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Old 01-31-2011, 05:35 AM
DrPepper DrPepper is offline
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Default What causes a generator to sputter and backfire?



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I decided to power up my Powerboss Honda 7000/10000 generator last night prior to the incoming Midwest winter storm. It started great on full throttle, however, when I pushed in the throttle to run at normal speed it sputtered and backfired with flames shooting out. Any mechanics out there who can suggest what may be causing the problem? Thanks!
Old 01-31-2011, 05:38 AM
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how long has the gas been sitting in the tank? if it has been a while, that could cause stuttering... a little moisture in the lines. try adding STABIL or another additive next time you put the generator to rest. After the initial problem did you get it running OK?
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Old 01-31-2011, 05:47 AM
stanimal stanimal is offline
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That was my first though too. Or if it has been awhile since it was fired up, if you didn't run the fuel line dry, could there be some varnish that built up in the line?
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Old 01-31-2011, 06:11 AM
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It sounds to me like its trying to flood out. Does it have a bowl and float on the carb? A lot of times if it sits with gas in the carb bowl too long the gas will varnish over in the tiny spaces (around pins and orifices) and cause the float not to rise and fall properly. Its a relatively simple fix. Just take the bowl off and remove the float (one screw through the bottom of the bowl, just be gentle, theres small springs and the float pin-valve that can be lost very easily) and spray in some carb cleaner and wipe out with a clean rag.

Also, whens the last time you changed the spark plug and is the plug wire on all the way? Sometimes if a small engine is left in storage it gets bumped around and the wire gets loose.

Just remember, MOST gas you get these days has ethanol added. Ethanol will cause the gas to separate in a matter of weeks if left to sit. During that separation water condensation forms and that could also cause the sputtering.
For that reason, you need to make sure you close the tank valve and run all the gas out of the carb before storing whether you put a fuel stabilizer in the tank or not.

Since youre getting flames out of the exhaust, that sounds like youre getting raw gas into the exhaust either by a valve not closing or too much gas going into the engine, or incomplete combustion from low spark.

Those are the easy things. Hope it helps.
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Old 01-31-2011, 06:20 AM
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Quote:
Originally Posted by DrPepper View Post
I decided to power up my Powerboss Honda 7000/10000 generator last night prior to the incoming Midwest winter storm. It started great on full throttle, however, when I pushed in the throttle to run at normal speed it sputtered and backfired with flames shooting out. Any mechanics out there who can suggest what may be causing the problem? Thanks!
Sounds to me like a lean condition. Full throttle runs on the main jet and when idled down it runs on the idle jet which sounds clogged. Drop the bowl on the carb and either remove the jets hit with carb clean and compressed air and that should do it.
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Old 01-31-2011, 06:45 AM
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I ran it dry before storing it. I put fresh gas in it. Thanks for the replies so far!
Old 01-31-2011, 08:14 AM
trukboss trukboss is offline
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did it sputter and backfire only when you pushed the throttle in or the whole time it was running at that rpm? in other words did it do it just when dropping the rpm or the whole time it was running at the slower speed. if it only does it when the rpm drops,it could just be unburned fuel igniting in the exhaust but first things to check: loose carb, loose exhaust-hole in the exhaust, has the exhaust been modified? its sucking air in somewhere.it will usually only backfire thru exhaust with the presence of oxygen. if it does it the whole time it runs at the rpm your set at, again exhaust, lean condition or inconsistant spark, check carb. backfire at rpm drop= exhaust/unburned fuel, steady backfire= lean or bad spark
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Old 01-31-2011, 08:33 AM
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Has to be either fire fuel or air. Have you checked the fuel filter
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Old 01-31-2011, 10:54 AM
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can you give historical data..ie last fired, fuel age..anything to help me. I can most likely point you in the correct direction.
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Old 01-31-2011, 10:56 AM
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I did not see the other questions..sorry. I will figure this out soon.
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Old 01-31-2011, 11:27 AM
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My generator does not empty the bowl when I run it dry. I found that out the hard way earlier this past spring. It basically ran as yours is doing, surging, backfiring, and flooding badly. The gas in the bowl had started to go bad and was making my needle valve stick open. So much so that it would run, but gas was overflowing out of the air cleaner. Had to turn the fuel tank shut off valve almost closed, to stop the flooding but keep the engine running. Do not assume that your carb is dry when running it out of gas.
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Old 01-31-2011, 08:12 PM
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Originally Posted by sixgun67 View Post
My generator does not empty the bowl when I run it dry. I found that out the hard way earlier this past spring. It basically ran as yours is doing, surging, backfiring, and flooding badly. The gas in the bowl had started to go bad and was making my needle valve stick open. So much so that it would run, but gas was overflowing out of the air cleaner. Had to turn the fuel tank shut off valve almost closed, to stop the flooding but keep the engine running. Do not assume that your carb is dry when running it out of gas.
sixgun
I bet that is exactly what happened. I always used to leave gas in the tank for months and never had a problem restarting it on the first pull. This is the first time that I ran it dry and there was probably some gas left in the carburetor. I have not run it in over a year thinking it was safely stored.

