Small Engine Question

jib-tmb
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jib-tmb
Edited Date/Time 5/14/2013 9:58am
I have an old lawn mower with an 18 HP twin cyl Briggs & Stratton engine. Anybody know what would make the RPMs fluctuate up and down while just sitting there running? The only way I can smooth it out is to have the choke on about 3/4. Usually the carb is the problem but I've cleaned the carb a few times with no luck. I put fresh gas in it and changed the fuel filter. Any ideas?
I can hear my grass growing outside my window!
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MR. X
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MR. X 4/21/2013 5:59pm
4/21/2013 5:59pm
Will it smooth out if the engine has a load on it , say like engaging the blades
jtomasik
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jtomasik 4/21/2013 6:04pm
4/21/2013 6:04pm Edited Date/Time 4/21/2013 6:19pm
Could be a wandering governor that has little to do with the rest of the engine. Spray some ether (engine start) around the carb area (don't get it into the intake/air cleaner), and if the r's pick up, you might have an intake leak.
tunedlength
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tunedlength 4/21/2013 6:08pm
4/21/2013 6:08pm
Jtom Roosted me!

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TerryK
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TerryK 4/21/2013 6:08pm
4/21/2013 6:08pm
If you back the throttle down does it even out?
jib-tmb
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jib-tmb 4/21/2013 6:44pm
4/21/2013 6:44pm
MR. X wrote:
Will it smooth out if the engine has a load on it , say like engaging the blades
Yes it does. Usually after engaging the blades and mowing a while it smooths out and runs pretty good at low or high throttle. However I haven't mowed yet this year and it seem a little worse than usual. I've never had to pull the choke out this far.
jib-tmb
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jib-tmb 4/21/2013 6:48pm
4/21/2013 6:48pm
@ Tunedlength & JTom - I'll give that a try in the morning.

@ TerryK - No, it starts to break up and stalls out.
borg
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borg 4/21/2013 6:59pm
4/21/2013 6:59pm
Many possibilities. Start with Tunedlength & Jtom. After that, some governors react from the engine cooling fan. Make sure that the air ways are clear of crap like grass buildup.

There is also a sensitive spring that may be losing it's tension.
reded
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reded 4/21/2013 7:02pm
4/21/2013 7:02pm Edited Date/Time 4/21/2013 7:04pm
I had the EXACT same problem with my 18hp Briggs on a Craftsman mower. I pulled my fucking hair out over it. Cleaned the carb 3-4 times, checked valve lash, plugs and wires, checked the governor, new fuel pump, new fuel lines, pulled the tank and cleaned it, pulled the wire loom looking for a bare wire. I spent an entire year trying to figure out what was wrong and had my initial suspicions confirmed when I pulled the carb apart the last time. There was a tiny hole that had varnished over and I simply had not seen it. It's ran like champion ever since.
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Sandberm 4/21/2013 7:21pm
4/21/2013 7:21pm
reded wrote:
I had the EXACT same problem with my 18hp Briggs on a Craftsman mower. I pulled my fucking hair out over it. Cleaned the carb 3-4...
I had the EXACT same problem with my 18hp Briggs on a Craftsman mower. I pulled my fucking hair out over it. Cleaned the carb 3-4 times, checked valve lash, plugs and wires, checked the governor, new fuel pump, new fuel lines, pulled the tank and cleaned it, pulled the wire loom looking for a bare wire. I spent an entire year trying to figure out what was wrong and had my initial suspicions confirmed when I pulled the carb apart the last time. There was a tiny hole that had varnished over and I simply had not seen it. It's ran like champion ever since.
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Bill_Carroll
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Bill_Carroll 4/21/2013 8:01pm
4/21/2013 8:01pm
jib-tmb wrote:
I have an old lawn mower with an 18 HP twin cyl Briggs & Stratton engine. Anybody know what would make the RPMs fluctuate up and...
I have an old lawn mower with an 18 HP twin cyl Briggs & Stratton engine. Anybody know what would make the RPMs fluctuate up and down while just sitting there running? The only way I can smooth it out is to have the choke on about 3/4. Usually the carb is the problem but I've cleaned the carb a few times with no luck. I put fresh gas in it and changed the fuel filter. Any ideas?
I can hear my grass growing outside my window!
Had that problem, it was an air leak between the carb and Cylinder body. Try taking the carb off and clean the gasket area and replace with new gasket. should take care of the problem
jib-tmb
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jib-tmb 4/21/2013 8:08pm
4/21/2013 8:08pm
reded wrote:
I had the EXACT same problem with my 18hp Briggs on a Craftsman mower. I pulled my fucking hair out over it. Cleaned the carb 3-4...
I had the EXACT same problem with my 18hp Briggs on a Craftsman mower. I pulled my fucking hair out over it. Cleaned the carb 3-4 times, checked valve lash, plugs and wires, checked the governor, new fuel pump, new fuel lines, pulled the tank and cleaned it, pulled the wire loom looking for a bare wire. I spent an entire year trying to figure out what was wrong and had my initial suspicions confirmed when I pulled the carb apart the last time. There was a tiny hole that had varnished over and I simply had not seen it. It's ran like champion ever since.
My mower is also a Craftsman! Sumbitch is around 25 years old and has been a pretty good machine other than dealing with the carb every year.
reded
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reded 4/21/2013 8:30pm
4/21/2013 8:30pm
Mine's closer to 10yrs old but if I don't fill the tank half full of Seafoam before the last mowing of the year I may as well pull the carb off for the winter.
MR. X
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MR. X 4/22/2013 2:59am
4/22/2013 2:59am
Its the damn corn in the fuel , i used the treatment this past year on my "around the house" gas jug , so we'll see how my mower starts this year.
FlickitFlat 4/22/2013 4:07am
4/22/2013 4:07am
I would do the air leak checks like others suggested I think that is a good place to start but if it was me I would have never thought of doing that as a place to start. I would have just started it and went directly to the governor because it sounds like a wandering governor to me. I would have started it, and tried revving it with the governor and see how much it bounced when you let up. Then I would rev it with the governor slowly and try to hold it from bouncing and see if it runs smoothly in that process. If it does, turn the screw a little and you should be able to walk the miss out out of it. You might notice when you do that, you may have a spring missing or stretched or even a wire that came unconnected. You can also tell if it is running really rich or lean by the sound of moving the governor and that would indicate something more like an air leak that the others suggested. Face it, it is a Briggs. I don't care if you put a brand new plug in it last fall. Change it. You might be surprised. Especially if it is a Champion plug.
TerryK
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TerryK 4/22/2013 7:38am
4/22/2013 7:38am
On a related subject, I use Sta-Bil in the gas when storing any engine for more than a month and it is a miracle fluid. My snowblower will start first pull after 8 months in storage. Stamp it.
jib-tmb
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jib-tmb 4/22/2013 5:48pm
4/22/2013 5:48pm
Well, I cleaned the carb again, dumped some Seafoam in the tank and made some adjustments to the throttle cable. I checked for air leaks and didn't find any. It seemed to be running better so at least I was able to get my lawn mowed. I only had to pull the choke 1/4 of the way out instead of 3/4. Still not right though and by the time I was finished it was getting rough again. I'll try adjusting the governor this week.

