Downeast Johnny Posted April 12, 2013 Report Share Posted April 12, 2013 Girl friend has a John Deere GT235 lawn tractor with a Briggs & Stratton vertical shaft V twin 18 HP motor. The motor has an occasional stumbling miss that reduces power and RPM by about 25%. Miss doesn't seem to be worse at operating temp. and can happen hot or cold. Motor may run fine for 2 minutes or 20 before the stumble occurs. Doesn't completely drop a cyl. and will clear up and run fine if you shut off the PTO and let her run without load for a few seconds or up to 1/2 minute. I keep up regular maintenance on the mower and have also adjusted the valves and cleaned the carb since this problem started. My gut tells me that it's an ignition problem like a coil going bad or something similar. Thanks for any thought's Y'all have to offer. Quote Link to comment Share on other sites More sharing options...
2003_SuperSport Posted April 13, 2013 Report Share Posted April 13, 2013 Check plugs and wires for good spark and arcing burns at the top of each plug. make sure your running the right plugs. Also pull plugs and check the bottoms and verify both are burning a nice tan color.. If one is oilier smells like fuel or more carboned up you may be fouling that plug and needs replaced... It could also be the governor going bad or a stressed governor spring... It is hard to diagnose a small gas engine without actually being there lol.. check the fuel filter or add an inline filter as some fuel filters are intank and may be bad.... Also take a small fuel sample in a clear dry plastic bottle such as a pop bottle or plastic whiskey bottle LOL by disconnecting the fuel line from the Carb and getting about a cup to two cups full and letting it sit for 10 minutes... If you see any separation with a clear substance at the bottom and gas on top you have water in the tank and the tank needs to be emptied completely dried out and run a little sea foam and fresh premium gas in it... Try all that and let us know... Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted April 13, 2013 Author Report Share Posted April 13, 2013 Check plugs and wires for good spark and arcing burns at the top of each plug. make sure your running the right plugs. Also pull plugs and check the bottoms and verify both are burning a nice tan color.. If one is oilier smells like fuel or more carboned up you may be fouling that plug and needs replaced... It could also be the governor going bad or a stressed governor spring... It is hard to diagnose a small gas engine without actually being there lol.. check the fuel filter or add an inline filter as some fuel filters are intank and may be bad.... Also take a small fuel sample in a clear dry plastic bottle such as a pop bottle or plastic whiskey bottle LOL by disconnecting the fuel line from the Carb and getting about a cup to two cups full and letting it sit for 10 minutes... If you see any separation with a clear substance at the bottom and gas on top you have water in the tank and the tank needs to be emptied completely dried out and run a little sea foam and fresh premium gas in it... Try all that and let us know... Thanks for your input. Understand about it being hard to diagnose without being with the machine. The carb was not overly nasty when I had it apart and cleaned it up - reassembled. New filter went on at that time. I had just started wondering about the governor function and spring and I will pursue that today. I'll empty a whiskey bottle this morning and if I can still see after that I'll check the gas for water. Thanks again SSGT. I'll report back later. Quote Link to comment Share on other sites More sharing options...
2003_SuperSport Posted April 13, 2013 Report Share Posted April 13, 2013 It sucks trying to find intermittent problems with engines. At least you will be able to cover your basics.. Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted April 14, 2013 Author Report Share Posted April 14, 2013 I ran the mower for quite awhile yesterday without the hood and air cleaner so that I had access to the carb and governor mechanism. (Didn't engage the PTO so as not to kick up dust that would enter the carb). I also filled a clear jug with gas from the fuel pump and checked the plugs. Plugs look like the text book picture for proper burn and the gas stayed clear and clean all afternoon. The motor stumbled / missed several times while I was riding it around the yard and I had the chance to observe the gov. function and fiddle with it as the miss was occurring. In my mind I have eliminated the gov. as the source of the miss as the stumble just ran it's coarse through my manipulations of the gov. as the miss was happening Next move is to take the covers off the top of the motor and see if I can find any signs of chafed wires that may be occasionally touching ground. After that I'll have to try to find a way to bench test the coils or just buy one and replace the original coils one at a time and see if that cures the problem. Any further thoughts are welcomed. Quote Link to comment Share on other sites More sharing options...
silverado_ss_04 Posted April 14, 2013 Report Share Posted April 14, 2013 Get the gun.... Quote Link to comment Share on other sites More sharing options...
JC03SS Posted April 14, 2013 Report Share Posted April 14, 2013 It's prob the gas what kind? If you running ethanol gas it hates little engines. My brother has a lawn service and the gas is killing all his equipment one at a time. They do almost the same thing. They get so hot I'm assuming the gas is splitting. My buddy and my brothers neighbor are going thro lots of similar probs. his weed eaters get so hot they won't recrank. Maybe drain the gas and put non ethanol and give it a shot. Quote Link to comment Share on other sites More sharing options...
