Home › Forum › Ask A Member › 1957 Big Twin 35hp questions oil, engine "Bucking"
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pappy.
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June 9, 2015 at 6:10 pm #1723
Hello Everyone,
I recently took my boat out this weekend, and I mixed my oil/gas at 50:1 accidentally, but the engine started up on first try, and ran really really well. I used the Pennzoil Premium Plus Marine synthetic blend, and ethanol-free gas of course. I only ran the motor full throttle a few times for just a few seconds or so because there was a lot of big wake, and I don’t like the hull crashing around hard…it’s a wooden runabout. I mostly just puttered around at slower speeds, and was running for about 3-4 hours for the whole day, stopping often to relax.
Could I have messed the motor up buy running the motor so lean for just the one day, and should I absolutely go back to a mixture of something like 35:1 forever?
*****An important question: Sometimes while I’m running the motor, I’ll notice the engine "buck" a little bit, and it will do it every 5 seconds or so. It doesn’t happen all the time, just sometimes then it will stop "bucking" and everything is smooth as silk.
It doesn’t seem to matter what speed I’m going, but sometimes it’s like there is a second where there is maybe no gas (or air) getting to the engine, and you’ll just feel and hear the engine "buck" a little bit…it’s like a quick "shock", as if a water skier is quickly and abruptly pulling hard on the ski rope…you know that feeling?
The motor never throws out of gear or anything like that, so it’s not the lower unit gears. Any ideas on what that could be? I noticed it a few time last season as well, but overall the motor performs like a champ!
Thanks for any and all insight guys!
Danny
June 9, 2015 at 6:46 pm #17862the bucking is a lean sneeze, turn the mixture knob a little richer and that should stop the bucking, turn it a little at a time while running under load, you will find a spot where it runs good and smooth. As for the mixture not familiar with that motor so will let someone else answer that.
Doug
how is it motors multiply when the garage lights get
turned off?June 9, 2015 at 7:57 pm #178631957 I would run at minimum 24:1. If it were mine, I would would go even richer than that, but that is not required…
http://www.richardsoutboardtools.com
classicomctools@gmail.comJune 9, 2015 at 9:07 pm #17865Run her at 24:1
Adjust the needles as follows. With a helper, run at Wide Open Throttle. Then, turn the high speed needle in, clockwise, until it wants to die down or lose RPMS. At that point, back it back out, CCW, 1/4 turn.
Then bring motor to a low idle. Do the same for the low speed needle, the top one. Turn in, clockwise, until you hear it lean sneeze (what you heard). then back it out 1/4 turn.
The initial static settings for the needles are 1.5 turns out from seated for the low, and 3/4 out from seated for the high. those are the starting points. Then tune from threre.
As stated though, sounds like you need to richen up the needle a 1/4 turn or so. After you have them dialed in, take off the dials, and re install so that they point in at one another. Then tighten down the packing nuts, 7/16" nuts behind them. That will keep them from moving, and having them point in from one another will let you know if they got bumped or moved.
June 9, 2015 at 10:04 pm #17866Well, today’s oils are a lot better than what was available back in 1957, so I really don’t think 50:1 did any harm. And, I don’t think the bucking is related to the 50:1 mix.
If the engine seems to buck at high speeds as well as low speeds, my guess is the problem is ignition related. But, I have to ask how you know for sure that the engine is not jumping in and out of gear.
Is the engine electric start? If so, I would use a timing light to monitor ignition performance when the engine "bucks". This test is best done at dawn or dusk when the light is more visible. Clip the timing light to one spark plug wire at a time, you will probably need to remove the cover completely in order to connect the timing light and not pinch the lead. Have an assistant run the boat while the engine is bucking and watch the timing light. If the light is intermittent while the engine "bucks", then the problem is ignition related. Repeat this process with the other cylinder as well. Keep in mind that the timing light will be intermittent if you have a bad spark plug, so please to overlook the simple stuff. I suppose the vacuum switch could be causing ignition problems as well, but this probably would not be happening at higher speeds with the carb butterfly mostly open (least amount of vacuum to the switch).June 10, 2015 at 1:49 am #17878Thank you all for the feedback and guidance! I’ll take this advice and see how it works out. As far as the 50:1 mix, I can’t imagine the engine was damaged in any way recently. It ran so nicely, and really clean…If there was a problem, wouldn’t I have seen some problems?
I won’t do it again, and will go back to my 35:1 ratio…I truly believe that mix is absolutely perfectly fine.
Take care, and thanks again!
June 10, 2015 at 1:59 am #17880re: the bucking. Does it feel like you hit a submerged log? Sometimes what gets described as bucking turns out to be a clutch dog problem in the lower unit. The bucking is actually the engine slipping out of geat…and then immediately re-connecting. Worn cluth dog and/or gears…or if you’re lucky…just a linkage adjustment.
Or; if you’re **really lucky** it’s not gear related at all…but more what the other guys are describing as a lean sneeze.
Hope you’re really lucky lol….
June 10, 2015 at 2:20 am #17885I just had the lower unit rebuilt because my skeg was cracked, and I found a good unit from a 1957 Johnson Seahorse 35hp. My mechanic used the new gears as mine were a little worn, and the shift dog, etc. were all fine. He interchanged a few items..he used the best from both motors.
It doesn’t feel like hitting a submerged log, it’s as if the engine switched into reverse at high speed for 1/2 a second, then corrects it self..It actually feels like and sounds like an air pocket makes it’s way into the engine, hiccups, then catches the fuel and back to normal…the gears never slip at all…ever, and I can shift really smoothly (although I jerk it quickly at idle as I’m supposed to) but I notice I can push the lever into gear a lot easier than last season since the lower was rebuilt.
June 10, 2015 at 12:58 pm #17903OK, if the engine is loosing RPM momentarily when it "bucks", this is not a clutch dog issue. Have you tried new plugs? Just cuz the plugs are new, doesn’t mean they are any good. Next, try the timing light to monitor ignition performance.
June 10, 2015 at 1:27 pm #17908It’s funny, but I’ve had the boat for 2 years now, and I have never changed the spark plugs…I’ve checked them before, but never changed them. Perhaps I’ll do that today and see what happens.
Thanks!
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