# 1975 Sear SS16 - sparks out exhaust



## mdroll7780 (Apr 26, 2017)

Hey everyone-

I bought a 1975 Sears Auburban SS16 back in March, and been working out the bugs ever since. You guys have helped me on a few things and thought I was good to go, until last week. Here the symptoms:

1) It seems to have been harder to start lately. Cranks strong but doesn't seem to fire. A spray of starter fluid in the carb gets it started up and running. This isn't all the time, but often. This may be a separate issue, but my first thought was the fuel pump wasn't working well, and maybe starts to work better once its running. Just wanted to mention this.
2) Once running, and give 45-60 seconds to warm up a bit, I can go on running no problem. After about 10 minutes, running with the mower deck engaged, it sputters and stops. I also noticed some sparks flying out the exhaust as shee was sputtering and quitting. Im not sure what would cause this, as it looked like sparks, not backfire flame type.
3) Once she quits, it does not like to start right away, but give 15-20 minutes to cool off it seems to start up again, but will have the same issue 10 minutes later.
4) While running WOT and mowing, there seems to be a lot of heat coming back at me from the motor. I seem to remember my Dad's 1978 SS18 always having a lot of hot air so figured maybe these Onans just run kinda hot. Not sure but wanted to mention. 

Oil levels checked and OK. Im concerned the sparks are being created by hot metel to metal contact inside the engine and spitting them out exhaust? I don't know, but worried about damaging the motor. Any insight, or things to check is much appreciated. 

Here is sears model and Onan numbers:

Sears model is 917.25884
Sears Serial 8155

Onan model: BF-MS/2833D 
Onan serial : D753110349

Marcus


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## Bill Kapaun (May 8, 2007)

Sparks are probably burnt carbon.

Clean the debris from under the cooling shroud.
Replace fuel filter.


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## mdroll7780 (Apr 26, 2017)

I replaced fuel filter, and checked all the cooling shrouds. There was no debris stuck in the shroud. Quite clean actually. I used it this past weekend and it ran for about 25 minutes, maybe 30, and thought I was in the clear, but then did the same things as originally described. 

Would the diaphragm fuel pump be a possible suspect? Sometimes I wonder if its drawing strong enough, as I noticed the fuel filter looks like not much fuel inside it when running. Should the filter be completely full of fuel while running? I don't know if this might cause these symptoms if so?

I am perplexed at the timing of when it happens. Possibly an ignition coil that acts funny when it gets hot? More pondering I suppose. Let me know of any other thoughts, and as always appreciate your guys input.

Regards,

Marcus


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## Searsnutt (Nov 17, 2013)

mdroll7780 said:


> I replaced fuel filter, and checked all the cooling shrouds. There was no debris stuck in the shroud. Quite clean actually. I used it this past weekend and it ran for about 25 minutes, maybe 30, and thought I was in the clear, but then did the same things as originally described.
> 
> Would the diaphragm fuel pump be a possible suspect? Sometimes I wonder if its drawing strong enough, as I noticed the fuel filter looks like not much fuel inside it when running. Should the filter be completely full of fuel while running? I don't know if this might cause these symptoms if so?
> 
> ...


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## Searsnutt (Nov 17, 2013)

Start by replacing the diaphragm fuel pump with an electric one. May not solve all your problems, but solved the fuel delivery issue I encountered with my tractor. About $12-15 on ebay. Search for:Universal Car - Boat - Generator 12V Low Pressure Fuel Pump Diesel Gas Fuel Oil


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## Bill Kapaun (May 8, 2007)

Check the quality of spark when cold and again when the problem occurs.
Compare before/after.

Likely the coil is heat sensitive, thus my recommendation about cleaning under the shroud.


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## Larry/car (Sep 1, 2017)

mdroll7780 said:


> Hey everyone-
> 
> I bought a 1975 Sears Auburban SS16 back in March, and been working out the bugs ever since. You guys have helped me on a few things and thought I was good to go, until last week. Here the symptoms:
> 
> ...


Replace points and condenser, possibly coil gets hot and electrical circuit opens.


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## jhngardner367 (Apr 5, 2011)

When it shuts down, IMMEDIATELY put a spark tester on it,and see how the spark looks.
If it looks good(blue),then the trouble could be :
A) A blown head gasket.
B) A bad valve.
C)fuel pump ,or carb problem.
D) Carbon built up on a piston,or valves.


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## belchermw (Apr 4, 2017)

Burned exhaust valve


Sent from my iPhone using Tractor Forum


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## Arkie (Aug 6, 2014)

Onan engine.

Parts kinda costly.

