HydraMac 8 Onan problems

[grebma]

Hey all. Great site and info. I have a HydraMac Mitey Mac 8 with an Onan NH/MS 22.5 BHP motor (according to the manual). It runs good when cold then runs rough, very rough when hot- after about 15-20 mins. I have a link to a You Tube video I posted running after about 15-20 mins. https://www.youtube.com/watch?v=AR3PExxveV0 Had carb rebuilt. I'm thinking points are bad? Both cylinders at same temp when hot so I don't think that we have a dead cylinder. We can't remember if valves have ever been adjusted either. Any help is greatly appreciated. grebma

 

[vinito]

Hmm. Sounds like a hit&miss engine, i.e. the ignition totally drops out until it's back down to slow rpm. It might be points or coil or something, but I wonder if the ignition timing has slopped off pretty bad. I'm not good at small engines, but to me it certainly sounds like an ignition problem. I guess it could still possibly be a fuel starvation problem, but if you were me you'd start with checking out ignition stuff first and rule it out before moving on to fuel or whatever else it might be. Just start with the simpler stuff for sure. Sorry this isn't much help.

 

[Tazza]

Hmm. Sounds like a hit&miss engine, i.e. the ignition totally drops out until it's back down to slow rpm. It might be points or coil or something, but I wonder if the ignition timing has slopped off pretty bad. I'm not good at small engines, but to me it certainly sounds like an ignition problem. I guess it could still possibly be a fuel starvation problem, but if you were me you'd start with checking out ignition stuff first and rule it out before moving on to fuel or whatever else it might be. Just start with the simpler stuff for sure. Sorry this isn't much help.

It could be fuel too.... But i thought when you ran out of fuel, it runs lean so it will jump up and down. If it was a spark, would it back fire? as one stroke it may not fire, then the next does and burns the air/fuel mixture in the exhaust?
I like the idea of checking or replacing the points/condensor if fitted. There is a possibility that if it is a magneto style coil, that it is bad and when it heats up the spark jumps inside and not at the plug.

 

[12CHydraMac]

Hmm. Sounds like a hit&miss engine, i.e. the ignition totally drops out until it's back down to slow rpm. It might be points or coil or something, but I wonder if the ignition timing has slopped off pretty bad. I'm not good at small engines, but to me it certainly sounds like an ignition problem. I guess it could still possibly be a fuel starvation problem, but if you were me you'd start with checking out ignition stuff first and rule it out before moving on to fuel or whatever else it might be. Just start with the simpler stuff for sure. Sorry this isn't much help.

if you have facebook i run a hydra mac group on there with over 160 active members. www.facebook.com/groups/hydramac share it along to those with HMI / IH Skid loaders too! Thanks