2 cycle carb question

Discussion in 'Mechanic and Repair' started by Doublewide6, Oct 16, 2013.

  1. Doublewide6

    Doublewide6 LawnSite Member
    Posts: 203

    I have a small chainsaw PowerMac 310 with a walbro carb. I just rebuilt the carb gaskets except for a new needle. I put in new fuel filter and inspected the fuel lines. Saw runs great once started, but will not cold start. Hi and low are both adjustable and out about 1.5 turns. The saw is not getting fuel at the plug when I try to cold start the saw, about 30 pulls and no fuel on the plug. There is no primer, just a manual choke. Do you think this is a needle problem or a fuel line issue? Fuel lines look good, but maybe they are collapsing?
  2. Landrus2

    Landrus2 LawnSite Platinum Member
    Posts: 4,814

    It's more of a choke problem:waving:
  3. herler

    herler LawnSite Fanatic
    Posts: 5,144

    Possibly a linkage didn't go back the way it's supposed to.
  4. tigerepairdotcom

    tigerepairdotcom LawnSite Senior Member
    Posts: 325

    1 thing do a compression did you do a compression test on the machine? What was it? Was it over 120. If not, you're wasting your time.

    What I do when I put the needle back is blow into the fuel in line and tap tap tap the needle pivot to see if its stopping and starting flow. It sounds like your carb is not being choked properly. Is it possible you put your diaphragm upside down? the metal with the large disc with the holes should be toward the needle seat area. Also your carb could have been too dirty and you didn't clean out all the debris.

    In my shop we use a thermal controlled (175 degree water) ultrasonic parts cleaner its an electronic generator that transmits high-energy and high-frequency vibrations to a fluid-filled container used to remove particulate matter from dirty carbs.

    Even with such advanced machinery some carbs are pretty tough to clean.

    Also your high and low jet adjustments are not just something you can 1.5 and 2 turns that. They are a very fine adjustment and take some experience to do just right.

    http://www.youtube.com/watch?v=D7mnQKIVMXs is a carb adjust video also to properly set your carb you want your engine to be warm 5 6 min warm.

    Also on the high side when you are adjusting full throttle you give it too much gas it will start to putter then you go back in and then youll hear the engine go insanely high like a bumble bee. Bumble bee is bad. you want it somewhere in the middle between 4 stroke running and bumblebee these adjustments can be the difference between a well running machine and destroying your motor.
  5. Doublewide6

    Doublewide6 LawnSite Member
    Posts: 203

    Thanks for the help. I did an ultrasonic cleaning on the carb. All gaskets are correct. I work on these machines pretty regularly. The choke is a manual choke that I can physically see is choked on the outside of the carb. I'm going to investigate the needle it does not seem to be letting fuel in, like it is stuck?
  6. tigerepairdotcom

    tigerepairdotcom LawnSite Senior Member
    Posts: 325

    Did you pull the needle out when you cleaned it? Needle may be stuck sometimes they get pretty gummed up. Just take the (usually) phillips screw out and careful not to loose the spring. you DONT get those in a kit. and pull the needle out. if its hard to pull out you found your problem.

    There's a vacuum tester out there called the mity vac 8500. a must for diagnosis on small engines, theres a slew of tests you can do from checking feul line collapse to proper carb function to leak down tests.

    Fuel Delivery Inspection
    Check the integrity of the fuel tank (pressure test)
    Check the fuel line(s) and filter (pressure test)
    Verify fuel vent operation (both directions pressure test/vacuum)
    Fuel Supply System Inspection
    Check carburetor for tightness
    Check manifold, boots, gaskets and hoses
    Pressure test carb.

    and many more!
  7. BigFish

    BigFish LawnSite Gold Member
    Posts: 3,265

  8. Sharpcut 1

    Sharpcut 1 LawnSite Senior Member
    Posts: 450

    He said he did an ultrasonic cleaning on his carb, so needle had to come out, screen should of been boiled even if he did'nt take it out.
  9. Doublewide6

    Doublewide6 LawnSite Member
    Posts: 203

    I'm going to get the mitivac 8500. I looked at the mitivac 8000 at harbor freight because it is close to my house, but that kit is only vacuum, so I don't believe it will work. The needle has been removed. I'm thinking if needle is leaking the sparkplug should be flooded right? Anyhow I'm ordering the kit, but besides leak down test and needlepop test what else can I do with it as far as carbs go. Is there a PDF on how to test carbs with it because it is made for car diagnostics. Thanks again for all help. In the meantime I will replace the fuel lines that is the only thing besides the needle that is not new.
  10. tigerepairdotcom

    tigerepairdotcom LawnSite Senior Member
    Posts: 325

    whats your email address I will send you redmax's carb testing procedures for warranty for advanced diagnosis technicians.

    You can take the intro class pretty inexpensively. The mity vac 8500 is the best way to go blow is crucial also the procedure for leak down test and other VERY valuable things you can test. It's easy to destroy a carbs gaskets unless you familiarize yourself with the test procedures so be careful. There's a slew of tools that are very useful I will send you some resources in the email.

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