Thanks to everyone for your help. I really appreciate it!!! I hope I can return the favor someday!
jib-tmb
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jib-tmb 4/22/2013 5:52pm
4/22/2013 5:52pm
TerryK wrote:
On a related subject, I use Sta-Bil in the gas when storing any engine for more than a month and it is a miracle fluid. My...
On a related subject, I use Sta-Bil in the gas when storing any engine for more than a month and it is a miracle fluid. My snowblower will start first pull after 8 months in storage. Stamp it.
Last fall I put Sta-Bil in my generator, snow blower and my spare gas cans..........but never gave the lawn mower a thought.Blush

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500guy
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500guy 4/22/2013 7:11pm
4/22/2013 7:11pm
Pulling the choke out is compensating for lack of fuel or to much air.

Stay away from the governor.
reded
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reded 4/22/2013 7:18pm
4/22/2013 7:18pm
Yep, I'd bet my next paycheck that you missed something in the carb. The thing about mine was it would run fine for a few minutes and then progressively start running rougher but would clear up if I kept inching the choke out until I ran out of choke. Then it would die and I'd have to push it back to the garage. I swear I pushed that fucker further than I rode it that summer.
TerryK
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TerryK 4/22/2013 7:22pm
4/22/2013 7:22pm
500guy wrote:
Pulling the choke out is compensating for lack of fuel or to much air.

Stay away from the governor.
Yeah I'm guessing that for sure. Low speed circuit plugged.
FlickitFlat 4/22/2013 10:11pm
4/22/2013 10:11pm
500guy wrote:
Pulling the choke out is compensating for lack of fuel or to much air.

Stay away from the governor.
TerryK wrote:
Yeah I'm guessing that for sure. Low speed circuit plugged.
x2 or 3 I've still had the same thing happen with a bad plug. Just saying. I know that doesn't explain why you have to pull the choke but Briggs motors do funny things. It costs $3 to find out.
jib-tmb
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jib-tmb 5/11/2013 6:29pm
5/11/2013 6:29pm Edited Date/Time 5/11/2013 6:32pm
I finally got this thing fixed. I kept taking the carb apart and cleaning it but it didn't make any difference. It got to the point where it would run until it used the gas in the bowl then it would shut off. The float valve seemed to be working but I thought maybe the rubber tip on it was swelled enough that it wasn,t letting gas pass through. I called the local lawn mower repair shop about a new valve and he said he could get me a repair kit but he thought the problem was probably the bad gas. He said I couldn't clean the varnish out of it with just carb cleaner and an air hose like I was doing and I should bring it in and let them put it in their ultra sonic clean tank. He said that's the only way to braek it up. It took about a week for me to get it back bcause they are real busy so I didn't have a choice. The ultra sonic cleaning and the kit did the trick but in order for me to completly remove the carb, I had to disconnect the governor. I've never messed with one but after watching the vid Tunedlength posted I finally got it adjusted and running good. I learned a lesson at least with my mower, that when adjusting the governor, there is a very fine line between "Wow, that sounds pretty good! and SHUT IT OFF!!! SHUT IT OFF!!! Laughing

