Optimal RPM range for Yamaha 30 HP 2 stroke

[Mallards Only]

I recently purchased a used Yamaha 30 HP and after a number of boat mods and adding a Tiny Tach finally got it on the water to see what kind of RPM's I'm getting. This thing is running around 9000 RPM at WOT. What is the ideal range for this motor? I don't have the manual. Am I under-propped?

[DRAGRACR]

What rpm are you seeing at idle? More than likely your setting is not correct on the tiny tach. I have tried 2 different brands of them, now they are sitting in my tool box. If you have a 2 cylinder you MIGHT get it to work but if you have a 3 cylinder do yourself a favor and buy you a marine tach either analog or digital. I did the same thing and now I own a yamaha digital and saved myself a lot of headache and it works perfect.

[Mallards Only]

Hadn't really considered that it might be the tach. I'll run it on the hose tomorrow and get back to you on the idle RPM's.

[DuckLn]

What yamaha digital?

[DRAGRACR]

The one I bought was Pt # 6Y5-8350T-83-00. There are others that will work but this is the one I have.

[FrenchPhil]

Somethings not right. Most smaller 2 strokes should be around 5500-6000 rpm at WOT .

[Tiller guy]

I have the same motor and was wondering the same. Yamaha claims that it makes it's 30hp @ 5000 rpm. I was planning on using 40hp carbs, but now I'm going to bore out the factory set. It should be fun trying to get the jetting dialed in.

[Bill Van Steenwyk]

Tiny Tachs are notorious for giving incorrect readings, mostly because the tach is not set up correctly. Check and see if yours has settings for 2-4 stroke, number of cylinders, etc, before giving up.

Not to say there is not something wrong with the tach, as there are many complaints about them on this and other forums, but any tach unless set up for a specific engine needs to be set correctly so as to work correctly. I have heard also that how you run the PU wire can affect them as well as how it is placed around the plug wire and how close to the plug.

You might also Google "Tiny Tach Problems" and see if anyone else if having the same problems you are.

Good Luck

ADD:

9000 RPM sounds like about 2 times what the motor should be turning so it is another tip the tach is set up wrong for the motor and 2-4 stroke.

[Mallards Only]

Sorry for the delay. So, it appears that the TT was on the wrong setting as my idle RPM's were running about 2050. Problem now is I'm not sure what setting is the correct one. The TT has settings for SP ARK PER REVOLUTION. If it's a 3-cylinder motor, do I need to have it on 3P1r or 3 sparks per revolution? Or is it based on 2-stroke and therefore 2P1r? If someone knows what the idle RPM's should be, that would help me as well.

[Bill Van Steenwyk]

[QUOTE=Mallards Only;146947]Sorry for the delay. So, it appears that the TT was on the wrong setting as my idle RPM's were running about 2050. Problem now is I'm not sure what setting is the correct one. The TT has settings for SP ARK PER REVOLUTION. If it's a 3-cylinder motor, do I need to have it on 3P1r or 3 sparks per revolution? Or is it based on 2-stroke and therefore 2P1r? If someone knows what the idle RPM's should be, that would help me as well.[/Q


Mallard:

A two stroke motor fires ONCE each RPM (revolution per minute) for each cylinder. Three cylinders, one firing impulse each revolution per cylinder = 3 firing impulses per revolution for this motor.

Hope this helps. When you get it (the TT) adjusted correctly you should read 5000-6000 RPM at WOT depending on prop pitch.

[Mallards Only]

[QUOTE=Mallards Only;146947]Sorry for the delay. So, it appears that the TT was on the wrong setting as my idle RPM's were running about 2050. Problem now is I'm not sure what setting is the correct one. The TT has settings for SP ARK PER REVOLUTION. If it's a 3-cylinder motor, do I need to have it on 3P1r or 3 sparks per revolution? Or is it based on 2-stroke and therefore 2P1r? If someone knows what the idle RPM's should be, that would help me as well.[/Q


Mallard:

A two stroke motor fires ONCE each RPM (revolution per minute) for each cylinder. Three cylinders, one firing impulse each revolution per cylinder = 3 firing impulses per revolution for this motor.

