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  1. #1
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    Johnson 115 compression plus rebuild

    Hi guys I got an 83 Johnson 115 and I've been running around chasing my tail for over a Month.
    First I had a fuel problem, so I rebuilt the carbs and pump took her out and she ran good at wot but when idling she kept stalling when I put her in the water, on the hose not a problem.
    Now today I took it out she ran fine till I decided to pull over and change my prop. I noticed the spark advance poped off so I put her back on and she wouldnt start. Sprayed fuel in the carbs still not firing so its not fuel, which leaves compression and spark. I kept trying to start her and she seemed not to fire. I got home checked the compression on my new compression tester and they read 60 to 65 on all 4 a lil low???
    I then took my plugs off and checked they all had a healthy blue spark. So any ideas? S
    hould I rebuild? If so I want to add a lil power so ill shave the heads anyone know how much to take off?
    Or any other easy mods?

  2. #2
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    Likely that V4 engine has the low compression bathtub heads. Compression in the 90-95 range would be normal, except on the 140 crossflows-which would be higher. It's acceptable to have compression vary about 10%, but yours is definitely low. Low compression also indicates the ability of the engine to suck fuel thru the carbs is reduced. Try checking compression with another gauge. Check compression when all 4 plugs are out and it's cranking 250 rpm's-with a strong battery. Shaving crossflow heads is tricky. Better to look to get a set of used 1979 140 heads (or early 135 heads) instead. Also add the 4 (NLA) rubber intake filler blocks- good for 3-5 hp. Just for starters.
    Last edited by EMDSAPMGR; 03-03-2015 at 05:44 AM. Reason: edited

  3. #3
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    If you can get it to run I would decarbon it before I rebuild it might be carboned up. I have brought compression up by a simple carbon treatment. Look down the cylinder with a bore scope see if the pistons are gummed up.

  4. #4
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    As mentioned above do a decarb before you tear it apart. But yes, your compression is low. Or your tester's broke ...

    It'll probly have the lower comp heads. But not that low ... There's also the possibility someone put low comp head gaskets on it.

    I'd double check your compression readings with another tester before proceeding. Did you have the carbs wot?

    As emd inferred there's not alotta room to monkey around with these heads. I've been told .020 or so is pushing it. Coarse all motor's are different so you'd have to do a squish test to determine just how much you can knock off. We took .004 off mine cuz they had a lil wang in em. Comp is 135 and climbing a lil as it breaks in. But that's with '78 hi comp heads.

    Keep in mind if you start getting up over 145-150psi you'll need to buy fuel with a lil more kick than pump premium. Meaning 100 octane AVGAS.

    Does that have the bubble butt exhaust or is it flat back. That, combined with the reed stuffers and bigger carbs is the po man's way to hop up that motor.

    Bleve the estimate of 90-95 to be a lil low. My stock '86 90 was 120 following a rebuild?
    '71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
    '81 Baja 15 SS - "nine-paged" '77 140
    '81 Carlson C500 Metric - Currently in foster care
    '70 something Speedcraft - Allison 16R clone - Undergoing restoration
    '79 Carlson CVZ 19 - Far back burner
    WALK TALL AND CARRY A BIG BILGE PUMP

  5. #5
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    Reason I said try decarb it was they are all even could be gummed up I have shock treated them also but that is tricky. Man last time I did a motor at the marina you could not see 2 feet the smoke was real bad.

  6. #6
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    So I gave them a shock decarb and comp is picking up I'm seeing 70 70 80 and sadly still a 60 so I pulled the plugs and sprayed decarb in there to let her soak a lil. And no I didn't test at wot. After I let her soak ill run her for a bit then wot test. Comp tester is a brand new sp tools comp tester so it shouldn't be broken.

    As for the bubble back exhaust I wouldn't have a clue. How do I tell?

  7. #7
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    the back exhaust plate will either bee flat or humped..... here'e a bubbleback...Click image for larger version. 

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    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  8. #8
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    Edit dupe post
    Last edited by javelin 63; 03-08-2015 at 03:35 AM.

  9. #9
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    That ones huge compared to mine, my exhaust housing id say is flat and quite small.
    I also did another treatment and comp test today. I got 70 60 top 70 80 bottom. I then sprayed oil in the 60 pot and no change could that mean reeds or gaskit problem?

  10. #10
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    83 is that a crossflow? Check your crank seals, everything . I run a inline crossflow with 170 psi and 36* timing on a boat that is 1150 lbs. Always used 91 or better (AmsOIL) and with no Alc 91 Shell never ever had it miss. 93-94 or 100 low lead is better but I'm just saying maybe 4 new coated pistons and a clean up if you can swing it is the way to go.

  11. #11
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    you need a rebuild,60-70 is too low unless low compression headgaskets are now in place.I'd pull the heads and inspect.the old ball and sockets on timing arms should be changed to newer BLACK style,same number.good fun with your project.-th

  12. #12
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    Ya those numbers are purty lame. (No offense!) I'd bet you'll wind up wanting to do an overbore.

    If ya wanna hop it up during the rebuild. Keep your eyes open for some high comp heads. There's a chance that motor might already have the reed stuffers, if not you'll want them too. Bubble butt exhaust cover w/fillers. Your block will have the 'bosses' to attach em. You'll want 1 5/16", or better yet 1 3/8" carbs. You probly have 1 3/16. A set of aftermarket reeds will definitely perk it up a lil.

    'Pends on how far you want to go "machine" wise when it comes to the block. Buncha things you can do. Square off the ports, smooth out the intake & exhaust manifolds, scallop the block & pistons, etc, etc.

    The mid and/or tuner is another place to monkey around. Saw off/shorten the tuner, drill the mid, etc.

    You're only limited by your imagination. Well, that and the depth of yer pockets ...?
    '71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
    '81 Baja 15 SS - "nine-paged" '77 140
    '81 Carlson C500 Metric - Currently in foster care
    '70 something Speedcraft - Allison 16R clone - Undergoing restoration
    '79 Carlson CVZ 19 - Far back burner
    WALK TALL AND CARRY A BIG BILGE PUMP

  13. #13
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    So I got a bubble back exhaust on the way is there anything else I need to convert to bubble back? Click image for larger version. 

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    Yes she's the crossflow motor. I believe the heads are the 90psi low comp heads
    Last edited by javelin 63; 03-08-2015 at 03:29 AM.

  14. #14
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    Click image for larger version. 

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ID:	315934You are half way there. You need the exhaust filler blocks which bolt into the exhaust chest. Bombardier used to sell a filler block kit, 392000, but it's been discontinued. Once you get these two blocks installed, you have to cut the face of the exhaust chest so that it's perfectly flat-to match the flatness of the gasket and inner exhaust manifold. See the pic of the exhaust blocks properly installed and machined flat. Obviously, best to completely tear down the engine in order to put the block on a horizontal mill.

  15. #15
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    I've read that you can leave out the blocks. Can I do this until I decide to rebuild? I know it won't be as good but should be better then the flat back shouldn't it?

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