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1977 D160 Onan Ignition Issue?

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Hey guys - sorry for such a long post I'm just trying to be as thorough as I can be...


I've had issues w/ my D160 in the past where it would run for ~15 mins then stall and needed to cool down before it would startup again. To fix that I've done the following:


1) replace the coil & wires (testing w/ Ohm meter it was slightly out of spec)

2) replaced the flywheel (teeth were worn)

3) replaced the starter (sounded terrible & didn't have enough power to crank the engine during compression, turned out 2 of the contacts were shot and the bearing/sleeve around the shaft was sloppy)

4) replaced sparkplugs (so I could read how it was running - turns out it's too rich)

5) replaced the points & condenser (because I thought this was the crux of the problem).  When gapping the points I couldn't quite get them closed enough.  I was wondering if perhaps the lobe on the crank is worn or maybe the pin that pushes the points was...  In any case, I closed them as much as it would allow.

6) disassembled & cleaned the gas cap


The above seemed to resolve that problem and it ran like a champ at full throttle and purred like a kitten at idle.  It was running the best it has since I bought it 5 yrs ago and continued to work great for 15-20 plowings of my 1/8th mile driveway over the past month or so.  I was psyched that it was running in top shape that is until yesterday...


I was plowing snow drifts when it started sputtering.  Not wanting to get stuck pushing I headed back to the house.  By the time I got home (~700') it was really hurting and sputtering a lot.


My friend gave me a hand today and here's what we did today:


1) cleaned the carb & verified no water present in the fuel/bowl

2) cleaned plugs & checked for spark.  For having new points, condenser, coil, plug wires and plugs the spark doesn't seem all that strong / doesn't jump that far from plug to ground nor across properly gapped electrodes when plug is grounded.  My friend suggested converting to an electronic/solid state ignition.  I couldn't find one online.  Does one exist for the Onan 16HP twin cyl?

3) adjusted high & low mixtures

4) verified ground by jumper cables from batter neg to plug

5) verified intake manifold is tight

6) readjusted the points & confirmed condenser was tightly grounded

7) confirmed oil level


The way it sporadically cuts out then revs then cuts out seems to me like an ignition issue.  It was also backfiring on occasion (also a sign of ignition issue?).  It's consistently sporadic whether cold or warm.


Other stuff that's been done over the past year:


1) replaced the ignition switch

2) carb has been rebuilt w/ new jet & gasket kit

3) fuel filter has been replaced

4) fuel pump has been carefully cleaned


Thanks in advance for any suggestions/recommendations.



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Is the fuel pump vacuum driven? Check the line is not plugged and has good vacuum. The diaphragm could be leaking our the crankcase gasket so the vacuum drops too low to get enough fuel.

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Thanks for the input guys.  The carb has was spotless, but we did clean it again for good measure.


I think it is a diaphragm type fuel pump.  I just saw a video on youtube of a guy testing one from a homelite chainsaw using a pressure pump & loading it w/ 10 PSI.  Would that also be a valid test for an Onan 16HP?  When I bought the rebuild kit for the carb it came w/ a fuel pump so maybe I'll replace that too (and check the line from the pump to the case.


Looking at the spark, it didn't seem all that strong and would only jump about 1/32" - 1/16" from the plug to the engine.  When properly grounded the arc across the electrodes was weak at best and redish/orange in color vs bright blue.  I can't help but think this is somehow electrical in nature.  I also want to try w/ a full charge on the battery.  Then replace the condenser lead to the coil and hotwire the positive directly from battery (+) to coil (+) in case it's a bum lead or ignition switch.  The ign switch is fairly new, but from China and we all know how that goes...


Thanks again for the input.  Looking forward to other suggestions as well.

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Did you check for good fuel delivery to the carb.  Just pull the line off at the carb , stick it in a container and crank it over. You should have a good supply of fuel. If not, start working your way back to the tank.  If fuel supply is good to the carb and  you are positive the carb is clean, then I agree it is a weak spark.   BTW, I cleaned my 220 ONANs carb 3X before I got rid of the surging.     :twocents-02cents:

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You can pull the fuel line at the carb and check how the fuel flows while cranking to test the pump. If the fuel does not flow well you can pull the house from the crankcase and hold your finger to it while cranking to see if you are getting vacuum.

My D160 had problems with the ground to the engine and I ran a second ground cable directly rather than relying on the frame ground.

I had problems with the coil wires as well so I pulled them off the coil, trimmed the wire back a little and pushed them back into the coil and that problem cleared up.

Make sure the condensor connection is solid.

You might want to verify good compression on both cylinders as well.

Everything else you have done or suggested has been spot on so there are not many other things that could be the cause. You might try disconnecting the electric pto to make sure it is not causing a drain on the system in case it is shorting.

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Thanks for the additional suggestions guys.


I'll have to check the fuel pump.  I did that back when I had the other issue (which turned out to be a bad needle valve).  Initially the pump was flowing 'meh' just ok, so I disassembled and cleaned it carefully so as to not tear the diaphragm.  There was gunk on the back side of the diaphragm.  After cleaning it flowed better, but I'll retest it to confirm it's still ok.


Re: ground - we used a set of jumper cables to ground directly from the battery to the outer sparkplug with plugs fully installed.  No not the insulation, to the metal where the socket goes. :)  Regardless, a ground cable is good advice and certainly won't hurt.


As thorough as I was trying to be, I forgot to mention that we had tested the plug wires (Ohm meter) and had cut off 3/4" and reattached to the coil.  The aftermarket plug wires & coil don't connect the best...


I'll have to disconnected the elec PTO and try that.  It did engage/disengage fine when the switch was thrown tho.


Now I'm wondering if a bum battery would cause the coil not to charge enough thus not throw enough power to the plugs.  I'll also try fully charging the battery...


A guy who sells Onan parts PM'd me.  I have to give him a call - maybe he's got the answer to this riddle...


All of your inputs are greatly appreciated!



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Update from tonight's activities:  It appears that the replacement points & condenser I picked up off fleaBay are not exactly to original spec.  The points were fairly cooked (despite only having a few hours on them).  This was presumably due to either not being able to properly gap them or a cheap condenser.  I had sanded them clean w/ 320 grit and doubled-up the gasket under the points box in order to shift the whole assembly up so I could properly gap the points.


She runs much better now, but still not quite 100% as it still missed a couple firings.  I'm considering re-replacing the fleaBay points & condenser w/ OEM parts... Boy, I sure wish an electronic ignition was available.


Thanks again everyone!

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Hopefully this is my final update on this issue:  Problem returned after driving a total of less than a 1/4 mile.  I spoke to another member here (Boomer) who shipped me the newer style (top cover) points box, points & condenser.  When I had bought this tractor the seller included some spare parts (including new NEPCO points & condenser from John Deere that fit this style points box).  I replaced them & re-gapped and everything seems fine now...


Thank you Boomer - you're now my 1st stop for any future Onan parts.  All the best to you, my friend!

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