If I do need the generator in the next day or two, would it be harmful to run it on full throttle for 24 hours? It is a very nice generator and I would hate to ruin it.

Thank you all for the great responses. It is amazing how much knowledge is available on this board and how many helpful people there are here. Unfortunately, I will probably need to take it to a small engine repair shop because taking apart the carburetor is more of a job than I am willing to tackle.
Old 01-31-2011, 09:55 PM
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I wouldnt go that far DrPepper. Although it wouldnt hurt the engine, I doubt it would be healthy for the generator package. Besides that, I doubt it would serve any purpose.

You dont have to pull the entire carb apart, just the bowl. Should be one screw through the bottom of the bowl. Most floats are held in place by a hinge-pin and the needle valve is either resting on top of the float or sometimes locked into a clip on top of the float. Once the float is removed, you spray carb cleaner up inside a couple of times, spray into the bowl and wipe it out with a rag to make sure theres no rust or varnish particles, inspect the needle valve O-ring if it has one and throw everything back together.

The whole process may take 10 minutes. If you take it to a shop theyll charge at least $65 plus 2 trips worth of gas. Worst case, you cant get it back together and you take it to them in a box and they charge you the same thing to put it back together. Best case, you get it right the first time and can stash a little small engine knowledge to your survival skills.
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Old 01-31-2011, 10:17 PM
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mine has a low oil sensor and does that if its low on oil and not quite level
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Old 01-31-2011, 10:18 PM
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This may or may not be the case but i had one do the same thing, turns out the alcohol in the gas attracted some condensation and the fuel line was freezing slightly. I drained the gas and put new gas in with some SeaFoam, works like a champ now.
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Old 01-31-2011, 11:03 PM
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Originally Posted by crb2012 View Post
This may or may not be the case but i had one do the same thing, turns out the alcohol in the gas attracted some condensation and the fuel line was freezing slightly. I drained the gas and put new gas in with some SeaFoam, works like a champ now.
Didnt think about that. DrPepper, you can remove the air filter and run it at full throttle while slowly pouring SeaFoam down the air intake. Just have to be careful, pour the SeaFoam too fast and it smothers the engine altogether and its a booger to restart. But that only helps clean the carb past the air filter and the cylinder/piston and exhaust/intake valves and spark plug. Smokes like a freight train too. You might give that a try before cleaning the bowl out. But if it doesnt help go for the carb bowl.
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Old 02-01-2011, 06:41 AM
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Quote:
If I do need the generator in the next day or two, would it be harmful to run it on full throttle for 24 hours
Mine wouldn't run without the sputtering/almost dying, even at full throttle. I definately couldn't open the choke, had to leave it slightly choked to keep it running. I really don't recommend running it this way, as you cannot expect the electricity generated to be smooth and even, I'd expect spikes and drops bigtime. Just my thoughts.
sixgun
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Old 02-01-2011, 07:23 AM
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While you're in there, I'd change the plug too. Let us know what you find. Good luck!
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Old 02-01-2011, 10:57 AM
Wy_Wulf Wy_Wulf is offline
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I repair a LOT of small engines and this is one of the most common problems I see. 99.99999% of the time it is the jets in the carb that are varnished.

You can clean everything with the carb on the engine, but it's a pain in the butt most of the time. It only takes a couple of minutes to pull it off and do it on the bench. Keep track of all the little levers and springs and such that attach to the various points on the carb!! Hint - use your camera and take a few pictures to help you get it all back together.

Once on the bench pull the bowl and float, then remove the jets and needle valve. Use carb cleaner and compressed air to clean the jets and then blow cleaner and air through all the ports in the carb itself. The hole in the idle jet is very small, you may need to find a small piece of wire to poke through it to get it clean. Be careful not to make it any bigger.

When you put it all back together make sure the jets are tightened down well, depending on the carb you may need to 'customize' a screwdriver to get the jets out and back in. If they aren't all the way tight the vibration of the engine will cause them to back out and fall into the bowl, then the engine will really run bad. Ask me how I know
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Old 02-11-2011, 01:30 PM
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As expected, several people here correctly diagnosed the problem. Unfortunately, I am not very knowledgeable about motors, so taking apart the carburetor (let alone just finding it), was more than I wanted to tackle. So I took my generator to a local small engine repair shop. They cleaned out the carburetor along with a few other maintenace items for $80 and my generator now works like a dream. I learned a very valuable lesson--keep stabilized gasoline in the generator year round and just run it a couple of times a year if it has not been used. Thanks for all of the helpful advice.
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