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  1. #1

    1390 break-in procedure and priming?

    About to fire up my lowell 1390 build. He recommended 125/150 jets at 1 and 1.25 turns on the screws, 2.0 N&S, black 80g springs. Sounds a bit rich to me but I'll see what it does.

    I also have have the groupk fuel air separator and external fuel pump. I was wondering if I need to prime the pump some way or if it will shoot the fuel quick on initial start so I won't be dry cranking too long?
    Also, how do you guys recommend a break in? I was thinking run on the water hose for about 5 mins, set the idle, then let it cool down. Then run in the lake 15 mins just above idle and cool down. Then burn the rest of the tank below 4k rpm. Then begin opening it up on the second tank premix 32:1. I've got it at about 25:1 on the first tank in there now.


  2. #2

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    25:1 is too much oil in my opinion, realize for each additional amount of oil you lean out the fuel a bit. I have the same build on one of my boats and we squeaked a piston just after break in running 145 mains (cause I thought Lowell's recommended 155 was too rich) Listen to the voice of experience. 150 should be fine, ours is at 155 and a bit rich, but still flies.

    You can pre-prime the carbs by removing the return line from the carbs at the tank, and run a regulated air source to the fuel tank thru the return line fitting. (like 5 psi) This will push fuel thru the lines and carb bodies and when you have all fuel and no air bubbles coming the return line you are done. Really easy, and no extended crank times.

    Your break in plan should be fine, but you are going to have a hard time keeping it under 4k. Remember to go fast enough that you are planed out and not cause extra load and drag by going too slow.

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  4. #3
    Haha! Thanks for the info lt1. I can't wait to open it up. It might be a little less oil maybe 28 or 30:1. I went a couple ounces more than 32:1 so I'm guessing. Good point about the oil displacing fuel, I didn't think about that. Do you think the screws are in about the right spot? Did you have to move your highs in or out?

  5. #4
    LT I put a little air on the return line to prime the carbs. Fuel began to flow to the carbs from the external pump, air/fuel began to spit out the restricted return, then began pouring out of the throat of the number 2 carb. The return quit spitting anything. Not sure what happened, only put a little air on it. Maybe the restricted return tripped the pop off since they are lower now with 80g black springs. I let it sit for a few minutes (thinking the spring would close the needle). Tried again, started doing the same. Not sure if this is normal or OK. Anyone know what's up?

  6. #5

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    How much air pressure did you put on the tank? You may want to pull that #2 carb and check it out, might have damaged the needle or seat, or got something stuck under the needle. A couple of pounds of pressure should not make fuel pour out the carb, the fuel pump puts out up to 6psi when revved up.
    Are you sure you aren't pushing fuel into the carb throat thru the primer? Try pinching off the primer supply hose to see it thats not it.
    You did block off the accell pumps right?

  7. #6
    I only put two short bursts with the air hose and capped the reserve off with my finger. Tank was full. I disabled but did not block off the accel pumps, maybe that has something to do with it as #1 and 3 didn't spill any fuel. Which hose is the primer supply? I may pull that carb and see what's up if I can't get it to do right.

  8. #7
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    Any ratio of oil higher then 32:1 is a waste of oil. It will not burn off, so mixing 25:1 or 28:1 will do nothing but leave I unburnt oil behind.

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  10. #8

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    Quote Originally Posted by Roberd42 View Post
    I only put two short bursts with the air hose and capped the reserve off with my finger. Tank was full. I disabled but did not block off the accel pumps, maybe that has something to do with it as #1 and 3 didn't spill any fuel. Which hose is the primer supply? I may pull that carb and see what's up if I can't get it to do right.
    The primer supply hose is the one that goes to the primer pump. Actually doesn't matter which of the primer pump hoses you pinch off, either will do for the test.

  11. #9
    Ok, pinched the primer feed line. Put my lungs on it this time. Seemed to prime up fairly well. Never did get all of the bubbles out. Anyway, it cranked after about 15 secs of cranking. Idles and revs fine it seems. I will work more on the break in part tomorrow and see if anything screwy happens.

    Another quick dumb question probably. I noticed the exhaust gaskets have tiny holes in the water jacket to let water through. Why don't they make them larger to allow more flow? It sort of baffles me.

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