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Thread: Leaking Primer

  1. #11
    walt.buskey's Avatar
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    Default More Kohler primer pump stuff

    This time, it's the o-rings and.....

    When I take out the plunger tube, I'm not seeing a "small o-ring" in the far end of the tube. Is it possible that the "needle" on the plunger is a metal-to-metal seal, without an o-ring, or is it just another case of "male pattern blindness" as my daughter puts it?

    Also, when the plunger is out, there's a small drip of fuel that doesn't seem to stop. I have removed the check-balls and springs and cleaned up in there, but the drip continues. That shouldn't be possible, should it?

    Thanks, WBB in NH

  2. #12
    Gilbert Pierce's Avatar
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    Default Re: More Kohler primer pump stuff

    The plunger "needle" on the tube pushes a spring that forces the check valve ball against the seat to seal off the primer outlet when the plunger is in and locked. If you get trash in that seat fuel from the head pressure in the wing tank will leak thru the check valve and out into the primer ports, into the intake tubes behind the intake valve then down the intake tubes thru the carb and out onto the hangar floor. If you think your carb is leaking, disconnect the fuel supply to the primer and cap it off and see if the fuel leak stops.

    I thought I had a bad carb needle and seat but turned to be the something in the check ball seat keeping it from sealing. When talking to the carb repair shop about sending him my carb he said " you did check your primer didn't you?" Ding Ding-out to the hanger and disconect the primer input. The leak stopped. Reconnected the primer, pushed is about 10 times to clear and the leak was gone. Same me about &700.

  3. #13
    walt.buskey's Avatar
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    Default Re: More Kohler primer pump stuff

    DSC04116.jpgDSC04118.jpgDSC04123.jpgDSC04125.jpg

    Thanks, Gilbert. I didn't have a problem with fuel dripping on the floor, I'm trying to track down a condition that's existed since the fellow who sold me the airplane first bought it, seven years ago. He was told, and this was just after an engine overhaul/"restoration" of the airplane, "Don't run full rich, it'll foul the plugs; keep the mixture pulled out a bit and it'll run just fine."

    Which is what he's done for time he owned it, about 6 years and 750 hours, and apparently it has run just fine... the primer pump also didn't work (from the same time period), and he was told to use the accelerator pump on the MA-4SP carb, which has also worked OK for him. I have to admit, the engine does seem to start quite well.

    Problem is, my CFI doesn't like that situation, and I can't say I do either. So I'm trying to track it down.

    In my primer pump, I only saw two check valves, which I took to be on the inlet & outlet lines to facilitate the pumping action. Each of those check valves was accessed by a screw, one on the top and one on the side (photo 2) of the pump body. Beneath the screw was a rather soft (5/16" or so long) spring and a ball beneath that (photo 3). Is there another check valve in there at the end? I also had a slow drip of fuel when the plunger was removed and the pump body was hanging below the instrument panel, about one drop every 40 seconds or so.

    So far I have disconnected each of the three primer lines, one at a time, and pumped 2 or 3 slugs of fuel through, then cleaned the fittings with a clean paper towel. I also inspected the fittings going into the head, pulling out some small pieces of crud buildup in the hole. Not much, really, just a few specks. Also blew out each of the lines (by mouth) to make sure they were clear.

    The one line on the left side, however, looked different: instead of a ball-type end where it hooks up to the engine, it looks like a ferrule was used, and it looks rather messed up. Hard to see in the pic, I know. The other end of that same line, which is a 1/8" flare where it connects to the tee, looks like it's been split. Both ends are looking like they were mis-aligned and then over-tightened. I'm planning to replace that line; the other two lines on the right side looked fine.

    Appreciating any & all help, this site has been a great resource. My learning curve is wicked steep, but I'm getting there. WBB in NH
    Last edited by walt.buskey; 05-20-2012 at 04:36 PM.

  4. #14
    Gilbert Pierce's Avatar
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    Default Re: More Kohler primer pump stuff

    The first three pictures look normal to me. Pict #4 doesn't , can't really tell what the problem is but the output fitting should be identical to the input. My primer lines all connect with a ferrule and B nut.

    With everything hooked up but the out put line, I actually disconnect my output on the engine side of the firewall, there should be NO fuel coming from the primer when it is in and locked. If fuel drips through it then for sure the vacuum on the intake stroke will suck more fuel in.

    Unless it is really cold I do not used my primer. Just one stroke of the throttle and she goes. The risk of using the throttle pump to start is flooding the carb and starting a fire. That is why I have the engine turning over when I push it ONE time. Never in 16 years of doing this have I had a problem.

    Spark plug fouling at idle or on a long taxi is not that unusual with 100LL. One reason some of use MOGAS. The engine should idle at about 650 rpm. With the engine idling pull the mixture to idle cutoff. The engine should surge about 50 rpm higher and then die. If it doesn't, your idle mixture is probably set too rich. That will exacerbate the fouling issue.
    At higher field elevations it is normal to lean on the ground. I would not think your 800' field elevation would cause an over rich mixture on the ground.

    It is not my intention to insult anyone's intelligence, I was accused of that when I gave detailed reply a while back. If you have not a primer apart as you have Walt, some folks may not realize that pulling the primer out causes a vacuum in the primer chamber. That vacuum causes the fuel on the inlet line to unseat the inlet check ball pulling it back from the seat against the spring and pulling fuel in from the gascolator into the plunger chamber. At this point the spring has the outlet check ball seated and shut off. When you push the primer in the pressure of the fuel you pushing against aids the spring in seating the inlet check ball and pushes the outlet check ball off the seat and that sends the fuel to the primer nozzles.

