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Was given an old Searay with a Johnson 70 on it. Looking for advice

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  • Was given an old Searay with a Johnson 70 on it. Looking for advice

    Good afternoon all. A few months ago I was given a 17 foot 66 Searay with Johnson 70 HP triple 2 stroke on it. Model number is 70ESL-74M. Am redoing the interior but that is for another post. My questions are, Do these engines have any form of charging for the starting battery or to power the lights, radio, and such? Are there any do or don't I should know about besides the normal 2 stroke stuff? I'm assuming it uses a 40:1 mix. Does that sound right? I've rebuilt the water pump and replaced what was left of the thermostat and tested. Engine runs great and once ran for a few moments fires right up. I need to fiddle with the choke to get it to fire on a cold start but for it's age that doesn't surprise me. Any thoughts on what to do there would be appreciated as well. My plan is to restore the entire boat to original so help finding the correct decals for the engine cover would be helpful as well. Thank you all in advance!

  • #2
    All 1970 model 70 HP have a flywheel alternator / battery charging system.-----Mix is 50:1.----Decals can be found online.

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    • #3
      Actually, it is a 1974. And yes it does have an alternator.

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      • #4
        Meant to say----all 1970's model 70 HP----

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        • #5
          OK, got her in the water. Have a few more questions. Replaced the water pump (that was fun) and I was under the impression that water was supposed to come out of the 2 holes about midway up the back of the engine. This engine does not "pee". I took the lower end back off and hooked a garden hose directly to the water pipe inside the intermediate assembly and still nothing. Cracked one of the bolt on the cover of the thermostat and there was plenty of water coming out. Does this one just not pee? Also when I took it out on the water, it idles around the rivers just fine and when I give it a little throttle it seems to work fine but when trying to get up on plane heading out to Tampa Bay, it winds up then dies. Engine is not getting hot. I tested by taking the cover off and using my hand on the head. It's hot but not so hot that I can't keep my hand on it. I'm assuming that fine, Yes? No? I replace the entire fuel line, bulb, and filter. Am using fresh gas with a 40:1 mix. At no point has it peed. Do I have a cooling problem or should I rebuild the carbs. It did sit for a few years but idles well and with a garden hose on the clip on the bottom thing. It will rev right up. As son as you put it in the water, it just won't rev up. I'm at a loss here. Don't want to bring it somewhere and get screwed. I've done some research but can't seem to get a decisive answer. The boat was given to us by our favorite uncle (even before he gave it to us). and want to keep it as it was back then as a tribute to him. Sorry if my questions aren't clear. I'm trying to figure out why it seems to work fine out of the water and then as soon as I put it in the water, poof no power. I've looked for rebuild kits for the carbs but cant seem to find any. I don't have a problem doing the work, just don't want to waste my time fixing stuff that isn't broke.

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          • #6
            Do a compression test.-----Then check for spark that jumps a gap of 3/8" on each lead.----Post your results.

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            • #7
              It is cooling. Otherwise, you would have burned it up within the first few minutes. OK, it does not have a pee thing. The two holes on the backside of the midsection are the indicator. At least a mist of water should blow out of them. Having said that, the entire midsection fills up with water before any overflows and blows out. But mostly, water goes out with the underwater exhaust. The midsection will not fill up if the rubber seals at the bottom are missing or trashed.

              Your story seems to indicate clogged high speed jets in the carbs. Worth checking anyway.

              I can look up the carb kit numbers and get back with you.

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              • #8
                Thank you both Found the correct sierra part number for the carb rebuild kit and have verified it is correct (18-7042). Will rebuild carbs and have already checked compression. Was 120,123,121 (top to bottom). Will check spark and replace plugs.

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                • #9
                  F_R , Is there some kind of seal that goes between the lower unit and rest of the engine? There is water coming out of the small gap between them. If not should i use some form or gasket sealer (like I used for the thermostat) or is that "normal" for a 40+ year old engine in salt water most of it's life? Carb kit ordered and on the way!

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                  • #10
                    racerone new plugs ordered and are you sure on the 3/8 gap thing, everywhere else I've searched said 7/16. Is 1/16 difference even a thing? I ask because my experience is with cars and bikes and never used one before. They either have spark or not in my experience (Champion L77JC4 unless you recommend something else). I'm assuming I don't gap them to .375. Never use more than a .065 gap on a plug but outboards are new to me so I ask. What should I gap them to?

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                    • #11
                      Test your ignition system and look for STRONG spark !

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                      • #12
                        Originally posted by Frickinfrack View Post
                        F_R , Is there some kind of seal that goes between the lower unit and rest of the engine? There is water coming out of the small gap between them. If not should i use some form or gasket sealer (like I used for the thermostat) or is that "normal" for a 40+ year old engine in salt water most of it's life? Carb kit ordered and on the way!
                        Leaks between the gearcase and exhaust housing mean nothing. Anything that leaks out there was headed back to the lake anyway. But they did uses some sealer for cosmetic reasons.

                        The other seals I mentioned are the one on top of the water pump housing and the big rubber donut where the inner exhaust tube sticks into the lower unit.

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                        • #13
                          L77JC4 original gap was 0.040", later changed to 0.035". Either one is ok. Also, plugs were changed to QL77JC4 for radio noise suppression.

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                          • #14
                            I replaced the plugs (L77JC4's with .035 gap) and rebuilt the carbs. Tested spark, was good and bright at 7/16 gap. Just for kicks, I opened the gap tester up to an inch and still got a spark but it wasn't very consistent. I got nothing at 1 1/4 inches. Took her out to test on Sunday. Got her up on plane but had to baby her up there with the throttle slowly. Is this normal? I assumed you just dump the throttle and hold on, maybe I was wrong. When I dump the throttle, it winds up to about 3500 RPM's and just "plows" for a bit then tries to stall until I throttle back to about 50%. Once on plane it's much more responsive. Needless to say we have marked improvement! Now I have another problem, I bent the prop by being in water that was too shallow (rookie mistake) and hit a submerged log. Prop is aluminum and pretty chewed up anyway. Pretty sure it's original. Seeing as how I need to replace it anyway, is there something I can change to help her get up on plane easier or do I go back with the original spec prop? Once up, she was able to get up to 20 pretty quick but had to throttle her back due to wife screaming at me because it was kinda choppy and the boat rides pretty rough. I'd estimate top speed at about 30ish. I'd say it's about right for a 50+ year old boat with a 40+ year old motor. If this doesn't sound right let me know. The tach does not work but i'd say she was spinning at about 4500-4700 @ 20 MPH. I've read that it likes to run at a max of 5000-5500 RPM. This is where i'm guesstimating the 30 MPH top speed. I used to have a 3 Cyl 2 stroke motorcycle so I have an ear for that. I will replace the tach at some point just not right now. Want to get her working as good as I can first. Then will replace lights, horn, gauges, install radio (for music, it already has a VHF) and maybe GPS. I want to keep it as stock looking as possible. I'm liking the looks and conversations it starts. Vintage boating is my thing, I guess. Who knew?

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                            • #15
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                              Disconnect the throttle cable at the motor, Now, using your fingers where the cable was attached, push the lever aft (motor not running, duh). Observe that the carburetors' throttle shafts move very little until the spark advance reaches full advance, then the carbs open fully. That is how it is supposed to work. But if the spark advance is sticky, the carbs may open prematurely. That will cause a stumble or even stall when accelerating from an idle. Cure is to clean and re-lube the spark advance timer plate.

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