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Engine Problems - Briggs 14HP


Bucky33

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I am looking for some input to help troubleshoot an engine problem I am having on my Baron 3414H and know this is the place to ask. So here it goes. The tractor still has the original 14HP Briggs Engine. The symptom is when I am mowing the lawn with the engine at 3600 rpm (mower deck engaged) the engine wants to hesitate and cut out. It loses power and is able to pick back up when the mower is stopped and the tranny is in neutral. When the engine is at idle I hear what sounds like a little miss as well. It also seems to be more pronounced as the engine warms up. I also have to add that the engine was running great and then the issue just appeared. What I have done to try and fix it was clean the carb as I originally thought it was starving for fuel (bad gas or junk in the jets from the fuel tank, etc). I did not change any of the slow or high speed circuit settings when I reassembled the carb and also did not find any debris in the floatbowl or jets. I replaced the points this past winter and rechecked the gap and it was still at 20 thou. What I did find was that I could induce the symptom by moving the wires from coil that connect to the condenser/points. Thinking that there was a short in the wires, I ran new wires to the points from the coil and did not connect the wire that allows the switch to kill the engine. I thought that maybe the wire from the switch was grounding out in the engine or chassis somewhere, but the wire looked good after I removed it. After all this was done I thought I fixed it as the engine sounded normal again. I then took it around the yard and the symptom reappeared. So what might it be? Coil under the flywheel is shorting out? Or is it fuel related? Or could I have a faulty points and condenser, even though they are new? This has me stumped. Thanks in advance, Bucky33
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You might want to check your fuel filter and fuel tank to see if you have a piece of debree that is pluging the filter or fuel tank outlet. HT
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I had similar problems that vexed me on a 16 a few years ago. That turned out to be a partially sheared flywheel key which threw the ignition slightly out of time. Would run without a load , but add a load and it would spit sputter and try to die. Probably why the previous owner was using battery ignition to run the engine rather than the original mag. Points could be out of adjust ment too, or the points plunger could be worn. All these affect the timing. I'm no expert by any means, just tossing ideas..
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Bucky33: You could try to richen the mixture, as it starts to drop RPM's, by putting the choke on quickly. If this helps, it could indicate that you're running lean for whatever reason. Regardless, I would recheck the fuel inlet needle seat, in the carb. This is the one operated by the fuel bowl float. I just found, after a carb cleaning, that fresh contamination had reinserted itself into this fuel inlet. (Apparently it came from the fuel pump body, but it can be stuck in numerous places/hoses, etc....) If you're not getting improvement with a richer mixture (by choking it) you might consider the coil. When you say
quote:
"It also seems to be more pronounced as the engine warms up."
I'm reminded of the fact that coils that are failing can sometimes be quite affected, negatively, by heat, similar to what you describe. Let us know. Peter
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Maynard: I hear you about the spark plug. Recently, a plug in a 5hp Briggs rototiller I have looked okay, but it was carbon-fouling, down between the center electrode and the side. It gradually got worse, with increased missing/backfiring, then silence. Cleared the carbon and it's all better now. Good point. Peter
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You might want to go a little deeper, if you feel adventurous. Remove the valve cover and check the valve lash. As an engine wears, usually the exhaust valve "gets too long". Simply, what happens is that the seat burns and wears, as does the valve stem. with the valve closed, cold engine, you should have at least .020 space between the valve and its lifter. If you do not, as the engine heats up in normal operation, it loses compression because one of the valves may not be seating properly, or not closing at all. I do all my own work and have the tools to do so. All do not. If this is your problem, the only way to solve it is to remove the head, remove the valve, then grind the stem to get the proper spacing. Or, take it to the shop. But, it does sound like a fuel problem, instead of the valves. It is rare, but I have seen new, brand new, spark plugs that are cracked somewhere in the porcelain. The engines run great at idle, even at speed, but do not under loads. You might also try removing your carb again, this time, check to see if the float is 'waterlogged', or has gas inside it, if so, replace it. While there, check to see that the needle does not have a 'shoulder' worn into it from sitting idle last winter. Also rare, check to see if the needle seat is loose in the carburetor body. Sounds like a fun project to me, but, then, I enjoy the challenge of fixing something noone seems to be able to ! Good Luck!
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Hi, You are correct on the valve clearances. I would try the plug first. We have seen plugs with 15 mins on them with a tiny black carbon streak down the side of the insulator from the tip and it caused all kinds of problems. Needed a magnifying glass to see it, rest of the tip was still white. Normally good advice, change the plug first. A condensor is easy to change, or try just connecting the wire under the screw with the original, and hold the body against the original or hold the lead and body across it. Watch your feet under the mower when trying this, have someone else engaged the mower. If the original is open you can tell if this fixes it. Check the little side holes in the nozzle of the carb to make sure they and clear and the float level is correct. Flywheel key is also a good possibility. Does it do it right away, or after running under load a while. I have seen these units that the exhaust pipe breaks off the muffler and exhaust heat boils the gas in the carb. Usually they pour out the black smoke and are super rich after running under heavy load for a while and then sometimes die from vaporlock and fuel starvation. Al Eden
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Thanks to all for you input. I think I got it figured out. After checking to see of the float had a hole in it and going through the rest of the fuel system I found nothing. I decided to replace the coil. When finished, I did a neutral run up and again verified the carb was set correctly. It ran fine without hesitation. After a test ride around the yard, it started acting up again. A new spark plug did not address it either. So now I have a clean carb, new coil with new wiring to the new condensor and points. The points are correctly gapped. I decided to put on the old condensor. Waaa Laa, no issue since. After it was fixed I was told that as the condensor heats up the capacitance reduces, which in turn reduces the spark energy. It all makes sense now. Again thanks for your input.
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