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running problem


cole's Avatar
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06-09-03, 05:57 AM   #1  
cole
running problem

I have a 12hp Briggs on a snapper mower.
About a week ago the motor broke a rod
so I replaced the rod everyting went back together fine.
But the motor will only run it I have air filter off of the carb.
If I put the filter on the carb it chokes it down. Does anyone
know what the problem might be????

Thanks
Cole

 
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mower17's Avatar
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06-09-03, 08:01 PM   #2  
First thing is to check to see if your filter is dirty. If it is replace it. It is clean, then you will have to lean out the mixture, to do this you have to turn the mixture screw about a 1/4 turn clockwise.

 
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06-09-03, 10:21 PM   #3  
I agree, your filter is probably restricted..either by dirt, or a common problem when an engine blows, is it blows oil out the PCV valve and that oil soaks into the filter and restricts the flow of air. Let us know what you find.


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06-10-03, 04:50 AM   #4  
cole
I have a new filter on the carb. I'am getting a lot of blow back coming through the carb. If you look at carb. while it is running
you can see some gas and feel some air coming back through.
It should be sucking air?????

Thanks
Cole

 
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06-10-03, 11:58 AM   #5  
Ahhh...ok, That tells us what is wrong. Your valve clearances are most likely too tight, or the valves are out of time. Are you sure the cam/crank lineup dots were aligned properly before reassembly of the engine? If they are lined up properly, and your flywheel key is not sheared (did you tighten the flywheel nut really tight?), then your valves need to be adjusted.


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06-10-03, 12:19 PM   #6  
cole
I almost sure that I line up the two dots. How can I adjust the
valve clearance??? When I removed the fly wheel to replace the rod. The fly wheel key was sheared. When I put the fly wheel back on I just lined up each keyway and replace the old sheared key with a new key??

Thanks
Cole

 
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06-10-03, 04:14 PM   #7  
To set the valves you need a feeler guage (leaf guage) and correct size wrench to fit the nut. To set the intake valve, roll the engine over until it is on the compression or exhaust stroke. Then get the proper thickness feeler guage and stick it between the push rod and the rocker arm. Then adjust the rocker arm until you obtain a light drag on the feeler guage, then lock it down, then recheck with the feeler guage. If it still has a light drag( not really tight or loose), then you can move on to the exhaust valve. Roll the engine over until it is on the power stroke and do the same thing to it as you did with the intake valve. Keep in mind that usually the exhaust valve will have a slightly larger clearance than the intake valve due to the heat the exhaust valve is exposed to. Hope this helps you out!!!!!

 
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06-10-03, 11:37 PM   #8  
OK, before doing anything to the valves, re-check your flywheel key. If the flywheel nut or bolt was not tightened tight enough it will shear the new key pretty quick. Check that first.

On this engine, if you have to adjust the valves, There are no rocker arms and there no adjustment nuts. You have to remove the PCV valve which is also the valve cover. Check the clearances with feeler gagues with the engine on top dead center. If the clearances are too tight, you have to remove the valve from the engine and grind off a little of the valve stem and reinstall, and recheck. Be careful when grinding the valve stems to make sure the surface stays flat and even, and don't grind much at a time...we're only talking about thousandths of an inch here.


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06-11-03, 05:11 AM   #9  
cole
Last night I checked the checked to see if I lined up the timming
dots and they were. I took the cam out just to look at it and
I saw that the cam shaft was bent??? This was causing the intake
valve too stay slightly open when it should have been closed.
I'm gonna replace the cam and I think this will fix the problem.
Thanks for your help. I will let you know if this works..

Cole

 
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06-11-03, 10:36 PM   #10  
That'll do it! One other thing to check while the cam is out....if it was hit hard enough to bend it, I would bet that the cam socket is also cracked. Look at the hole that the end of the camshaft fits into in the block for a small crack, usually seen at the "V" cutout. If it is cracked, the block is bad. Hopefully it's OK, and even if it is cracked, it might run quite a while, but it may come apart at any given time (might run 5 years, or 5 minutes).


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