New Problem HELP! Possibly big onan troubles?

[Jeff]

When I got my saw from doug I noticed that the oil was over full. One of the first things I did was drain it and change it. Fast forward. I have had a series of issues with the way the engine has run. I have cleaned the carb, I have replaced the coil, coil ignigion wire, sparkplugs and the circuit board. I just got into some real sawing the last week or so. Red pine around 12 to 16 inches, 12 feet long. I have had some real issues with power. engine idles good, runs smooth when powered up, but loses power as soon as you start to cut.

Back to the changing of the oil. A couple days ago I noticed what I though was a fine mist coming out of the exausts again. I had seen it before, then I saw what looked like specks of oil on things.  I shut the engine down and checked the oil. Now, I could not remember if I actually checked the oil when I changed it after first getting it. I looked up the amount of oil in the manual, and added exactly that to the engine. The oil wasa once again, over 2 inches over the full mark on the dipstick.  I thought well heck, I must have made the same mistake doug made. So, I drained the oil and changed it again. THis time, I didnt look at the manual, I just added oil until it was exactly full according to the dipstick. Exactly 2 quarts it took. (Engine is the P24)

Well, I sawed two more logs after that. I have benn using what I though was way to much fuel, but being new to this, didnt really know. Probably 5 gallons to saw 550 feet of lumber. I just went out and checked the oil again, and its over 3/4s of an inch OVER the full line again.  Its gotta be gas going in the oil.

Please tell me there could be a simple answer to this. I have been leaving the gas tank connected, never occured to me to disconnect it when leaving the mill set.


Another symptom. The mill starts hard. You have to crank it quite a bit, but then it takes off and smokes then clears right up. It acts like it is flooded almost.

[Paul_H]

Float needing adjustment?

Do you have some close up shots of the carb and intake?

[Fla._Deadheader]

 Some Onan's have a vacuum fuel pump, mounted on the cooling shroud. Could it be the diaphragm has a hole and the crankcase is being slowly filled that way

[Bibbyman]

I've seen fuel pumps fill crank cases on small block Chevy engines.  Was at a garage one time where they were putting in a new engine in a Suburban.  The mechanic was telling how the owner worked for days trying to get it started so they had it towed out to the garage to have a new engine put in it.  (that sounded drastic to me but…)  As he continued the story,  he went over to take the timing cover off the old engine.  Gas and oil came pouring out.  Yep,  the crank case was full of gas.   Probably nothing wrong with the engine a new fuel pump wouldn’t fix. 

I have no idea if that’s an answer to you’re problem but I’m happy to tell my story…

[Paul_H]

Fuel pump makes more sense don't it ? I doubt WM would have a gravity feed setup on their mill.

Hopefully the problem is solved for the price of a new diaphragm

[Jeff]

I thought that fuel pump was "Impulse" or something like that? It actually has some sort of line going through that shroud?  I do have parts here. I got a pretty good gift at the pig roast. Kevin_H brough up his onan that he has cracked the block on and gave it to me. So I have a complete parts engine here.  I just hope the heck it aint a major engine malfunction.

[Paul_H]

The good news is the impulse comes from the crank case so it is probably slowly feeding back to the case.I think you're in good shape having a spare pump handy,as long as the diaphragms in that pump are OK

[ladylake]

Jeff  Sounds more like the carb to me. a bad fuel pump wouldn't put gas in the intake making it start hard and wouldn'd cause a power loss untill the oil got way overfull.  I'd check the float level as mentioned. Also the float for leaking Maybe it doesn't  float anymore, and put in a new needle and seat. Make sure everything is tight in the carb.   Steve

[ARKANSAWYER]

   Most of the time the carb is the problem like what you are talking about.  You can take the line off and do a vaccume check on the back side to see if the pump leaks.  You can take the line off that runs to the block and suck on it and if you get a gas taste then your pump is leaking.  Most likly it is a bad float or needle seat valve in the carb.  I would check it as the gas in the oil is causing lots of wear.
  Most of the time when the pump is bad the engine will die while under load but a leaking seat valve will drip gas into the oil the whole time it is off and cause the hard starting after setting for any time so I think carb.

[hiya]

I had a rototiller that the float would stick. I had to turn the gas off or the oil level would be way high the next time I would go to start it. Had a spair carb, that took care of it.
Richard

[twoodward15]

Yep, sounds like you need to do a carb rebuild.  It's probably actually the needle that is stuck in it's orifice, causing the float to constantly be down and letting gas pour in.  You could probably get away with just getting a new needle and float.  Be gentle when you pull that pin out that the float rides on, those ears can break off.  Fortunately it'll work fine with only one to hold the float, you just don't want to break both of them.

[Ironwood]

Jeff, My Gator HPX was loading the crankcase as well. A simple carb adjustment and now it's fine

               REID

[Bro. Noble]

We had a similar problem with our Onan.  Finally put a new carb on it and everything was allright.  There was a diaphram in the old carb that was bad.  I had a thread on it a couple of years ago.

[Jeff]

I'm thinking what ever is wrong has been wrong due to the oil level being off when I got it. I think what I will do is switch out the carb. I have the one Kevin brought up. I'll take it apart while I have it off and give it a cleaning. I didnt see anything wrong with mine when I had it apart to clean it. I did have the needle out of it when I had the top off the carb,

[Rockn H]

Jeff, I have a 24 hp Onan myself and you couldn't have described a problem I had any better.  Unless you had mentioned the oil smelling of gas.  It was the needle and seat in the carb.  None of the lawn mower shops in a 60 mile radius that I checked could get parts for an onan.  I would have went to Cummins so my local shop used various parts to make a rebuild kit.  Cost me $5.00.  Anyway a new needle and seat fixed me up. 

[Lenny_M]

 Jeff sure does sound like the needle valve and or float.with the fuel system full and engine off disconect the fuel line and blow into it. air should not go in. start engine with fuel disconected and let it run till it stalls out.blow into fuel line and air should go in.
 5 Gal for 550ft is too much, I usally get about 1500ft

[Jeff]

Do you think its worth a try to first just take off the top of the carb and try to clean the needle and seat with carb cleaner? Or should I just change it out or change the carb since I have the one from Kevin.

[Rockn H]

If the needle and seat look good ,and it is still letting enough gas through to fill up the crank case you may want to check the float.  Take it out and shake it , so you can listen for any gas inside.  Letting a mill set will often cause condensation to form and water will often cause carb parts to rot.

[sparks]

Jeff, I checked with our engine man here and he says definitly the carb.   Thanks

[Bro. Noble]

If it has a rectangular plate on the front lower left,  there is a diaphram in there that will cause your symptoms if it has a hole in it. 

I was told that there wasn't such a thing and that I must have the wrong carb on ours.  A friend who is an Onan dealer for his own use (he has a contract to maintain gen sets for a communication tower outfit) said he would see what I was supposed to have ane get one for me.  It was just like the one I had----with a diaphram in it   That fixed my problem.  I had cleaned the carb,  changed needles and seats,  and adjusted the float numerous times.  It was the DanG diaphram that it didn't have