I recently bought a 10 year old lawn tractor. It has a 17.5 hp Briggs and Stratton OHV one cylinder engine. After the engine heats up, it begins to miss. The miss doesn’t happen often at first, but as the engine gets hotter, the miss gets worse until it finally stalls out. After a couple of minutes, I can start again, only to have it miss and stall a couple minutes later. First, I tested the ignition coil. When the engine was about to stall, I blew compressed air on the coil to cool it down. The engine would smooth out and run correctly for another minute or two, then get ready to stall again. So I replaced the coil. To my surprise, the engine still stalls after about 15 minutes or so, this time compressed air will not help it. The carb has been taken apart, checked, and cleaned. The electric fuel shutoff is working properly. I have changed the oil and cleaned grass clippings out of the cooling fins on the cylinder head. The only things I haven’t tried are to check the adjustment on the valves and replace the spark plug. I’ve read that improper venting of the gas tank can cause this, but I can see plenty of fuel in the fuel filter when it stalls. The plug appears to be OK but at this point I’m running out of options. Am I missing something here?
Next time it stalls immediately try it to check for spark…is there any? Gap the plugs and clean them then try it again. Check the fuel filter - is there black flecks in the fuel? Could be burning oil…
You already replaced the coil…hmmm
We had this same problem with the snow blower this winter. After each season, we let it run to drain the fuel so we don’t have to deal with last year’s gas when starting it fresh. At the first snowfall, I gassed it up, turned it on and it ran well for the first 10 minutes or so. It would stall out and start easily again. We cleaned the carb, replaced the spark plug, drained some of the fuel out of it, checked the fuel system for leaks and added fresh gas.
Those seemed to do the trick in getting it to work again and we didn’t have any more problems in using it the rest of the year. We have had it for 5 years and prior to that my parents used it for 5 years.
Oh, I forgot to mention that I replaced the fuel filter and fuel line. The line was cracked badly so I replaced that before I even started the mower for the first time. After it started acting up, I replaced the fuel filter. The filter was clean and the gas coming out of it was also clean. This was all before disassembly and cleaning of the carb. As far as vapor lock is concerned, it is a possibility i suppose, but the fuel line is routed properly so I’m not sure. I see I’m going to have to check the spark after it dies, which will be tons of fun seeing as how its about a foot above the muffler and it gets HOT in there! I got a new plug for it to try first. I’m thinking maybe there’s a very small crack in the ceramic that expands as the engine heats up. I guess if the valves are improperly adjusted and not sealing correctly, I’d be able to hear a whisping sound as the air blows by the valve, but this isn’t happening either. I’ll check back after I replace the plug and check the spark.
Your test results seem to clearly indicate that the old coil was heat-sensitive. I can’t help but wonder if the new coil is defective, or of low quality. I’d be inclined to try another replacement coil, of better quality if available.
First, though, it makes sense to do some tests. Test the spark output from the coil when the engine is cold and will run well. Test again when it dies and won’t restart. If the spark is weak or nonexistent when hot, there’s an ignition problem. The coil is the prime suspect, but electronic ignition components, like anything electronic, can get heat-sensitive when old and failing.
Also when it dies and won’t restart, spray some starting fluid (ether) into the intake and see if will start and run for a couple seconds. If it will run on ether, there’s likely a fuel delivery problem. Fuel in the filter doesn’t preclude this; if vacuum is building up in the tank the fuel won’t move anywhere, it will just sit where it is. Of course if there’s vacuum in the tank, that is instantly fixable by removing the cap, and usually detectable by the “whoosh” sound when doing so.
Odds are there’s just one problem, but it’s not impossible to have more than one.
A mower that I own has a 17.5 Briggs & Stratton OHV engine and I believe that I can save you plenty of headaches in solving your problem.
FYI the engine is used on a Troy Bilt Pony N779 model however makes no difference as the motor is the same.
This is a somewhat trial & error problem that can be tricky to track down. By the time I had replaced the ignition module, spark plug, solenoid, battery, removed all safety switches, cleaned the carb, and literally wired direct to the anti-afterfire fuel solenoid to ensure no interference of voltage supplied to the solenoid…I was extremely fustrated.
I mean…wow…I had removed and resolved almost every possible cause. I knew the engine was fine as it ran great for the 15 minutes I could cut grass…I had suspected the ignition because I tested the fuel shut off on the carb bowl with a nine volt battery and it tested fine…HOWEVER as a last ditch effort of sorts I removed the bowl to inspect the fuel shut off and decided to alter it to make sure that it would always permit fuel flow even without voltage. I reinstalled everything and with some doubt tested the mower out.
The mower is running great thank Jesus for that!!
Problem= faulty anti-afterfire fuel shut off…or simply fuel shut off solenoid located on carb bowl.
I hope this helps as I only registered to be able to answer this question. I had searched and googled this problem only to be continually disappointed.
Remember, fixing your equipment is cheaper than buying a new one…most of the time.
[quote=“Gary_T, post:6, topic:541818”]
Your test results seem to clearly indicate that the old coil was heat-sensitive. I can’t help but wonder if the new coil is defective, or of low quality. I’d be inclined to try another replacement coil, of better quality if available.
