Small Engine Help - B&S/Craftsman
 

Neighbor brought over his snowblower, it's never really run right and he's tried a few things.
He admits should have had it checked out under warranty, too late now.
8.5 horse B&S Powerbuilt Snow.

OK starts ok with full choke, runs and stalls.
I took apart the float etc cleand it.
Now it starts and runs, but you have to play with the choke to keep it running.
Also stutters, even a bit of backfire.
Acts like it's running rich, but there is no mixture adjustment that I can find.

He replaced the Magneto.


Should I suspect his Magneto replacement, he did something wrong somewhere ??
Or what else can I look at / do ??

Check the gap of the plug...sounds as if it's a bit too big.

Also, use choke and carb cleaner to clean the choke really well.

Check the gap between the magneto and flywheel, I believe there is a spec for it, but I am unsure as to what it is.

Ask if he used the woodruff key in the crank, if he removed the flywheel during the magneto replacement.

A carb kit is about $15, and simple to put on. Could easily suffer from a dead diaphragm if there is ethanol in the fuel.

~Nate

hmmm, thanks for the thought. I had about forgotten how ethanol effects these little engines. I have a Kawasaki 110cc pit bike that won't run unless the choke is closed off. I'll try rebuilding the carb with a new kit. I've already been through the carb a couple times but did not install new rebuild parts.

http://www.msnbc.msn.com/id/25936782/ns/business-consumer_news/

Theres a few articles out there, but the main thing is that ethonol attracts water which leads to corrosion, and the turns the tiny passageways in the rubber carb kit to mush.


The b&s carb kits are very cheap, under $15, and any small engines place will have them in stock.

They're easy to f up, so take care during install to not tear the diaphragm on the spring, or misplace any of the clips.

http://www.youtube.com/watch?v=DqPXjtWO0KE
Part 1 of 3, the rest are on his "channel"

It looks like a very good video, and he explains everything very well.
~Nate

I doubt the carb has a diaphram, as they are found mostly on 2 stroke engines. I think the carb has some obstructed passages or jets and these can be addressed without a rebuild kit. As to the ethanol in fuel, it's been in fuel 'round here for years and the only consequence I have found in any of my powered -2&4 stroke- equipment is the clear vinyl fuel lines get hard and either crack or come loose on their fittings.

OK Spark plug is correct and gapped right, although Black.

I am thinking it's the flywheel key too.
Unfortunately it's not easy to get to, even to check.

It starts, must use full choke.
Then choke down one click, runs ok
After several seconds (5 or 10) revs up (seems high to me) then dies.
Fiddling with the choke can keep it running, but not always.
Mist, does smell gassy, coming out of the carb, why I think the flywheel key is off a bit.
Don't think it has a diaphragm, but does have parts that ethanol could affect.


WHY WOULD ANYONE IN 2005+ DESIGN AN ENGINE THAT HAS PROBLEMS WITH ETHANOL !!!!!!
Here in IL I don't think you can buy gas w/o it geesh.

I won't go into a full rant here.
B&S if this engine was deigned by US designers WE'RE DONE FOR.
If this engine was designed over seas, they are laughing at us, and you.

just for example, carb cover, two wing nuts to remove but it's tethered by the safety switch wires and the carb pump. Disconnecting the saftey switch wires means it runs, great saftey feature.

If it starts on full choke, then it seems to run on 1-click choke, then after a few quick runs on the throttle it seems to flood out?

Sounds like a sticky float and/or the needle valve is sticking. The carb probably needs a real good cleaning, then a check of all things rubber/plastic.

When I went through the carb I did not see a diaphragm anywhere. There is some rubber on the float needle that controls the flow into the carb bowl. The one I have that is giving me issues is a Keihin carb. It is doing pretty much the same thing but falls on it's face when you twist the trottle, just like fuel starvation. Now that I have typed it out it just occured to me that it may be as simple as the gas hose from the tank to the carb has gone bad. I'll check it tomorrow.

My prediction is a new carb will cure it. Will probably cost you 50.00. You can get them on Ebay or other sources on line. That was my experience. I tried rebuilding and that didn't help. I blame the ethanol gas but I can't tell you the scientific reason why, just that is my experience. You can get non-ethanol gas at farm co-op's if you have any around. In any case use Stabil which might help. B&S has good diagrams and parts lists available on their site. Good luck.

OK I now have it running, if you call it that, on full choke.

Runs rough, backfires I figure rich fuel getting into the exhaust.

Carb has a rubber seat for the needle, needle valve is all steel, float is all nylon unadjustable.

I'm gonna put some seaform or whatever like that I have laying around and run it for awhile. If that doesn't solve it yea probably a new carb. Well it's up to him.

One question, I can't call the neighbor right now.
Seems strange that it basically runs at full throttle period.
I would think it idles or slower until you engage the drive +/or auger.

How strong is the suction at the carb with the air filter removed?? Vacuum and gravity is what feeds these carbs fuel. Look for a small gasket leak between the air filter and carb, and carb and manifold.

A new carb isn't the fix, changing the gasket would be.

It's definately a fuel supply problem. It's not getting enough fuel so you have to choke it but the choke is not a fine enough control to make it run right.

Then, as the engine uses fuel faster than it's being supplied, it starts to run correctly for a short time, then finally dies of starvation.

Most all of the B/S engines I've worked on have an underslung fuel tank and a fuel pump of sorts that uses intake pulses to pump fuel into a pre-tank where it's used by the engine.

If this one is the same, I'd be willing to bet that the fuel pump is stuck and not functioning properly. It's housed under a plate on the side of the carb held on by about 5 screws.

Your problem is either-
1. a clogged jet
2. the float is full of gasoline
3. a bent flywheel key

The fact that it will only run on full choke points toward a clogged jet.
The fact that it backfires points towards a bent flywheel key (i.e. the timing is off)

My bet is the jet is clogged. At the bottom of the bowl, there is a bolt. Pinch off othe fuel with vise grips at the rubber fuel line. Remove the bolt. You will find that the bolt is hollow with a pin-sized hole on the side of the bolt. Soak that bolt in carb cleaner and blast it with compressed air. Make sure the pin-sized hole is clear as well. put it back in.

If you want to check the plug gap, it should be .30
If you want to check the air gap on the magneto, a business card sandwiched between the magneto and the flywheel is the proper gap.

If the jet is clean and it still backfires, I would take the float out and shake it to see if there is any liquid inside it.

Start with a clean plug if yours is black. Magnetron ignition is very reliable, either it works or it doesn't, but it doesn't have the energy to fire a fouled plug. As others have pointed out, you most likely have a clogged jet in the carb. Some later snowblowers, espescially entry level models, run at a fixed speed. Save your time on the flywheel key. If it was sheared, the engine will kick back and pull the rope out of your hand.

When you're done for the season, store the fuel system completely dry.