Tohatsu 20hp rev limiter or timing?

[fishndirk]

Anyone know what it sounds like when the rev limiter kicks in on a motot when it engages? I have a 2010 Tohatsu 20 hp 4str that after 6 months started making a sound at the very top end of rpms. I have switched to stainless steel props since then and now it does it even more. Lately its getting to the point where I'm having to adjust the throttle linkage so that the carb does not open all the way when the boat is under a light load. But when the boat is under a heavy load it does not do it at all. I can run it all day just under WOT and no problems but then as soon as you pass a VERY specific throttle position it immediately starts making the sound and tops accelerating. Sounds like the motor misses. I'm a little confused and sick of having to mess with the throttle linkage to get it not to do it. Would it be a timming issue if it only does it at peak rpms? The motor runs very well from idle all the way up to plane

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

Additional notes/better explanation - I broke it in with an aluminum 9 1/4 X 10 then switched to a Solas Stainless 9 1/4 X 10. I damaged that prop so I ordered a new one just like it. Well I guess they redesigned it cause the new one is lighter and the blade shape is slightly different. I've ran the boat once with the new one which pushes very hard and gets the boat up to speed so fast that now I'm having to adjust the throttle linkage to where the carb doesn't open all the way so that it doesn't do the sputtering thing. It did it with the old stainless under a light load and now it does it even easier with this new prop. I'm wondering if the props I'm running arejust spinning too fast for the load their pushing in my boat or if I'm developing a timing issue that is only noticeable at the very top end of rpms if that's possible. Any expert opinions out there? I have no idea what it sonds like when a rev limiter kicks in and can only guess that might be it. My setup is a 12ft Valco mod v which weighs 125lbs boat only, Tohatsu 20hp 4 stroke with a Solas Stainless 9 1/4 X 10 prop

 

[xjma]

Re: Tohatsu 20hp rev limiter or timing?

when you hit the rev limiter, the motor will miss, then catch again, and if it goes right back up past the limit it will continue to do that.

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

So it basically stops the spark as soon as you try to exceed an exact frequency? Meaning if you try to hold it above this position it will continue to run but miss continiously so it does not exceed that value? Would increasing to an 11 pitch make enough of a difference if that is the case? Being that I don't want this brand new prop to become an expensive paper weight can it be "adjusted" at a shop to an 11 pitch? Or should I just leave the throttle linkage so the carb opens fully like its suppost to and just learn to back off the throttle a little when its just me in the boat?

 

[xjma]

Re: Tohatsu 20hp rev limiter or timing?

I'm no prop expert so I'll let someone else answer that but from what I know it sounds like you've got the gist of it, either throttle down or get a different pitch prop. I don't believe that you can tweak a SS prop, only Al, but again, I'm no expert on the subject.

However, I am somewhat of an expert when it comes to bouncing off the rev limiter!! There used to be a nice .gif out there that illustrates it but I can't find it. Here is a youtube video that shows a guy with a car, mind you in neutral, and he has an adjustable rev limiter....some computer adjustability gizmo. Anyways, first he hits the rev limiter at a low rpm, then he cranks it up and hits it, and then cranks it back down. Most people aren't able to do this as the rev limiter is set at the factory within the electronics and you need to know your **** to mess with it. Anyways, whatever the rev limiter is set to, once you hit that RPM, the RPMs will drop and then you'll be able to rev again. In a moving vehicle it feels like someone just cut the gas line....the rpms drop more quickly than if you just let off the gas. At highway speeds in a vehicle if you hit the rev limiter and didn't have a seatbelt on (not a good idea on both fronts, but just saying) you very well could hit your head off the steering wheel. In 4wd low range when you hit the rev limiter, the gearing is so low it's just like someone cuts the gas for a sec and then the wheels are spinning again in a second. Good times.

Here's the vid.
http://www.youtube.com/watch?v=-M6ITkLd-Bc

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

In order to determine whether you are hitting the ESG limit, you must have a tach. No shortcuts here. That video is pretty much correct. When the ESG kicks in, the ignition is staggered, running "rough", until you ease off the throttle to get below the cut-in RPM. If you are exceeding the correct WOT RPM, and the ESG is engaging, you will want a steeper pitch.