I really appreciate all the great suggestions guys. It' hasn't run this good in years!
MR. X
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MR. X 5/11/2013 6:31pm
5/11/2013 6:31pm
jib-tmb wrote:
I finally got this thing fixed. I kept taking the carb apart and cleaning it but it didn't make any difference. It got to the point...
I finally got this thing fixed. I kept taking the carb apart and cleaning it but it didn't make any difference. It got to the point where it would run until it used the gas in the bowl then it would shut off. The float valve seemed to be working but I thought maybe the rubber tip on it was swelled enough that it wasn,t letting gas pass through. I called the local lawn mower repair shop about a new valve and he said he could get me a repair kit but he thought the problem was probably the bad gas. He said I couldn't clean the varnish out of it with just carb cleaner and an air hose like I was doing and I should bring it in and let them put it in their ultra sonic clean tank. He said that's the only way to braek it up. It took about a week for me to get it back bcause they are real busy so I didn't have a choice. The ultra sonic cleaning and the kit did the trick but in order for me to completly remove the carb, I had to disconnect the governor. I've never messed with one but after watching the vid Tunedlength posted I finally got it adjusted and running good. I learned a lesson at least with my mower, that when adjusting the governor, there is a very fine line between "Wow, that sounds pretty good! and SHUT IT OFF!!! SHUT IT OFF!!! Laughing

I really appreciate all the great suggestions guys. It' hasn't run this good in years!
A week without a lawnmower this time of year and you are going to need a combine now not a lawn mower.
Rooster
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Rooster 5/12/2013 11:55am
5/12/2013 11:55am
TerryK wrote:
On a related subject, I use Sta-Bil in the gas when storing any engine for more than a month and it is a miracle fluid. My...
On a related subject, I use Sta-Bil in the gas when storing any engine for more than a month and it is a miracle fluid. My snowblower will start first pull after 8 months in storage. Stamp it.
I just buy premium gas for anything related to small engines around the house. The premium gas has less ethanol (usually), but the main reason is they put stabilizers into the gas because it sits for so long in the tanks at the station. I've never had a problem with getting stuff started come spring time.
chuck317
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chuck317 5/12/2013 2:10pm
5/12/2013 2:10pm
I use 100% gasoline
jib-tmb
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jib-tmb 5/12/2013 4:16pm
5/12/2013 4:16pm
I'm using premium in all the small engines now. There's also a gas station near me that sell the ethanol free.
tunedlength
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tunedlength 5/12/2013 8:29pm
5/12/2013 8:29pm
If you have an airport nearby, fill up a can of Av gas.
Blended to be stable for over a year.
Bill_Carroll
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Bill_Carroll 5/14/2013 9:58am
5/14/2013 9:58am
jib-tmb wrote:
I finally got this thing fixed. I kept taking the carb apart and cleaning it but it didn't make any difference. It got to the point...
I finally got this thing fixed. I kept taking the carb apart and cleaning it but it didn't make any difference. It got to the point where it would run until it used the gas in the bowl then it would shut off. The float valve seemed to be working but I thought maybe the rubber tip on it was swelled enough that it wasn,t letting gas pass through. I called the local lawn mower repair shop about a new valve and he said he could get me a repair kit but he thought the problem was probably the bad gas. He said I couldn't clean the varnish out of it with just carb cleaner and an air hose like I was doing and I should bring it in and let them put it in their ultra sonic clean tank. He said that's the only way to braek it up. It took about a week for me to get it back bcause they are real busy so I didn't have a choice. The ultra sonic cleaning and the kit did the trick but in order for me to completly remove the carb, I had to disconnect the governor. I've never messed with one but after watching the vid Tunedlength posted I finally got it adjusted and running good. I learned a lesson at least with my mower, that when adjusting the governor, there is a very fine line between "Wow, that sounds pretty good! and SHUT IT OFF!!! SHUT IT OFF!!! Laughing

I really appreciate all the great suggestions guys. It' hasn't run this good in years!
The last part brings up a funny point, My neighbor is an A-hole and i'm sure he thinks the same about me but I don't let my F**in dogs bark all night at there shadows, anyway, he was all bragging and shit about this mower he just bought at the flea market for 70 bucks and he started it and it was wound out to the gills top end, he shut it off and says with a smile "thing runs faster than any mower I ever had" I said yup, sounds great, knowing the governor was off or the spring was caught I didnt let him know what was going to happen. Sure enough after 3/4 of his lawn was done B...A....M! I sat in my Garage laughing my ass off and I'M still laughing. Took me two weeks to ask what happen to his mower with a straight face...Whistling

Ahh love Spring time!

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