craftsman tractor won"t start, back fires

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  #1  
Old 12-29-11, 03:49 PM
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craftsman tractor won"t start, back fires

I have a craftsman tactor dyt 4000 model 917.273640 with 18.5 b&s moter. Someone gave it to me so I not sure when it stoped working. I turn the key and the engine cranks but won"t start, than it backfires. I checked the flywheel and it looks lined up right, the key way looks in tact. I took the valve cover off the front and there was oil in there, not sure if that is normal. Took apart the carburator and it lo0oked clean. not sure where I should be looking and what I should be looking for. Thanks for any help
 
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  #2  
Old 12-29-11, 04:04 PM
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You need compression, fuel and spark for the engine to run. Compression is the least likely to go wrong and if you feel compression when you pull the starter cord it's not worth worrying about at first. Next, unscrew the spark plug and then attach the spark plug wire to the plug, hold the plug to the engine's case and pull the starter cord hard. If you see the spark... you have spark. If no spark than you might have a bad plug, wire or coil.

The fuel thing is hardest to test and is probably the thing that goes wrong the most often. If you think you have compression and you saw the spark put a teaspoon of gas into the spark plug hole and re-install the plug. Then give it some good hard pulls of the starter cord. If it chugs or runs for a second then you have a fuel problem and a dirty carb is the usual culprit. Also shine a light into the fuel tank and see if there is varnish or sediment in which case you need to clean the fuel tank and flush or replace the fuel line.

Did you actually remove the flywheel from the crank and look at the key? If not it is possible that the key is partially sheered, throwing the timing off.
 
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Old 12-29-11, 06:01 PM
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model number of engine would be helpful.
 
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Old 12-29-11, 07:04 PM
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Just checked it and I have spark, I held the plug against the block while I turned the key and it had a good spark.
As far as the fly wheel, I didn't remove it but I removed the bolt that goes through the fly wheel into the shaft and I could see where the 2 grooves lined up and the key was in there.
Should I remove the fly wheel and investagate further?
Could it be just a carburator issue? If so I'll take it apart and try cleaning it out.
I looked in the gas tank it looked clean as far as I could tell.

Here is the number taht I found on the engine hopefully it helps
31p7770348e1

*040205zd26181

Thanks for your help
 
  #5  
Old 12-30-11, 12:23 PM
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If you looked at the keyways between the crank and flywheel and they looked perfectly in line then I would not mess with it now. Just keep it in the back of your mind if you get the engine running ans something just isn't right. Usually the key sheers or get's a "Z" shape if the engine has been stopped suddenly which can throw the ignition timing off a degree or two.

Yes, it is normal for some oil to be up in the valve cover area.

When in doubt the carburetor is usually a good place to start since it is so easy to clog a small passage or needle orifice with a speck of dirt or varnish. This page should have a diagram for the carburetor. Easiest to do is remove the bowl from the carb and see if you can get the flow of fuel to start & stop as you gently raise and lower the float.

Where is the fuel tank located on this tractor? If it's directly above the engine than it gravity feeds but if it's located under the seat then you also have to verify that the fuel pump is getting fuel up to the carb.
 
  #6  
Old 12-31-11, 05:35 AM
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What color was the spark at the spark plug...orange, blue or white? Some machines will have a fuel pump even if the gas tank is above the carburetor so don't necessarily rule out a fuel pump problem. Follow the fuel line from the tank all the way to the carburetor looking for the fuel pump, if utilized, along the way. Pull the fuel line off at the carburetor and using a coffee can to catch any fluid (only gasoline hopefully) and crank the engine over (if equipped with a fuel pump - otherwise, if gravity fed, then just a steady flow) and see if you get good flow from the fuel line.
 
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Old 01-02-12, 11:47 AM
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Thanks for all of your advise. The fuel pump is working and so is the float in the bowl. I took the carb off and cleaned it all out with carb cleaner and my air compressor but no luck, I will try to soak it next but it looks pretty clean. I looked at the spark and it looked white to me, it has a good strong spark. When I try to start it I have to turn the engine for a good 10-15 seconds before I get a back fire, not sure if this helps.
 
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Old 01-02-12, 01:01 PM
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Did you put a teaspoon of gas in the cylinder and try starting it? If it fires well a few times or runs for a second it pretty much confirms a carburetor problem.
 
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Old 01-02-12, 01:12 PM
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No I didn't. I did try some starting fluid and sprayed it through the carb. The teaspoon of gas, should I take off the carb and pour it there? thanks for your help
 
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Old 01-02-12, 03:06 PM
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Starting fluid will do the same thing. Did it run on the ether?
 
  #11  
Old 01-02-12, 03:50 PM
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No same result with both starting fliud and the carborator. I would crank the key and than it would backfire, really loud.
 
  #12  
Old 01-03-12, 06:27 AM
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If you are absolutely certain the spark was white then you have a weak ignition, which would also explain the backfire. If you don't have a bare wire (plug lead or kill wire) and you know you don't have a safety circuit problem and you know the airgap is proper (.010") then you will need to replace the ignition armature (coil) and is Briggs part number 795315.
 
