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Anybody know anything about small engines?

Discussion in 'The Lounge' started by shane74, Apr 22, 2004.

  1. shane74

    shane74 1/2 ton status

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    I have a Jacobsen mower with a Briggs & Stratton engine. I think it's a 3HP. I rebuilt the carb on it last night because it was over fueling and it couldn't seem to get enough air. I can't get it to run right at all. It's still over fueling. I can't seem to get the adjustment screw set right and It doesn't want to run for longer than 30 seconds before it backfires through the carb. /forums/images/graemlins/angryfire.gif

    Any ideas? /forums/images/graemlins/dunno.gif
     
  2. Muddytazz

    Muddytazz 1 ton status

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    are you sure its that and not the choke?
     
  3. shane74

    shane74 1/2 ton status

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    I'm not sure. It appears to me that the choke is part of the carb itself and not adjustable. The rod that controls the butterfly valve in the body is part of the diaphram. Where the rod goes through the diaphram, there is a spring mounted on the other side that goes down into the bowl.
     
  4. Muddytazz

    Muddytazz 1 ton status

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    True, but there is some adjustability in there somewhere
     
  5. shane74

    shane74 1/2 ton status

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    Hmmmm...The only thing I could find that was adjustable was the needle valve. Time to call the shop where I got the carb kit from.
     
  6. Corey 78K5

    Corey 78K5 1 ton status

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    Have You checked the timing /forums/images/graemlins/thinking.gif
     
  7. civicstomper

    civicstomper 1/2 ton status

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    who makes the carb?
     
  8. shane74

    shane74 1/2 ton status

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    How do you do that on a mower engine? I didn't there was any timing on a 1 cyl. engine?
     
  9. shane74

    shane74 1/2 ton status

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    Well, it says Briggs & Stratton on the carb, so I'm assuming its them. I feel like a complete dope! I can design complex equipment, but I can't figure out a STINKIN' LAWN MOWER!!! /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif

    Time to go to the repair shop... /forums/images/graemlins/tongue.gif
     
  10. Corey 78K5

    Corey 78K5 1 ton status

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    [ QUOTE ]
    How do you do that on a mower engine? I didn't there was any timing on a 1 cyl. engine?



    [/ QUOTE ]
    Every enternal combustion engine has to be timed regardless of the number of cylinders. I used to be a Briggs mechanic so stick with Me.
    If You look at the flywheel under the starter shroud You will see a magnet on the outer rim of the flywheel. At top dead center it (the magnet) needs to be inline with the magneto (coil). The flywheel only mounts to the crankshaft one way. It is held in place with a keyway and a nut on the end of the crankshaft. The blade is mounted solid to the other end of the crank and sometimes if You hit a solid object with the blade it can stop the blade and crank for a fraction of a second but the flywheel will still turn due to centrificul force and either partly or compleatly shear the keyway which is made to do so in a situation like I described. The only fix is to remove the flywheel and replace the keyway.
    Now Im not saying that this is the case, but its a posibility with the back fireing.
    Its not a major thing to remove the flywheel. All You need to do is remove the nut and have someone hold the engine up off the work bench. Then use a brass drift about 1" in diameter and hold it on the end of the crank and give it a few taps with a hammer. Dont get crazy and smack the hell out of it and dont hit the crank its self with the hammer cause You will break it. The brass is softer and will keep from breaking the crank or maring the threads. The end of the crank is tapered as well as the hole in the flywheel. This is where the keyway is located and on older models there will be a small tin cover to house the points ( I dout You have points). The keyway is made of aluminium and is around 1/2" long and around 1/8th" thick on all sides. Like I said sometimes they can partially shear but not all the way.
    Also to get a ball park setting on the carb turn the adjustment screw in all the way (dont force it go easy) then back it out 1 and 1/2 turns. This will get You close and a slight turn either way should work.
    Also did You get a rebuild kit with the fuel pump diaphram added? Did You soak the carb in carb cleaner for at least 24 hrs? Did You replace the screen on the end fuel pump pick up tube?
    Oh and if You ever want to know if the engine has good compresion just unhook the spark plug wire and give the starter a pull. The fly wheel should spin around several times and then turn slightly backwords (known as bounce back) when it hits the compresion stroke. If it keeps turning then You either have a blown head gasket, bad rings, burnt piston, stuck valve, worn lifter or a flat cam loab.


