First 4 Stroke
 

Trying to fine tune my first fourstroke...its a .91 ThunderTiger and I just can't quite get it to "slow down"...or idle I suppose would be a better word. My guess is its too rich but before I fiddle with it I wanted to get some feedback. I've fiddled with it before and only made it worse. It cut out on me in flight and the results were not pretty. My RPM tester gets as high as 7000 and that is it. Engine manual says it should reach as high as 11,000. Too rich?
Thanks!
Pat

RE: First 4 Stroke
 

Do a quick search of the forums. Tuning a 4 stroke is essentially the same as a 2 stroke, except that you HAVE to use a tach to set the top end. I just went thru the same thing with a Saito .56, my BEST advice would be to find someone at your local field or hobby store who is willing to walk you thru it for the first time. It's really not hard, but it takes a little time. You have run a gallon or so of fuel thru it sloppy rich already, right?

BTW, a 4 stroke should idle at approx. 2500 rpm. You might get one to slow down more after it's broken in a bit.

Andy

RE: First 4 Stroke
 

Break it in some more and let the compression increase with the better fit.

RE: First 4 Stroke
 

The TT 91 is one of the more powerful of the 90 class 4-stroke engines (excluding YS) but have a little longer break in time. One other thing is you need to have the choke installed on the engine. It acts as a ventury for the engine and you won't get it to run very well with out it so I have been told. Once you do have it boke-in you will have a real power house engine. I too agree with a65l but if you can't get the idle down a little, Maybe a little leaner on the low end might be needed, TT does not always have there new engines set well but do make a great engine.

Dauntae

RE: First 4 Stroke
 

If you can't get it to go above 7000 RPM, you are either too rich, or your prop is too big, or your carb is not fully opening (Or you have crappy fuel).

First I would try running a 14x6 or 14x8 prop (Or my personal pref, a Graupner 13.5 x 8)

VISUALLY check to see that the carb is opening FULLY.

Use a good (As in fairly NEW) 15% Fuel.

Crank it up, bring it to WOT and turn the needle valve RICHER at first. This should cause the engine to run worse and start spitting fuel out of the muffler (if it isn't already)

So now that you KNOW it's rich, slowly turn thr needle valve in. The engine should run up to peak and then start to sound a little sick (You don't need a tach, you'll hear it). Don't go too far! 4-strokes don't like to run lean and will backfire spitting the prop across the field. Just return the needle to where it sounded best, then open it a little more but not so far that the the RPM go down again.