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Engine runs rough
#1
K
ktpnw
K
ktpnw
This weekend I picked up a riding mower for $50 from a buddy manages a farm, it is a Craftsman LTX1000 with a Briggs & Stratton 24HP Commercial Series engine (not the stock engine).
My buddy described the engine as "blown". He said he was mowing, heard a loud bang and lots of black smoke, and the mower died. Since he was on a farm he just pushed it into the barn and grabbed a different mower to finish his job, and the mower sat there as is until I picked it up (I think around a year or more).
When I got it home, I noticed that one of the spark plugs was missing - so I think the "bang" was the spark plug blowing out. The threads seem totally fine, so I threaded in a new plug (replaced the other side as well), added a new fuel filter, sprayed some carb cleaner in it, and drained/replaced the fuel. I also confirmed that it has at least some amount of compression by putting my finger in the spark plug hole and manually turning the flywheel. It has alternating pressure/vacuum in the chamber, and both sides feel the same. It now fires up, but runs real rough - lots of black smoke, throttle is inconsistent (as the throttle is increased it goes from idle to super high revs to low revs and then dies at full throttle). It has enough power to drive around but definitely not the 24hp it's supposed to have, and it dies easily when the mower deck is engaged and it's under load. I have run about a half tank of fuel through it, so it's not just the carb cleaner burning off or anything. It does run slightly better with the air cleaner removed (I have a new air filter on order) but still not well. It also has a cracked vacuum hose that runs the fuel pump (I have a replacement hose on order as well) but I electrical taped it up and it seems to be relatively air tight for the time being.
Any ideas on what to try next? I am not very experienced with lawn mower engines but am extremely mechanically inclined - used to be a professional bicycle mechanic, and have rebuilt carbs on my Honda motorcycle and done a fair amount of work on cars and trucks. Thanks in advance for any advice.
My buddy described the engine as "blown". He said he was mowing, heard a loud bang and lots of black smoke, and the mower died. Since he was on a farm he just pushed it into the barn and grabbed a different mower to finish his job, and the mower sat there as is until I picked it up (I think around a year or more).
When I got it home, I noticed that one of the spark plugs was missing - so I think the "bang" was the spark plug blowing out. The threads seem totally fine, so I threaded in a new plug (replaced the other side as well), added a new fuel filter, sprayed some carb cleaner in it, and drained/replaced the fuel. I also confirmed that it has at least some amount of compression by putting my finger in the spark plug hole and manually turning the flywheel. It has alternating pressure/vacuum in the chamber, and both sides feel the same. It now fires up, but runs real rough - lots of black smoke, throttle is inconsistent (as the throttle is increased it goes from idle to super high revs to low revs and then dies at full throttle). It has enough power to drive around but definitely not the 24hp it's supposed to have, and it dies easily when the mower deck is engaged and it's under load. I have run about a half tank of fuel through it, so it's not just the carb cleaner burning off or anything. It does run slightly better with the air cleaner removed (I have a new air filter on order) but still not well. It also has a cracked vacuum hose that runs the fuel pump (I have a replacement hose on order as well) but I electrical taped it up and it seems to be relatively air tight for the time being.
Any ideas on what to try next? I am not very experienced with lawn mower engines but am extremely mechanically inclined - used to be a professional bicycle mechanic, and have rebuilt carbs on my Honda motorcycle and done a fair amount of work on cars and trucks. Thanks in advance for any advice.
#2
K
ktpnw
K
ktpnw
I forgot to mention, he said it was a basically brand new engine when it "blew". Less than 5 hrs, and from looking at the oil and general state of it, I believe it. My guess is he didn't tighten the spark plug enough in assembly.
#3
B
bertsmobile1
B
bertsmobile1
Start by going to outdoor power Equipment and look at how to properly clean the carb you have
#4
S
slomo
S
slomo
Sounds like the carb linkage needs adjusting. OP can't get a solid desired rpm from throttle lever. Probably bolted on the new engine and never dialed in the linkage/choke.
Running rough is possibly a sticking needle in the carb. Sounds like he is getting fuel from the black smoke comment. Dirty carb alert from sitting for a year.
Valves should be ok since this engine has less than 5 hours on it.
I would order a new foam pre-air filter and main paper filter. Oil the foam with 30w oil, wring out in a red shop towel.
slomo
Running rough is possibly a sticking needle in the carb. Sounds like he is getting fuel from the black smoke comment. Dirty carb alert from sitting for a year.
Valves should be ok since this engine has less than 5 hours on it.
