Anyone know how many sparks per revolution on a 5O HP 4stroke Tohatsu?
Trying to set up a tiny tach to check prop.
TIA
Ray
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Anyone know how many sparks per revolution on a 5O HP 4stroke Tohatsu?
Trying to set up a tiny tach to check prop.
TIA
Ray
A 4 stroke engine fires 1 time for every 2 crank revolutions..
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Intake stroke and compression stroke make one revolution of the crankshaft, power stroke and exhaust stroke make the second revolution. Your plug fires at the top of the compression stroke. A 4 cylinder 4 stroke would fire 2 times per crankshaft revolution, a 6 cylinder 3 times and so on. I think a 50hp outboard is 3 cylinders correct?
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Not always. Many have a waste spark system that fires every revolution, especially multi-cylinder engines which have companion cylinders, where one is at TDC exhaust, while other is at TDC compression, in which case both cylinders can be fired by one dual-plug coil.Quote:
Originally Posted by Tex_79
Many small magneto engines fire once per revolution as well, the coil is energized every time the flywheel magnets go past it, whether the engine is on the compression stroke or not.
I have no idea if any outboards are set up that way, but I would not be at all surprised if it fires once per revolution, doing it that way is often much simpler.
I think they all use that waste spark now days. So it would be 1 spark each revolution.
That is very true but I’m pretty sure 3 cylinder outboards don’t use a wasted spark system but I could be wrong.. an easy check would be to see what your tach reads at idle, should be +/- 800 rpms, if it’s reading +/- 1600 and obviously not idling that fast your spark per revolution setting is too low. If it’s reading +/- 400 and obviously not idling that slow your spark per revolution setting is too high.. it will for sure either be 1 spark per 2 revolutions or 1 spark per revolution it’s not going to be higher then thatQuote:
Originally Posted by Atimm693
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Well, no consensus but at least a starting point.
I'll see how it goes.
Well it must be 1 spark/revolution. That's the setting I had to use to get correct reading.
Is your motor a 3 cyl? I want to get a tach for my 25 hp 3 cyl suzuki but cannot find a tiny tach that indicates it can be used for a 3 cyl. Please advise if you get one to work on your motor if it is a 3 cyl. 4 stroke. Thanks
Mine is a 3 cylinder. I had an older one that works but my new boat is a stick steer so I had Tiny Tach make me one with 16' lead wire so it would reach front seat. Got it in less than a week.
The only outboard they say it won't work on is a Honda, no idea why it won't.
My older one was not made by TinyTach.
Lots of different versions on line. I ordered this one directly from Tiny Tach. Good customer service and fast.
I use to have a Tiny Tach. It worked great but the only thing I didn't like is you couldn't change the battery. But it did last for many years. I used it when I needed a tach for a motor I was working on.
Should of listened to Tex. Tach read 2700 at WOT. I had set for 1 spark/rev. Obviously it was off by factor of 2. So I set for 1 spark/2 revolutions and will try tomorrow. Also put SS prop on to test.
I'm waiting on your post. I received my TT2AM in the mail yesterday and will install it today on my 40 hp Tahotsu 2017 model. I am confused on the spark setting also but the fellow at Tiny Tach said to install the red wire around the bottom spark plug wire. I tried the new 11x13 SS Prop last week and didn't notice any difference from the 11x14 aluminum prop.
Well I can't get mine to read correctly. Shouldn't matter which plug it is on since it be it's counting sparks.
Set at 360° it is reading 1spark/revolution. It was reading half of what it actually was turning but it seemed pretty accurate.
When I set it to 720° it bounced all over the scale.
I'm going to need a higher pitch than 13" . At 28-30MPH I think I was around 5500-6000 RPMs. With the 15" aluminum it runs around 35MPH at 5600.
I'm not looking for more speed, I needed the SS for some if the flooded forest I fish.
The erratic readings are more likely to be a wiring problem then a setting problem. I’d double check your wraps on the plug wire and make sure they’re good and tight and that the wire is running as far as possible from the other plug wires and coils to be sure you’re not getting interference from them. Also make sure you have a good ground connection, a bad ground will definitely cause problems.
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Agree. I'm going to recheck everything.Quote:
Originally Posted by Tex_79
Got to try my tach today and it worked fine set at 360* 1 spark per revolution. I didn't get a WOT reading the canal was to short on streightaways and to many cypress trees, 3/4 throttle read 4000-4200 rpm's which seemed about right. For a fishing report I got skunked, gonna go to the river Wednesday for a better test.
Thanks. Set at 360° mine reads fine at idle but maxes out at 2700 at WOT.
Set on 720° it bounces all over at idle, 800-200 RPMs.
Gonna recheck wiring and maybe put a pice of tape over wire wrap.
After talking to dealership they think a 15 SS prop will be fine the boat only weighs 600# without motor, batteries,etc.
I got to test mine again yesterday, WOT showed 5870 rpm's with the 11x13" prop. What I'm finding strange is I reach that rpm at 3/4 throttle and when I turn the throttle the rest of the way there is no change in rpm's. This is my first 4 stroke engine and have only 2 stroke motors to compare to. Top speed was 30 mph on my phone. I'm thinking I should have gone with a 14 or 15" prop
I ordered a 15" after trying the 13. Don't have it yet but I ran the boat yesterday with Tach set at 720. Showed 850 at idle then 5700 at WOT, 35MPH. OK great I thought. Restarted later and it went crazy again, idle RPM reading 2700, etc.
Regardless I know the 15" SS prop won't over rev the engine.
By the way your engine has a Rev limiter that won't let it over rev so you may be maxing out at 3/4 throttle.
A Yamaha or Mercury prop in same HP range will fit your motor if you can find one with more pitch to try.
You can get plastic wire loom pretty much anywhere and it makes it easy to shield it from the other wiresQuote:
Originally Posted by SeaRay
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So it's not a cavitation issue rite ?
No, it attaches to a spark plug wire. I suspect the 16' lead I had them put on it may be the issue.Quote:
Originally Posted by Mbsbeek
I finally got to try the 15" wheel yesterday, the boat gained 2 mph " on my phone " and the tiny tach went to hell. It started giving good readings up to half throttle @ 3200 rpm's then would drop down to 2870 at WOT, gonna call Tiny Tach today and see what they have to say. I searched the web and found aftermarket tach I'm thinking about trying.
Skip, got my 15" SS installed and will test tomorrow. I bought this one after trying the 13" . My Tiny Tach worked one time and then it's back to doing same as yours.
My control box has tach leads somewhere. After Christmas I'm going to locates those leads and install a real tach.
I did this on my previous boat. Only problem is I don't have a dash to mount it so I need a stand alone type mount.
Let me know what Tiny T. has to say.
Ray, when you decide on tach you might look at something like this for a mount.
Universal Single Gauge 52mm Console Dashboard Pod
Thanks, hadn't seen that one.Quote:
Originally Posted by Cray
Got to try the new prop today. 15 pitch SS same as the factory aluminum prop. Boat did fine, may have gained 1 or 2 mph but basically just needed to switch to SS due to some areas I fish.
On a side note, my fickle tach decided to behave today and worked just fine. Maxed out around 5600 RPMs.