518-H ignition, Onan 18

[dwcphoto 7]

Hi Folks,

  I've been having some trouble getting my 518-H, onan 18, started. I put in new plugs and with a spritz of carb cleaner, it ran.  Today, with a spritz of carb cleaner it fired, but would not stay running. I looked at the spark on the front plug and while I could see it, it did not apprear "hot" to me.  Tracing back, plug wires and coil next?  It turns over well enough.  Fairly new battery and i've been keeping the battery indoors this winter.  Any ideas? thank you, david

[AMC RULES 36,945]

Sounds like a fuel supply problem, not electrical.  

[dwcphoto 7]

Well, I started looking it over and following a vacumn line (?) from the air clearer toward the dash I saw a wire dangling.  I think it's the air cleaner sensor switch (?). I connected that wire and was able to get the tractor started. I let it run for 15 minutes and called it a day.  I still wonder if I need a new coil for more spark.

 I ruled out the fuel as it seemed to flood before and there were fuel vapors coming out of the exhaust.

Thank you! dwc

[dwcphoto 7]

Hi Folks,

  Back with another question. I took my 518-H out in the woods to cut some firewood today.  The other day I got it running once I saw the wire on the air cleaner sensor was disconnected and plugged it back in. Today, I couldn't get it started until I sprayed a little carb cleaner in the carburetor. Then it fired and continued to run. I let it run while I cut wood for a half hour, figuring it needed to exercise a bit. I shut it off briefly back at the shed and then it started right up without any cab cleaner.

  I replaced the spark plugs recently, but wonder if I'm in need of a new coil or plug wires.  All that stuff is probably original.

  Any ideas?  Thanks for all your help. best, dwc

[JackC 616]

When was the last time the carburetor was cleaned.  As long as there is good spark, I am always amazed at how well an engine starts and runs after I clean its carburetor.

[dwcphoto 7]

If you mean giving it a good spraying with carb cleaner, I did that last week. Cold engine, not running. Maybe I need to give it a more thorough spray?  I took the air cleaner apart and took off the air deflector plate so I could spray down in there. thanks, dwc

[WH nut 553]

You keep asking about coil or wires, but you say you have to spray fuel into the carb. That says you have a fuel problem, or god forbid low compression. Make sure your choke is closing all the way before you start it next. If it is and still wont start without a drink you need to check fuel pump output.

[dwcphoto 7]

Very good. I'll give it another try tomorrow.  I did check the line at the fuel pump last summer and it was pumping. How do I know if it's pumping fast enough?  Thanks, d

[WH nut 553]

If it squirts while cranking, its enough

[dwcphoto 7]

I'm pretty sure it's getting gas, as it seems to flood if I crank it very long. I can see vapor coming out of the exhaust.

[WH nut 553]

I'm pretty sure it's getting gas, as it seems to flood if I crank it very long. I can see vapor coming out of the exhaust.

But you say you have to give it a squirt. If that's the case it isn't flooded

[dwcphoto 7]

Just to be clear the squirt is carb cleaner.  What's the vapor I see sometimes? thanks, d

[WH nut 553]

But it starts when you squirt it doesn't it?

[dwcphoto 7]

Yes, then continues to run. d

[flyovrcntry 115]

It does sound like a dirty carb.Spraying carb cleaner will not clean the internal parts of a carb.Without taking the carb apart I have had excellent results using Seafoam carb cleaner that you add to the gas.

You can get the directions on the can,but this is my method.I use about 2 oz per gal of gas.Run the engine about 5 min at various speeds.Let it sit for an hour or so and run it again at various speeds. I do this a few times then just run the rest of it as I normaly would.

This works for me and beats the crap out of taking the carb apart.

[dwcphoto 7]

That sounds like a plan. I like to tinker, but I'm not interested in taking the carb apart and then having to pay for a fix!! Thanks for your help. best, dwc

[WH nut 553]

If it starts with a squirt, then get away from electrical and concentrate on fuel like I mentioned above.

[gomer gump 8]

I,ve heard a lot a guys  complaining about the onans not working correctly and I,ve told a few guys this I,ve rebuilt about 12 520,s w onans and 9 times out a 10 the motor surges i tried sea foam  yes it worked for a few weeks then back to surgeing again , so im pretty good w electric so I started looking at the schematic,s almost every tractor was wired wrong at the gauges and some at other areas. I  corrected the problem by wireing it according to the schematic . now every tractor I got dosen,t surge . a lot of the gauges had  hot wires on ground terminals and ground wires on hot terminals . some dummys just put them any where they could shorting out the motor causing it to surge . trust me  check your wireing . it could be a fuel problem but check wireing  especially at gauges ,also a lot of gauges the nuts holding the wires to the terminals were just loose. good luck

[dwcphoto 7]

Thanks for your views on this. One thing I found was a wire. Probably from taking the battery out to keep inside during cold weather, a wire came off the sensor that has the vacum line going to the air filter. Why it's all the way back in under the dash could be explained to me, but once I found that wire off and reconnected things worked much better! Go figure... Anyway, my tractor is blocked in by lots of snow right now, so I'll get back to it when it warms up a bit. Thank you very much, david