First, though, it makes sense to do some tests. Test the spark output from the coil when the engine is cold and will run well. Test again when it dies and won’t restart. If the spark is weak or nonexistent when hot, there’s an ignition problem. The coil is the prime suspect, but electronic ignition components, like anything electronic, can get heat-sensitive when old and failing.
Also when it dies and won’t restart, spray some starting fluid (ether) into the intake and see if will start and run for a couple seconds. If it will run on ether, there’s likely a fuel delivery problem. Fuel in the filter doesn’t preclude this; if vacuum is building up in the tank the fuel won’t move anywhere, it will just sit where it is. Of course if there’s vacuum in the tank, that is instantly fixable by removing the cap, and usually detectable by the “whoosh” sound when doing so.
Good intel. Confirm if it’s fuel or ignition for sure.
If fuel, make sure you don’t have another hidden filter/screen in the tank or carb that’s getting covered with junk, shutting down the engine, dropping the junk, and restarting.
It’s probably ignition. If your motor is older than the machine, you may have points and condenser. If so, change the condenser and you’ll be fine. If no points, then you probably have a spark box or CDI unit in addition to the coil. Is the new coil spaced correctly off the flywheel with a business card?
[quote=“andyleonard, post:8, topic:541818”]
His problem is going to be the electronic fuel shut off…it is not old enough to have points…problems such as failing ignition module…spark plug, fouled fuel line or carb will all exhibit problems from the point of start…
The fuel shut off can fool u though and appear to be funtioning properly when tested…however has the solenoid warms it slowly begins to allow the piston to close against the fuel jet inside the carb which at the very beginning will cause rough idling and if you throttle it down it will smooth out however when the piston closes off the jet the engine shuts down.
My fuel shut solenoid tested fine however after heating up it was not able to maintain a strong enough magnetic field to keep the piston open.
I forgot that I posted this here, since it has been resurrected I should point out that nothing seemed to work on this thing. Until this year that is. I noticed sometime after making this thread that the problem became much worse when I disengaged the blades. It would really stall out then. However, since I got the thing out this spring, I have not been able to get the thing to stall. Hell, it doesn’t even miss anymore. Damnedest thing I ever saw! It’s like it fixed itself somehow. I know that isn’t possible, but I have to wonder if something was just clogged and it managed to unclog itself?
I am glad you are rid of the problem…mine drove me nuts for about a month or so.
Depending on your model it will have a switch with a set of two dry contacts that when you disengage the blades the lever pushes and depresses a button…sometimes the switch gets a little crazy…
From your description it sounded almost exactly like the symptoms my Briggs was giving me.
I have a question but don’t think it warrants anew thread.
I retrofitted a Briggs & Stratton 17.5 hp 500cc engine to my John Deere lawn tractor last year. I suspect it is similar to the one being discussed. (mine is a 31C707-0026-G1)
I bought it new but surplus. It didn’t include a fuel pump. I have not been able to find out what an OE install of this engine looks like but I bought a vaccuum operated pump which I am running off a fitting I braised onto the top of the valve cover . This works ok for a while until oil fouls the diaphragm in the pump.
I’ve considered an electric pump but they all seem to be too big. I wondered about using a 12 volt air pump to pressurize the fuel tank but haven’t tried that.
I’d like to know how it is done on a tractor that used this engine as original.
Any thoughts? Thanks!
[quote=“hvac_two, post:9, topic:541818”]
That’s sound information. I had the same problem with my mower engine (Kohler) missing after about an hour of operation. I replaced the spark plug and ignition module with no success. After reading the above comments, when the engine started to miss again, I cut the engine off and cooled the fuel shut-off solenoid with a cold cloth. The engine ran fine and I finished my cutting. THANKS.
Awww…RIGHTY…!!!
I have read through the whole thread looking for answers to the same problem. My Tacumse 17.5 HP OHV mower engine would run okay cold but would develop stalling fits when hot. I continued to get worse. I vainly rebuilt the carborator, installed new spark plug and fuel line filter, I got gasoline without ethenol… nothing, until I discovered a missing bolt holding my exhaust manafold to the cylinder block…!!! So, for $2.98 I replaced two bolts, got a new gasket and some lock washers. I’m good now…! Check it out… The missing bolt hole was stripped I found out because I couldn’t torque it down completely, it would click and jump thread so I should have applied some high heat Loc-Tight but I didn’t, so you do that too.
Ok folks, here is how to fix this issue (as a few other have said) REPLACE your gas cap. :smack:
I had the same problem where I would lose compression after about 30 mins.
I thought I ruled out the gas cap being a problem by being able to easily blow through the outer hole and when I would lose compression I would take the gas cap off and that didn’t help. Thus it couldn’t be the gas cap right :dubious:
2. So then I replaced the fuel filter
3. I replaced the fuel lines
4. I cleaned the gas tank
5. Adjusted the valves
6. Replace the ignition coil
7. Took out fuel solenoid (replaced with bolt to Test to see if it was the solenoid)
8. Cleaned the carburetor (took completely apart).
After all of this, still was losing compression so I went and bought a new gas cap ($5).
OH SNAP, she didn’t lose compression at all. Problem FIXED.
Thus, it was not losing compression from over heating, it was losing compression due to the lack of air (due the vacuum over a 30 min period).
I post this here not to brag that I fixed it or to make myself look like an idiot (as I worked on this for about 2 weeks) but to share the solution to this problem.
Happy cutting 