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Stumped on Onan Again

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Guest
I've been trying to get the BF Onan on my Sears SS16 running correctly for a while now but haven't made much progress and have run out of things to try. Here's a list of what was done so far. Replaced points, plugs and condenser Checked timing with timing light Rebuilt carburetor by cleaning it and replacing all of the gaskets Checked cylinder compression - 110 and 75 psi, 125 and 120 after squirting a little oil into the cylinders Followed Onan's manual for checking the governor Replaced fuel filter Changed oil Replaced air filter I can get it to idle smoothly with a little cajolling but it sputters, hesitates and generally won't hold a steady higher speed. The only thing I haven't done is replace the high speed needle. It wasn't included in the rebuild kit. I went through the same steps above when sucessfully attempting to tune the CCKB Onan on my Pmax. Granted I probably deafly stumbled on the solution but it worked. What am I missing this time? Is the low compression in one of the cylinders a concern?

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D-17_Dave
The low pressure in one cyl. may be a clue. Check the valve lifter clearance. If no luck do a leakdown test. Sounds like a valve not closeing or seating properly. Provided the ign. stuff has been done correctly with good components. Might want to swap a coil off one of the other engines and try that.

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Guest
I'll have to bone up on the checking the valve lifter clearance and doing a leakdown test. Both are new to me. The ignition components were all new Onan stuff and I checked the points twice to be sure they were set correctly. I forgot to mention that I also checked the primary and secondary resistance on the coil and they were both within specs.

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firefoxz1
Fuel pump?, float level? Jet is still a little clogged, or not getting enough fuel to meet demand. Here's a tip on points, Once gapped and set run a dollar bill between the contacts to give it a final cleaning. Your test with the oil tells me it will probably be fine once it actually runs. (from experience) I have a GT18 with a B48M. Make sure the battery is good for the ignition as it don't run right with much less than 12v.

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Guest
Fuel pump was rebuilt along with the carburetor. I took off the electric pump that the PO installed. The engine runs the same with or without it. The float level was also checked and adjusted to specs. I'll check the high speed needle and port again to make sure it's not obstructed. Dollar bill between the points? That's a new one. I'll give it a try. The battery is new and supplies in excess of 12v.

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dhardin
I posted a while back with my onan generator "saved the holiday" I think it was called. http://www.simpletractors.com/club2/topic.asp?TOPIC_ID=41881 I know you said you changed the condeser, but you might check it again. Take the points cover off and start it up, turn off or down the lights in the shop as much as you can. Look at the spark at the points contact. It should be a fine clean consistent spark in one general area of the points. It the spark is jumping all around (but still within the contactors) end of the point, and or some sparks are brighter than others. I think you need to try another condeser. Oh yes now i remember, also the screw holding the wire of the condenser to the termenal is very fickle (a close fit). It can be sorting out as you put the cover on. If its to low it will ground to the frame, to high it will hit the cover. That happen to me, a bad condenser and a grounded condenser acts the same. hope this helps. Dan H

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Guest
OK, here's what I have so far to additionally check. Condenser Blockage(s) in carburetor Valve lifter clearance Leakdown test Carbon deposits under cylinder heads (my own idea after reading the Onan manual while looking for how to check the valve lifter clearance) Clean points with dollar bill Anything else?

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BigSix
How cold is it where the engine is? How old is the gas? This winter, "summer" gas from July failed to start my boat, in December (as the River ice was knitting up, AUDIBLY, around up. I have never had a problem in cold before, but it ran along at the same speed as the starter only, and only when starter engaged. In desparation, we shot WE40 directly into the carb, while cranking and feathering the throttle. This flammable stuff acted like starting fluid, and Whoosh! Right as rain, and this was after two batteries of cranking, and a j/s had failed to start it. Later, I remembered that in summer, the oil companies produce gas that has a higher vapor pressure, meaning it gives off less fumes. In winter, they make gas that has a lower vapor pressure, meaning it's more volitile. I believe there are multiple reformulations thoughout the season, but these are the main ones. Most people I talk to have never heard of this concept. Some fresh, winter gas would be easy enough to try--let us know? Thanks, Peter

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Morris
Beeser, when you replaced fuel filter, did you replace with the type originally on tractor? I recall a conversation where someone put a small automotive-type filter on and got the exact same symptoms you were describing, and finally went back to the original type. Problem was solved. It had to do with greater restrictiveness of the filter and the weaker pulling of fuel to the tractor. Or if tank has a screen in it it could be clogged. Does sound like a fuel issue. My 700 is doing that; waiting til spring to work on it.

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Guest
Take the point box cover off and start the engine. Look inside box and see if you see internal arching while engine is running.

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HubbardRA
I've never had the dollar bill cleaning help anything on my tractors. It always requires filing or sanding the points till they are clean and the corrosion layer is removed. I've had points that looked great and were unburned, but would just not fire consistently till they were properly burnished. As Mike says, watch the spark across the points when the engine is running. It should be a sharp, white or blue looking spark, and it should look the same each time the points opens. If it jumps around or varies in brightness, then you either need to do more work on cleaning and squaring up the points, or just replace them.

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Guest
quote:
Originally posted by Morris
Beeser, when you replaced fuel filter, did you replace with the type originally on tractor? I recall a conversation where someone put a small automotive-type filter on and got the exact same symptoms you were describing, and finally went back to the original type. Problem was solved. It had to do with greater restrictiveness of the filter and the weaker pulling of fuel to the tractor. Or if tank has a screen in it it could be clogged. Does sound like a fuel issue. My 700 is doing that; waiting til spring to work on it.
Actually, the tractor didn't have a fuel filter or screen on it originally. So, I removed the tank, flushed out the inside and made sure the opening wasn't clogged. Then a very small clear plastic fuel filter was added along with new fuel lines. I can see the gas travel through the filter when idling. I suppose the filter could be restricting enough to starve the carburetor but it's the same one used on my CCKB without problems. I'll try and bypass the filter to see if that makes a difference.

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Guest
quote:
Originally posted by BigSix
How cold is it where the engine is? How old is the gas?
I'll have to rule this one out. The gas is new and the weather here in San Diego has been in the mid to upper 70s lately.

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Guest
And the answer is .... Looks like Dan was the closest if not dead on with the solution. I ran the fuel line straight without a filter. No change. Same thing after putting on a new filter. Then I replaced the condenser with a new one and routed the wires a little different inside the point box. The points were also cleaned (ran some fine grit sandpaper between the contacts) and reset. It worked!!! I haven't put the engine to task yet but it runs much much better. Thanks to all that contributed with a suggestion and thanks especially to Dan for coming up with an apparent solution.

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comet66
quote:
the weather here in San Diego has been in the mid to upper 70s lately.
Boy, there'a a news flash;) I found that so boring I moved back to Michigan, where we get a change of seasons. Of course that was when I was young and dumb. I'm no longer young.:p:o)

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Guest
John - I experienced the same thing when first moving here (from Michigan) and was actually excited when we had clouds in the sky to obstruct the sun or best of all, rain. There's even a mild form of depression for some people that I later learned was associated with it. I finally came to my senses though. It's nice to be able to plan activities outdoors any time of the year without having to check weather forecasts first.

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dhardin
Thanks Breeser, I only speek from experence and hope to pass it on. That points box is a small cramped place. I have found the key to my sucesse in life, "I am not proude to say I have made all most every mistake in life there is, but lucky enough to make then only once".

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