2003_SuperSport Posted April 14, 2013 Report Share Posted April 14, 2013 You can test the coils by checking their resistance with a ohms/voltage meter... Don't just throw parts at it... Pull the plugs and attach them to the plug boots then turn the engine over and see if you have strong spark arching from the plug to a good ground location.... It maybe a bad wire but still sounds fuel related. Also try using premium gas and put a quarter to half bottle of sea foam in the tank and running it for awhile... May want to clean the jets in the carbs again... I used to be a small gas engine mechanic and have ran into problems like this alot... Also make sure your air filter is clean and not saturated with gas and dirt... You may want to pull the carb and soak it in some carb cleaner again... Also try to use new gaskets as some gaskets tend to deteriate especially the old cork ones lol.... Might as well trace the ignition wires and kill switch wires to find rubbing too... Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted April 15, 2013 Author Report Share Posted April 15, 2013 Get the gun.... Too much grass to mow, (About 7 acres), and the growing / mowing season is just starting, but the thought has some appeal. It's prob the gas what kind? If you running ethanol gas it hates little engines. My brother has a lawn service and the gas is killing all his equipment one at a time. They do almost the same thing. They get so hot I'm assuming the gas is splitting. My buddy and my brothers neighbor are going thro lots of similar probs. his weed eaters get so hot they won't recrank. Maybe drain the gas and put non ethanol and give it a shot. Hey Jason, It had crossed my mind that the stumble does act like water in the gas or vapor lock but it is really an intermittent problem. I am using ethanol. We are out in the boonies and finding non ethanol is really tough. She has a second JD mower, (20HP Briggs motor), that gets the same gas with no troubles. Really wish the corn lobby wasn't so powerful. Lots of boats in this area and lots of folks with nightmare story's of ethanol disasters in marine engines. You can test the coils by checking their resistance with a ohms/voltage meter... Don't just throw parts at it... Pull the plugs and attach them to the plug boots then turn the engine over and see if you have strong spark arching from the plug to a good ground location.... It maybe a bad wire but still sounds fuel related. Also try using premium gas and put a quarter to half bottle of sea foam in the tank and running it for awhile... May want to clean the jets in the carbs again... I used to be a small gas engine mechanic and have ran into problems like this alot... Also make sure your air filter is clean and not saturated with gas and dirt... You may want to pull the carb and soak it in some carb cleaner again... Also try to use new gaskets as some gaskets tend to deteriate especially the old cork ones lol.... Might as well trace the ignition wires and kill switch wires to find rubbing too... Thanks again Sarge, I will test the coils and you are right, of coarse, in advising against throwing parts at it. I know better but am getting frustrated. I will go through the carb again and replace the gaskets. (I've gotten a quote of a rebuild kit for the carb of around $80.00) (New carb is around $300.00) After I cleaned the carb (In pro grade carb cleaner), the first time the motor ran a pretty good while without acting up and I thought that I had cured the problem till it did eventually start acting up again. I put in a new fuel filter when I cleaned the carb and it is a see through and the gas in it looks fine still. The air filter and pre-filter are new as of just a few weeks ago. I have put some thought into removing the fuel cell and cleaning out and starting over but that's going to be a big job, (Gotta remove most of the bodywork), and I've been thinking that if that was needed I should be seeing water in the gas and or trash in the filter? I'll check and see if there is a drain in the fuel cell and try fresh high test and some sea foam and report back again. Thanks again guys. I'll keep searching for the trouble. Just thinking about this before I hit the post button and remembering that the fuel filter that I replaced was really nasty, (I took over maintaining the mower pretty recently), and now I am thinking that it's possible that there was a good bit of trash in the fuel line from the filter to the pump and carb that went right into my freshly cleaned carb. So it makes sense that I may need to clean it out again. I'll keep y'all posted. Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted May 9, 2013 Author Report Share Posted May 9, 2013 Figured that I would resurrect this post just in case anyone is interested. The intermittent miss got bad enough and long lasting enough that I had time to get off the tractor and pull the plug wires, (one at a time), and sure enough one cylinder was dropping out. Threw a new coil on her and no trouble in four or more hours run time since. Quote Link to comment Share on other sites More sharing options...
JC03SS Posted May 9, 2013 Report Share Posted May 9, 2013 Nice John glad to see she's purring like a kitten now Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted May 9, 2013 Author Report Share Posted May 9, 2013 Nice John glad to see she's purring like a kitten now Thanks Jason. It' nice to have it figured out and fixed. Been going on a long time but happened so irregularly that it was hard to figure out. Quote Link to comment Share on other sites More sharing options...
Muggs Posted May 9, 2013 Report Share Posted May 9, 2013 Glad to hear you got it bro Quote Link to comment Share on other sites More sharing options...
Downeast Johnny Posted May 10, 2013 Author Report Share Posted May 10, 2013 Glad to hear you got it bro Thanks MuggSS. I scratched my head over this one for awhile. Nice to have it behind me. Quote Link to comment Share on other sites More sharing options...
JC03SS Posted May 10, 2013 Report Share Posted May 10, 2013 Yeah I hate chasing gremlins. Good thing you got it fixed cuz the grass is growing like crazy now lol. Quote Link to comment Share on other sites More sharing options...
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