I would order a new foam pre-air filter and main paper filter. Oil the foam with 30w oil, wring out in a red shop towel.
slomo
#5
K
ktpnw
K
ktpnw
This is a great resource, thanks muchStart by going to outdoor power Equipment and look at how to properly clean the carb you have
#6
K
ktpnw
K
ktpnw
Excellent, thanks. Yeah it sounds like opening up the carb is the next step. As I said I've done that on a Honda CX500 (V-Twin motorcycle) so I've got no problem getting in there. I did also just now notice that the oil seems quite thin and has a gas smell - it seems like there's gas in the oil. Could that be caused by a dirty carb as well?Sounds like the carb linkage needs adjusting. OP can't get a solid desired rpm from throttle lever. Probably bolted on the new engine and never dialed in the linkage/choke.
Running rough is possibly a sticking needle in the carb. Sounds like he is getting fuel from the black smoke comment. Dirty carb alert from sitting for a year.
Valves should be ok since this engine has less than 5 hours on it.
I would order a new foam pre-air filter and main paper filter. Oil the foam with 30w oil, wring out in a red shop towel.
slomo
#7
S
slomo
slomo
S
slomo
Oil that smells like gas is a carb issue. The carb needle is sticking OPEN allowing fuel into the oil, where it doesn't belong. Dump the oil ASAP. FIx the carb with a new needle and seat or new carb ASAP. Dump the oil again. Gas will thin the oil way down. Smell your oil dipstick. If it smells like gas, dump the oil.Excellent, thanks. Yeah it sounds like opening up the carb is the next step. As I said I've done that on a Honda CX500 (V-Twin motorcycle) so I've got no problem getting in there. I did also just now notice that the oil seems quite thin and has a gas smell - it seems like there's gas in the oil. Could that be caused by a dirty carb as well?
slomo
#8
T
Tinkerer200
T
Tinkerer200
Well I would check that it is actually running on both cylinders first thing. Put pug wires on loosely and remove one at a time or just remove one at a time when stopped and see if it will start with just one wire on at a time.
Walt Conner
Walt Conner
#9
DerekShellman66
DerekShellman66
This weekend I picked up a riding mower for $50 from a buddy manages a farm, it is a Craftsman LTX1000 with a Briggs & Stratton 24HP Commercial Series engine (not the stock engine).
My buddy described the engine as "blown". He said he was mowing, heard a loud bang and lots of black smoke, and the mower died. Since he was on a farm he just pushed it into the barn and grabbed a different mower to finish his job, and the mower sat there as is until I picked it up (I think around a year or more).
When I got it home, I noticed that one of the spark plugs was missing - so I think the "bang" was the spark plug blowing out. The threads seem totally fine, so I threaded in a new plug (replaced the other side as well), added a new fuel filter, sprayed some carb cleaner in it, and drained/replaced the fuel. I also confirmed that it has at least some amount of compression by putting my finger in the spark plug hole and manually turning the flywheel. It has alternating pressure/vacuum in the chamber, and both sides feel the same. It now fires up, but runs real rough - lots of black smoke, throttle is inconsistent (as the throttle is increased it goes from idle to super high revs to low revs and then dies at full throttle). It has enough power to drive around but definitely not the 24hp it's supposed to have, and it dies easily when the mower deck is engaged and it's under load. I have run about a half tank of fuel through it, so it's not just the carb cleaner burning off or anything. It does run slightly better with the air cleaner removed (I have a new air filter on order) but still not well. It also has a cracked vacuum hose that runs the fuel pump (I have a replacement hose on order as well) but I electrical taped it up and it seems to be relatively air tight for the time being.
Any ideas on what to try next? I am not very experienced with lawn mower engines but am extremely mechanically inclined - used to be a professional bicycle mechanic, and have rebuilt carbs on my Honda motorcycle and done a fair amount of work on cars and trucks. Thanks in advance for any advice.
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#10
S
slomo
slomo
S
slomo
I wouldn't. OP said there was a fuel in the oil issue. I would tackle that first. No sense running an engine with 0w oil thinned down from gasoline.Well I would check that it is actually running on both cylinders first thing. Put pug wires on loosely and remove one at a time or just remove one at a time when stopped and see if it will start with just one wire on at a time.
Walt Conner
slomo
#11
K
ktpnw
K
ktpnw
Thanks all. I cleaned the carb and drained/replaced the oil and filter (which by the way, what a mess. Need to get one of those quick drain tube things). It now runs better, still doesn't like full throttle but runs plenty well enough to drive around and mow. I haven't yet noticed more gas in the oil, but will certainly keep an eye out for that. I've pulled both plugs and both are covered in soot (before cleaning the carb) so I'm guessing that meant it was firing on both sides. I did put new plugs in it when I got it, so they are brand new. I'll try pulling the wires individually as well, but it's at least working better now.