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Thread: Proping my j 3 cub

  1. #1

    Proping my j 3 cub

    Hello out there, this is my first airplane< a j 3 cub! having a hard time getting started after 20 times of swinging the prop through it started. need help please.

  2. #2
    Dana's Avatar
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    Jul 2011
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    Prime it more, or [more likely] prime it less, closed throttle, cracked throttle, every engine has a particular combination that it likes best. Get it right and it should start on the first or second flip unless there's something wrong. What is it doing (pop, run and quit, kickback, nothing)? Beginners often overprime and flood the engine; if that happens switch off, throttle wide open, and pull the prop backwards 5-10 times, then close the throttle, switch on, and try again.

  3. #3
    Quote Originally Posted by Dana View Post
    Prime it more, or [more likely] prime it less, closed throttle, cracked throttle, every engine has a particular combination that it likes best. Get it right and it should start on the first or second flip unless there's something wrong. What is it doing (pop, run and quit, kickback, nothing)? Beginners often overprime and flood the engine; if that happens switch off, throttle wide open, and pull the prop backwards 5-10 times, then close the throttle, switch on, and try again.
    hi, well you prop it at 10;00 and you cant get it go past 6;00 . compressions are 70,7670 and75. it doesn't backfire or anything like that once its running its running fine. we had a guy prop it at 6;00 and it started. we prop it through 4 times each had compression at 6;00 4times. have amechanic coming to look at it we where thinking prop was on wrong.

  4. #4
    rwanttaja's Avatar
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    Where the prop is at shouldn't affect whether the engine starts, but the guy starting is can get better leverage if it's at the right position.

    The C-85 on the Bowers Fly Baby prototype wanted a procedure like this:

    1. Switch OFF, brakes set

    2. Carb Heat OFF

    3. Throttle cracked (about 1/8-1/4"

    4. Prime the engine. 3 squirts if temps are below 50, 2 squirts 50-70, one squirt if the temp is higher. If the engine has run within the last hour or so, NO priming (unless the weather is really cold).

    5. Turn the engine over six blades.

    6. Brakes Set

    7. Switch ON

    8. Prop engine.

    With this procedure and a cold engine, it would start within 2-4 blades.

    Do your magnetos have impulse couplings? If not, you'll need to fling the prop harder. If so make sure you're starting on the mag(s) which has the coupling.

    If the engine was hot (recently run) it was VERY easy to flood it out. Recovery per Dana posting.

    Ron Wanttaja

  5. #5

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    PLEASE,... post on only ONE section and not all over the web site so our answers aren't scattered all over the place.

  6. #6
    crusty old aviator's Avatar
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    The two phrases of communication between the competent pilot at the controls and the person spinning the prop are: Switch Off and Contact! NEVER use the phrase "switch on," or the guy out front may get the chop and the pilot will get totally grossed out, which will probably ruin their whole day.

  7. #7

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    I found having the mags checked and the timing set made a big difference to starting, but it wasn't until I had the carburettor serviced that I could start it on the first or second swing (after priming and sucking in when cold). I use a similar process to rwanttaja and Dana posts.

    Christopher

  8. #8

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    Make certain its secure, tail tied and even also chocked. Barely crack open throttlle like a fast idle. Try 3 primes if cold. Some people think the primer is a pump. but not really. You have to pull the primer out and wait bout 20 sec until it fills before pushing it in. Switch on and prop/ It should fire in a pull or two, If it fires and seems to run "heavy' with some smoke it may be too much prime. Try 2 strokes and if engine is warm only one or no prime. Some people like to turn prop once after prime with switch off. Be careful stay out of prop arc it can fire anytime. Dont rush, go slow and think each step. If still hard to start it may be carb is just lean. A good Cub like my C90 should fire in 2 pulls cold and 2 or 3 hot. I watched a Cubs doing rides at the seaplane base and start on first pull over and over.

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