Motor buckin’ a bit

Hey-

My motor is bucking a bit when I open the throttle up. basically when I am moving forward at a minimal clip, it works perfectly. When I open the motor up, it feels and sounds like it is ‘down shifting’. After decelerating and accelerating a couple of times we were able to get the motor humming at full speed.

i am thinking that it sounds like a spark plug issue but am wondering if you have any other ideas on what else could be causing this.

the gas is new, with the correct amount of seafoam.

thanks
Dan

Try new plugs, they are a cheap way to keep your motor running good.

plugs then coil on non-EI motors. B4 check for solid spark at each plug. Also check condenser if you have one.

Dan,

What motor is it?

Merc, Yam, Joh, Suz

2 or 4 stroke

EFI, DFI, Carb

Is this the first time out for the year?

May help the guys respond.

Thanks for the replies:

40 hp Johnson, 2 stroke

Second time out, but it happened both times.

thanks

If it is not shifting properly, maybe change the lower unit fluid. might have water mixed in with the fluid. or old fluid. Maybe not getting the right pressure to shift because of the fluid.

sounds like its starving for gas! if it runs fin at low RPM’s only having problems getting it to open up then you have fuel supply issues! could be clogged jet or maybe lift pumps going bad!(if that motor has them) basically there is enough passage or supply for lower rpms but when she gets hungry the waiter is a little slow!

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If it is not shifting properly, maybe change the lower unit fluid. might have water mixed in with the fluid. or old fluid. Maybe not getting the right pressure to shift because of the fluid.

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I really hope you are kidding… Its not an automatic transmission like on a car nor hydrostatic.

From your descriptions its hard to say. Everyone has different terminology. When you say “bucking” I think of a miss fire on a cylinder. When an engine misses it will cause the motor to slightly jump or “buck” to one side till that cylinder fires next REV. Misses can be electrical or Fuel related. Electrical misses can be spuratic if the part it failing of a connection is loose or when a coil gets hot. But generally you will know it is electrical if the motor jumps or shakes irregularly.

However thats not to say it cant be fuel. If it is a 2 carb system one cylinder can miss too. The difference is it will happen when RPM are changed. (jet clogging) One tell take sign of fuel starvation is loss of power when you alter the RPM. Such as engine runs fine trolling but will then “dog” when you try to accelerate or plane out.

keep in mind just because you use seafoam does not mean you cant clogg a jet with dirt or fuel breakdown. I personally dont believe in the stuff.

If it ran fine last season and you left gas in the carbs all winter, id bet you need the carbs cleaned. Always run your motors dry when not in use for longer than 2 months. Im sure some will disagree with that but I ask, How many carbs have you cleaned in your life?

also if it were plugs or coil it would be sputtering and misfiring!@ if it just seems to slow down and sound like its sucking more air and not missing its fuel supply!

Could be drawing air. Check both connectors on your hose.

I would check gas line for cracks also, and primer ball

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I would check gas line for cracks also, and primer ball

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i had a 75 hp johnson that did the same thing..old gas line with cracks i could not see..replaced and it was solved.. a cheap fix

Thanks for the responses.

I will replace the plugs and fuel line and see if that solves the issue. Hopefully so because I don’t know how to clean the carbs unless that means just fogging them.

Dan

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Thanks for the responses.

I will replace the plugs and fuel line and see if that solves the issue. Hopefully so because I don’t know how to clean the carbs unless that means just fogging them.

Dan

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Normally a miss under load such as accelerating is usually caused by bad plugs or coils. You are on the right track.

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Thanks for the responses.

I will replace the plugs and fuel line and see if that solves the issue. Hopefully so because I don’t know how to clean the carbs unless that means just fogging them.

Dan

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Normally a miss under load such as accelerating is usually caused by bad plugs or coils. You are on the right track.

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Normally, I’ve also found engines need fuel to run.

Mechanic by comittee.

I’ve had both kinds of problems myself but I’ve yet to fix one just with new spark plugs. I know it is possible. A spark tester is like $5 and you actually see what is going on vs throwing parts at the problem.

I had a similar problem, had a 13* prop and it was tripping the deliminter switch and back firing, installed a 15* prop and all is good..

So today we put in new plugs and are still having the issue. We could find a fuel line at the store we got the plugs so we did not replace that.

If we need to look to clean out the carbs, can someone tell me what I would need to do?

Thanks for all the help, I appreciate it.

Dan

replace the fuel line!!!!

In the next couple if hours we will see if the replaced fuel line was the culprit. Let’s cross our fingers.

Thanks again for the help.

so we replaced the fuel line and still are having the issue.

There are times when the motor runs great on full throttle but other times it won’t go.

Could this still be the old gas working it though it? we have had it running for about 30 minutes overall in the four outings.

Do you have any other ideas on what this could be or what we should try next?

thanks

Siphon the old gas out and start over with clean new gas.
Then when you are done, use the old gas to start fires…

we replaced the whole fuel line, connectors and gas. This did not have any effect on how it ran.

Is the next steps that think we should look at is the carborator?

Thanks….quite frustrating to say the least as we didn’t have any issues last year

Could be that the power pack is taking a dive?I would check all the connections.I would check the ignition components before taking the carbs apart.

My 35hp Johnson pontoon motor was acting up similar to your issue. Finally found out that some engine paint was partially (intermittently) insulating the grounding of the power pack….removed power pack, sanded the paint off, re-installed and no problems since.

Well, we brought the boat into the shop and they told us it was the switch boax that control the electrical and not the carbs or anything else.

We are having them replace this and then load test it to see if this solves the issue. (it better )

hopefully this will solve the issue.

I’ll keep you posted.

thanks for all the inputs

I had a couple 40HP Johnny and Evi 2 cylinders. tough as nails! Don’t forget about the gas lines under the hood. they tend to be over looked quite often. There are several that are very easy to replace. The carbs are super simple to rebuild see youtube for more video info. You could also run it with the hood off and have someone spray carb cleaner on the internal fuel lines and carb bases while running to see if it changes the idle speed ie. leaking air into system. Let us know what you find out.

My # tip is ALWAYS run Non-Oxegenated gas in all of your small engines! MSRA website has a Non-Oxy gas station location list.

Ferny.

As my Bro Dan K indicated the switch box was replaced and the boat ran great – for two trips out. On the third trip out, the motor once again was not powering up in gear and only going forward at an idle speed.

We disappointingly brought it back to Supreme Marine and they indicated the Stator went bad now, most likely due to the switch box being replaced and putting out cleaner/stronger amperage to downstream parts. Apparently not uncommon to have this “downstream failure” after replacing upstream parts – after all the motor is almost 20 years old.

Supreme Marine expedited the fix on the stator and the boat has been running awesome again. Unfortunately for us, we have dropped nearly $1000 in fixes here…Aside from this major debacle, it’s been a very reliable motor and just probably due for some failure after having this for 8 years without much of any issues.

Oh well – nice to have a fishing partner to share boat costs with! Case closed!

Catchin’