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Hi guys , i have an old 1974 ariens model 910016 with a 8 hp Tecumseh engine , while using it a night i notice that once in a while some sparks would come out of the exhaust and i also a slight loss a power. Anybody ever had this issue . Thanks . Jason
 

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It could be running lean, try adjusting the carb (turning-out the main jet).

for reference: The starting positions are 1 1/2 turns out for the main jet (bottom of the float bowl) and 1 turns out for the low-speed jet (side of the carb).

excerpt from the service manual:
FINAL ADJUSTMENTS (NON EMISSION ENGINES)
Start the engine and allow it to warm up to normal operating temperature (3 - 5 minutes). Set the speed control to the
HIGH or FAST position. From the recommended preset position, turn the main mixture adjustment screw in (clockwise)
slowly until the engine begins to run erratic (lean). Note the position of the screw. Now, turn the screw out (counterclockwise)
until the engine begins to run erratic (rich). Turn the screw in (clockwise) midway between these two positions. This will
be the best setting. (diag. 21, 22 & 23).
Set the speed control to the IDLE or SLOW position. Adjust the idle mixture screw following the same procedure used to
adjust the main mixture adjustment screw.

if adjusting the carb doesn't clear things-up, it's fairly common on these engines to have inadequate clearance between the lifter & valve.

 

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more than 50% of snowblowers i service with tecumseh engines need a valve adjustment. its a very simple repair, first timer can get it done in an hour and a half experienced person can do it in half hour to 45 minutes. all you need is a bench grinder, set of feeler gauges, screwdrivers, and a new head gasket. pull off carb assembly intake and all, muffler, and valve breather plate. remove two gas tank holding bolts and two top recoil shroud bolts. remove plug wire and sheet metal plate. remove all head bolts. pull head towards dipstick tube, the recoil shroud can stay on. now grab a flathead screwdriver and pry up in between the valve spring and valve keeper plate, use another screwdriver to push off keeper plate. now with the valve sitting loosely, push down on the valve and try to insert .10000 feeler gauge, if you cannot grind down on an angle grinder until you can insert the gauge(go very slowly here and take your time. repeat for other side, reassembly is reverse order
 

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I think the little 'sparks' you are seeing are pieces of carbon flaking off somewhere in the combustion chamber being heated til they start to burn and being forced out of the muffler. I also think the carbon build up is caused by a slightly rich mixture instead of being lean.
 

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I think the little 'sparks' you are seeing are pieces of carbon flaking off somewhere in the combustion chamber being heated til they start to burn and being forced out of the muffler. I also think the carbon build up is caused by a slightly rich mixture instead of being lean.
A valve adjustment would also be a good idea but with an engine this old carbon build up and valve/valve seat wear would be my first thought. The common practice of running with the choke partially on for a richer fuel/air mixture over the years will cause a carbon build up condition for sure.
 

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donyboy73 has a youtube video dedicated to showing a machine with that problem. Can't remember exactly what he shows as the typical reason for that symptom. I recall something about exhaust valve though. You should look that up on his youtube channel.
 

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I think the little 'sparks' you are seeing are pieces of carbon flaking off somewhere in the combustion chamber being heated til they start to burn and being forced out of the muffler. I also think the carbon build up is caused by a slightly rich mixture instead of being lean.
It likely ran rich at some point in it's looooong life. A lean condition could be what's cooking-off the built-up coke. You can go rich-to-lean with a temperature (warm-to-cold respectively).

Regardless, that engine is likely long overdue for some TLC.

I pull the head off of every L-head that ends-up in my garage for the 1st time; +1 on what 43128 said, at least half of them have little/no valve lash.

A decarb, valve job (stem adjust & lapping), new gaskets (head, breather, intake), new fuel line, clean/adjust points, set spark advance and a carb clean/rebuild is often what's needed for these old L-heads to run like new again.
 
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