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Old 01-06-12, 12:45 PM
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I doubled checked the spark with a new plug and it was a whiteish blue, I compared it to my other tractor and it was the same, so I ruled that out. I did a compresson test and it came back 0. So I took the valve cover off and noticed that the top rocker arm was really loose and rod was not connected. Took the head off and everything looked ok except the top valve doesnt close all the way. Not sure if thats normal, but the way it seats when it shuts there's a space on the side of the valve.
So I'm not exactly sure if I just need to tighten up the rocker arm or what I need to do. thanks
 
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Old 01-06-12, 01:35 PM
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Que to somber music... It sounds like you need more serious repairs. Was it the exhaust valve that does not close? Now might be a good time to ask around town for a good small engine repair shop unless your interested in learning how to do more in depth engine repair.
 
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Old 01-06-12, 03:15 PM
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I was hoping to do the repairs myself. I enjoy working on small engines and stuff just dont have much experience.

Yes its the exhaust valve. Looking at it it almost looks like the head where the sits closed is a little bit on a angle. If you look through the exhaust hole, you could see alittle space along the valve.
 
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Old 01-06-12, 03:48 PM
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The exhaust valve probably stuck. Carbon deposits gum up passage where the neck of the valve slides back and forth. Eventually it sticks hard and the rocker arm tries to push it down and it wont budge. As the weakest link the long, thin valve stem and lifter rod often bend and sometimes other stuff gets dinged in the process.
 
  #17  
Old 01-06-12, 04:40 PM
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I was just looking at it and comparing it to pics that I found in the web and it looks like there is a sleeve inside where the valve slides up and down. The sleeve has lowered it self down about an 1/8 inch and is on an angle, so when the valve seats it stooping it from going all the way back which is making the rocker arm loose.
I looked on the briggs and stratton parts breakdown and I don't see this as a replaceable part. Tomorrow I'm going to try to remove the valve and see if I can't push the ring flush with the head, if not I think I might have to buy a new head.
Any thoughts


Thanks again for all your help Pilot Dane.
 
  #18  
Old 01-06-12, 08:44 PM
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Yep, sounds like the head got hot and the valve guide came loose. Now the head is cool and contracted and won't let the guide move back. You should be able to pick up a used head cheap at your local shop or on ebay.
 
  #19  
Old 01-07-12, 07:00 AM
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Flywheel key

You said the key ways look like they are lined up and the key was present? I had a friend who had the same problem. He swore the key ways were aligned and the key was there when he called me for advice. Having learned this lesson the hard way, I insisted he pull the flywheel. After several days of messing with it he was about to scrap it when I went down and pulled the flywheel. The sheared key fell out on the ground. We replaced it and he is still using the mower. Just thought I would mention it.
 
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Old 01-07-12, 05:04 PM
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Thanks cheese for answering my next question on weather I should buy a used one or a new one. When I put the new one on what is the torque setting for the bolts. Also there are 2 rods 1 steel and 1 aluminum. I 95% sure that the top rod, the one for the exhaust is the steel one. If some one could pleae confirm that for me I'd appreciate it. Thanks
 
  #21  
Old 01-07-12, 09:15 PM
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You're right on the push rod. The torque is 220 inch lbs on the head bolts.
 
  #22  
Old 01-17-12, 05:23 PM
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The head came in the mail today and the used one that I brought didn't have the rocker arms or bolts. So I'm taking them off my old one and I noticed that the bolts that went into the head had so sort of sealant on the threads. Is this just pipe dope or is it more like a loctight. I'm not to sure, just want to know before I put it together. Thanks in advance
 
  #23  
Old 01-18-12, 01:08 AM
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It's basically locktite. You should be fine just putting your parts onto the new head.
 
  #24  
Old 01-21-12, 08:42 AM
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I put the head on the motor and everything looked good, But when I try to start it the starter doesn't seem to have enough power to turn the motor over. I can manually turn the motor by spinning the top, but the starter barely makes it turn. I can hear the compression being made. I tried hooking up jumper cables to my truck to give the starter more power but same result. If I take out the spark plug it will spin the engine faster but there is no load on it. I believe that it has a weak starter but how can I diagnose this before I buy the part and than realize it's something else. Also can I just replace the brushes or a part in the starter or do I need to replace the whole thing. Thanks
 
  #25  
Old 01-21-12, 10:37 AM
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Did you open up the engine case or just replace the head? Did you check the valve gaps?
 
  #26  
Old 01-21-12, 07:30 PM
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Sounds like the valves need to be adjusted. Did you adjust them?
 
  #27  
Old 01-21-12, 11:57 PM
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No I didn't, not to sure how to. I took the valve cover off and could see the valves getting pushed in and releasing. How do I adjust them? Any special tools required? Thank you
 
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Old 01-22-12, 11:14 AM
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Standard wrenches and feeler gauges are all you need.
 
  #29  
Old 01-24-12, 06:03 PM
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All set. There was a little spacer/cap that went on the intake valve that was missing, I realized when I was comparing the new head with the old one. Put everything back together and everything runs great. Thanks again for all your help, I really appreciate it.
 
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Old 01-24-12, 06:07 PM
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Great, glad you got it!_________________
 
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