Originally Posted by 1QwkSport2.5r

By only changing the high speed setting and having to use the throttle to get the engine started tells me you still need to adjust the idle mixture. If you have to open the throttle in order to get the engine started and keep it running, your idle mixture is too rich.

Taking the readings at the glow plug is good, but if the gun you end up finally using has an adjustment for the surface being tested, it may give funky results set for aluminum as you're likely to get a reading off the glow plug itself. This is neither here nor there as most infrared temp guns should read relatively close to one another. I use a radio shack temp gun and when I take readings, I put the end of the gun right on top of the head aimed at the plug as it sounds like you were doing too. The accuracy improves greatly when you're closer to the object being tested.

I would lean lean your low speed so you can start the engine without adding throttle and have the car keep running. Sometimes when cold they may quit, so once the engine starts, drive it around to get some heat in the engine. Once it warms up some, then you can start tuning it. Have the engine completely warmed up before making final adjustments. When you tune the engine, set the high speed for good throttling - smooth power and smooth revving to WOT. Note the temp - if it gets real hot (above 250F), richen the main needle. Once it's stabilized on top, set the idle mixture so it will idle nice and low and throttle cleanly. You want it to be slightly loaded up after 15-20 seconds. It should burble a little bit, but not flame out. If it flames out, lean the idle 1/16th turn and run a WOT pass and test the idle again. Once you get close, make your final needle adjustments when at 1/2-1/3 tank of fuel so when the tank is full it's rich and tank empty is pretty much at the peak setting. This will give you good performance and not run the engine too lean and hot.

Originally Posted by 1QwkSport2.5r

I don't believe there's a midrange adjustment on that carburetor, but I could be wrong. Either way, you wouldn't need to mess with it if it has one. The low speed needle is in the end of the slide valve, the high speed on the fuel inlet. The only other screw that should be present is the idle stop screw - usually on the back of the carb towards the cylinder. Measuring the idle gap can be tricky, but I would see if you have some sewing needles or pins around. Measure it with a caliper and shave it down if needed with a dremel or piece of sandpaper. Paper clips will work too if you can shave the end down a little. Chances are based on your description, your idle gap is probably pretty close to where it should be.

New engine or old, it should start and idle relatively easily. If it doesn't, I never hesitate to lean the needle down a little at a time until it does. Some higher strung engines take longer to break in which can exaggerate the problem, but I doubt yours is such a case.

I just looked at the carb online and it indeed does have a midrange adjustment screw in the end of the carb where the fuel inlet and high speed needle holder is. Don't adjust that screw - it's rarely if ever necessary. Just worry about adjusting the idle mixture and main/high speed needle valves and idle stop as needed.

Originally Posted by jaka

Hi!
Thank´s! One never stop to learn!
May I counter with a question what happened to a friend last Sunday.
He was running his MVVS 10cc engine (airplane engine) for the first time using Rubicon fuel containing 10% nitro and 18% synthetic oil (rest methanol) and a 12x6 APC prop, glow-plug was a Nova Rossi 6 (standard on all MVVS 10-15cc engines) and as soon as he removed the glow ignitor and throttled down the engine quit! The engine ran and throttled well with the ignitor on but quit every time he removed the ignitor despite changing the needle settings.He tried an OS 8 plug but no difference...
What was wrong do you think?

Originally Posted by Murtasma

I believe I've found the problem with my engine and it had nothing to do with the tune. The fuel tank O-Ring has gone bad. It was so bad yesterday I couldn't even get the engine to prime - this is how I discovered it went bad. If I press down on the cap hard I can get pressure back. Thankfully I had a new 150cc tank to replace the 125cc tank. I have yet to try it but I'll be giving it a shot today. I believe this was probably the cause of the issues. This would explain the large tuning differences and temps between days. I guess the last time I ran the truck I had a better seal in the tank than the first day. Really hoping this was the problem, certianly not helping anything. I'll be giving it another try today when I get home and let you guys know what I discover.

Originally Posted by jaka

hi!
Okay! I answer it myself!
To much nitro! Or too high compression.
As soon as we tried another fuel containing 5% nitro (15% Motul "Mikro" syntetic oil and 3%castor oil) the engine ran just fine.
Soo you that have a 10 -15cc MVVS engines, do not try to run them on 10% nitro.

Originally Posted by 1QwkSport2.5r

Make sure you oil the engine before you store it long term or the bearings will rust. Air tool oil or automatic transmission fluid works great - or you can use marine fogging oil as well. The latter is in an aerosol can and it foams up really well so it gets everywhere.

Originally Posted by blw

Tim- you got my meaning a bit wrong. I meant it to come across as a statement that I'm all ears around car guys. They know more than me with those engines. I didn't mean it to sound like you are just arguing. No way.

Jan- why do you always dictate one to tune engines by ear? If you have a tach or like them- use em. They are more accurate than your ears or mine. If you like doing by ear, then do it. I like my ears but I also like my TNC. Now, I will agree with you if you're after a 'sweet spot' on an engine.

Originally Posted by blw

I never use the pinch test.

For tuning the low speed on 2 strokes I use the 30 second idle test. A really good 2s engine that is tuned well should accelerate well after a 30 sec idle period.