Yet another Craftsman/B&S tractor that won't start

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  #1  
Old 07-05-07, 08:33 PM
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Yet another Craftsman/B&S tractor that won't start

OK, this one's driving me crazy. Just received a barely used 20HP Craftsman/B&S tractor (model # 917.271920) from my father-in-law. It was purchased in 2002, but looks brand new. Unfortunately, it won't start.

The starter motor turns it over just fine. If I spray starter fluid or pour fuel from the gas tank down the carb, it runs great for 5 seconds until the fuel runs out. Ignition is fine. If I pull the hose off of the fuel pump outlet, I can see that it is squirting out fuel just fine. So fuel is getting to the carb, and if I pour fuel down the carb throat it runs. So, the carb is somehow blocking the fuel.

I am beginning to suspect the rider safety circuit. You know, the one that's supposed to shut off the engine if there's no rider on the seat. The reason is that I get the same behavior whether I'm sitting there or not. So if I'm not on the seat and I pour fuel down, it will still run until it consumes the fuel. That tells me that it probably operates by shutting off the fuel flow. That leads me to believe it is malfunctioning. But I can't figure out how it works. The switch under the seat seems to work fine. It is closed when I sit on it and open when I get up.

Any ideas? Anybody know where I can get a schematic to figure out this safety circuit?

Thanks,
Peter
 
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  #2  
Old 07-06-07, 02:17 AM
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I'm guessing you have the parking brake locked while you're turning it over? That would allow it to run without you on the seat. The safety system stops spark, not fuel so that is not your problem. Definitely points to carburetion issues. What we need is the model and type numbers from your engine so we know what you're dealing with. More than likely it is a stuck needle, or float not allowing the bowl to fill with fuel, or a plugged jet not allowing the engine to draft the fuel it needs.
 
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Old 07-06-07, 02:19 AM
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You don't have a safety system issue, you have a carburetor issue. If the fuel solenoid attached to the carburetor is functioning properly then you will have a carburetor in need of reconditioning, most likely due to varnish buildup. You will see a module attached to the carbuetor bowl with one or two wires running to it. With a test light, you need to be sure you have 12 volt power going to this module. Set your parking brake, turn the key to the run position (just before the start position), ground the tester and touch the probe end of the tester to the hot wire of the module. If this lights up then you have power to the module (solenoid) and will then remove the solenoid and bench test this for proper operation. Remove such and with a jumper wire ground the solenoid body to the ground post of your battery and use the jumper wire between the positive post and the hot terminal of the solenoid and see if the pin on the business end of solenoid retracts. If so then you have a carburetor that needs to be removed, disassembled, soaked, reconditioned with a Briggs rebuild kit and reinstalled.
 
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Old 07-06-07, 03:30 PM
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Thank you both very much for your thoughful comments. The engine label says: "family: YBSXS.7242VF 274844".

It makes sense that this is a carburetion issue. So I took the connector off of the fuel solenoid. It checks out with 12V with the ignition on run. Then I pulled the float bowl off of the bottom of the carburetor. It was full of fuel, so I guess that means that fuel is getting that far.

I'll check the functioning of the fuel solenoid next. If that works, then it sounds like you both believe there is some varnish or debris gumming up the works, right? The only thing is that this engine looks brand new. It was used last fall, but probably has less than 20 cummulative hours on it. Can a varnish build up from just neglect?

Thanks again. I really appreciate your help.

--Peter
 
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Old 07-06-07, 03:34 PM
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Here are some more identification numbers from the valve cover:
407777 - 0167E1 code: 020618YG

Thanks again!
 
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Old 07-06-07, 03:54 PM
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OK, so the fuel solenoid checks out fine. The little pin retracts when I give it 12V. So there's fresh fuel in the bowl, the bowl fills quickly when I turn the engine over, and the fuel solenoid works

Now is it time to pull the carb, or can I get to it by removing the black plastic shroud that covers the top of the engine and the carb? If I need to pull it, how do I remove the carb from the engine? Is it attached to the engine only by the intake manifold? And does anyone have a clue where I can find a diagram of this carb?

