Tohatsu 20hp rev limiter or timing?

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

Its a Valco U12. I boats puts it at 125lbs boat only. Its the only model with a 64 inch beam and the only model that rates a 20hp. Is it possible that a ss prop of the same picth as an aluminum could be that much faster to where your having to adjust linkages to not hit the rev limiter? Or do you suspect there may be something else going on here?

 

[Sea Rider]

Re: Tohatsu 20hp rev limiter or timing?

Don't know Tohatsu 4 strokes, only work with 2 strokes. Are you playing with timing stoppers & nuts limiting max carb aperture ? Only work with standard original alum props. That issue will need to be investigated by yourself under trial & error with a tach.

Happy Boating

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

Thanks pvanv, if your saying don't put it in gear and run it above idle out of water no I won't do that. The rev limiter kicked in in nuetral. If this is bad too let me know but I'm assuming netral in the water is the same as nuetral out of water. Iether way the CDI box should read the rpms in gear or not. Its just picking up the frequency from the pulser coil if I'm not mistaken? But I do see your point about running it no load. I re mounted my trolling motor and bought 2 new anchors so I'm headed out on the river now to see what I can do. Cross my fingers, hopefully its enough. If not, iboats will have another order request for another prop. Its spring time, I gotta be on the water

I am saying that if you run above fast idle, you must be in gear, in the water, under a load. Otherwise, you could scatter parts of connecting rods everywhere, along with bits of engine block and crankshaft. Quite the shrapnel.

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

Its a Valco U12. I boats puts it at 125lbs boat only. Its the only model with a 64 inch beam and the only model that rates a 20hp. Is it possible that a ss prop of the same picth as an aluminum could be that much faster to where your having to adjust linkages to not hit the rev limiter? Or do you suspect there may be something else going on here?

Clearly you need more pitch than you have. Period.

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

Got it on the water, total load weight was around 550lbs. I got it to run just under 6100rpms at the normal speed it always has been with a 10 picth prop (24-25mph). Here's my question though, when I first had the motor with an aluminum 9 1/4 x 10 it would run wide open with the carbureator throttle lever just about all the way against the stop post on the carb. Now with this prop I'm having to slide the lock collar and screw farther up on the throttle linkage rod so that when I turn the tiller handle all the way it moves the carb throttle lever to about 1/2 inch of the stop post. Its kicking in the rev limiter when I try and set it so it moves past that. This new prop is a 9 1/4 x 10 only its ss. It couldn't make that much of a difference could it? When the throttle is at its lowest idle, where should the knob be inside the throttle rod? The rod has an oval loop at the end where a wheel and knob rotate to move it. Ill try and post some pictures to clarify

As I said in post 17, "Your throttle is correctly adjusted when it ranges from idle to completely WOT at the carb, without any additional cable or throttle rod adjustment." If you are adjusting the throttle rod so that you are not making it all the way to WOT, even when the tiller throttle is advanced all the way, you are going about this all backwards. What you need is a correctly-pitched prop, and the throttle properly adjusted so that WOT on the tiller handle opens the carb butterfly all the way to WOT.

 

[Sea Rider]

Re: Tohatsu 20hp rev limiter or timing?

What don't get is : why do you want to be on the max rpm stated for that engine, are you going to race against other mates, keep in mind that going that extreme will loose best hole shot, worst with added weight, passengers. Not justified to achieve 3-5 miles per hour at most at wot while burning more gas.

Personally would stay with a prop that gives me above middle range rpm, SS or alum, the one you like best. Will have best hole shot with slight less top speed, anyway nobody runs at wot all the time, gasoline is already expensive. As recommnded by Paul, put back your throttle setting to factory specs and just play with correct prop pitch.

Happy Boating

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

I understand what your saying completely and all the current things point towards that. I will end up having this prop adjusted or just buy a different one. I just don't understand how over time it could have started hitting those higher rpms when I've been running 10 pitch props on it the whole time and the load its been pushing really hasn't changed a whole lot over time. The Tohatsu prop chart says that I'm propped right for the load I'm pushing. If I switch back to an aluminum prop should I stay with 10 pitch or go to 11? I know if I stay with ss I should go to 11. That's what I'm wondering about now. I'm not really trying to race or anything. I just want a rig that can get up on plane and cruise well with a load between 500 and 700 pounds. That's what I had to start with. I could really care less if it goes over 25mph. That's what its had the whole time and I'm fine with that.