8hp engine cuts out while switching gears
Posted by PhillySpecialist@reddit | sailing | View on Reddit | 15 comments
This is almost certainly due to user error. I am a beginner sailer. I just purchased a 1970s trailer sailer with a 2000s 8hp 4stroke Honda outboard.
The engine starts right up and runs great except for one issue. Occasionally, when I switch gears, specifically into reverse, the engine cuts out. This is bad for docking as I am still learning and therefore switch gears a lot while trying to get in and out of slip. Is this issue caused by me switching gears too quickly and not waiting in neutral for a second? Admittedly I am in panic mode while docking so it’s hard to think clearly. I do go slowly while docking, probably too slowly.
Is there any mechanical problem with the engine that would cause this? Again, I am assuming it’s just me.
Atomic_meatballs@reddit
This could be caused by your engine's idle speed being set slightly too low, so when changing gears at idle throttle, the engine it juuuust at the cusp of stalling, and sometimes does stall.
However, the more likely culprit based on your description is that you are likely going directly from reverse to forward or forward to reverse without stopping in neutral.. Best practice is to pause for a few seconds in neutral to let the prop stop spinning before changing direction. If the prop is still spinning backwards, and you shift directly into forward, there will be extra load caused by the engine having to stop and reverse the shaft immediately. (Not to mention, shifting directly without a pause in neutral is really hard on the gear box).
I would try shifting more slowly, and pausing 3-5 seconds in neutral when shifting from forward to reverse. Take your boat out to some open water, and practice shifting forward and backward a bunch while you have plenty of sea room, and see if shifting more slowly with a pause in neutral reduces stalling.
(This is also a good time to practice your boat handling skills under power. Get a feel for how fast you can stop your boat in an emergency. Get a feel for backing your boat under power , for example, backing up into the wind, back with the wind, backing in a circle and/or figure 8, against current, with current, etc). Sailboats do not back well under power, so experience here is extremely valuable.
The more practice you do with boat handling and shifting gears in open water, the better you will feel about approaching the dock. Generally, you want to figure out issues either tied safety to the dock, or in open water. Approaching the dock is not the time to be worrying about issues like this.
If the stalling continues, even when pausing in neutral, than you may need to increase your engines idle speed a tiny bit. This can be done usually via a screw under the engine cover. Don't set it too high, or you will be roasting your gearbox every time you shift.
PhillySpecialist@reddit (OP)
Thank you for this thorough response. Out of curiosity, can you provide some more detail about what causes an engine to stall when shifting gears too quickly? Is it overheating? What exactly do you mean by extra load? I understand how it would damage the gear box. But I also want to understand how it stalls or cuts out as a result of gear shifting.
PepperTop9517@reddit
Think of a manual transmission car, you don't slam it in reverse you bring the car to a stop, stift to neutral then to reverse. Similar here, you shift from forward to neutral, to reverse. The wheels are the prop. In forward it turns one way and in reverse the opposite. Shifting from first to reverse without stopping the car will put extra load on the wheels, driveshaft, gearbox and engine because they are all coupled together.
The stalling can be an issue with engine speed to prop speed. Again think of the car, say you're going 5mph forward, then you shift into 2nd gear, the engine stalls because the engine speed isn't fast enough for the gear desired. Similar to the boat, it stalls because the engine speed isn't enough to overcome the force required to get the gear box spinning.
A test you can do is take the boat out into the lake, put the boat in forward at idle, then shift to neutral, then to reverse, if it stalls, restart but giving it slight throttle, just above idle then do the exercise again, once you find the point it doesn't stall you then know what the engine should sound like at idle in neutral and can adjust the screw the other poster mentioned.
Atomic_meatballs@reddit
I am not an expert here, but high level - it takes less power to start moving a stopped propeller, than to reverse a propeller that is moving in one direction.
The engine idle speed should be such that the engine can idle in neutral, shift into gear, and continue idling in gear. Therefore, it needs just enough RPM to overcome the inertia of a stopped propeller.
Shifting directions without letting the propeller stop meanings that the engine's output must be used not only to turn the propeller, but stop the propeller and reverse it. The act of reversing the spinning propeller buts a lot more load on the engine than simply starting a stopped propeller. If the engine idle speed is not high enough to overcome this extra load, the engine will stall.
As an example - think about a human pushing a car on flat ground. It is hard to do, but doable. Now, thinking about a human stopping a car that is already rolling, and pushing it back the other way. It takes A LOT more energy to stop and reverse the mass of a car (or propeller or whatever) than it does simply to start moving a stopped mass. The whole "things in motion want to stay in motion" etc.
