Help troubleshooting a snowblower engine?

[NetWareHead]

Wondering if you guys can help with this set of symptoms please?

Honda HS55 snowblower with commercial quality Honda GX engine.

The engine starts normally with fuel open and choke closed. As engine warms up, I gradually move the choke more and more to the fully open position.

The issue is when the choke is fully opened, the engine begins to run rough. Rough as in the sense that it runs in "fast cycles" as if it were slowing down and then speeding back up. It sounds to me like when an engine is running out of gasoline and not at a consistent sound or rpm. (Not sure if describing this properly)

At first, I thought the engine just wasnt warm enough so I left the choke at half position and gave it a few more minutes. Even after letting the engine warm up for more than 5 minutes additional time, when I moved the choke to fully open, the fast cycle of rough running returns.

I can get the fast cycling to go away if I refrain from opening the choke fully. Actually the engine runs perfectly and has a consistent sound and rpm when the choke is open at I estimate 75% position.

My theory based on my limited knowledge of engines:

Choke closed provides engine with a rich mixture so it can start more easily. As engine warms up, rich mixture not needed and choke can be opened (allowing more air and creating less rich mixture). My theory is when choke is fully opened, the engine is perhaps receiving too much air and creating a lean mixture. IMO, this is why it sounds the best with choke 75% open as this creates the correct fuel mixtures.

It also sounds like shop that did previous work never adjusted the carb accurately. So should I be looking for ways to correct this overly lean condition? Anything to watch out for (keep me from messing up my engine)?

Can you see anything wrong with running engine under load (snowblowing) with choke set at 75% position?

 

[monkeydelmagico]

try some carb cleaner yet? Even better take carb off and soak it?

 

[NetWareHead]

try some carb cleaner yet? Even better take carb off and soak it?

The carb is new. Snowblower sat for years in a basement. Dug it out and sent it to a shop where the cleaned it internally (years old gas in the tank, sludgy oil in crankcase etc...) Replaced the carb.

 

[PottedMeat]

i would have guessed fuel obstruction, but if the carb is new and the tank has been cleaned it may just be out of adjustment - check here for the workshop manual for that engine (GX??? whatever) http://www.uni-power.co.uk/wsm.html and set the screws to their default positions. also check that all the linkages are in their correct holes.

 

[Zivic]

carb just needs to be adjusted

 

[LTC8K6]

The carb is new. Snowblower sat for years in a basement. Dug it out and sent it to a shop where the cleaned it internally (years old gas in the tank, sludgy oil in crankcase etc...) Replaced the carb.

Call the shop and tell them it doesn't run properly?

 

[imagoon]

carb just needs to be adjusted

Seconded. Hunting like that means it is set to lean. 75% choke to make it smooth generally indicates that also, barring anything obvious like a leaking intake gasket (did you use a new one?)

If that carb is like many of the small engine carbs, there is going to be a main jet and a smaller jet adjustment. The smaller jet is similar to an "idle jet" and keeps the engine fueled when running unloaded at run speeds. Adjust this one slowly until the hunt just disappears. Shut the engine down. Count the number of turns until the screw bottoms out. (Back out the screw this number of turns.) Write this down, it is your base line. The main can be a bit harder since it needs to be adjusted under load so you may need to start moving snow and see how it responds if the engine starts to buckle, you will need to adjust out (lean it a bit) if it starts to hunt a bit, go in (richen.) Shut the engine down and count the turns to bottom the jet. (Back out the screw this number of turns.) This is the base line for the large get. Once that is good I normally like to add anywhere from a 1/16 of a turn to a 1/4 turn to the small jet so I am not so close to lean. Engine sound should change a little but otherwise sound like you haven't done anything. Repeat with the main jet. If you start to have issues back out in small steps.

 

[NetWareHead]

Call the shop and tell them it doesn't run properly?

Im kinda trying to research this issue and understand it before I involve the shop and point fingers at them. But it is something I am considering.

 

[NetWareHead]

Seconded. Hunting like that means it is set to lean. 75% choke to make it smooth generally indicates that also, barring anything obvious like a leaking intake gasket (did you use a new one?)

I have no idea but could see where leaking air through the intake gasket could lean the mixture up.

If that carb is like many of the small engine carbs, there is going to be a main jet and a smaller jet adjustment. The smaller jet is similar to an "idle jet" and keeps the engine fueled when running unloaded at run speeds. Adjust this one slowly until the hunt just disappears. Shut the engine down. Count the number of turns until the screw bottoms out. (Back out the screw this number of turns.) Write this down, it is your base line. The main can be a bit harder since it needs to be adjusted under load so you may need to start moving snow and see how it responds if the engine starts to buckle, you will need to adjust out (lean it a bit) if it starts to hunt a bit, go in (richen.) Shut the engine down and count the turns to bottom the jet. (Back out the screw this number of turns.) This is the base line for the large get. Once that is good I normally like to add anywhere from a 1/16 of a turn to a 1/4 turn to the small jet so I am not so close to lean. Engine sound should change a little but otherwise sound like you haven't done anything. Repeat with the main jet. If you start to have issues back out in small steps.

Thanks for this write-up. Never tuned a carb before.

 

[LTC8K6]

A lot of carbs are not readily adjustable these days due to emissions regs.

 

[imagoon]

A lot of carbs are not readily adjustable these days due to emissions regs.

Most "unattached" ones are. If they were not shipped with an engine, there is no way to turn it.

 

[bruceb]

My Snapper with a Briggs 6HP does a similar thing. I think it has to do with the crap winter fuel blends and the fact that they have some ethanol in them. Best bet, next time you get gas, try the Premium 93 Octane. Shell has one the best 93 with little ethanol in it.

 

[NutBucket]

I have old and new small engines. They seem to be fine with our E10 gas. But I always add Stabil when I refill my red fuel container.

 

[Mandres]

Does sound like you're running lean. Could be an air leak, a blocked jet (unlikely if the carb is new), blocked fuel filter or just an incorrect setting on the high speed circuit.

I also vote take it back to the shop and get them to make it right if you already paid for work.