Craftman Rider Back fires in the carb

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  #1  
Old 03-13-06, 07:14 AM
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Craftman Rider Back fires in the carb

I was fixing an oil leak on my craftman rider and took the engine apart to change the lower gasket and messed up the timing. I took it back apart and there were two dots on the crank gear and the valve gear I matched them up and put it together and now it back fires into the carburator. The engine model is a 28n707. help
 
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  #2  
Old 03-13-06, 09:00 AM
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Thats not cool when that happens, I would defenatly say the valve timing is off. Its sparking to soon while the intake valve is open. Ive never worked on this same engine but have had this before. My engine had no marks on the gears, I hope someone here can tell you exactly how to fix the problem. If they cant the valves should be open just a little a TDC so you have to take the head off and turn the engine by hand and keep changing teeth in the cam until both valves are open just a hair when the piston is all the way up. I hope you find a easier waythough. good luck
 
  #3  
Old 03-13-06, 02:36 PM
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It sounds as though you have a partially sheared flywheel key. This likely is as a result of the valve timing having been off...Kickback! You may be able to tell if this is so merely by removing the flywheel nut but you will have to remove the flywheel itself to get a clear picture of such and to replace, if needed. Be sure to torque the nut to specification (85 ft.lbs.) when reinstalling otherwise you'll be replacing another one (key) on the next run.
 
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Old 03-14-06, 12:22 AM
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I agree with Puey61. Check the flywheel key, it is probably sheared. If you lined up the crankshaft/camshaft dots, your valve timing should be fine.
 
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Old 03-14-06, 07:49 AM
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Originally Posted by puey61
It sounds as though you have a partially sheared flywheel key. This likely is as a result of the valve timing having been off...Kickback! You may be able to tell if this is so merely by removing the flywheel nut but you will have to remove the flywheel itself to get a clear picture of such and to replace, if needed. Be sure to torque the nut to specification (85 ft.lbs.) when reinstalling otherwise you'll be replacing another one (key) on the next run.
Thanks, I did check that and it is fine I had that happen to me on another craftsman. Is it possible that the gear on the crank needs to be put in with the mark down instead of up. It said something to that effect on a Briggs web site but I was not sure. Also someone said the key way should line up with the corresponding mark. I am going to take it apart again and take some pictures so I can show you what it looks like. Thanks a lot for your help.
 
  #6  
Old 03-14-06, 07:50 AM
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Originally Posted by cheese
I agree with Puey61. Check the flywheel key, it is probably sheared. If you lined up the crankshaft/camshaft dots, your valve timing should be fine.
Thanks, I did check that and it is fine I had that happen to me on another craftsman. Is it possible that the gear on the crank needs to be put in with the mark down instead of up. It said something to that effect on a Briggs web site but I was not sure. Also someone said the key way should line up with the corresponding mark. I am going to take it apart again and take some pictures so I can show you what it looks like. Thanks a lot for your help.
 
  #7  
Old 03-14-06, 10:25 PM
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There is a dot on the cam gear, and a dot on the crank gear. Line them up together and the valve timing should be right. You can tell without tearing the engine down by rotating the engine to TDC, but not on the compression stroke. Have it at TDC between the exhaust and intake stroke. With the piston all the way at the top, both valves should be closed. Rock the engine back and forth and the intake and exhaust valves should both open slightly, depending on which way you rotate the engine back and forth around TDC. If this happens as described, and both valves close when the piston reaches it's topmost position, then the valves are timed correctly. Have you tried another plug?
 
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Old 03-15-06, 03:32 AM
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As far as the crank gear goes, no, the match mark (dot) does not face toward the crankpin, it faces out. As far as the relation of the mark with the gear keyway, I'm not absolutely certain but I believe they do not line up. I believe that with the keyway at 12:00, the mark will be at about 2:30. Cheese mentioned being able to check the gear timing by watching the valve action. With all due respect, Cheese, if the gear is only off by one tooth, it will be near impossible for a person to decipher if it is exactly on time. I'd remove the sump to be certain, if you question it. With the gear off by as little as one tooth, there will be a noticeable, albeit subtle, performance loss. BWalters, you said you checked the flywheel key...how? Did you actually remove the flywheel or just do a visual by removing the nut?
 
  #9  
Old 03-15-06, 05:43 AM
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Originally Posted by cheese
There is a dot on the cam gear, and a dot on the crank gear. Line them up together and the valve timing should be right. You can tell without tearing the engine down by rotating the engine to TDC, but not on the compression stroke. Have it at TDC between the exhaust and intake stroke. With the piston all the way at the top, both valves should be closed. Rock the engine back and forth and the intake and exhaust valves should both open slightly, depending on which way you rotate the engine back and forth around TDC. If this happens as described, and both valves close when the piston reaches it's topmost position, then the valves are timed correctly. Have you tried another plug?
Yes I removed the nut and saw that the key way and the crank key way were lined up and the key was in place. Also in trying to at least view the piston and the valves together I canít because the head hast to come off. Also I took the rods out when I first took the engine apart one is not longer than the other is it? Also one was black which one goes with which valve? I have another craftsman very similar to this would it be helpful to take this one apart and look at the position. This mower was given to me and it was given to the person that gave it to me. When I got the mower as soon as you put oil in it, it would leak out. After taking the engine off I found that a half dozen bolts were loose and one missing. After taking the lower unit off I noticed the gasket was mostly gone. Also when I took the lower unit off the crank gear came off with it. I am telling you this because I never had the engine running so it is possible that this was explored before by someone else. Now you know the rest of the story.
 