I would get a old spark plug ready and when she quits pull a plug wire, connect the spark plug and ground it good and take a look. Do this on both cylinders but always keep one plug wire connected to a plug. (they are in series for spark on those engines Called waste spark ignition system.
One open plug wire weakens fire to the other plug.
You also need to make sure some Bubba has not installed the wrong spark plugs. Pull a spark plug and tell us if the tip is sooty or clean.
If you have good spark remove the gas line and the carb and put it in a catch can and crank the engine while it's hot and check for good fuel deliver. If weak fuel delivery from a pulse/vacuum type fuel pump place the input line in a little can of gas and see if it then pumps. If so your fuel line to the tank is bad, filter screen in tank restricted, or pump is sucking air.
The sparks are mostly likely just carbon that is coming out as it hiccups.
You need to determine if the issue is ignition or fuel.
I had one doing that and it was both the ignition coil and the points. (If it's a bad coil be sure you get the correct one)

I've got one of them old SS16's with a Briggs Twin and it just keeps going like the energizer Bunny. I have a little trailer behind it and use it almost daily around the place as a GO for (GOPHER) rig and it tows a wood splitter thru the woods where a larger tractor or vec won't go..


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## Scmdrdj (Aug 14, 2015)

mdroll7780 said:


> I replaced fuel filter, and checked all the cooling shrouds. There was no debris stuck in the shroud. Quite clean actually. I used it this past weekend and it ran for about 25 minutes, maybe 30, and thought I was in the clear, but then did the same things as originally described.
> 
> Would the diaphragm fuel pump be a possible suspect? Sometimes I wonder if its drawing strong enough, as I noticed the fuel filter looks like not much fuel inside it when running. Should the filter be completely full of fuel while running? I don't know if this might cause these symptoms if so?
> 
> ...


I’m a Cummins/Onan Tech, the most common problem with the older engine is the valve need adjusting, book recommend adjusting every 500 hours, but most will run 1000-1200 hours before valves will not open. This will give you symptoms that you are experiencing. Your fuel filter is working as long as fuel is in contact with the fiber element. Search this site for the Onan p216 engine manual the valve adjust procedure and specs are the same for your engine.


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## 47ford (Oct 1, 2019)

You might check valve clearance


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## Bob Driver (Nov 1, 2017)

I agree with Scmdrdj --- It is critical on the old Onan opposed twins (P216, B43, B48) to keep the valves adjusted. The other thing you have to watch for on older Onan opposed twin flatheads is carbon buildup on the heads. Take a look at the design... The exhaust ports come out the TOP of the engine, not the bottom, or the side. You're fighting gravity to get rid of the exhaust carbon build up and there is very little exhaust gas swirl around the back side of the exhaust valve to help chuck carbon out the exhaust like an OHV engine. It's the great engineering flaw in the flathead design. Carbon buildup on say a 5HP Briggs flathead is not a common problem because the exhaust exit is horizontal, not vertical like an Onan. I've seen Onan engines carbon up so bad that the exhaust manifold will glow red. Arkie is also right --- You're gonna pay a premium for any part that comes in that green box, but those old Onans are hard to beat for reliability.


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## 47ford (Oct 1, 2019)

Scmdrdj said:


> I’m a Cummins/Onan Tech, the most common problem with the older engine is the valve need adjusting, book recommend adjusting every 500 hours, but most will run 1000-1200 hours before valves will not open. This will give you symptoms that you are experiencing. Your fuel filter is working as long as fuel is in contact with the fiber element. Search this site for the Onan p216 engine manual the valve adjust procedure and specs are the same for your engine.


Usually valve clearance needs adjusted because the the valve stem has stretched over time and not letting the valves close all the way, causing backfire, hard starting and excessive heat


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## Denver (Mar 30, 2020)

mdroll7780 said:


> I replaced fuel filter, and checked all the cooling shrouds. There was no debris stuck in the shroud. Quite clean actually. I used it this past weekend and it ran for about 25 minutes, maybe 30, and thought I was in the clear, but then did the same things as originally described.
> 
> Would the diaphragm fuel pump be a possible suspect? Sometimes I wonder if its drawing strong enough, as I noticed the fuel filter looks like not much fuel inside it when running. Should the filter be completely full of fuel while running? I don't know if this might cause these symptoms if so?
> 
> ...


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## Denver (Mar 30, 2020)

I just went through this on a tiller with the diaphragm carb. Pulsa jet. Replaced the diaphragm, cleaned fuel tank, purrs like a kitten.


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## deerhide (Oct 20, 2016)

Is there a chance it could be running real lean(air/fuel mix)?


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## steve wherley (Apr 7, 2020)

Warm it up and at about half rpms and add sea foam until dies then let it set 20 mins to soften carbon then start and clear it out. ps do it out side. will smoke alot . If is valve you nothing to loose.


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## Bob Driver (Nov 1, 2017)

steve wherley said:


> Warm it up and at about half rpms and add sea foam until dies then let it set 20 mins to soften carbon then start and clear it out. ps do it out side. will smoke alot . If is valve you nothing to loose.


3 year old thread... Guy hasn't logged in since August 2018


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## pogobill (Jan 31, 2012)

I wonder what his lawn looks like now?!? Either long or burnt, I suppose!


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## Phil B (Jun 11, 2020)

I had the quitting problem on a JD tractor mower. It would run fine, then quit. I would wait, and it would run. The air vent in the gas tank cap was plugged. Cleaned it and it ran fine til I sold it.


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