thats also fine... I always check that first... no problems with fuel getting in at the needle...

so what are bearing replacement symptoms to look out for? what can I look out for else apart from the previous puffing of smoke in air...

If the bearings are smooth, and no wiggle in the crank, they are fine. In any case, they are not your problem.

When you've tried everything and the problem is still there, it's time to take a deep breath and start from the beginning again and forget everything that you have done so far. Tearing down and replacing parts are just shots in the dark that will only cost you money and possible damage to the engine in the process.

This probably has nothing to do with it, but when you punch a four stroke engine in the air, it puffs until it's up to speed. A glitching throttle servo may cause rapid throttle changes. I've not seen a two stroke do this, but it should be an easy check out.

If I were tackling this problem I would start by replacing all lines in and from the fuel tank. Make sure the bung is tight and thetank is intact. Iwould then tear down the carb completely and give it a good cleaning. Iwould replace the O rings. If you haven't owned this engine from new, Iwould make sure all the carb parts are the correct ones. Once you are satisfied that parts are clean and correct, put it back together and set it for the "factory settings" and give it a go.

The reason I suggested a review of the parts in the carb is that I acquired a Saito 180 with just a few hours on it, but it wouldn't run well. After cleaning and setting the carb to factory in ital settings, I could hardly get it to run at all. It seemed to hinge around the idle mix. When I checked the Saito parts, the 180 and 150 carbs are the same with the exception of the idle mix screw. I ordered out the 180 screw and compared it to the one in the carb. There was a slight difference in length. With the new mix screw, the engine fired straight up and with minor mix adjustments, it is a very good running engine now.

Start over and ignore nothing as "already checked that", you have most likely missed something.

One thing came to mind just now. If the engine has been taken down before, is it possible that the cylinder sleeve is not installed correctly? IE the ports don't align properly with the case?

Don

no the engine has run before with no problems... then I had a crash... took apart the needles to clean them... cleaned the carb... after that the engine has flown twice with a big 14x8 prop... then I changed to 12x8 and different pipe than standard and problems arouse (puffing)... then I went back to 13x8 prop and stock muffler and now this problem came up...

Hi!
The first thing you should do is to replace the tank and get a the best there is: a Tettra "Bubbleless tank! 12-15 oz depending on what time you want to fly. Second best is to use a " Uni-flow" set up in an ordinary R/C tank.
I would use use 5% nitro and 20% oil (Castor or a synthetic or a mix). For this fuel I recommend a Rossi 5 or 6 glow plug when using a pipe. Remember that using a pipe makes the compression go up as a pipe acts like a compressor on a model engine, thus requiring lower nitro contents to work well

As for props there are few that can rival RAM (British made) and APC! 12x8 or 12x9 is just fine if you want speed. Even smaller props with more pitch could be tried if the plane is small. 14x6, 14x8 and 15x4W APC is for large lumbering airplanes like scale type warbirds like P-50 Mustangs and semi scale aerobatics Velox and Cap types.

Switch_639,

I have reordered your statements above just to follow the problem in chronological order.
After you crashed and cleaned the carb the first time, how the engine worked when flown twice with a big 14x8 prop?

it was running fine after the crash with stock muffler and 14x8... then I switched to 12x8 with rossi ultra thrust muffler... then you guys said it might have overspeeded or something like that cause fuel wasn't getting burnt fast enough so it causes to rich condition hence puffing... today I swapped to stock muffler again with 13x8 prop and I cant go more than half throttle and engine dies... I turned open the HSN 4 turns to make sure its getting enough fuel... and started leaning from there... but didn't work engine still dies beyond half throttle...

OK, thanks.
Then neither the prop nor the stock muffler are the cause of this problem, which may be new, or the same one that contributed to the previous puffing (helped by underprop).

This new or agravated problem is a carburation problem on high air-fuel volume condition.

Any crankcase leak that you suspect would mess up the low rpm's, when the air intake is chocked by the throttle, and the vacumm inside the case is strong.

What is limiting the air flow? Nothing.
What is limiting the fuel flow? Only obstruction or poor tank back pressure.

If you want to verify that hypothesis before doing anything else, connect a long silicone tube to the pressure line of the tank and blow hard with your mouth into the tank while trying to rev up the engine.

I hope you have not cleaned the high end valve seat with any metal, since that may have damaged it.
If it is in good condition, clean it again with alcohol and a piece of wood.
Once the needle is out, check for surface smoothness and for good condition of any seal.
Replace the seal(s) if not sure or add high vacumm grease for extra sealing.

Clean inside the nipple at the muffler and make sure is not pointing down, since oil would clogg it during normal operation.

Reinstall and check.

Inside the fuel tank,there is a clunk on the end of the line. Some of these have a really fine mesh screen in them. Worth a look. If you removed the carb to clean it make sure everything is lined up and it is seated on the o-ring well. The o-ring itself could have a crack or something. Check the little o-rings in the needle seats as well. Sounds like it is pulling air somewhere for sure.

when does an engine run reliably and efficiently for years and years like people sometimes describe? I just always seem to have to fix things... a friend has a evolution 0.60 engine... its been running now over 2years no issues what so ever... it just simply starts all the time every time... and can idle so low its insane... doesn't seem to want to die no matter how low the idle gap... I thought I would buy something expensive like an OS, suppose to be awesomely reliable and for many people they are... don't know why I always buy the ones with issues...

Check this thread out:

http://www.rcuniverse.com/forum/m_88...tm.htm#8844410

These engines are simple combustion machines.
Engines that operate consistently well are the ones that keep the three elements of combustion inaltered during long periods of time: heat, oxigen and fuel.
I believe that fuel is the element over which we have more influence regarding chemical composition (type-brand-degradation of nitromethane due to Sun light), humidity content (age and exposure to atmosphere), volume fed to the engine for the whole range of rpm's (needle valves adjustment), cleanness (filters, many filters, as many as possible).

By keeping the same brand-type of glow plug and combustible, as well as all the hardware elements in top condition, our variables reduce to two needle valves.
Once we hit the sweet spot, we will enjoy reliable high and low rpm's (ideal proportion of air-fuel for each of both regimes) for as long as the conditions remain.
Changes in air temperature and density may require small adjustments.

Quality engines are normally trouble free from the factory.
Our little mistakes in break-in, operation and tunning may make them a pain rather than a joy.