Great Site!! Briggs Question

Discussion in 'Mechanic and Repair' started by wkumatt, May 16, 2007.

  1. wkumatt

    wkumatt LawnSite Member
    Posts: 16

    I will begin with this site is excellent would have loved to have run across you folks years ago.
    My Problem, mower starts instantly and only at full throttle and choke. Once running will die if choke is fully depressed. Can mow at a snails pace with no power at about 1/4 choke. Interesting part..Mower during snails pace operation will occassionally "cough" throw a lot of bluish white smoke and run full rpms and power...this never lasts longer than a few seconds.

    The Mower. MTD
    The Motor:
    16HP Twin II Model 42A707 Type 1238 01 Code 9602125B
    Three screw fuel pump.

    Attempted fixes so far. Fuel pump rebuild kit..Very thouroughly cleaned carb drained all fuel. Rinsed tank (with fuel)..new fuel lines..new fuel filter...twice..first was cheapy with wire screen second time with bosch with paper element...and needle valve replaced.

    Inherited this from grandfather and even though it is not a classic or collectors mower it still holds value to me and is irreplaceable. Really want to get this thing going right. Thanks if you have advice of any kind.
     
  2. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

  3. wkumatt

    wkumatt LawnSite Member
    Posts: 16

    should have mentioned compression check was fine.
    Further Question
    If I am unable to repair with the info I anticipate from you folks; is Briggs repair manual 271172 the right repair manual for this motor?
     
  4. wkumatt

    wkumatt LawnSite Member
    Posts: 16

    117B This is the jet that screws into the body with an allen wrench if I am reading this diagram correct. I did remove this and clean it and the hole it came out of. The parts house guy assured me that this needed just to be snugged back in and no specific torque was needed.
    By depressed. On this mower the choke is operated by pulling out or pushing in. When I say depressed I mean pushed in. This is open I think. If that doesn't sound right let me know I will go pull air filter real quick.
    Thanks for the quick response.
     
  5. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    "is Briggs repair manual 271172 the right repair manual for this motor?"
    According to the Briggs website it is.

    "This is open I think."
    Really need to know if open or closed. Else I think I might head down the wrong fork in the road.
    Closed is where you normally start a cold engine.
     
  6. wkumatt

    wkumatt LawnSite Member
    Posts: 16

    Sorry for the odd terminology, so what are you thinking?
     
  7. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    "Once running will die if choke is fully depressed. "
    I need to know if by depressed whether you mean the choke is open or the choke is closed.
    "depressed" is not a word commonly used to describe a choke position.
    IF one is trying to troubleshoot the wrong scenario, they just waste a lot of time & effort.
    Speaking of time, supper is ready.
     
  8. wkumatt

    wkumatt LawnSite Member
    Posts: 16

    Depressed = open
    I am saying the mower dies when I open the choke all the way. Funny it's supper time here as well. Spaghetti anyone?
    Thank you for taking the time to talk to me.
     
  9. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    I think maybe I understand the terminology problem.

    I need to know if the choke valve pn# 108A is blocking the air flow or not.
    Blocking is a CLOSED choke
    Not blocking is an OPEN choke
    When running, closing the choke often results in the engine stalling out. You are flooding it.
     
  10. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    "I am saying the mower dies when I open the choke all the way."
    OK:)
    This sounds like the engine isn't getting enough fuel for some reason-
    To Verify-
    Do you have a pump oiler or similar that you can put a bit of gas in? With the engine running, pump a bit of additional gas into the carb throat. IF engine picks up, it indicates insufficient fuel. IF so, keep pumping faster, while opening the choke to see if you can obtain higher RPMs. On RARE occasion, that might dislodge any SMALL specks of crud.

    Often when disassembling/re-assembling fuel lines, filters etc., little bits of debris get dislodged and flow to the carb.
    Possibly, a larger "chunk" may be restricting the fuel inlet to the carb just before the needle & seat. If this is the case, you would have to remove needle again and "blow" back through that area to force any chunk back out. (The spray tube on your carb cleaner should work, or compressed air).

    2.Possibly one of the check balls in the fuel pump body (pn# 391) is not closing fully. (speck of crud again). OR one of the passages is clogged.
    2B. The breather hose going to the fuel pump is leaking. The pump needs the "air pulses" from the crankcase to move the diaphragm to pump.
    2C Crankcase breather reed valve is clogged. (no pulses)

    I would also reinspect the Main Jet again. Look for ANY TINY hole you might have missed. Some jets may have more than 1 hole.

    Look for obvious air leaks on carb/intake & intake/engine mounting surfaces.

    That should keep you busy for a bit.
     

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