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Hi guys. I'm sure this question gets asked all the time on these forums. And I have tried searching on them, but my question is a little more specific then most. Okay, here goes:

I have a mid-90s Troy bilt mower with a briggs and stratton 5hp engine on it. I bought it off craigslist since I'm a young adult with not much financial backing. I live in a city so my yard (front/back) is probably 500 sq. ft. total. I noticed immediately that white smoke was coming from the exhaust/muffler. So, in all, I changed and replaced the oil. No more white smoke. After a dozen or so mows, my mower wasn't starting. I had read online that a dirty carb could be a major problem (especially since I bought my mower of an old lady who probably didnt keep up with regular maintenance). I cleaned the carb very thoroughly, and even took an elongated paper clip to clean the little holes. It looks brand new. I also just replaced the spark plug with a brand new one (old one had a dirty-black end). Today after doing all this I was excited because all the rain had my grass in the back yard about 10" high. NOW-the damn thing runs perfect and smooth for 10 minutes then stalls, like I have no gas in there (I do), then dies. I read online about a gas cap vent, so I took the gas cap off after letting it sit for 5 minutes, and it starts fine; it then runs for 10 minutes, stalls and dies. Then it is unable to start for another 5 minutes. What gives???! Sorry for the long post and thank you guys /gals sooo much!!

EDIT: changes oil, cleaned carb, new spark plug, new air filter. Mower runs for 10 minutes and dies.

EDIT 2: sorry for the errors, I'm typing this on my cell phone. Thank you.

You might need to check your valve clearances, you may need to shorten a valve or two.

A proper valve job would be better, but adjusting them would probably suffice. Post your engine's model numbers so we know what you have.

I would agree with fish but this white (perhaps blueish) smoke makes me think of excessive oil consumption / worn piston rings or valve guides, especially if the old lady did not change the air filter regularly. Dirt is disastrous for inlet valve and guide.

but shortening the valves would likely keep it running for now. Hard to say without looking at it eh?

Hey, thank you two. It's a 1998 Troy-Bilt 63902. I took of the head to check the piston and valves and man, are they dirty as s***! Excessive carbon buildup (possibility). Tomorrow I will clean them and the head. Also, I read online about the ignition coil. Do you think that could be a diagnoses? For all the money I'm putting in this mower, I am trying to avoid a $25 ignition coil if possible (I payed $50 for the damn thing). Lastly, could you explain this valve process that you are talking about? Thanks again.

Well if you clean off all of the crud, it will likely make your problem worse, but go ahead and do it, it needs cleaning...

abf said:

Hey, thank you two. It's a 1998 Troy-Bilt 63902. I took of the head to check the piston and valves and man, are they dirty as s***! Excessive carbon buildup (possibility). Tomorrow I will clean them and the head. Also, I read online about the ignition coil. Do you think that could be a diagnoses? For all the money I'm putting in this mower, I am trying to avoid a $25 ignition coil if possible (I payed $50 for the damn thing). Lastly, could you explain this valve process that you are talking about? Thanks again.

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If the air gap between flywheel and coil and you see a spark when cold and hot, I believe you should not worry about the coil. I remember the air gap is 0.25 mm (metric) with a filler gauge. If you don't have a filler try adjusting with a business card in between.

Valve clearance should be +0.20mm (again metric) at Top dead centre. If considerably less, you basically have to remove valve springs and retainers, take out valves and carefully grind bottom side to spec. However I would follow fish's advice for the time being.

I had almost same problem with Briggs quantum 675. Felt like running out of gas- would die after around 10 minutes. My first thought was not getting gas. Loosened the cap and checked oil level- all was good. I removed plug to check for spark. Being by myself I could not pull rope and see the plug at same time. I reluctantly held the coil wire and pulled the rope. It didn't bite as hard as I thought it should so set off the the mower shop and bought a new coil, spark plug and a carb kit since I was already there. Parts guy said they see very few bad coils, maybe one a year. I went ahead and bought it anyway, ended up paying around $80 for the coil, kit and plug. did not know what I spent in parts was almost half what a complete new motor cost. Reset the air gap and plug gap- no change. Pulled carb apart- it was clean as a whistle inside but went ahead and ran wire thru all the passages, sprayed down with carb cleaner and replaced gaskets. no change, still dying. Pulled gas tank off and rinsed out with clean gas and replaced fuel line- this model doesnt have a fuel filter. Motor still dying and now starting to get pissed. During the heat of the moment, I ordered a new motor. Knowing the dying problem would drive me nuts by not knowing what the problem was, I contunued fiddling with it. Removed the carb a few more times, finally replaced the needle and seat that came in the kit even though the old one looked good. BINGO- has not dies since. and now have a new boxed motor setting in the garage.

tuit said:

