Frustrating B

have a B that starts and runs well, for awhile, after maybe 10 to 15 minutes of running and running at normal temp,it seems like the governor advances spark and starts to run rough to the point of killing the motor. gets noisey probably from detonation and losses power, leave it sit for a few and will start right back up without a hint it just died. want to go for a ride into town but am afraid to leave yard until this is figured out. Tank was replaced with real clean one and all lines cleaned, have tried at idle and faster rpm to see if it changes outcome and it does not, any ideas from the experts ?

will replace coil and condenser, so close to enjoying this thing, 

it is a mag 6v system, so maybe change plugs as an option also?choice of plugs?

Autolite 295   is the  plug of choice ...another quick check  when it goes into one of its fits and dies  give it a taste of starting fluid if it wont pop  off  you dont have spark 

Try running it with the gas cap off. My B would run for a while then shut off like it ran out of gas. Cleaned the fuel bowl no change. Checked gas flow at the carb. Finally loosened the gas cap and it ran fine. Good luck and if you get it going be sure to tell us what you did!

Jim, is my brother and we are working on these so you will see posts from two of us on the same tractor from time to time. We put a different and better condition tank and bowl on it to see if it would increase fuel flow and any issues that may cause and it was much bettter than old tank and sediment bowl. We also have an extra carb we are going to try, to help eliminate the fuel possibility. After that we will put in the plugs I am ordering in the morning. Can a condenser cool down quick enough to restart?  and stay cool enough to run or is it not temp related just a bad part somehow? Planning on ordering that also. Really curious as to what a governor senses to advance the spark? Vacume or RPM? And yes we will try them one at a time so we can try to give an update to you for your help. The intermittent part is not fun to deal with as I know you are all aware so if this can help the next guy so much the better. Thanks again for all your help. 

I keep an old lawn tractor tank, sediment bowl and plastic line with filter for trying a different engine. I've bought tractors that I had to use the small tank to load/unload them.

Edited by John426 - 14 Jun 2022 at 11:05am

got a C doing the same thing and now it wont even fire! --- got spark at points and all kinds of juice down there but cant get it to the plugs. tried 3 different cap and wire units and still no go!

My biggest/longest fight with a gas tractor was caused by the rubber tip of the needle valve in the carb. The tip would swell when it was warm and lean out the mixture and created all the misfires and detonation you get with a lean mixture. Carb had not been apart for eons so I suspect ethanol in the gas on a rubber needle tip made for gasoline only. Eventually it it would die and not restart. It was swelled up like a sore thumb. Replaced needle valve and problem solved. Most of the time we only ran this tractor for a short period at low power and it was fine, but when you ran it 30 or 45 minutes working harder it would fail. Generally you could limp back to the barn and it was fine the next day. had plenty of flow to the carb, just not getting in there. Been a long time but I think I took the drain plug out of the fuel bowl on the carb to prove there was no gas in the carb.

Ok, update time, tank was changed, no change.  changed the plugs, plug above oil filter turned out by hand,HMMMMM. no change, . Got condenser in mail ,installed and has run for 1 and a half hours with no problems. Condenser maybe the culprit. Thanks to everyone for the list of options to pin this down, i think a long ride is in order.Making lots of headway on these 2 B's we have thanks to this forum

While you're at it, get a spare condensor and test to make sure it's good and put it up.