Hope this helps. When you get it (the TT) adjusted correctly you should read 5000-6000 RPM at WOT depending on prop pitch.
Thanks. Exactly the information I needed. At that setting on the TT, RPM's are 650-700 at idle. Sound about right? Haven't taken it out and run it WOT yet but what's interesting is that WOT on the hose in neutral is only giving me 3500-4000 rpm's. Do these motors have a "governor" that won't allow you to take it to WOT unless in gear?

[FrenchPhil]

Avoid over-idling on the hose.

[Bill Van Steenwyk]

[QUOTE=Bill Van Steenwyk;146948]
Thanks. Exactly the information I needed. At that setting on the TT, RPM's are 650-700 at idle. Sound about right? Haven't taken it out and run it WOT yet but what's interesting is that WOT on the hose in neutral is only giving me 3500-4000 rpm's. Do these motors have a "governor" that won't allow you to take it to WOT unless in gear?




Mallard:

I am not intimately familiar with your motor to be able to answer the question about idle speed, although is does seem to be about right.

BUT, as French Phil states, you should not rev the motor without a load ( i.e in the water and with the motor pushing the boat) as you might do damage to various components. It sounds as though there may be some sort of interconnect between the CPU on your motor and the gear shift lever so as to prevent it from reving past 3500-4000 RPM's unless it is in gear or a load on it. I would strongly advise you not to try to bypass these features AND put it in the water to check your WOT revs.

Glad to try to help, but you can't cure stupidity if you know what I mean. If the motor won't rev past the RPM you state then there is a reason for it. I realize you want to solve the problem as easily as possible, but the motor was made the way it is to protect it from just what you are trying to do. NO LOAD AND EXCESSIVE RPM'S WILL TEAR THE MOTOR UP!! You have your tach set correctly now, so go to the lake to check it further.

Not calling YOU stupid, just you have gone about as far as you can go with what you have done. Now you need to go to the lake!!


Good Luck!!

[Mallards Only]

Understood. That was my plan. I only took the throttle up briefly to see how high the readings were. I didn't run it there without a load for more than a few seconds. I'll take it out on the water for the next test. Thanks.

[Bill Van Steenwyk]

Understood. That was my plan. I only took the throttle up briefly to see how high the readings were. I didn't run it there without a load for more than a few seconds. I'll take it out on the water for the next test. Thanks.


Mallard:

I seem to remember that the older motors (before EFI and computer controls) had a simple carb linkage that unless the motor was shifted into "forward" would not allow the throttle to be advanced to WOT, or blocked it until the lever was in forward. Perhaps yours has something as simple as this.

Let us know whether this solved the TT problem as there are many posts about this tach on this and other forums. They can be frustrating if not set right.

[Mallards Only]

Will do. Thanks for the help.

[Tiller guy]

[QUOTE=Bill Van Steenwyk;146948]
Thanks. Exactly the information I needed. At that setting on the TT, RPM's are 650-700 at idle. Sound about right? Haven't taken it out and run it WOT yet but what's interesting is that WOT on the hose in neutral is only giving me 3500-4000 rpm's. Do these motors have a "governor" that won't allow you to take it to WOT unless in gear?

My Yamaha 30 has nothing to prevent over revving in neutral. Nothing has been removed or played with as far as I know. The cdi doesn't have any way to detect gear position either.

[Fastjeff57]

Try wrapping the plug wires next to the one you're using with aluminum foil. That keeps the interference down and improves operation.

Jeff

[Fastjeff57]

Aluminum foil tape works even better.

Jeff

[Mallards Only]

Alright, finally got the boat back on the water to check the RPM's again. Something just doesn't seem right though. With the TT set at 3p1r as Bill suggested, my RPM's range from 400(idle) to 3200(WOT). With the TT set at 2p1r, RPM's are running 600-4800. Even at the 2p1r setting, that seems low and the 3p1r setting is REALLY low. I know it's not overpropped. If anything, the prop on it now is pretty worn and a little chewed on the edges--not enough to create increased drag on the RPM's though. Now what? I'd take it to a Certified Yamaha mech to have them check it but I don't have one within 100 mi.

