larry8200 Posted May 3, 2011 Posted May 3, 2011 My 725 runs perfect for about an hour towing a lawn sweeper, and then cuts out over half throttle, still runs OK at half, but try to go higher and it cuts right out. Done it 3 times now. Had a J19LM that looked good in it, replaced it with a new J8C, no difference. I haven't layed my hands on a condensor I'm confident is good, but I doulbt thats it. Twice I've taken the main jet needle out and a steady continuous stream, albiet small comes out, so I dont think it's a fuel flow problem. Any Thoughts? Thanks
perry Posted May 3, 2011 Posted May 3, 2011 im haveing the same problem with my 16hp big ten and 19D on a 725. i have not messed with them yet. but i am going to start with cleaning the points real good and regap. back blow thru the gas line. if that doesn't work then im thinking the coil maybe getting weak. my big ten has a mega-fire so it maybe gas issue or the coil on that one.
Burntime Posted May 3, 2011 Posted May 3, 2011 My 3416 did the same thing after 20-25 minutes. In the end it was running lean. No idea but I opened it up a quarter of a turn and she purred for 2 hours before I shut it down.
larry8200 Posted May 3, 2011 Author Posted May 3, 2011 Thanks, I played with the mixture as well as the choke, no difference. I dont think the plug is the problem but I also dont know what plug a 19D should have in it. Having a J19LM in it doesn't mean it's the right one...
Burntime Posted May 3, 2011 Posted May 3, 2011 Hey Larry, half the fun is getting them to run!:D Just ask Brettw:D:D:D
larry8200 Posted May 3, 2011 Author Posted May 3, 2011 quote:Originally posted by Burntime Hey Larry, half the fun is getting them to run!:D Just ask Brettw:D:D:D I dont know, I think maybe the ole 725's telling me not to run her for hours at a time...
henroan Posted May 3, 2011 Posted May 3, 2011 Mine was a fuel issue. There was debris in the tank. When I cleaned that the engine wouldn't stop.
Talntedmrgreen Posted May 3, 2011 Posted May 3, 2011 Sounds like fuel...Might want to check for any leaks that sprung in the manifold gasket or head gasket. Sometimes they don't reveal themselves till their nice and hot. Try backing your main jet out a half turn..not enough to flood, but just a touch. Maybe even a quarter turn at a time. This did the trick on my 2110. Has that carb been rebuilt? If so, the jet may be slightly different.
HubbardRA Posted May 3, 2011 Posted May 3, 2011 Larry, check your valve clearance. You may not have enough clearance for the valve to close at high rpm after it heats up and the stem gets longer. Most of the valve clearance problems show up in about 15 minutes when running a mower, but in this case yours was not heavily loaded while pulling the sweeper, so it may have taken longer. Valves are the most overlooked problem on these old engines. After one of these old engines has run for many years, it has beat the valve seats farther into the block, which reduces the valve clearance. Always a good thing to check on an older engine.
larry8200 Posted May 3, 2011 Author Posted May 3, 2011 I haven't rebuilt the carb, but the entire fuel system was spotless from the tank, sediment bowl, air filter and what I can see inside the carb. The inside of the tank looks BRAND NEW. Adjusting the main jet causes lean roll at about 1 turn out and rich roll at about 3. I included that I was pulling a sweeper to indicate the kind of load, light. And I get good flow out of the bowl at all times. I suspect the magneto, but Rod may very well be right. in any case pulling the head is easy and a gasket only $10, which my local Simplicity dealer probably has on the shelf. Here is a picture inside the tank....
Simplicity314 Posted May 3, 2011 Posted May 3, 2011 Yep--Hubbard nailed it. Most likely a valve. Could also be a coil, but bad coils usually act up sooner than an hour's time before they cut out. Trust me. I've learned from the best!