    At the end of the stroke the primer is pushed all the way in and locked. Both check balls should be seated preventing gravity fuel flow from the tank to the primers. That small shaft on the end of the primer plunger insures the outlet ball is seated.
    Last edited by Gilbert Pierce; 05-20-2012 at 08:20 PM.

  5. #15

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    Default Re: More Kohler primer pump stuff

    The primer on my O-320 works very well. 3 pumps cold (below 50 F), 2 Pumps warm (above 50 F) and it will start on first impulse firing. I know this from the several times I had to hand prop due to several battery issues. I never pump the throttle but move it in about 1/2" from full closed.

    I still haven't figured out a hot start. It seems that half a primer pump with throttle full closed works best but it still takes several revolutions of the starter.

    I am very afraid of pumping the throttle for a start. I caught a C-182 on fire one time trying a very cold start and had it backfire. At least it only burned up the gas in the cowl and carb heat box.

  6. #16
    walt.buskey's Avatar
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    Default Re: More Kohler primer pump stuff

    Steve, thanks again. The 4th pic is of the line that actually goes to the cylinder (left side, forward cylinder, the only one on that side; rear cylinder port is plugged- future MP gauge?). All those feed lines have a 1/8" flare fitting where they connect to a tee, and then this molded/soldered/? "ball" end --with a flat shoulder on the top-- on both right side lines where they connect to the engine. Looks like a ferrule would also work, just that the one on the left side was slightly mis-aligned. Perhaps that one line was replaced at some point and the others were "factory made"? It is wicked tight in there, next to the baffle. I'll stick another pic here, which is the line and fitting in pic 4 above, before removal; sorry, I didn't think to take a pic of the "molded" ball-type end thing on the right side lines, just figured they were all the same-- until I got to the left side, that is.

    The engine does cut off when pulling to full lean at idle, but I don't remember how much of a rise in RPM accompanies that. One of the A&P mechs who has looked at it checked that right off: while I moved the mixture control in & out, he watched the carb connection. He said there was full travel, hitting the stops, and then asked if the engine would cut off when pulled full lean at idle. I told him Yes; he said that was good, showed that it was in fact altering the mixture.


    DSC04037.jpgDSC04038.jpg


    MN flyer-- yeah, that's what I've been told is the thing to watch for... Steve's suggestion of having the engine physically cranking BEFORE stroking the carburetor's accelerator pump was what I was planning to do, specifically to avoid having raw fuel laying around down there. I've got to say-- I've worked on many types of downdraft and sidedraft carburetors in both compensating jet and constant velocity versions, but this is the first UPdraft carb I've ever seen.... (Must be an airplane!)
    Last edited by walt.buskey; 05-21-2012 at 05:20 AM.

  7. #17
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    Default Re: More Kohler primer pump stuff

    Walt
    hope I didn't read this wrong- my apologies if I did:
    "then cleaned the fittings with a clean paper towel. I also inspected the fittings going into the head, pulling out some small pieces of crud buildup in the hole. Not much, really, just a few specks"

    have you removed the primer nozzles and cleaned them? the hole in the nozzle is quite small and easily plugged and won't atomize the fuel.These nozzles are so close to the intake valve that they carbon up. Not all the nozzles carbon up equally so one cylinder gets all the prime......
    please go to this url to see a pic of the 2 types of nozzles. sometimes folks mistakingly use AN fittings.
    http://www.google.ca/search?q=lycomi...w=1024&bih=438

    hope this helps
    Shane

  8. #18
    walt.buskey's Avatar
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    Default Re: More Kohler primer pump stuff

    Shane, that's very useful info!

    No, I did not pull those fittings from the head, as I had no idea what they were; I thought they were simply a kind of reducing fitting or some such. After seeing the pics on the link and thinking about it, it certainly makes sense that the fittings would entail an injector nozzle of sorts; it just never occurred to me. (There's that steep learning curve again....)

    When I'm back on it again, I'll pull them from the head to inspect their tips, thanks! Is there any special procedure for re-installing the nozzles-- are they just NPT, or do they require some additional "goop" or anything that you know of?

    Very grateful-- WBB in NH

    PS- absolutely no apologies necessary; as you can tell, I'm an absolute newbie when it comes to aircraft, but I refuse to not learn what makes my airplane tick! (Once a gearhead....)
    Last edited by walt.buskey; 05-21-2012 at 07:50 PM.

  9. #19

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    Default Re: More Kohler primer pump stuff

    They are a standard 1/8" NPT. Don't use any goop or sealant. Also make sure you don't over tighten them, it's simply a brass fitting into the aluminum cyl head so "just snug" is as tight as you want to go when you insert them. Cleaning them is best accomplished by letting them soak in some Hoppes #5 gun cleaning solvent (available at any sporting goods store or department). Leave them sit in the solvent for 15 minutes or so and all the deposits are broken down and they are clean. Rinse off, blow them out and re-install. Don't push wire or drills etc into the holes.
    Tom Ferraro
    PA22/20-160 N25TJ

  10. #20
    walt.buskey's Avatar
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    Default Re: More Kohler primer pump stuff

    Sounds good. Hoppe's, I got. Thanks again!

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