The faster the propeller is spinning in one direction when gears are reverse, the more mass the engine has to stop and reverse. And because of how gears typically work in outboard engines, that load is applied instantly to the engine. If this load exceeds the engine's torque at idle, the engine will stall.
There could be something else happening - like shifting too quickly is causing the gears to bind up and stall. However, I suspect that reversing the spinning propeller instantly is putting more load on the idling engine than it can overcome.
PhillySpecialist@reddit (OP)
Thanks! Your comment on load exceeding torque directly answered my question.
jzwinck@reddit
An 8hp engine only produces 8hp at fairly high RPM. At idle it makes very little power, let's say 0.05hp. That is enough to keep it turning over, but maybe not enough to start the propeller spinning.
Higher idle speed (which is a common adjustment) means more power at idle. Obviously you don't want to overdo it or you'll waste fuel and make the boat harder to control at low speeds.
Dwight_scoot@reddit
I came here to say exactly this. But there is no way I would have done it so throughly.
Nice work!!!
Atomic_meatballs@reddit
Thank you! I am happy to help a new boat owner. I spent a season with an outboard with too low of an idle speed, and it caused all sorts of stressful situations via poorly timed stalling. It took like 10 seconds to increase the idle speed once I looked up how to do it.
drroop@reddit
I'd assume it is bogging down from idle when switching to reverse.
You can't really shift it slower. Moving the lever slow just grinds the gears. A second between forward and neutral isn't a bad idea, but it doesn't take too long for the prop to stop spinning. If you shift it, and it is cutting, might be there's not enough fuel or whatever to have it fight the prop, it bogs down and stops. Like letting the clutch out too fast in a car without giving it throttle.
Try shifting it with the throttle just a touch above idle, or get on that throttle quick after shifting.
New spark plugs are a cheap and easy way to make outboards happy and solve a lot of woes. Sea Foam is nice too. Fresh gas, all the normal things. Maybe take the carb off and clean it.
In theory, you shouldn't need reverse coming into dock. Try to judge the speed, and put the motor in neutral a few boat lengths ahead of time, so your speed coming into dock is not too fast that you can't stop it with the stern line. If I need to reverse when docking, I consider that a failure of mine.
I had a 70's vintage sears 5hp. No gear shift, if the engine was running, the prop was turning. To go from high speed to low speed, you had to re-adjust the mixture, which only worked about half the time without stalling it. So, I'd come in toward the dock in high speed mode, and kill it. Then drift in toward dock. Trick was to read the conditions to kill it at the right time/speed. Erring on the side of too slow just meant skulling the last few feet, so I'd tend to shut it down too early, as it was less risky. Too fast is damaged fiberglass, too slow is only a problem if it is really windy and the boat gets away from you before you get in, but in that case, you can just fend off the other side.
This horrible motor made me a better sailor, either from doing that, or having to sail all the way into dock. I couldn't count on the motor, so I'd have to rely on the sails.
PhillySpecialist@reddit (OP)
I am pretty confident docking a power boat (90hp to 150hp bow riders and deck boats) and I do that by clicking in and out of gear (including reverse) as I approach. Do you shift gears less with a sailboat?
drroop@reddit
I occasionally dock a pontoon, and the engine is more important, as you need power to steer, and without a keel it is more likely to be blown sideways. So you drift in slow, and click it in gear if you need to adjust position left or right. Using the power to steer though increases your speed, and so you need reverse at the end to stop.
With the sailboat, you can steer with the rudder even if you are moving relatively slow, and the keel helps to keep you from being blown sideways, so you need less engine docking a sailboat than you do a power boat.
kmg6284@reddit
How old is the gas and does it have ethanol? Nothing beats a few gallons of new ethanol free gas in a small outboard. I have 3.3 hp merc 2 stroke
PhillySpecialist@reddit (OP)
I don’t know. It had gas in the can when I bought it a few weeks ago. Could be from beginning of season in April. It’s getting hauled out in another few weeks at which point I will take the engine in for full servicing.
jh937hfiu3hrhv9@reddit
That is odd. I would look at the mechanism while shifting gears to see if it is hitting a wire.
bernoulli33@reddit
Outboard engines have two keys in the carburetor. One for power and a smaller one for idle. The idle sounds gummed up for you. Fortunately, someone on YouTube has a tutorial for disassembling and cleaning the carb on your exact motor.