# Onan 18hp problems



## mkinsey7 (Jun 13, 2011)

Hi. I have an old, probably 40 years old, sears tractor with an 18 hp Onan motor. Pulled into shop, ran for 2 minutes and quit, will not start. Put new condenser and points, have fire when I touch points with screwdriver. but not spark at all when starting it with starter.. Coil checks out good. used a jump wire from coil to battery and still no spark to plugs. I have a spark checker, plugs into plug wire and has wire to attach to plug or ground and has a small viewing glass to see spark. can see spark when key on and open and close points with screwdriver, but the second I try with starter, nothing. Thought might be switch but jumped coil to battery. Really at a loss. Did also check fuses, ng.
Need some good old wisdom.


----------



## bbirder (Feb 26, 2006)

Try a different spark plug. I've seen new ones fire outside but will not fire under compression. It may also have a hairline crack not visible.
Also, are you sure you are getting fuel. Try cranking with some starter fluid or wd40 to see if it will pop. Needle valve may be stuck.


----------



## FredM (Nov 18, 2015)

do you have a good strong blue spark or a faint orange spark ?.


----------



## Bill Kapaun (May 8, 2007)

Post the Sears 917.xxxxx number.
Possibly a schematic is available that would help pin point possible problem areas.

I'm thinking possibly a bad key switch, but without a schematic....


----------



## jhngardner367 (Apr 5, 2011)

Check the rod that activates the points ( # 13,in diagram).
A small push rod,under the points,that rides on the cam.
They're noted for wearing ,or breaking,and not opening the points.

View attachment 28427


----------



## mkinsey7 (Jun 13, 2011)

Thanks for all the info. points open and close no problem, .24gap. BY diagram #12 under points is missing. turn on key, use screwdriver to open points, lots of fire. even shot some gas down carb, but no spark to plug. even with new plug. I have a spark tester which hooks to plug wire and either to ground or hook to plug, no spark. I am at a loss.


----------



## FredM (Nov 18, 2015)

mkinsey7 said:


> Thanks for all the info. points open and close no problem, .24gap. BY diagram #12 under points is missing. turn on key, use screwdriver to open points, lots of fire. even shot some gas down carb, but no spark to plug. even with new plug. I have a spark tester which hooks to plug wire and either to ground or hook to plug, no spark. I am at a loss.


sounds like the HT leads are shot or even the coil, how did you test the coil ??.

being battery ignition and by bridging the contacts, you will get spark, interested to know how you tested coil !!


----------



## jhngardner367 (Apr 5, 2011)

# 12 is simply an oil barrier.
Double check the points mounting,to make sure they aren't grounding out,at the mount.


----------



## Bill Kapaun (May 8, 2007)

Maybe because .24 is about 11X the correct point gap?


----------



## jhngardner367 (Apr 5, 2011)

Was thinking along that line,but couldn't find the spec on it !
I know Kohlers sometimes use .020.
That could cause the points to "bounce",and the condenser may not charge ,fully.


----------



## Bill Kapaun (May 8, 2007)

If the gap is far too wide, the coil probably just doesn't have enough charge time when cranking.
IF the engine isn't running and the points "touch", the coil has as long as you want to charge.

Since the OP didn't feel it was necessary to post the Sears number, one isn't sure WHICH ONAN he has, thus I won't post a point gap on pure speculation.


----------



## mkinsey7 (Jun 13, 2011)

tractor is old and has no numbers (917) anywhere, but do have Onan numbers. BG-MS/3272A and Mod D773-248562. as for coil test, took points wire off coil, hooked jumper to post and then touched jumper end to ground and the plug wire fired. and was blue. used ohm meter from wire for points on coil to points, 12v. what is weird is that it was running when I pulled it in, then quit and since then nothing, wanted to reply sooner but could not login, password problem. I really appreciate all the help.


----------



## Bill Kapaun (May 8, 2007)

I can't come up with that number in my "stuff", but I see point gaps of .021 to .025" for a couple different models.
So, You can at least reduce the point gap to .025".

Is this a 16 HP engine? Those were the ones with the wider gap in my limited resources.


----------



## mkinsey7 (Jun 13, 2011)

thought I had posted a reply. Got onan running. reset point gap to .21 and it started right up


----------

