1986 Onan BFA 4 - Suddenly running rough
Well... as they say... "spark or fuel." I have my own suspicion, but I'd like to hear yours... She's been running great for the last 2 years / 25 to 30 hours since plugs, points, cap and rotor, oi...
Forum Discussion
Gas, Spark, and Air.
I had the same symptoms on my newer 5.5 Onan. Check the easy things first
Float bowl: did a piece of dirt get through? Clean out float bowland jets.
Plugs: is one fouling? Pull and check plugs.
Fuel pump/filter: Is it pumping enough fuel? Is it getting weak after it gets hot? Is a dirty filter restricting flow? Check filter and pump.
Vacuum leak: Vacuum leak will cause your symptoms. Check carb gaskets. Check vacuum line going to choke pull off. Check vacuum choke pull off.
My issue ended up being the vacuum choke pull off. The pull off had a bad diaphragm. This caused the choke to stay completely engaged until the electric bimetallic spring opened the choke. This caused it to run rough the first few mutes until it warmed up. The secondary effect was once the choke was open the vacuum leak would cause the generator to run lean. Lean caused it to run hot. Eventually it would start to surge and then shut itself off.
I replaced the pull off and no more issues.
Good luck
I had the same symptoms on my newer 5.5 Onan. Check the easy things first
Float bowl: did a piece of dirt get through? Clean out float bowland jets.
Plugs: is one fouling? Pull and check plugs.
Fuel pump/filter: Is it pumping enough fuel? Is it getting weak after it gets hot? Is a dirty filter restricting flow? Check filter and pump.
Vacuum leak: Vacuum leak will cause your symptoms. Check carb gaskets. Check vacuum line going to choke pull off. Check vacuum choke pull off.
My issue ended up being the vacuum choke pull off. The pull off had a bad diaphragm. This caused the choke to stay completely engaged until the electric bimetallic spring opened the choke. This caused it to run rough the first few mutes until it warmed up. The secondary effect was once the choke was open the vacuum leak would cause the generator to run lean. Lean caused it to run hot. Eventually it would start to surge and then shut itself off.
I replaced the pull off and no more issues.
Good luck
