small engine (snowblower) question

[echo4747]

Here are the details/problem:

-Older Honda HS621 snowblower..
cold start,pull choke , start by pulling cord, as the snowblower warms up push the choke lever back,start snowblowing and machine runs operates fine. After 10-15 mins the snowblower starts popping/backfiring see a little fire pop out the muffler when this happens.

Anyone have any ideas what is causing this problem?

btw: gasoline is fresh

 

[LTC8K6]

Valve adjustment needed?

http://cdn.powerequipment.honda.com/pe/pdf/manuals/31747700.pdf

 

[RLGL]

Might be running lean

 

[boomerang]

What happens when you try to restart it? If it needs to cool down for a while before it will restart, check to see if you have a spark as soon after it dies as is possible.

How's the oil level? Does it have a low oil cutoff switch?

Could be valve adjustment could be running lean as others have said. Just trying to eliminate the basics as a cause first.

 

[echo4747]

What happens when you try to restart it? If it needs to cool down for a while before it will restart, check to see if you have a spark as soon after it dies as is possible.

How's the oil level? Does it have a low oil cutoff switch?

Could be valve adjustment could be running lean as others have said. Just trying to eliminate the basics as a cause first.

Doesn't need to cool to restart. It will restart when hot and resume popping/backfiring. Oil level is good. not sure if it has a low oil cutoff ( its my next door neighbors blower) Again when starting from cool it will operate fine for about 10-15 mins.

 

[boomerang]

Doesn't need to cool to restart. It will restart when hot and resume popping/backfiring. Oil level is good. not sure if it has a low oil cutoff ( its my next door neighbors blower) Again when starting from cool it will operate fine for about 10-15 mins.

Then I would agree with the other posters that it's either valves or running lean.

See if the carb is loose, if the mounting screws have come loose and the engine is sucking air after the carb. You may want to remove it to inspect the gasket. It does sound more like valves. I wouldn't want to run it too much longer before adjusting them. Burning a valve or valves would mean an expensive repair versus a simple valve adjustment.

One thing worth doing IMO would be to remove the spark plug and take a look at it. If the insulator around the center electrode is really white, that indicates a lean condition. Also if it has been running lean for a long time, there could be damage to that insulator. Chunks broken off and missing.

Edit: Just took a quick look at the owners manual and I see there is a "fuel strainer cup". Essentially a fuel filter. It wouldn't be a bad idea to remove that and give it a cleaning. There could be water in it. I don't see how that would cause the problem that's going on, it's not something that would rear it's ugly head in 10 to 15 minutes of running, but it's a good thing to do yearly. Water is heavier than gasoline and if there is a lot of water in it, theoretically it could disrupt the flow of fuel.

 

[echo4747]

Then I would agree with the other posters that it's either valves or running lean.

See if the carb is loose, if the mounting screws have come loose and the engine is sucking air after the carb. You may want to remove it to inspect the gasket. It does sound more like valves. I wouldn't want to run it too much longer before adjusting them. Burning a valve or valves would mean an expensive repair versus a simple valve adjustment.

One thing worth doing IMO would be to remove the spark plug and take a look at it. If the insulator around the center electrode is really white, that indicates a lean condition. Also if it has been running lean for a long time, there could be damage to that insulator. Chunks broken off and missing.

Edit: Just took a quick look at the owners manual and I see there is a "fuel strainer cup". Essentially a fuel filter. It wouldn't be a bad idea to remove that and give it a cleaning. There could be water in it. I don't see how that would cause the problem that's going on, it's not something that would rear it's ugly head in 10 to 15 minutes of running, but it's a good thing to do yearly. Water is heavier than gasoline and if there is a lot of water in it, theoretically it could disrupt the flow of fuel.

Thanks for the info ... maybe when this engine gets hot expansion is causing the exhaust valve not to seat/seal properly; then ignition occurs with some fuel that finds its way past the exhaust valve in the exhaust port firing out the muffler

 

[Meghan54]

Question.....are you using gas that is ethanol blended? If so, what grade/octane? While I cannot speak for older power equipment, much of my newer stuff, by Stihl and Echo, both require 89 octane gas due to 87 octane burning too "hot"/lean. Maybe try a higher octane gas as an experiment? Or possibly it's just old enough to have enough carbon buildup on the piston and head that the compression's gone up. Just tossing out thoughts.

 

[echo4747]

Question.....are you using gas that is ethanol blended? If so, what grade/octane? While I cannot speak for older power equipment, much of my newer stuff, by Stihl and Echo, both require 89 octane gas due to 87 octane burning too "hot"/lean. Maybe try a higher octane gas as an experiment? Or possibly it's just old enough to have enough carbon buildup on the piston and head that the compression's gone up. Just tossing out thoughts.

he is using 87octane 10% ethanol gas. Manual says 86 octane is the minimum acceptable and up to 10% ethanol is allowable. I have a bit bigger honda snowblower (hs928) an have been using 91oct ethanol free gasoline ever since reading on many forums that small engines run more trouble free with it. I actually noticed my riding mower actually produces a slight power increase with ethanol free gas vs 10% ethanol. ( engine doesn't seem to strain as much when mowing pacthes of thicker taller grass)

-I will let him try a tankful of some of my gasoline and see if it helps. In wetern ny very few stations sell ethanol free fuel anymore

 

[ghost03]

-I will let him try a tankful of some of my gasoline and see if it helps. In wetern ny very few stations sell ethanol free fuel anymore

I'm in CNY not WNY, but most stations here which you can access from snowmobile trails will have 91 ethanol free. Most sledders incl. me will skip on stations that don't have it.