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Fireworks out of carb


Jeepnut13's Avatar
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05-04-14, 02:10 PM   #1  
Fireworks out of carb

I have a craftsman 15 hp b&s I/c gold riding mower 917.257644. Exhaust valve was stuck causeing it to backfire took it apart freed it now works fine push rods straight but now it pops everytime it sparks. When i turn the key I get a lot of little backfires sounds like a pack of small firecrackers going off carb is clean and all nuts are tight what should I check next? Thanks for your help

 
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05-04-14, 06:36 PM   #2  
Is the valve adjusted too tight?


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05-05-14, 07:44 AM   #3  
Didn't make any adjustments just cleaned the valve shaft and it started working again. Pulling heads later today to double check there is not carbon buildup where the valve head sits

 
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05-05-14, 09:08 AM   #4  
You have to adjust the valves every time you pull the head and put it back on. Check that first.


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05-05-14, 12:56 PM   #5  
Oh ok how do you tell if they are correctly adjusted? The rocker is not tight enough to be stopping the valve return. Please forgive my ignorance this is my first attempt at fixing a motor with out experienced help

 
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05-05-14, 01:03 PM   #6  
Pulled head again exhaust valve was still sticking so I pulled it out and polished it with xxxx steel wool put everything back on but don't know what I'm looking for to adjust them correctly Thanks for your guidance and patience

 
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05-05-14, 01:41 PM   #7  
I backed the rocker nut out then hand tightened and added 1/4 turn to snug them i guess ill read the correct way later! Lol it was either that valve or the adjustment because I fired it up and purred like a kitten. Then smoked the neighborhood up. But after a few minutes it cleared up. Thanks for you help cheese and please let me know how to properly adjust the valves please.

 
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05-05-14, 03:15 PM   #8  
Your valve lash might be too narrow. To adjust them correctly do the following:

Your valve lash should be: intake 0.003" to 0.005" and your exhaust valve should be 0.005" to 0.007".

First remove the valve cover. Then remove the spark plug. Now turn the flywheel clockwise, by hand, and observe the movement of the valves to determine which one is intake and which is exhaust. (usually the bottom is the intake but make sure). When the piston is moving on the compression stroke, place the rubber end of a pencil in the cylinder hole onto the piston and observe when the piston is at top dead center. Now make a mark on the pencil and another mark 1/4" above it. This is just to measure the movement of the piston inside. Now turn the flywheel so that the piston is 1/4inch past top dead center (roughly. You are just ensuring that both valves are fully closed).

Now I like to measure the valve lash before and after adjustment, so do that now. If either needs adjustment, take a torx screw driver and loosen the lock on the hex nut. I think a 10mm wrench turns the hex nut. Once the lock is off, place a 0.004" feeler guage into the intake's valve lash and turn the 10mm wrench until the valve is very snug against the 0.004" feeler guage. Jiggle the rocker arm if you have to. Once set, tighten the torx screw to about 4 ft/lbs. Do this for both valves but remember that the exhaust spec. is 0.006, and then replace the valve cover.

 
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05-06-14, 05:26 AM   #9  
Got it. Thanks cheese! Best $20.00 mower I ever bought. Lol got it from scrape man on way to sell it for scrap!

 
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05-06-14, 09:16 AM   #10  
Good save! Glad you got it fixed!


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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