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Old 03-15-06, 05:44 AM
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Yes I removed the nut and saw that the key way and the crank key way were lined up and the key was in place. Also in trying to at least view the piston and the valves together I canít because the head hast to come off. Also I took the rods out when I first took the engine apart one is not longer than the other is it? Also one was black which one goes with which valve? I have another craftsman very similar to this would it be helpful to take this one apart and look at the position. This mower was given to me and it was given to the person that gave it to me. When I got the mower as soon as you put oil in it, it would leak out. After taking the engine off I found that a half dozen bolts were loose and one missing. After taking the lower unit off I noticed the gasket was mostly gone. Also when I took the lower unit off the crank gear came off with it. I am telling you this because I never had the engine running so it is possible that this was explored before by someone else. Now you know the rest of the story.
 
  #11  
Old 03-15-06, 11:47 AM
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Since you've never had this engine running, remove the head and rotate it until both valves are closed. Try to rotate the intake valve. If you can turn it even a little bit,the seat has worn down enough you've lost valve lash which doesn't let the valve close entirely.
Hope this helps,
Mike
 
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Old 03-15-06, 11:34 PM
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I figured it's easier to remove the head and inspect rather than the whole engine and sump. I've timed engines by watching the valve/piston movement on engines that are difficult to time otherwise. It's not hard to get it dead on if you pay close attention. Mostly, I do this when changing timing belts on OHC engines with poor access for viewing the timing marks. This type of engine is not common on lawn equipment though, outside of the honda HR3813 and 4213. Do you have good compression? Could be a valve problem as suggested. Maybe stuck open?
 
  #13  
Old 03-17-06, 04:41 AM
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I took the head off yesterday and took out the push rods. One is aluminum and the other is steal. The aluminum rod is about 1/8" shorter switched these to see if it made a difference from the aluminum on the exhaust to the intake side. It did but the engine still seemed to be firing just before TDC because it would not start but would fire and sometimes the engine fired and the engine tried to reverse its course. What do you think old wise ones, not that your old just a figure of speech.
 
  #14  
Old 03-17-06, 09:13 PM
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Either your valves are too loose, and the engine is hitting the compression stroke and can't get past it because of the valve clearances, or if the engine is actually firing before it gets to TDC, then the flywheel key is sheared. I know you said you checked it, but that is where the ignition timing is set. There is no other variable for timing other than possibly a bad coil, but I have never seen a coil malfunction in this manner. How are you setting the valve clearances? I think you may have a problem there. That would explain these problems.
 
  #15  
Old 03-18-06, 06:16 AM
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You need to remove the flywheel to inspect the key. I've inspected many by merely removing the nut and this does not give a clear indication of the key. If the key is sheared as little as 1/16", this will throw the ignition timing off by as much as 8 or 10 degrees...enough to give the trouble you're having. Time to install a zipper on this thing isn't it? LOL.
 
  #16  
Old 03-20-06, 08:45 AM
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Well I had a fun filled weekend I took the engine lower end off and rotated the engine until the timing mark on the crank gear was once around and back to its original spot that would line up with the valve gear. Now with the valve gear being larger it had only made it around half way so I repositioned the timing gear to match the new position of the crank gear. This now allowed me to have top of dead position of the piston with valves being closed. I put it back together and the engine fired and ran a little but seemed to be missing and sputtering and for a short time ran well but then started missing again. Being that the push rods are different lengths I switched them and tried again, one big back fire and nothing. So I gave up again. The aluminum push rod that is shorter by 1/8th of an inch has flat spots on the top of each of the ball ends. I checked the clearance before I switched these between the valve and the lifter and had about .04 or .004 inches of clearance. I need to get a wheel puller and pull the flywheel next and any other suggestions. Thanks
 
  #17  
Old 03-20-06, 08:54 PM
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I can't see how the push rod swap would have made any difference as to whether the engine ran or not. It should run either way, although the push rods should be in their proper positions long term. If the timing marks line up once, then the cam dot will be 180 degrees off in one engine revolution, then back lined up again on the next revolution.

I still think you either have valve clearance issues or a partially sheared flywheel key. Probably the latter. You can rent a steering wheel puller at Autozone, and use the bolt holes that the flywheel fan is installed with to install the puller bolts in.
 
  #18  
Old 03-21-06, 02:59 AM
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I suggest using only a Briggs flywheel puller to remove such. I've often seen owner removed 'wheels using a OD type puller and the owner now has to replace the 'wheel because it has cracked. Cast 'wheels are very fragile and if you are inexperienced removing such it is better to use the proper tool. I forget the Briggs part number but they do have one available. Check with your local Briggs dealer for one.
 
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Old 03-22-06, 01:22 AM
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No, don't use an outer diameter puller. You can use a briggs puller, but the steering wheel puller is not an OD puller. It pulls from the puller holes in the flywheel just like the briggs puller does, and of countless flywheels pulled, I've never had a problem using a regular steering wheel puller.
 
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