I have got about ten flights on my ultimate with the os 1.60 and I still can not get this thing tuned in. The os 1.6o came out of my lanier edge 1.20 and it ran beutifully. When I switched the engine to the ultimate, I put on a cline regulator because I moved the tank over the cg. I have a good idle and a good top end swinging an apc 18x6w prop. I tried a zinger 18x6 which was not enough prop, and a 18x6-10 prop. the apc prop is giving me the best rpm at 8100 but with all three props the engine just doesn't have a very good mid-range. As a matter of fact it stinks on all three props. I started out using 5% nitro and I am now using 10%. I have a brand new #8 plug, and all this is at an elevation of 4500 ft above sea level.
What do i need to do? I am in the process of using larger diameter fuel line, but does anyone have any other suggestions?
Thanks in advance for your help.

You might give this a try, it was posted by Aerosplat a while back and worked like a charm on my 1.60.

If you have a pump or Cline system on the engine, (and it is working properly) fuel delivery should be consistent independent of Muffler pressure.
First, open up the muffler and let the engine breathe. If you had some of the muffler outlet plugged before Pump / Cline, remove the restrictions.
Second, I say again, LEAN THE LOW SPEED NEEDLE. This particular OS carburetor seems to have more than its share of interaction between low speed needle and high speed needle settings. PEAK the high end, don't back off rich. Go to idle. If engine idles well, for 15 - 20 seconds, lean the low speed needle 1/4 turn. Go back to top and re-peak. Go back to idle. Same routine, if it idles, lean the low speed screw another 1/4 turn. Continue this process until the engine will NOT sustain an idle. It should speed up and die within 15 - 20 seconds. Now Richen the low speed 1/16 turn at a time until the engine will again sustain an idle. After each adjustment on the low speed, go to top end and peak the high speed. AS soon as it will sustain an idle, leave the low speed alone. Each flying day, just re-peak the top end and back off 150 RPM rich for flying. You HAVE TO GO LEAN TO THE NO IDLE POINT on the low speed, then come back to get it set right. Transition from idle, midrange, 3/4 throttle, or anywhere on the stick should now be crisp without sputtering. When tuning the top end for flying, peak the needle and back off no more than 150 RPM rich. More than that will cause the midrange to load up and sputtering transition is back. If you run this engine with rich high speed, you will have lousy transition, and midrange running.

Addendum: Idle speed should be 1900 rpm or less. If you are above 2000 rpm at idle your are still interacting with the high speed setting. Get the idle down to 1900 or less to set the low speed. My OS 1.60 will idle at 1800 - 1850 for over a full minute and still go to full throttle without sputtering.

If your regulator is mounted directly behind the carb, the motor will be difficult to tune. On the OS160FX, the regulator should be mounted just before the needle valve fuel entry. Use no more than 1" of fuel line between the two. It can just hang there or you can mount it against something if it is convenient.

That is all I can add.

Mark

I mounted my cline between the needle and the carb and it works flawlessly. It will work in either location though...

There is one other possibility to your problem though, overheating. Running these motors in a cowled installation can result in overheating and that shows up as a loss of power. Try flying the plane with the cowl off and see what it runs like. If there is a marked change in power, reinstall the cowl and retune the setup. I have noted that all of my cowled engines need a pretty rich setting on the ground to compensate for the higher temps encountered while running under the cowl in flight.

I don't have an over heating problem, as I have checked it with a new infra-red raytek minitemp, I checked the head behind the exhaust port and it read 178 degrees, I believe this is a little cold, tells me I'm running too rich. I tried moving the cline regulator back to just before the high speed needle and there were air bubbles galore. I also tried the tuning method mentioned earlier, but after doing this and seemingly getting it to run good and idle at around 1800 rpm and transition smoothly and no mid-range sputtering, the damn thing won't start again, even after letting it cool. So, I opened the low end needle a half turn and now it will start, but the mid-range sputters again. Either this thing has gone ultra sensitive and I can't tune it or something else is wrong. Any more suggestions?

The only other thing I can think of that may be the problem is that, The muffler I have on the os 1.60 if the slim line pitts style, with the pre-heater for the smoke oil. Could this be causing too much restriction in the exhaust? It's the only muffler I have for this engine so before I go out and but a new one, tell me what you think. Thanks for the help so far.

After the install of a cline system on the OS 1.60 all the needles will now be much richer than before due to the excellent fuel delivery. The problem should disappear when the engine is adjusted properly. 8100 rpm is very low using the 18x6W APC prop. I tach around 9000 to 9200 rich for flight according to the humidity that day. We have alot of humidity here on the Gulf Coast. Switching to an OS F plug should help also.

I have taken temp readings with a meter and on the ground they usually peak on the low side as well. However, in the air the engine is loaded and depending on cowl inlet/outlet, aircraft attitude/speed and other factors can exacerbate things. The only way to be sure is to remove the cowl and fly it, put the cowl back on and compare results.

You probably don't have a problem with high temps but lousy trasitions at mid to high throttle are usually what I have experienced with engines that are running to hot.

It may be the slimline muffler. I had almost the identical problem. I had my 160 on Hanger 9 EDGE with a bisson pitts muffler and the engine ran great. I then Purchased a slimline pitts with smoke chamber and the engine ran horrible had a lot of deadsticks and poor transition, especially in the midrange.

I then put the bisson back on and the engine ran great. The engine would only run at about 8100 with a Mejzlik 18X8 with the slimline but turns 9200 with the same prop and the Bisson muffler.I am using 15% nitro and 20% sinthetic oil. Altitude her is 6200 feet. Also using Perry pump.

I am not saying this is for sure your problem but it sure was my problem.