B&S 8.5 OHV snowblower almost runs....

[dnastrau]

Greetings:

My neighbor has a five year old Craftsman snowblower with an 8.5 HP Briggs and Stratton OHV engine. It is a constant speed engine (no throttle control.) It has low hours on it and now doesn't want to run. It has spark and the non-adjustable plastic carburetor was taken off and cleaned to no avail. The spark plug is new and the engine seems to have plenty of compression.

If you push the primer a few times and give it full choke, it will start to fire. Pumping the primer will barely keep it running. If you start to open the choke it stalls.

My neighbor thinks he should just get a new carburetor. I looked at the carburetor myself and it seems to be really clean internally and the float/needle look like new. I tried squirting carburetor cleaner through all of the orfices/openings that I could see and this did not help. He told me that he actually had it off and ran a piece of very thin, soft wire through the openings and did not find anything clogged. He mentioned the possibility of a sheared flywheel key, but I would think that it would not start at all if this were the case. Any thoughts on what could be keeping this engine from running?

Thanks!

Andrew S.

 

[nwjones18]

It sounds like its not getting gas to me. Is there a fuel filter on it, or is there one of the little fuel pumps in the carburetor on this model that could have gotten stiff from sitting? Possibly some sort of leak around the Carb where it could be sucking air in?

 

[boraticus]

Most likely fuel starvation. Make sure the fuel tank cap vent is working. Ensure the carb is securely fastened to the engine (tighten carb mount nuts/bolts.

Pull fuel line from carb and drain fuel into clear container inspect for water/debris. Water or dirt will create all kinds of havoc in a carburetor. Blow compressed air through all of the passages after cleaning with thin wire. Confirm float setting is correct. If the float bowl fills up there is probably a restriction elsewhere within the carb.


Try to start the engine and look/smell for gasoline in the combustion chamber via the spark plug and spark plug hole. If it's getting sufficient fuel into the combustion chamber, I'd start to look for things like valve lash adjustment and/or electrical issues. If it's not getting fuel, and the engine still doesn't run after the carb cleaning, a new carb is likely required.

I have no experience with plastic carbs. Not sure if they can be fixed or not.

Why would the owner think that the flywheel key would be sheared? Did he have a serious sudden stopping of the engine while under load?

 

[willix]

The carb bowl may have a fuel cut off solenoid on the bottom.

They can get crud in the orifice & restrict fuel flow& cause starvation. If you can access the carb bowl

It's Not too difficult to remove the solenoid then the valve & clear out the metering orifice.

The OHV engines can have valve & head gasket issues that result in vacuume problems with similar symptoms

 

[dnastrau]

Originally Posted By: boraticus
Most likely fuel starvation. Make sure the fuel tank cap vent is working. Ensure the carb is securely fastened to the engine (tighten carb mount nuts/bolts.

Pull fuel line from carb and drain fuel into clear container inspect for water/debris. Water or dirt will create all kinds of havoc in a carburetor. Blow compressed air through all of the passages after cleaning with thin wire. Confirm float setting is correct. If the float bowl fills up there is probably a restriction elsewhere within the carb.


Try to start the engine and look/smell for gasoline in the combustion chamber via the spark plug and spark plug hole. If it's getting sufficient fuel into the combustion chamber, I'd start to look for things like valve lash adjustment and/or electrical issues. If it's not getting fuel, and the engine still doesn't run after the carb cleaning, a new carb is likely required.

I have no experience with plastic carbs. Not sure if they can be fixed or not.

Why would the owner think that the flywheel key would be sheared? Did he have a serious sudden stopping of the engine while under load?


The fuel tank is clean and the cap vent is fine. The carb is getting plenty of fuel into the bowl - I checked that myself. The sheared key was just a guess on the owner's part - I doubt that is what the problem is. He pulled the head off to make sure the valves were opening and closing properly and he said everything looked fine in there. I am wondering if the carburetor may still be plugged up internally and is not metering fuel properly.

 

[dnastrau]

Originally Posted By: willix
The carb bowl may have a fuel cut off solenoid on the bottom.

They can get crud in the orifice & restrict fuel flow& cause starvation. If you can access the carb bowl

It's Not too difficult to remove the solenoid then the valve & clear out the metering orifice.

The OHV engines can have valve & head gasket issues that result in vacuume problems with similar symptoms


Nope - no fuel cut-off solenoid on this one.

The engine seems to have good compression but I will have to try and get a compression tester to be sure. I will also look for a vacuum leak.

 

[dnastrau]

Originally Posted By: nwjones18
It sounds like its not getting gas to me. Is there a fuel filter on it, or is there one of the little fuel pumps in the carburetor on this model that could have gotten stiff from sitting? Possibly some sort of leak around the Carb where it could be sucking air in?


