I have a new O.S. 70 surpass 4 stroke

One guy recommended that I get a tachometer for it since it's hard to hear how rich it's running.

I am going to use a 13-6 prop on it. Now that I have the tach, can someone that knows about breaking in a 4 stroke tell me what rpm I should be looking for so I don't run it too rich?

Any tips on breaking it in?

please reply before winter is over here in ohio

big dan

If you read and follow the instructions that came with the engine you will have an engine that will last many years and give you good service. The reason we use tacho's on 4strokers is to set the RPM so they won't over rev in flight. After break in go to full throtal and slowly(SLOWLY) lean out while watching the tacho(DO NOT GO OVER MAX STATED RPM). When rpm stops to increase richen up a couple of clicks and it will be set.

Cheers

After you get used to the engine, you most likely will not use the tach anymore?

That engine will not over rev with a 13-6 on it so don't worry abnout over reving.

Like was said earlier, when you find the peak, richen it back up 2 or 3 hundred rpm.

Enjoy,

Jim

The beauty of a tach is that if you have a good ear, the tach will quickly teach you how to get along without it. And if you happen to be one of those guys born with a bad ear, you need to have a tach. And you won't know if you have a bad ear unless you either use a tach or you don't and wind up burning a couple of engines up with lousy needle settings.

Want a little chuckle? Awhile back, a guy asked me to set his 4stroke for him. He said he couldn't seem to get it right. When I came over with my tach and set his engine (and both hi and low speed needles were bad off) he said that he had a tach but had quit using it because no matter what it said the engine always sounded the same.

Thanks guys for the good info. I will be using it shortly as I too have my first 4-stroke coming in the mail for my new Christmas plane. It is a Saito 100, & I was wondering if I should get a tach or not. I will be running a Graupner 14x7 on it, a little more expensive than some other suitable choices but I have it on good authority that this will be a good prop for it. I guess I better start pricing some new Tachs now as well. Thanks again.


Mark

The Graupner 14-7 is a excellent prop for the Saito 100.

After you get the needles set, you will find it to be a nice engine with plenty of power

Enjoy,

Jim

I own a tach. I bought it a few years ago for an engine review I was doing just so I could show what the engine's RPM was.

Aside from that, I would never use one - especially for tuning a 4-stroke.

If used as stated, you should be ok, but as w8ye said, you will not over-rev it with a 13x6 - But here is where the novice can get into trouble with a tach...

Someone (or the manual) will say you should get (let's say) 9,500 RPM. If your prop (or fuel, or weather, or whatever) will only allow 9,000 RPM, but you keep leaning it out to try and reach 9,500, you can throw a prop, or damage the engine.

Just use a prop in the recommended range specified by your engine's manufacturer, and tune it like a 2-stroke. That is, start rich, lean it till it reaches it's peak (It will go slightly sick once you pass peak) then back it off 1 or 2 clicks from where it started to peak

Works for me, I 'd rather spend the $$$ on a shiny new spinner to wrap around the Graupner


Mark

The reason to use a tach is to be able to set the engine slightly rich from max rpm. No one's ear is good enough to discern 200 rpm, especially with a 4-stroke. As was said before, starting from a rich needle setting, slowly lean the high speed needle while watching the tach. When the rpm has reached the max value, open the high speed needle a little so the rpm decreases by a few hundred rpm.

For safety, never rev a 4-stroke up while you or anyone else is standing in front of the prop. They like to throw props if the engine ever gets a little lean.

Hell, I can hear it - and I have bad hearing.

Hi!
I have several tach's but only use them to compare props and fuel... never for setting an engine, be it two or fourstrokes.

200 rpm is easily recognizable!

Regards!
Jan K
Sweden

I have to agree with Minnflyer and Jaka, 200 RPM is very easy to hear.

Ken

One bit of advice. I never use a tach from in front of the engine. That's asking for trouble. I always use mine from behind. Much safer.

Good point 2slow...

Just for a public service announcement:

There is only one time you (Or any part of you) should be in front of a running engine, and that is right after you started it (At idle).

Once the engine is running, ALWAYS get behind the prop before increasing the RPM, making adjustments, removing the glow igniter, etc. !!!!!

Thanks for all the advise...

Another guy told me to run it to 10,000 rpm and back it off to 9300 with the 13-6 prop.

I'm glad it's winter because this astro hog is taking some time to build. Need a chainsaw like a guy told me.

big dan

Hi guys,
I bought a tach last summer to check RPMs of my engines. Some guys say you need one and others will say you don't. I can only tell you I don't think they're worth the price. I tune my engines by sound and never burned up one. I start out with the engines running rich and slowly lean them out until they have a nice smooth sound, then I leave it there. If while flying I hear the engine running rich, I'll just lean it out a couple of clicks and again, leave it there. I may need the tach when I start flying my B 25 with 4 strokes to syn the engines.
Larry