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

Thank you, I will look into getting a tach or taking it to a shop to have that checked. Does anyone know what the rev limiter should be kicking in at for these motors? Also, if that is indeed what is going on can I have this stainless prop ajdusted from a 10 to 11 picth? Is there any disadvantages to having that done to a prop? The steepest pitch you can buy for this size is 11 or 11 1/2 as far as I know.

 

[Sea Rider]

Re: Tohatsu 20hp rev limiter or timing?

The factory working parameters for that engine are : 5400-6100 rpm, yes get a tach and full throttle to see at which rpm the engine begins to engage rev limiter. What happend with the prop that came factory delivered, it's supposed to work in the middle range, good hole shot with slight less top speed, a good overall working prop. If you are seeking for more top speed, will loose best hole shot. You cannot change prop pitch, are factory molded. You must make a tach wot test with your boat/engine combo on water not at a shop.

Happy Boating

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

The original factory prop was heavily damaged by rocks when the water level dropped on Nolin River in KY. I took the opportunity to upgrade to a stainless of the same dimensions for a little more top end and better fuel efficiency. It ran very good at first but started making the sound shortly after at WOT. It was barely doing it with a light load however so I was able to overcome it by simply adjusting the throttle bracket where it opened a few degrees less at full tiller turn. I ran that prop for almost 2 years like that and rarely had it hit the rev limit once I found the sweet spot. 3 weeks ago something must have hit the prop while towing cause it had a big tear in the leading edge of one of the blades. I ordered a new one which I THOUGHT would be the same exact prop. NO!!! Turns out Solas redesigned the Saturn (how was I suppost to know) to where it physically feels lighter and has a different blade shape. Well now this new Saturn is turning so fast and geting up to speed so easy that now I'm having to adjust my throttle bracket down again but this time to such a rediculous amount that it may not work for my boat. Wish they would tell you these things before you order it. You would figure if the part number is the same that it WOULD be the same exact thing. I'm reading online that a stainless prop can be adjusted 1 inch in pitch and and 2 inches for an aluminum. If I can't make this work than I basically have a 130 dollar brand new paper weight on my hands. Lesson learned I guess, call the manufacturer to make sure the product hasn't changed. I guess if it won't work ill buy a steeper pitch prop. But tghen do I go with steeper pitch alluminum since they are typically slower anyway? Ughhhhh....

 

[Sea Rider]

Re: Tohatsu 20hp rev limiter or timing?

If the factory delivered prop was working fine, I would buy same pitch, if wanting slight more top speed drop1 pitch, don't know if it's good investment to place stainless steel props on portable motors, anyway, will need a tach to experiment different props and their achieved rpm at wot so not to damage your horse....

Happy Boating

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

The ss prop I had on there before they changed the design actually ran very good for a long time. Because it was the same pitch as the factory aluminum that came on the motor I only noticed a slight increase in top end speed. Where you did notice the big difference was the ability to cruise and manuever in and out of turns better. With the ss you could actually get up on plane and reach WOT then back off the throttle a bit and the boat would stay on plane with much lower rpms and only slowing down a tad bit. The aluminum wouldn't do this. Going from a stainless back to an aluminum will be like going from a fillet minion to a beef chuck. Maybe it got me spoiled but ill try to find a way to make this one work without hiting the rev limiter. And ill get a tach to make sureits still operating within range. If it absolutely can't be done with this new design than I guess I gotta consider other props at that point. Thanks to all

 

[Star]

Re: Tohatsu 20hp rev limiter or timing?

You could always get a fat girlfriend hat will do it!

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

The ss prop I had on there before they changed the design actually ran very good for a long time. Because it was the same pitch as the factory aluminum that came on the motor I only noticed a slight increase in top end speed. Where you did notice the big difference was the ability to cruise and manuever in and out of turns better. With the ss you could actually get up on plane and reach WOT then back off the throttle a bit and the boat would stay on plane with much lower rpms and only slowing down a tad bit. The aluminum wouldn't do this. Going from a stainless back to an aluminum will be like going from a fillet minion to a beef chuck. Maybe it got me spoiled but ill try to find a way to make this one work without hiting the rev limiter. And ill get a tach to make sureits still operating within range. If it absolutely can't be done with this new design than I guess I gotta consider other props at that point. Thanks to all

Typically, an SS prop flexes less than an AL prop, so you sometimes get the effect of a slightly steeper pitch when changing to SS. However, there's no guarantee that your original AL prop didn't have a flaw. It does happen sometimes. Sounds like your most recent "good" prop was damaged... but might be repairable, which might be an option, if the local prop shop has a good tig welding setup, which they should.