No fuel pump in the carb on this one - it is a traditional float carb that is getting plenty of gas. I think my next step is to look for vacuum leaks and make sure compression is up to snuff. If that is OK, then I think it may be time to try a new carb as it may be damaged or plugged internally.

 

[JTK]

So this machine will run with the choke on? Sounds like a circuit in the carb is plugged, or like said, a vacuum leak causing it to lean out too much. I'd try a new carb if it's available and cheap enough.

Joel

 

[dnastrau]

Originally Posted By: JTK
So this machine will run with the choke on? Sounds like a circuit in the carb is plugged, or like said, a vacuum leak causing it to lean out too much. I'd try a new carb if it's available and cheap enough.

Joel


Well, it will fire and barely run if you keep pressing the primer with the choke on. I am going to check for vacuum leaks. I really wish this had an adjustable carb because I could at least richen it up and possibly get it to run well enough to aid in the diagnosis of the problem. These fixed-jet emissions carburetors allow no tolerance for air/fuel problems at all.

 

[boraticus]

An adjustable carb suffering from the same issues (probably jet/passage/gallery blockage) wouldn't make things any better. You can't adjust air/fuel mixture if the fuel isn't getting where it needs to be. I've pulled carbs apart, thought I cleaned them, put them back on and still no go. Took them off again, went over them very carefully and found every conceivable fuel passage and cleaned them again. They worked afterward. Some orifices are so small they're difficult to see with the naked eye. Often they'll be in the carburetor venturi and on some carbs that I worked on, that tiny little orifice was for the low speed operation range. Being that the engine you're working on is a fixed speed, there likely won't be a low speed circuit in the carb. I'd venture to say that the main jet/passage is clogged.

 

[flatlandtacoma]

Originally Posted By: dnastrau
I tried squirting carburetor cleaner through all of the orfices/openings that I could see and this did not help. He told me that he actually had it off and ran a piece of very thin, soft wire through the openings and did not find anything clogged.

Originally Posted By: boraticus
Some orifices are so small they're difficult to see with the naked eye.


Bingo. Dollars to donuts he missed one. There is a tiny one in the threads in my Tecumseh carb I never would have found without being shown where it was.

 

[airimo]

I have the same snow blower and took the carb apart 3 times cleaning it with carb cleaner each time.Fuel gets through the line but thats it. The float bowl was always empty. I figured there was something in the needle seat that was clogging it so I used a sewing needle to unclog it. That was a mistake. I think it gets too much fuel now because when I use it the muffler turns red hot. So I ordered new parts. This was a recall problem to begin with. When I get the new seat and install it I would like to adjust the carburetor but can't find info on it. Would appreciate it if someone has the know how.

 

[yeehaw1960]

I looked at a blower with a Briggs on it yesterday at the local shop. Its carb looks suspiciously similar to the ones I see on Chondas. The Chinese carbs are hard to clean and have to be replaced 50% of the time. Oh Briggs and Stratton...have you gone over to the dark side? Tecumseh used to have a bail type (plastic bowl) carburetor that was unfixable/uncleanable. They dont' put adjustment screws on very many carbs anymore. They tried to make them impossible for a layman to adjust, but folks got around that. The EPA is the enemy of the small engine product.

 

[engineerscott]

Originally Posted By: yeehaw1960
I looked at a blower with a Briggs on it yesterday at the local shop. Its carb looks suspiciously similar to the ones I see on Chondas. The Chinese carbs are hard to clean and have to be replaced 50% of the time. Oh Briggs and Stratton...have you gone over to the dark side? Tecumseh used to have a bail type (plastic bowl) carburetor that was unfixable/uncleanable. They dont' put adjustment screws on very many carbs anymore. They tried to make them impossible for a layman to adjust, but folks got around that. The EPA is the enemy of the small engine product.


Aren't EPA and CARB regs basically forcing makers to go to unadjustable (which usually implies some level of unfixable/uncleanable)? I think once the government forces the equipment makers to use non-adjustable carburetors that it isn't going to matter much who makes them, we're not going to like the end result.

BTW, there's been talk that new CARB regs will force engine makers got abandon carburetors all together. If so I wonder how much of a price bump an EFI equipped OPE engine will cost? This won't be entirely trivial as most OPE engines don't have a battery and personally I don't want to have one on my 5.5HP mower.

EFI was an improvement for automobiles though there were many years of trial and error and bad EFI systems before the industry got it right. At least the benefits were fairly clear cut there. For OPE engines, I'm not convinced that the benefit outweighs the cost.

Oh, on Briggs and the dark side. Since B&S is sourcing some OPE engines in China I wouldn't be at all surprised if they weren't sourcing carburetors there also. However, I've got a Honda with a carburetor that I suspect was made in China and I've never had much trouble from it in 11 years now.

 

[Nick R]

I've had to clean the bowl and orifice on our 675 Briggs about 4 times now. It is a pain. I keep a bottle of seafoam or techron handy to clean it with. It's likely still plugged up.