1980 LawnBoy 5277 Starting Problem

Discussion in 'Mechanic and Repair' started by LawnBoy517, May 14, 2008.

  1. LawnBoy517

    LawnBoy517 LawnSite Member
    Posts: 5

    My LawnBoy 5277, Serial Number 8322400 has a starting problem. I have changed the spark plug and cleaned the carb. It starts for less than 10-15 seconds and then dies. It seems that it is only getting gas from the choke. This is a re-occurring problem about every 3 years. Previous fixes have been identified as carb cleaning issue, but the current carb is clean. Please advise if you have run across this problem and know the solution. I suspect that the float may be bad. Thanks. :hammerhead:
     
  2. jkason

    jkason LawnSite Senior Member
    Posts: 548

    Float would have to have a hole in it to be bad. IIRC, these vintages had a cork float = no hole.

    Could also be:
    Stale fuel - sheared flywheel key - bad ignition - old age.
    Test the compression. If it less than 90 psi (2-cycle) or 60 psi (4-cycle), it's dead.
     
  3. LawnBoy517

    LawnBoy517 LawnSite Member
    Posts: 5

    Well, This is a re-occuring problem that once fixed the lawn mower returns to normal operation. So, I doubt it is the compression. If I slowly squeeze the primer button after if initially starts, it will run a little longer. I have checked the screen in the bottom of the tank and blow thru. Another clue is that vibration seems to help it run a little longer also. So I am sure it is some where in the fuel system. Please advise what could be wrong in the carb. It is a cork float that is about 5 yrs old.
     
  4. jkason

    jkason LawnSite Senior Member
    Posts: 548

    Get a carb kit.
    And keep one on hand for next time.
     
  5. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    There are two other things you can check. First make sure the lower seal is not blown. Second, turn the mower on it's side and check for excessive wear in the lower journal, both horizontal and vertical play. If there is excessive wear in the lower crank journal, the crank seal will become worn. This condition will contibute to the engine sucking air in through the seal and crank journal instead of fuel/air mixture through the carb. I've seen this problem numerous times with LB's that have exceeded their lifetime--this one being 30 years old.

    Dutch
     
  6. LawnBoy517

    LawnBoy517 LawnSite Member
    Posts: 5

    Dutch, I checked the lower seal and it looks OK and did check the lower journal horizontally and vertically. I am getting no play vertically and a little horizontally. How do I measure the play?

    This mower ran fine until me and my 14 yrs old cleaned the air filter. Because the lawn mower has the same behavior as previous failures, I still feel that it is a carb issue. Any ideas with the carb.

    Thanks,

    Bryan
     
  7. VT_Grassman

    VT_Grassman LawnSite Member
    from Vermont
    Posts: 56

    The fact that this problem started AFTER the a/f was cleaned points right to the carb being dirty. When the a/f was dirty, it was like using the choke + enriching the mixture. Now clean, the mixture is too lean for the engine to continue running. (Also your pushing the primer button is another "clue" that the carb is partly clogged.)

    Gas these days is so poor that it rarely is good beyond 30 days. An automobile can tolerate fule degradation but a small engine cannot. Remove the carb blow out all orfices w/compressed air, check the float level and reassemble. Check the primer bulb for holes (they rot out) by putting your finger over the end of the hose that connects to the carb after pushing the rimer. Observe whether or not the primer remains down when you do this. If it doesn't, you have a leak - either in the hose or the primer. If these are both original replace them. It should be inexpensive.

    Good luck. Those older Lawn Boys were great machines. I still have a 1981 model 6300 (Commercial) that still runs strong!
     
  8. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Even though a carb may look clean a little compressed air really cleans out the passageways. Also check the fuel shut off rubber seal.
     
  9. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    Those carbs aren't rocket science. Unscrew the main jet and make sure it's clean--can't remember right off hand if the main jet has small holes along the long axis of the jet or not, If so run a fine wire through those. The cork floats are susceptible to swelling due to immersion in fuel over extended periods. I have actually found some 1/8" to 3/16" thicker than a new one as well as larger in diameter. Most of the time you will have a flooding/leaking issue due to the float contacting the upper body of the carb before the needle can shut of fuel flow. On the other hand, if the float is not set parrallel to the carb body and it is swollen, it could be contacting the carb bowl thereby not allowing fuel to flow into the bowl at an adequate rate. I would compare the float to a new one and replace if enlarged.

    As far as the crank horizontal play is concerned, if you can hear any kind of "clunk" when you move it, it's getting escessive. The only way you're going to measure it accurately is disassemble the engine and measure the crank and the journal. I don't recall what the tolerances are but it is excessive, it's shortblock time. Even if a shortblock is available for the old F100 engine cost will be prohibitive, unless you're really in love with it and your pockets are deep.

    Dutch
     
  10. LawnBoy517

    LawnBoy517 LawnSite Member
    Posts: 5

    So, I gave up and sent the old mower to the lawn mower shop last week. The end result is that they advise replacing the reed valves and the main bearing. I will let you know how that works.

    Thanks,

    Lawn Boy
     

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