ReedS Posted May 3, 2011 Posted May 3, 2011 Ummm this might be obvious but did you check for spark when she quit?? No spark, no run! LOL At least that might point in a direction.
larry8200 Posted May 3, 2011 Author Posted May 3, 2011 Yep, It has a nice spark cold, and it looks just the same hot. But I know better than to draw any conclusions from that.
rpickle Posted May 3, 2011 Posted May 3, 2011 Mouse nest around the coil. Will run fine when the coil is cool, but after the engine heats up and the the nest around the coil keeping the heat on it, the coil fails. Just a shot. Rick
robob Posted May 3, 2011 Posted May 3, 2011 Your problem sounds similer to one i had with my 7.25 it would run great for the first 45 min then would begin to bog down even under light cutter loads even with full throtle it would stall.I thought it was the govenor and inquired to a dealer who said Naw thats a mechanical govenor fool proof but as it turned out it was the governor the original part is all metal construction and as it heated up (45 min)it would stick on the slide results no govenor the replacement part is metal and plastic no possiblity of sticking So it makes you wonder if they modified the govenor because of a heat expansion problem with the old metal part.something to consider if it matches your syntoms
MPH Posted May 4, 2011 Posted May 4, 2011 I'm with Rod on the valve steam length. The 23 D in my '64 LL had zero compression when I got it, stems were so long the valves wouldn't close cold. That's all I ve done to that engine and been working it hard for 4-5 years.
larry8200 Posted May 4, 2011 Author Posted May 4, 2011 Since it still runs fine at half throttle, even under load, and I'm REAL confident fuel isn't the problem, and since the problem is it cuts out at high RPM's only when it gets completely warmed up, Rod is making perfect sense. Well, I guess I park it for the moment. :( At least I dont have to push it to move it! And pull the head, breather cover and shroud, and clean and inspect everything, which ought to be done anyway on an engine this old. And there is no shortage of running tractors here... :D
perry Posted May 4, 2011 Posted May 4, 2011 does the engine seem to choke out when its losing power ?. clean and gap them points before you park it. my big ten puffs black smoke and wont run over half throttle. i have adjusted and re adjusted carb and still the same. im thinking its a spark / weak coil problem. unless the mega-fire is going bad. wire up a temporary 12V coil to it real quick to bypass the mag and see if it runs ok.
larry8200 Posted May 4, 2011 Author Posted May 4, 2011 quote:Originally posted by perry does the engine seem to choke out when its losing power ?. clean and gap them points before you park it. my big ten puffs black smoke and wont run over half throttle. i have adjusted and re adjusted carb and still the same. im thinking its a spark / weak coil problem. unless the mega-fire is going bad. wire up a temporary 12V coil to it real quick to bypass the mag and see if it runs ok. It doesn't choke out or lose power, it quits completely when you pass 50% throttle but still runs normally up to half, and only after it's run an hour. Makes me think ignition too BUT... The tractor sat in a garage for over 2 years and I haven't had anything apart. I could see no evidence of mice nesting, and usually when there is you will see some debris being blown across the head the first time it's restarted, and I watched. Still it IS possible there is nesting around the coil causing overheating. In any event I'm not going to park it really, just not work it. I can still go get the mail with it. :D Since I have 5 other large frames in excellent mechanical condition, and this 19D is 48 years old and sat for the last 2, it makes sense to me to do it right. This 725 took about 2 hours to make my permenant list. Many would say I should have pulled the shroud and head before I started it no matter how nice things looked. It would also be nice to find if it's been bored out, since it doesn't smoke it would be sweet to find it unbored....
perry Posted May 4, 2011 Posted May 4, 2011 quote:It would also be nice to find if it's been bored out, since it doesn't smoke it would be sweet to find it unbored.... yep, most all the 19D's i have had smoke
perry Posted May 5, 2011 Posted May 5, 2011 ok larry, my big ten would not run over half throttle last year. i dug it out today and it would still not run right . i hooked up a 12V coil to it and it runs like a champ. so that tells me the magneto is bad or rusty. ill just leave the 12V on it for now. and this one also had a active mouse nest in it last year .
HubbardRA Posted May 5, 2011 Posted May 5, 2011 Perry, Why remove the external coil? I have one that I first installed over 25 years ago. No plans to change mine back to a magneto.
goodtimo Posted May 5, 2011 Posted May 5, 2011 take the carb apart and clean out to goo in it. quote:Originally posted by HubbardRA Perry, Why remove the external coil? I have one that I first installed over 25 years ago. No plans to change mine back to a magneto.
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