I had almost same problem with Briggs quantum 675. Felt like running out of gas- would die after around 10 minutes. My first thought was not getting gas. Loosened the cap and checked oil level- all was good. I removed plug to check for spark. Being by myself I could not pull rope and see the plug at same time. I reluctantly held the coil wire and pulled the rope. It didn't bite as hard as I thought it should so set off the the mower shop and bought a new coil, spark plug and a carb kit since I was already there. Parts guy said they see very few bad coils, maybe one a year. I went ahead and bought it anyway, ended up paying around $80 for the coil, kit and plug. did not know what I spent in parts was almost half what a complete new motor cost. Reset the air gap and plug gap- no change. Pulled carb apart- it was clean as a whistle inside but went ahead and ran wire thru all the passages, sprayed down with carb cleaner and replaced gaskets. no change, still dying. Pulled gas tank off and rinsed out with clean gas and replaced fuel line- this model doesnt have a fuel filter. Motor still dying and now starting to get pissed. During the heat of the moment, I ordered a new motor. Knowing the dying problem would drive me nuts by not knowing what the problem was, I contunued fiddling with it. Removed the carb a few more times, finally replaced the needle and seat that came in the kit even though the old one looked good. BINGO- has not dies since. and now have a new boxed motor setting in the garage.

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Yes, unfortunately I know the story. A few months ago I bought a used quantum 48 that hadn't operated for years. It was owned by a doctor who, on a Sunday morning, pulled the rope a couple of times with no success, then simply went right to the store and bought a brand new mower. The overall condition of the mower looked good apart from corrosion on deck, mostly underneath, as the doctor used to mow wet grass. I cleared corrosion, applied permatex rust killer, then primer and after that a tar spray specially used for car body work underneath as humidity repellent.

Engine started but stalled. I went through coil, air gap, governor adjustment, gas tank etc. Cleaned the carb meticulously, changed o-ring on inlet (usually hardens and air is sucked), still no progress.

I dare to say that I even checked compression and found below 60s which I considered not good. In order to get over my sleep disorders I went through a series of night work, cylinder honing process, changed piston rings, lapped and adjusted valves (guides were good), levelled the slightly bent head and lots of other little things that may you think that the problem wil be solved.

As the problem persisted, I then went to the local b&s authorized repairer (very professional and knowledgable people I have to admit) and asked for a carb repair set. They gave me a new carb instead as the price was a few bucks higher but the purpose justified the expense. They told me that there is no worse thing than trying to clean a carb that has not operated for a significant period of time. It may seem to be clean in all aspects but still not work properly. Apparently they were right. The engine is as good as new but I have spent more than 80 bucks to rebuild, but I feel I have learned a few things.

abf said:

Hi guys. I'm sure this question gets asked all the time on these forums. And I have tried searching on them, but my question is a little more specific then most. Okay, here goes:

I have a mid-90s Troy bilt mower with a briggs and stratton 5hp engine on it. I bought it off craigslist since I'm a young adult with not much financial backing. I live in a city so my yard (front/back) is probably 500 sq. ft. total. I noticed immediately that white smoke was coming from the exhaust/muffler. So, in all, I changed and replaced the oil. No more white smoke. After a dozen or so mows, my mower wasn't starting. I had read online that a dirty carb could be a major problem (especially since I bought my mower of an old lady who probably didnt keep up with regular maintenance). I cleaned the carb very thoroughly, and even took an elongated paper clip to clean the little holes. It looks brand new. I also just replaced the spark plug with a brand new one (old one had a dirty-black end). Today after doing all this I was excited because all the rain had my grass in the back yard about 10" high. NOW-the damn thing runs perfect and smooth for 10 minutes then stalls, like I have no gas in there (I do), then dies. I read online about a gas cap vent, so I took the gas cap off after letting it sit for 5 minutes, and it starts fine; it then runs for 10 minutes, stalls and dies. Then it is unable to start for another 5 minutes. What gives???! Sorry for the long post and thank you guys /gals sooo much!!

EDIT: changes oil, cleaned carb, new spark plug, new air filter. Mower runs for 10 minutes and dies.

EDIT 2: sorry for the errors, I'm typing this on my cell phone. Thank you.

Click to expand...

A dirty black end on the spark plug means that you have a very rich mixture. Did you check your gas filter.

-- I dont believe I have a fuel filter. I did thoroughly clean the fuel tank though.

-- I cleaned the carb but tonight I'm going to re-clean the carb. If it still doesn't seem to work I may just buy a new one.

-- I cleaned all the carbon off the piston/valve heads. Didnt seem to do much good as mower is not starting now.

-- Thanks again for the feedback. Once I have it figured out, I will update this post as to help people in the future possibly figure out their problem.

Fish said:

Well if you clean off all of the crud, it will likely make your problem worse, but go ahead and do it, it needs cleaning...

Click to expand...

Yeah, like I said, you need to cut and adjust your valves.... Likely other things since this engine has had no care.