Tohatso/merc idle guestion

[OLDIRON]

I have a 1995 Mercury/Tohatsu 5hp.And I have a question on how smooth these 1 cyl motors are suppose to idle.It has always run a bit rough at idle, but smooths out at high speed.My '74 15 hp ,and '58 3hp Johnson run smoother than this Merc at idle.Do all 1 cyl motors run like this? I don't know because I have nothing to base it on.It seems like it bucks and has alot of vibration,but it's always ran that way.I bought it used,from someone I know,and it has always been well maintained.New plug,new fuel filter.There are no points to deal with.Has very good spark.Actually, the motor looks like new.I've only taken it out two times.You can let this motor sit for months, and it will start on the first,or second pull,after that,the first half pull.As a matter of fact, you really have to lay on the red button to kill it. Your input please,thanks.

 

[TOHATSU GURU]

Re: Tohatso/merc idle guestion

"Normal" is based on the experience level you bring to it. All one cylinder engines vibrate, some more than others. The Tohatsu doesn't normally do so anymore than most.

 

[OLDIRON]

Re: Tohatso/merc idle guestion

That's just it,I don't know what normal is for this motor.I have only experience with two bore Johnsons.I have spoken to the fellow I bought it from,and he told me it always ran like that.So I guess what you are saying is that a one bore will never be as smooth as a two no matter what the make.Is that right?It smooths out great at WOT,or less,but at idle, it's not.I have the original owners manual that came with it,and adjusted the idle as per specs.850-1000,and slow speed jet somewhere between 1 1/2 and 2 turns out.The only thing I don't know is the air gap between the pickup and the flywheel spec.thanks.

 

[TOHATSU GURU]

Re: Tohatso/merc idle guestion

It's a matter of perspective. For example:

Boater A has your engine, has only used a one cylinder before and thinks your engine runs smooth.

Boater B has your engine, has used dozens of small engines before and thinks your engine runs like a one cylinder.

Boater C has your engine, has never had a small engine and thinks it's about to blow up.

All have the same engine, but each one brings to the party their previous experience and that is how they view the engine. That's why it's difficult to determine from your question:

"Do all 1 cyl motors run like this? I don't know because I have nothing to base it on.It seems like it bucks and has a lot of vibration,but it's always ran that way"

It's relative...Your engine might be running rougher than the baseline of "normal", but without seeing it I can't tell. Instinct and probability tell me it's normal, but I can't know with certainty on this one.

 

[pvanv]

Re: Tohatso/merc idle guestion

Elvin's right. As a matter of perspective, the more cylinders, the more "pops" per revolution, smoothing things out. An idling 1-cyl inboard diesel has been known to shake the lifelines loose on a sailboat, BTW.