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Onan BF in Sears SS16 wont run


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#1 Tennblue59 OFFLINE  

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Posted December 04, 2015 - 02:22 PM

Having an issue with the onan in my Sears SS16. Wondering if anybody has worked throughsimilar issues....

I can get it to fire on ether/starting fluid but it dies after a second or two - even if I give it another shot of ether while its running. Carb is dry (no fuel) so it's not a carb issue. It should run on starting fluid for longer than it does.


It will light and die a couple times like that, then no more until I let it sit for 5 minutes or so... then same thing again....

Using a spark gap it is sparking, but not a really powerful one. I cleaned the points which look ok.....

I had pulled the heads before and checked the bores - no scoring or bad marks. I don't THINK it is a compression issue... Valves were moving and seating ok when I had the heads off. I don't think it is running long enough for a valve to start sticking - never runs long enough to get hot...


My gut tells me its an electrical (spark) issue. I don't have spare onan parts (coil, points, condenser, etc) to throw on to test though - hate to buy expensive onan stuff that wasn't the problems.....

This is my first onan, so I am not familiar with their idiosyncrasies.....


Suggestions?

#2 boyscout862 ONLINE  

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Posted December 04, 2015 - 02:49 PM

Relax and take some time to think this out. You want to troubleshoot this problem. Look in our Manuals Section for the correct manual for your engine. There should be a troubleshooting section that will take you through the steps to figure out what is wrong. Testing to identify the problem usually saves time and money in the long run. The troubleshooting sections in other brands of engines are fairly generic and very good.

 

I use lights that clip onto the sparkplugs to test for spark. Offhand you sound like you may have a loose carb or manifold. Good Luck, Rick


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#3 chieffan ONLINE  

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Posted December 04, 2015 - 03:01 PM

>>>"Carb is dry (no fuel) so it's not a carb issue."<<< 

 

If it has a carb i must be a gas engine.  Carb should have gas in the bowel to get to the engine.  Look between the carb and the fuel tank and see why there is not fuel in the carb.  Filter or line plugged?  Valve turned off?  Tank empty?


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#4 MH81 ONLINE  

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Posted December 04, 2015 - 03:58 PM

Condenser or ignition switch would be my vote.
Condenser breaking down and killing spark or switch only allowing juice to the coil when it's in start, not in run (hook a small test light up to the hot side for confirmation)

#5 crittersf1 OFFLINE  

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Posted December 04, 2015 - 04:17 PM

Float/needle valve in carb stuck?



#6 olcowhand ONLINE  

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Posted December 04, 2015 - 06:12 PM

Condenser or ignition switch would be my vote.
Condenser breaking down and killing spark or switch only allowing juice to the coil when it's in start, not in run (hook a small test light up to the hot side for confirmation)

 

Alan might have the answer.  I've had the same issue on GT's and full size gas tractors.  Easy to check, and if this doesn't check out to be the case, and points are contacting well, I'd lean towards a failing coil or bad condenser.



#7 Bolens 1000 ONLINE  

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Posted December 04, 2015 - 06:18 PM

I agree with the others.... what you describe is condenser or coil related



#8 JiminRI OFFLINE  

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Posted December 04, 2015 - 08:07 PM

I agree - coil or condenser - probably condenser.

Below is a coil test I found a while back when I thought I had a coil issue.

My readings matched those below.

All you need is a simple VOM.

I read on another site that you can run without the condenser, but not for long as it will burn out the points - primarily a starting voltage problem if remember correctly.

 

Good luck,

Jim

 

Coil Test:

While the engine is cold, remove all wires from the coil. Set your meter to ohms and test across the primary winding (the small posts). It should read 3.87 - 4.83 ohms. Now test across the secondary winding (the spark plug wire posts). It should read 12,660 - 15,400 ohms. If they fall much out of this range, the coil is bad. If they are OK, write them down and reconnect the wires.

Now start the engine and let it run until it quits. Immediately retest the coil. What does it test now, and how do the cold and hot readings compare?


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#9 JiminRI OFFLINE  

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Posted December 04, 2015 - 09:52 PM

If the coil and condenser check out, you might want to look at the carburation trouble shooting guide in this thread -

http://gardentractor...ing-and-tuning/

 

Good luck,

JiminRI



#10 bbuckler OFFLINE  

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Posted December 04, 2015 - 10:43 PM

The manuals for onan are really helpful.

http://gardentractor...n-16-hp-engine/


Edited by bbuckler, December 04, 2015 - 10:44 PM.

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#11 Tennblue59 OFFLINE  

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Posted December 05, 2015 - 11:35 AM

Thanks for the quick replies guys!

This is NOT a carb issue or a fuel tank issue - that is why I'm using starting fluid. I am doing this without any fuel CONNECTED to the carb at all - so the carb/line/tank is a non-issue.

I have had condensers that keep the engine from running at all, or that burn the points (usually runs ok for a while until they burn though from my experience). Never one like this, but who knows....

I should be able to throw a k series kohler condenser (one with the lead like the onan one) in there to test it, correct? a condenser is a condenser - at least for a few minutes to test the circuit?????

Thanks for the test procedure on the coil - ill check that as well. I had heard that you can replace the onan coil with a Harley sportster coil - easier to get locally. ????

I hadn't thought about the ignition switch start/run circuits! Will have to check that area out as well.

I have the manuals, but the troubleshooting section only addresses replacing the points! It did have the coil test procedure thought....
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#12 Tennblue59 OFFLINE  

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Posted December 05, 2015 - 06:06 PM

Well, looks like I'll be buying a coil..... The impedance of the coils secondary is way higher than specs according to the manual's test procedure....

Onan coils are $$$!!! I did some research on alternates - Harley twin coils are usable at around $45, instead of $70 or so for onan stuff. Better still, chevy made a twin post coil that is supposed to work as well - clones are available through auto parts places for around $35!

Sooo, I'm gonna hit the auto parts place and see if I can make one of those work! I'll let you guys know how it owrks out.....
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#13 wahoowad OFFLINE  

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Posted December 05, 2015 - 06:38 PM

Good luck. Hope a coil fixes it. I'm interested to know what you get for it.



#14 Bolens 1000 ONLINE  

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Posted December 05, 2015 - 06:49 PM

Thanks for the quick replies guys!

This is NOT a carb issue or a fuel tank issue - that is why I'm using starting fluid. I am doing this without any fuel CONNECTED to the carb at all - so the carb/line/tank is a non-issue.

I have had condensers that keep the engine from running at all, or that burn the points (usually runs ok for a while until they burn though from my experience). Never one like this, but who knows....

I should be able to throw a k series kohler condenser (one with the lead like the onan one) in there to test it, correct? a condenser is a condenser - at least for a few minutes to test the circuit?????


Not all condensers are the same! If they were there would only be one available for all the engines!
Even though some look the same the "Farads" are different and will burn your points out either over time or rapidly. If you got a machine burning through points the condenser is your main culprit.
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#15 Tennblue59 OFFLINE  

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Posted March 12, 2016 - 08:02 PM

Thought I would post a follow-up to this post. I got an onan coil and points/condenser set from another member on here and stuck them in. Engine started right up and runs decent.

Gotta remember how to put it all back together again! Hood and grill, fuel tank and seat still need to go back on. Then new drive belt and she should be good to go. Thanks again to all those who helped me out on this one.....
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