troubleshooting OS MAX 95 ringed

[tranquility bob]

I have problems with this engine in the mid-range, it gurgles loses power and stops running. Has anyone managed to resolve this issue with this type of engine. Apparently it is a wide spread complaint and I can't find any solution.
I've changed the tank replumbed it played around with needle adjustments.

[kip51035]

What fuel, how much nitro, what size prop, air bleed carb, idle needle carb, what glow plug?????? A little more information would be helpful. Buy the way this is the for sale section.

[tranquility bob]

just new on this site, can this thread be moved to go in the right area? in answer to your questions i'm running magnum fuel, 15% nitro, #8 plug,14 8 prop. There is a needle vaalve and also a set screw below it to adjust high end and low end performance. my next change would be to add an occilating pump.

[Gary Maker]

Bob. Welcome to RC Canada. Hope you enjoy the site.

I have moved this thread to the "Engines" general discussion forum which is correct forum. Being new to the site, I would suggest that you please take the time to read over the site RULES> This will help you to use the appropriate forums for your intended use. Thank you for your co-operation.

IF I can be of further assistance to you, please do not hesitate to contact me via PM. (Private Message) Gary Maker, RCCanada Administrator.

[kip51035]

Idle the Duke Fox method. After starting and warming the engine set the idle for around 2500 RPM, wait 15 seconds then pinch the fuel line just before the carb flat. The engine should increase RPM slightly then die. If it just dies the idle mixture is too lean. If it gains a lot of RPM then dies it is too rich. Belching a lot of smoke when you throttle up indicates too rich of an idle mixture. Using a pump usually makes the engine harder to set. A 14X8 prop is probably too much prop for a new engine.

[Cougar429]

Normally the High and Low needles only work in their respective throttle areas. The jet and needle profile would be most effective in mid range. On our earlier Fox carbs there was a notice on how to alter the needle to help correct a rich mid range condition. I would not advise anything like that here yet as there had been a lot of experimentation to get that profile correct on the Fox.

Although I don't have experience with that specific motor, there are a couple of other things that may help us diagnose what's happening. When at mid range, can you keep it running longer with the glow heat applied? That would tell us if you are too rich or lean. From the burbling I suspect rich. You should also get an increase in RPM in this condition by raising the nose.

Also, other than the burbling, is the throttle transition smooth all the way through?

One thing that can explain this would be a slight air leak. In this condition you would have to enrichen the high and low ends to compensate and it could therefore give a far too rich mid range. A few locations are at the carb base, throttle barrel bore, front bearing/oil return groove, (if it has one) and rear cover. Another problem is a lack of muffler pressure to maintain feed. Has the muffler been altered or replaced with aftermarket?

What I find common for these conditions is the need for gobbing rich ground adjustment to keep it running airborne.

One possible solution if it tracks back to the carb would be to replace the entire assembly with a different unit. Perry are a good choice.

NOTE: Adding a pump would likely not solve your problem. They are used to ensure a consistent supply for varying conditions. Yours does not sound like that is the case.

[kip51035]

In spite of what Cougar429 said, the Duke Fox idle mixture check works on all carbs except the YS pressure carbs. His "air leak theory" is just that just a bunch of hot air.

[tranquility bob]

Normally the High and Low needles only work in their respective throttle areas. The jet and needle profile would be most effective in mid range. On our earlier Fox carbs there was a notice on how to alter the needle to help correct a rich mid range condition. I would not advise anything like that here yet as there had been a lot of experimentation to get that profile correct on the Fox.

Although I don't have experience with that specific motor, there are a couple of other things that may help us diagnose what's happening. When at mid range, can you keep it running longer with the glow heat applied? That would tell us if you are too rich or lean. From the burbling I suspect rich. You should also get an increase in RPM in this condition by raising the nose.

Also, other than the burbling, is the throttle transition smooth all the way through?

One thing that can explain this would be a slight air leak. In this condition you would have to enrichen the high and low ends to compensate and it could therefore give a far too rich mid range. A few locations are at the carb base, throttle barrel bore, front bearing/oil return groove, (if it has one) and rear cover. Another problem is a lack of muffler pressure to maintain feed. Has the muffler been altered or replaced with aftermarket?

What I find common for these conditions is the need for gobbing rich ground adjustment to keep it running airborne.

One possible solution if it tracks back to the carb would be to replace the entire assembly with a different unit. Perry are a good choice.

NOTE: Adding a pump would likely not solve your problem. They are used to ensure a consistent supply for varying conditions. Yours does not sound like that is the case.

when glow heat is applied it does not stop. I installed an "F" plug and recalibrated high and low end throttle and removed the baffle in the muffler. That seems to have fixed the throttle response it is now constant throughout the range(The engine would quit in flight after transition from idle to mid range input). I will fly the plane either tomorrow weather permitting or next Monday. that should tell me if the ground work paid off. I appreciate the input as I was becoming a tad frustrated with this new engine.

[Cougar429]

Bob, the fact you continue to run while heat is applied is indicative of an excessively rich mixture. The "F" plug can help here by remaining hot in a much wetter environment since it was designed to remain that way through the exhaust/intake cycle on a four-stroke. I run them when my 2-strokes are inverted since the fuel/oil tends to flood the plug.

Since it was not mentioned in the original post I did not realize this was a new motor. Have you followed the break in procedure? How many tanks through it? I found the GMS engines horrible for requiring excessively rich mixture just to continue running during break in, but they ran more normally once loosened up a bit.

On that note, if the motor is not mounted inverted then you can switch to a normal #8 plug once the motor has a few tanks through it. I run the hotter #3 in the winter here since otherwise the motors have a tendency to quit at lower throttle settings.

Kip, your post on the mixture test must have been sent in while I was typing out mine.

Yes, I agree with the method and that's why I asked about the smooth throttle transition and changes with plane attitude. I was not planning to add any more until there was a response to those questions. The fact about the YS carb is irrelevant here.

And I also agree now that I know this is a new engine. Things will be a bit cranky until everything settles down and, in fact, you want to run it rich for the first few tankfulls.

I also should have asked if the motor is side mounted or inverted, so in your estimation I must have completely dropped the ball.

Bob, have to apologize if I sound a bit off. Early mornings waiting for the coffee to kick in while reading things like that tend to get to me.

Also, love your moniker. Have a copy of "Zen and the art of motorcycle maintenance" on your bookshelf?

[tranquility bob]

Well I took the plane out for a try and everything worked well. I have the engine mounted right side up and I have about 3/4 of a gallon of nitro through it. Had to tweek the carb a bit but it did not quit on me. It seems to like the mild rich setting and the mid range burble has lessed a lot it just seems to be liking running at he settings chosen. It probably does need more breaking-in time and that will be an ongoing plan for me.

Thanks for the information supplied . I'll keep you posted on my "adventure". You folks are great. It's nice to have a source of varied knowledge at hand and people to share that knowledge with others.

[tranquility bob]

well as promised i am keeping up my quest to end my problems with the engine. I did, It was a bad batch of fuel. one of the club members had some difficulties and just by chance had a jug of different fuel. tried it and low and behold runs like new again. I tried it and worked on my engine also.

SO again thanks to all who provided suggestions.

[Cougar429]

Glad you solved it and it was a simple fix.

How old was the bad fuel?

[tranquility bob]

It was a new batch but apparently the hobbyshop where i bought it told me that there may have been a bad batch or miss-labelled batch as far as nitro content was concerned.