[Tiller guy]

I don't use a tach, but based on my speed and prop pitch it's around 5700 rpm at wot http://continuouswave.com/cgi-bin/propcalc.pl/

[DuckLn]

Those yamahas have an anti rev in neutral mechanism. You can still "give her half throttle and choke it" to start it though.

[DRAGRACR]

Alright, finally got the boat back on the water to check the RPM's again. Something just doesn't seem right though. With the TT set at 3p1r as Bill suggested, my RPM's range from 400(idle) to 3200(WOT). With the TT set at 2p1r, RPM's are running 600-4800. Even at the 2p1r setting, that seems low and the 3p1r setting is REALLY low. I know it's not overpropped. If anything, the prop on it now is pretty worn and a little chewed on the edges--not enough to create increased drag on the RPM's though. Now what? I'd take it to a Certified Yamaha mech to have them check it but I don't have one within 100 mi.



Do yourself a favor and spend the money on a Yamaha tach and problem solved...... I went thru the same crap on 2 3cyl motors before listening to someones advice. For what you are about to spend on a mechanic you can have an accurate tach made for your engine...... Like I said I have 2 of the tiny tachs laying in my tool box....

[Mallards Only]

I don't use a tach, but based on my speed and prop pitch it's around 5700 rpm at wot http://continuouswave.com/cgi-bin/propcalc.pl/

What are you using for the lower unit Ratio in that calculation?

[Mallards Only]

Do yourself a favor and spend the money on a Yamaha tach and problem solved...... I went thru the same crap on 2 3cyl motors before listening to someones advice. For what you are about to spend on a mechanic you can have an accurate tach made for your engine...... Like I said I have 2 of the tiny tachs laying in my tool box....

Really? Hate to spend $300 for a tach. Wanted something small like the TT as well. Does Yamaha make a small digital tach similar in size to the TT? What's different about the Yamaha tachs?

[DRAGRACR]

http://www.ebay.com/itm/NEW-YAMAHA-ANALOG-TACH-W-WARNING-LIGHTS-FOR-YAMAHA-MOTORS-94-UP-6Y7835408000-/301701356732?hash=item463ecd5cbc&vxp=mtr

New analog for $114
Used analog for $39
http://www.ebay.com/itm/USED-YAMAHA-BOAT-MARINE-7000-RPM-TACH-GAUGE-/221832127783?hash=item33a639a527&vxp=mtr

Yamaha tachs are hooked directly to the motor via harness and are triggered by cdi box and not the outside of a plug wire.

[Mallards Only]

http://www.ebay.com/itm/NEW-YAMAHA-ANALOG-TACH-W-WARNING-LIGHTS-FOR-YAMAHA-MOTORS-94-UP-6Y7835408000-/301701356732?hash=item463ecd5cbc&vxp=mtr

New analog for $114
Used analog for $39
http://www.ebay.com/itm/USED-YAMAHA-BOAT-MARINE-7000-RPM-TACH-GAUGE-/221832127783?hash=item33a639a527&vxp=mtr

Yamaha tachs are hooked directly to the motor via harness and are triggered by cdi box and not the outside of a plug wire.

Thanks. Been searching for something smaller that I can mount inconspicuously. I don't really have a good place to mount a large analog tach like that as I stripped the boat of all the internals. Mounting a large analog like that would get torn off instantly in a duck boat by dogs, decoys, etc.:( Have you ever seen something smaller that could be mounted on the transom or cowling similar to the TT?

[Tiller guy]

Our motors have a 1.85.1 gear ratio. I use 6% slip when working with the numbers. I know it's not perfect, but it worked great for propping my boat and it gives me a ballpark RPM average. If I had the money for some different props and a jackplate then I would definitely buy a good tach.