Thanks again for your help!

--Peter
 
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Old 07-06-07, 04:46 PM
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http://www.briggsandstratton.com/ipl/pdfs/100/MS2987.pdf gives you a parts list / diagram. Sure sounds to me like I would go ahead and pull the carbs, do a good cleaning and throw in a kit. I can't answer your other questions because I don't know. I can answer the question of "Can varnish build up from just neglect" to which I would answer that is the #1 cause.
 
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Old 07-07-07, 04:09 AM
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Go to your local Briggs service shop and purchase a 499811, rebuild kit and a 100042 spray can of carb/choke cleaner. Go to your local Napa store and buy a gallon can of #6402, bath cleaner some rubber safety gloves and a pair of safety eyeware. Remove the carburetor from the intake manifold, strip the carburetor down removing any rubber and soft plastic parts, soak the carb in the bath cleaner for 20 minutes, remove the carb from the cleaner, spray down thoroughly with the Briggs cleaner, allow to air dry well (or, if you have compressed air, use this method to dry off), install the contents of the Briggs rebuild kit, reinstall the carb to the manifold and fire up the engine and have a listen to the purr. Be sure to use the hand protection and eyeware while using the cleaners, especially the bath cleaner.
 
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Old 07-07-07, 01:38 PM
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It Lives!!

You guys are awesome. Thanks a lot for your help! I couldn't find a local shop that stocked the carb rebuild kit, so for now I just picked up a 6402 can from NAPA. I tore the carb down as far as I could and soaked it for about 15 minutes. Then I spayed it with carb cleanaer and blew it out with compressed air. When I reassembled it, the engine fired right up. I was avan able to mow the lawn this morning.

There's just one thing, and I don't think it's very important: Even after its been running for 1/2 hour, I still can't put the choke lever all the way in without having the engine stall. So I've been running with the choke pulled out a little less than half way. Seems to run fine like that. If you think that means it might still be running lean from stubborn varnish, then I can still order the rebuild kit and soak it again. Oh, and I noticed that the oing around the fuel solenoid (inside the float bowl) was damaged from several assemby/disassembly cycles.

Thanks again for all your help!

--Peter
 
  #10  
Old 07-07-07, 01:44 PM
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Only running smooth with the choke is a fuel delivery problem. First replace the fuel filter (I like clear ones). If that doesn't do it, then purchase the carb kit. I'm guessing your problem is in the fuel pump which the carb kit will have a reconditioning kit for. Just be sure to note the position of the springs when you take apart the pump.
 
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Old 07-07-07, 04:32 PM
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Behind the fuel solenoid, in the carburetor, is the main jet, did you remove this and not soak it or did you leave it in place, in the carb, and soak it along with the carb? If it didn't get soaked then this may simply be your only trouble left to attend to, remove it and soak it, spray it off, reinstall it and see what happens. If you left it in place, in the carb, then it may not have gotten surrounded by the bath cleaner well enough to disolve any varnish and you should then remove it and soak it. The jet requires a 3/16" hex drive (allen) wrench and a ball type such driver is best (but not mandatory) if you do need to buy one, which Napa should have.
 
  #12  
Old 07-07-07, 07:55 PM
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Hmmm. Sorry, I'm not sure I understand. Where exactly is the main jet? The fuel solenoid is in the bottom of the float bowl, right? And the float bowl hangs under the carb. There's a black plastic appendage tha hangs down from the carb and seals around the fuel solenoid with the o-ring that is seated around the fuel solenoid. Inside that black plastic thing, there is a pair of two needles that hang down from the carb body with six little holes each. So, when I soaked it, I took the float bowl off and set it aside, and I left the fuel solenoid inside. I took the black plastic appendage off the bottom of the carb and soaked it with the carb. I wasn't able to identify the main jet from the parts drawing, but I'll look again.

By the way, I installed a new fuel pump a couple days ago. My father-in-law, who gave this tractor to use, mis-diagnosed this whole problem as a failed fuel pump, so I bought one before we got the tractor here. However, the fuel filter is old, so I'll replace that tomorrow.

Thanks again for your expert advice!
 
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