I have a 1974 or 1975 model 16 HP single cylinder B&S cast iron engine Model 326431 Type 0139-01 Code 7409261 on a 1975 model MTD 990 (145-990.026) with the Delco starter/generator and voltage regulator.
The engine will crank and run fine when cold. I can run it about 2 hours and cut it off to put some more gas in it and it will be several hours or the next day before it will have spark to crank and run again. I had bad points and/or condenser last fall and replaced them this spring along with a new spark plug. This problem started after about 10 hours of use. About a month ago, I cut it off to put some more gas in it and I never got it to run again until I purchased one of the later style coils with its on pickup (Oregon version (I think it was part #33-334)of the Briggs part#398811)and replaced the old coil (and disconnected the points and condenser) with the new coil (gapped with a "business" card provided with another Briggs coil I had purchased for another mower) and put in another new spark plug (gapped at 0.030). I have been told that on these old Briggs engines, the polarity on the flywheel is supposed to be reversed and Briggs wants you to send it to them to re-polarize it to work with the later style coils, but I found out that all you have to do is flip over the coil to reverse the polarity. I installed the new coil one way and it would not run, so I flipped it over and it cranked up. After I installed the new coil it cranked and ran fine when cold and I am still having the same problem trying to crank it when it is hot on several occasions. So far it has cranked again after cooling completely down to ice cold. The spark tester showed about the same amount of spark when cold with both the old and new setups, but the spark appears to be a little weak, more yellow than blue colored. I have tried it with all the wires unplugged from the ignition switch, so I do not think it has anything to do with the switch. The engine has several hours on it and is using some oil, but not smoking, but I do not think it is a compression issue or fuel issue, since it will not fire off of starting fluid. I have not put a tach on it, but I think the starter is turning the engine fast enough when it is hot, since I think I have heard that the new style coils need about 700 rpm to produce a spark.
Any thoughts on what the problem might be?
The engine will crank and run fine when cold. I can run it about 2 hours and cut it off to put some more gas in it and it will be several hours or the next day before it will have spark to crank and run again. I had bad points and/or condenser last fall and replaced them this spring along with a new spark plug. This problem started after about 10 hours of use. About a month ago, I cut it off to put some more gas in it and I never got it to run again until I purchased one of the later style coils with its on pickup (Oregon version (I think it was part #33-334)of the Briggs part#398811)and replaced the old coil (and disconnected the points and condenser) with the new coil (gapped with a "business" card provided with another Briggs coil I had purchased for another mower) and put in another new spark plug (gapped at 0.030). I have been told that on these old Briggs engines, the polarity on the flywheel is supposed to be reversed and Briggs wants you to send it to them to re-polarize it to work with the later style coils, but I found out that all you have to do is flip over the coil to reverse the polarity. I installed the new coil one way and it would not run, so I flipped it over and it cranked up. After I installed the new coil it cranked and ran fine when cold and I am still having the same problem trying to crank it when it is hot on several occasions. So far it has cranked again after cooling completely down to ice cold. The spark tester showed about the same amount of spark when cold with both the old and new setups, but the spark appears to be a little weak, more yellow than blue colored. I have tried it with all the wires unplugged from the ignition switch, so I do not think it has anything to do with the switch. The engine has several hours on it and is using some oil, but not smoking, but I do not think it is a compression issue or fuel issue, since it will not fire off of starting fluid. I have not put a tach on it, but I think the starter is turning the engine fast enough when it is hot, since I think I have heard that the new style coils need about 700 rpm to produce a spark.
Any thoughts on what the problem might be?