look for an exhaust leak. If you had a head gasket leaking that much, the engine would not have enough compression to start, and if started, would eventually burn out the head.
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Old 01-23-2011, 06:44 PM   #11
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Default Re: Craftsman snow blower not running well.

Quote:
Originally Posted by rscurtis View Post
Take the shield off and look for an exhaust leak. If you had a head gasket leaking that much, the engine would not have enough compression to start, and if started, would eventually burn out the head.
I can only start it with the electric start. I just don't know what else it could be and sure don't want to burn out the head.

I'll keep my eye out for a replacement with a bad motor just in case I need parts. I'm sure buying parts from sears will get pretty pricey.
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Old 01-23-2011, 07:28 PM   #12
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Default Re: Craftsman snow blower not running well.

Quote:
Originally Posted by rscurtis View Post
Take the shield off and look for an exhaust leak. If you had a head gasket leaking that much, the engine would not have enough compression to start, and if started, would eventually burn out the head.
I think that's an excellent idea. The symptoms fit, and it's not much work to check it out. It could still start with a small enough leak, which will probably only get bigger and may do expensive damage.
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Old 01-23-2011, 07:43 PM   #13
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Default Re: Craftsman snow blower not running well.

Quote:
Originally Posted by scipper77 View Post
I can only start it with the electric start. I just don't know what else it could be and sure don't want to burn out the head.

I'll keep my eye out for a replacement with a bad motor just in case I need parts. I'm sure buying parts from sears will get pretty pricey.
I agree with RSCurtis on the head burn probability. Depending on how bad the flame slot is and where it is located, frequently they can be welded and then head remilled flat. I weld a few of them a year for small engine shops and a couple of contractors.

A couple of weeks ago I did a flat head that had been run with a blown gasket, for an elderly gent. He is a fixture at my favorite coffee shop and it is known he lives on a small stipend from SS. He asked what I would charge to weld it. I told him I would do the welding for the price of a 1/2 order of biscuits and gravy, if he did the prep. I told him what was needed and he did the job to perfection with a hand file and hacksaw blade. The welding took all of 5 minutes followed by me floating the bead down with a Vixen file and a quick pass across a wide belt sander. From there he took it back home and lapped it flat on a piece of glass and 600 grit wet or dry sandpaper, using WD40 for lube. It runs like a charm, saw him out blowing snow with it just the other day.

My karma repair for the month.
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Old 01-24-2011, 12:00 PM   #14
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Default Re: Craftsman snow blower not running well.

What is involved in removing the head on my OHV motor?

Do I have to take off the rockers or will the head come right off leaving the push rods behind?

A new head is $77. If the head is damaged is it likely that the block is also?

These questions are to help me decide if I should tear it down now or park it and work on it in the spring when the weather is a little bit more friendly.
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Old 01-24-2011, 12:07 PM   #15
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Default Re: Craftsman snow blower not running well.

Basically, pull the sheet metal cover(s) off, remove the rocker cover, remove the pushrods, remove carb and exhaust connections, remove head bolts, remove head.


My 2 - running it may do (more) damage. You have to weigh that against the need to use the machine and the time it would take you to repair it. A head gasket isn't very expensive, it's mostly the time to replace it. Plenty of others on here have done it, so they can help. I have never had to do it (yet) on a small OHV engine, although I have done quite a few on flatheads.


Does the new head come with valves, etc? That's a factor in pricing and work.

Repair manuals can be bought, and would be a help.
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