Tohatsu M70A slipping

[Yuccagrub]

Tohatsu M70A intermittently will rev high rpm and not propel boat. I have replaced the dog assembly in lower unit had the rubber hub replaced in the S/S prop. I am not sure about the proper direction of the dog assembly (no manual) The prop appears to be in good shape 10.5 x 13 according to prop tech. the boat is a small 17' cajun bass boat. It is intermittent if you pull back on the throttle and ease into it some times it will take off normally. Any ideas??

 

[pvanv]

Re: Tohatsu M70A slipping

That's an oldie.

TG's website has a parts catalog that is probably the right one at http://www.internetoutboards.com/Pa... Catalog NS50C-60A-70A2 (1992) - (M256B).pdf

In my experience, these problems are seldom the clutch dog -- it's pretty much either in gear or not. I would test with another prop, just to confirm that the rubber in this one is in fact OK.

That aside, it's possible that you are ventilating -- sucking air into the prop stream when you jam on the throttle. If you ease on the throttle and can always achieve full speed that way, check that your rig is low enough in the water and properly trimmed.

 

[TOHATSU GURU]

Re: Tohatsu M70A slipping

Might be the gear facing. Since parts are no longer available for that model lower unit I would urge you to think long and hard about putting money in to it.

 

[Yuccagrub]

Re: Tohatsu M70A slipping

Thanks for the replies. I tore into the lower end again this weekend it all looks in new condition and after looking at the part catalog everthing is in the right place. I did mark the rubber hub compared to the prop. We will see if it is staying in place. I would add when trying to accelerate the trim is all the way down and the prop is well below the bottom of the boat. Can the prop pitch be changed? Would moving upp to a 14 make a difference or should it be 15 on the pitch? How would you determine if it ventalating? Thanks Again for the help.

 

[pvanv]

Re: Tohatsu M70A slipping

A prop shop can re-pitch your wheel if needed. Changing from 15 to 14 will give more RPM for a given boat speed. Selecting prop pitch is always a trial-and-error technique, on a boat-by-boat basis. You will want to know the WOT RPM to determine if you are in the proper range in order to decide what if any pitch changes to make.

If the wheel is really low in the water, it's probably not ventilating.