If your new replacement prop is the same spec, it should indeed work the same. If not, I would see if you can get credit for it towards one that does work the same. At a minimum, have the local prop shop check it. After all, it's always possible that you got a bummer, or one that is off pitch, and incorrectly marked/boxed. The folks in the prop forum here on iBoats may be able to advise you more in that area.

Regardless, if you are exceeding 6,100 RPM, that ESG has saved your bacon, by keeping the motor from flying apart due to over-revving. You will know more once you connect a tachometer. The Factory tach is Part# 3AC726400M, $77.96, available from any dealer, including me.

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

LOL! Star....what if she eats all the snacks out of my cooler while I'm getting bait in the water?.......I couldn't find a contact number for Solas, just an e mail which I sent and I'm waiting for a reply back. I'm also having the closest tohatsu mechanic look into the cost of having the prop adjusted which he said they outsource to do. If I can't gain any ground there ill take the boat out again soon, this time with a tach and see if I can find a throttle setting/weight distribution that will allow the motor to run within range without hiting the rev limiter. So as long as th rev limiter is cutting in somwhere between 5400 and 6100 than I'm good right? And all I need to do then is find a throttle linkage setting which brings it just under that at full tiller turn and I should be straight? Please somebody correct me if I'm underthinking this...

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

Assuming you are over-revving... yes, that would keep you within RPM specs... however, you would not be developing full power. Sort of like shifting your car into 2nd gear, and staying off the gas pedal. The best answer will be a prop that is correct for your boat and motor.

 

[fishndirk]

Re: Tohatsu 20hp rev limiter or timing?

Update - got a tach and ran my motor in the driveway on the muffs. Rev limiter is kicking in at 6380rpms. This seems a bit high to me but maybe its right. 2 questions remain now. 1. How was it reaching this speed on the water? According to the Tohatsu prop chart I'm right on the borderline of needing an 11 pitch prop when I'm by myself in the boat. I did tinker with the throttle linkage back when I had the aluminum prop on it to get the most of it. Is it possible that this weight/prop combo is just too light for what its capable of. I can easily just add a little more weight, even when I'm by myself. 2 - will I be able to adjust the throttle to run within range if I just add a little weight. I would rather my boat be able to handle a little more gear anyway and not have to be so picky about what goes on board. Ill take it out on the water tomorow and give all this a try now that I have a major piece to the puzzle

 

[pvanv]

Re: Tohatsu 20hp rev limiter or timing?

Don't, I repeat Don't, run the OB without a load on, at anything above a fast idle. Very bad things could happen.
Don't, I repeat Don't, run the OB without a load on, at anything above a fast idle. Very bad things could happen.
Don't, I repeat Don't, run the OB without a load on, at anything above a fast idle. Very bad things could happen.

Yes, it would normal for the ESG to engage maybe one or a couple hundred RPM above redline. Also keep in mind that not all tachometers are 100% perfectly accurate, so 6380 on the tach might well be 6200. Regardless, you have now verified that the ESG works, and that it is probably the limit you have been reaching.

The 3BAB645241 is an aluminum 11.5" pitch Factory prop, which would slow down your WOT RPM's some. There are also aftermarket and SS props in that range, as well as 4-bladed models. Your throttle is correctly adjusted when it ranges from idle to completely WOT at the carb, without any additional cable or throttle rod adjustment. Assuming that your prop has not spun a hub, your rig may just be a little light. In that case, yes, you could add a cooler of the beverage of your choice, and maybe some ice, to help stay in range.

 

[fishndirk]

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

 

[fishndirk]

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

 

[Sea Rider]

Re: Tohatsu 20hp rev limiter or timing?

Don't mess with factory adjustments & props, could bring nasty consequences to your engine, you must always wot test boat/engine combo on water in gear. At neutral/wot will blow your power head off!! By the way which type of boat is that engine mounted on ?

Happy Boating