    Stop by a small engine shop some time and ask if they have an old worn out engine You could take. Then tear it down and see how it works. You will be suprized at how simple it is.
     
  11. conoverbandit

    conoverbandit 1/2 ton status

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    Black smoke rolling out of exhaust? if so take a flat head screw driver and turn the fuel jet in easy untill you feel it bottom out. Then turn it out one complete turn and a half. This should make it run just probly "rich" you then turn the jet "in" slowly untill motor straightens out. Should be good to go. if it is back fireing you need to check the "flywheel key" to get to this you will need to remove the recoil top (part where the rope is) 3 bolts if it's a briggs. then take the protecter off (2 small bolts) take the screen off then the clutch off i do this by using a hammer and tapping the little ears on the clutch be careful though you can break them off........there is a washer inunder that, take it off and you will see a "keyway" on the crankshaft and in the flywheel they should line up if it looks kind of twisted or not lined up there could be one of your problems.The key is made from aluminum basically it acts as a "shear pin" in case you hit something hard and kill the engine or sometimes just pulling the rope can cause one to shear.Alot of peep's opt to go with a steele key instead of aluminum but i advise against it cause that is a shear point that keeps the crank and flywheel from granadeing.Hope this helps,
     
  12. Corey 78K5

    Corey 78K5 1 ton status

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    Damnit all to hell. I totaly forgot about the starter clutch /forums/images/graemlins/whistling.gif /forums/images/graemlins/thinking.gif /forums/images/graemlins/whistling.gif Good call its only been sixteen years since I worked on them /forums/images/graemlins/doah.gif
    /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     
  13. shane74

    shane74 1/2 ton status

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    [ QUOTE ]
    Then tear it down and see how it works. You will be suprized at how simple it is.

    [/ QUOTE ]

    Well since I'm not one to be easily intimidated, I tore into mine today after work. But first I'll answer a couple questions. Yes, I got the full carb kit with the diaphram (at least I think so, it's the big black gasket looking thing with a metal rod that hooks to the butterfly valve, right?) No, I didn't soak it in carb cleaner for 24 hours, but I used a whole can of brake clean on it till it looked new. I didn't replace the screen on the end of the fuel pick up, but I did clean it out very good. I did set the bleeder valve out 1 1/2 turns. Also, I put in a new spark plug, filter (soaked in 30 wt. oil and then wrung it out), changed the oil, and cleaned everything outside.

    I tore into the top of the engine today and looked at the points. I cleaned off the flywheel and coil. I used some sandpaper to clean the contacts on the points and reset the gap close to what it was. The shaft key is not broken or twisted. It wanted to run for a little bit today, but then decided not to. How can I tell if the coil is bad? The points? I think I need to replace the spring that controls the butterfly valve inside the tube on the carb that the carb fits onto. I pulled that tube off and made sure there was no build up inside it. Then I pulled off the spark arrester to see if it was plugged up. It isn't. I am out of ideas on this one. It's probably something simple, but I'm just not seeing it.

    Anyway, now it won't fire at all, so I'm thinking I'll pick up a new coil and points tomorrow, put them in, and see what happens. I know how a car engine sounds when it's lost a lobe off the cam. But I'm not sure about small engines. Looks like this is a perfect time to tear into one and learn something new! /forums/images/graemlins/waytogo.gif
     
  14. roadhawg

    roadhawg 1/2 ton status

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    if your going to replace the coil make sure to get a coil with magnetron electronic ignition and do away with the points all together. it should even come with a plug for the points plunger hole in the block. they really dont cost any more than the regular coil for points and last much better with no points problems. Also if you have the head off every other revolution of the piston is top dead center, with both valves down this is the compression stroke, you need to make sure you can not turn the valves while they are seated too make sure they have enough valve clearance. This is a common problem in older engines with many hours on them. hope this helps!
     
  15. Thunder

    Thunder 3/4 ton status

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    Sounds like an electrical problem to me. Tune it up. Points& condenser. Or get the electornic ign as said above.
     

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