Trolling Idle seems too low or too high, Tohatsu 9.8 2008

[Fishn4Funn]

I should preface this with the fact that in describing my problem I may not be aware of the proper terms so please understand I am trying without being too wordy.

Most of my fishing is done trolling yet when in neutral warming up, the idle is fine when using the warm up lever on the remote. However when I put it in forward gear, it knocks way down so I have to move the gear/throttle lever ahead so much that suddenly it is trolling at 3.0-3.5 mph land speed at its lowest forward movement, otherwise it shakes and occasionally chirps unless I idle up the set screw. That's way too fast for what I need.

I have rebuilt the card and fuel seems to be delivering nicely. I can see at the top of the engine the auto choke sensor (?) moving in and out as needed, so I know that works. I have installed new remote cables and they are smooth and easy to move. I have the idle screw at the carb, set so it is only 1/8" protruding on the idle plate, and the set screw which connects to the black throttle arm I have perhaps out of proper adjustment. This is the arm which one can rev up the carb by simply sliding the stainless rod an inch or so but must release quickly so the rpms aren't too high.

What I don't know, and this may or may not be my problem, is how many turns the end of remote cable connector needs to be spun in or out. One way gets me to within 1/4" of threads showing and the others shows 1" of threads. Somewhere in between is correct and this is what I don't know.

Motor is 2008 Tohatsu MFS8 9.8 with a white 3-blade prop from the factory as stock. I rebuilt the carb because it sat for a year, so I keep fuel stabilizer in every tank fill up.

 

[TOHATSU GURU]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

It can be anything at this point. Get it in to a dealer and let them determine what the problem is.

 

[pvanv]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

Or... grab a Factory service manual (available from any dealer, including me), and go through the rigging and carb correctly.

The idle should be set to 950 in N, 900 in gear, with the stainless throttle rod free at the loop end. Then the throttle rod is adjusted so that there is nearly zero clearance at the loop end, with the RC cable disconnected. This assures that idle is set by the screw, and not by the RC cable or throttle rod. Then... The throttle cable clevis should be dialed-in to zero clearance on the throttle arm when the motor is at idle and the RC lever is at neutral. That is accomplished by disconnecting the clevis and verifying that it just slips on and off the arm without any interference. Then re-install the R-clip.

In many, many cases, a carb with idle-passage varnishing will not idle down correctly to 900 in gear, and thus must be set to idle too fast to keep running. If, when you went through the carb, you did not soak it in real carb dip for 4 hours and then blow it out with aerosol carb cleaner afterward (and then reassemble it), that may be why you have to set an idle that is too fast.

Once that is all straightened out, if the prop pitch is too high, you may troll too fast. If that is the case, then consider lowering pitch, or switching to a High Thrust, low-pitch (4-blade) prop.

 

[Fishn4Funn]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

Thanks, TOHATSU GURU, but that's not the kind of help I registered at this forum for. Even a link to some reading would have been appreciated. But I can understand how many times you have helped others and I should let you know I did read a fair amount before I asked my question.

 

[Fishn4Funn]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

Thanks Paul, I'll try again following your instructions. I appreciate the thoroughness you have gone through and the great detail which should help my Son & I in dialing her in. We'll adjust this morning then take her out in the water for a full test. Many thanks.

 

[pvanv]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

Not a problem...

Keep in mind that you need a good shop tach to get that idle dialed-in. And... even though it's a 2-cylinder 4-stroke, the siamese ignition coil fires both cylinders every time, so there is a "wasted" spark on the exhaust stroke. That means that if using an induction tach (or any ignition-triggered tach for that matter), there will be a spark for each revolution of the crank, not one spark for every-other revolution, just like a 2-stroke motor. If you have a tach that can't be set for those conditions, you may show 1900 rpm in N and 1800 in gear. And you MUST be in the water to get good tach readings. It is still very possible that you will find that you are unable to get a good, steady idle at the right RPM. (I'm basing that thought on your notation that the motor sat for a year, and that you installed a carb kit.) If that's the case (varnishing in the idle or transition circuits), no rigging adjustments will fix the issue. The carb must be dialed-in correctly before the controls are introduced into the picture.

In Elvin's defense, I believe that he tried to help you based on your descriptions and probable resources. Since you didn't mention having the Factory service manual for the MFS9.8A3, and probably didn't understand how the RC cables (for any motor) should be setup, it was clear that you were working with one hand tied behind your back... starting to get in above your head... as far as resources and experience go. So... for him to recommend a dealer's assistance wasn't out of line. There are reasons that Tohatsu America requires dealers to install the RC motors, and does not allow them to be sold "in the box". To the uninitiated, the RC setup can easily be botched, ultimately causing bad problems, maybe even a blown-up motor, or loss of life. Fortunately, it isn't really rocket science, and it's quite reasonable for a person with average mechanical skills, decent tools, and the Factory service manual to learn how.

 

[TOHATSU GURU]

Re: Trolling Idle seems too low or too high, Tohatsu 9.8 2008

Thanks, TOHATSU GURU, but that's not the kind of help I registered at this forum for. Even a link to some reading would have been appreciated. But I can understand how many times you have helped others and I should let you know I did read a fair amount before I asked my question.

My Three Rules:

1) Look in your service manual first.
2) Have basic mechanical skill.
3) If you are confused, take your engine into a dealer.

You have failed on all three...