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Rich & Lean questions

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Old 03-17-2014, 08:09 AM
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Default Rich & Lean questions

It is my understanding that rich or lean is based on the actual volume of how much fuel is going into the engine. Would this be true or false? I was talking with a r/c pilot who has flown for over 40 years and he was telling me that rich or lean is more based on how much nitro content is in the fuel, not so much the actual volume of fuel being delivered into the cylinder.

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Old 03-17-2014, 08:32 AM
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Lone Star Charles
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A balanced (stoichiometric) mixture of fuel and air is one in which every molecule of fuel is consumed by a corresponding molecule of air and there are no fuel nor oxygen molecules left over in the exhaust. A rich mixture will have left over fuel in the exhaust and a lean mixture will have left over oxygen in the exhaust.
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Old 03-17-2014, 09:18 AM
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(LS Charles got it exactly right)
rich / lean refers to the relationship between fuel and air being burned inside the engine.
put VERY simply, the amount of air an engine will draw in (at a given throttle setting) is 'fixed' (typically, this assumes the needle valves are not 'bleed air' type)
the amount of fuel drawn through the carb (and then mixed with the air) is adjustable via the needle valve (S)
if you open the needle valve too much, that will allow too much fuel for the (fixed) amount of air, resulting in a 'rich' setting.
open the needle valve too little and that does not allow enough fuel for the (fixed) amount of air. resulting in a 'lean' setting

although changing the amount of nitromethane in the fuel may cause the engine to require a different needle valve setting, the amount of nitro in the fuel has nothing to do with the terms 'rich' or 'lean'

incidentally, gasoline engines (which don't use any nitro) can run rich or lean also... as can turbine engines.
I'm SURE the 40 year modeler was either confused, pulling your leg, or simply repeating something he heard.
absolutely positively rich or lean has nothing to do with nitromethane.

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Old 03-17-2014, 10:06 AM
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That's what I thought. The only thing changed from the day that it ran outstanding to the next day where it ran terrible was the fuel. I broke it in and ran an entire gallon of 5% nitro through it over a few months period of time. On the morning I did the maiden, I used same maker of fuel (SIG) but the fuel was the 15% nitro. At start up with the engine warm during the maiden, I would go through the preflight throttle check by running it up and it would die about half way up the throttle. That's never happened before when using the 5%. It also was running a little on the hot side. I run a 12x5 prop on it both during the 5% nitro and 15% nitro runs. I may run the 5% in it again and see if it goes back to what it was before I used the 15%. I don't think it was too lean though because it was blowing out a fair amount of oil in the exhaust. From my experiences in the past, really dry exhaust with no oil content tends to be one of the indications that it's running lean. A fair amount of oil was blowing out the exhaust though. I set it a little rich just because I wanted to make sure it got good lubricant because of the higher nitro content of the new fuel.
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Old 03-17-2014, 06:23 PM
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If you tune the engine with 5% and change to 15% without resetting the needles, you will wind up running lean. Nitro adds oxygen, which creates a leaner mix all else being equal. But the technical explanations given above are right- rich or lean are simply how much fuel there is versus how much oxygen there is.
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Old 03-18-2014, 07:31 AM
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I think the big issue is I didn't test run the engine the day before using the 15% fuel. Had I done that, I would have known that it was having issues running that fuel and I could have then dealt with it before having to do so at the field. What I do may be unnecessary but, before starting the engine, I always turn the needle fully closed and then a few turns to open it back up. After engine starts I fine adjust the needle to where the engine is running well, with some oil coming out of the exhaust. Not sure why I'm in the habit of doing that, perhaps it goes back to when I was a kid in the early 80's and someone who mentored me in r/c did that with their planes.

Would the engine need to run on 15% for an amount of time before it was used to running on that type of fuel? One of the guys at the field had mentioned something like that, where if the engine has only been run on 5% since initial break-in, it would have to go through sort of a second break-in phase, when changing to a higher nitro fuel mixture. Is there any truth to that?

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Old 03-18-2014, 08:12 AM
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Originally Posted by SushiHunter View Post
Is there any truth to that?
in a word, nope.

the 'break in' period is to allow the piston ring (if any) to 'seat' or 'wear in' and to allow any metal to metal moving parts to wear in, any left over metal flashing or casting leftovers will wear away.

once the engine is broken in, changing the fuel does not make the engine need to be broken in again.
(although Jester did make a very good point... going to a higher nitro content will cause an engine to run 'more lean' unless you adjust the needle valves to suit the new nitro percentage)

it's sort of like breaking in a new pair of shoes... once they're broken in, changing your socks doesn't make the shoes need to be broken in again
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Old 03-18-2014, 09:57 AM
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So far, the majority are suggesting it was running too lean. What about the oil out of the exhaust? While I was running it at the field on the 15%, I had lots of oil coming out of the exhaust, a little more than usual. I did so because I wanted to make sure it was getting proper lubrication. The issues the engine was having was I couldn't get more than 1/2 throttle out of it, if I went beyond that point, the engine would shut off immediately. What would cause the engine to behave this way? Too lean? Too rich? Prop I was running was ok, a 12x5 and the engine is a .65. and it's the same prop that was on the engine the day before when it ran flawlessly.
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Old 03-18-2014, 10:59 AM
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personally, I did not say that your engine was running too lean. I explained the difference between the terms lean and rich.
(and agreed that going from 5% to 15% nitro without adjusting the needles would likely make the engine run leaner)

you could have gotten some dirt/ grass/ foreign object into the spray bar, which will cause all sorts of odd behavior.
even when an engine (two stroke glow) is set too lean, there should still be plenty of oil left over to blow out through the exhaust.

typically, I will set the high end needle valve fairly rich (to the point where the engine is on the edge between two cycling and four cycling)
then I'll run the engine down to idle and set the low end needle.
then I'll run it up again and tweak the high end needle slightly more lean until it is not four cycling at all.
if the engine begins to 'load up' (get progressively more rich) while at idle, close the low end needle (just until it stops loading up at idle)
re-check the mid-range and tweak the high end again...

an engine that is loading up at idle will have an RPM that stays about the same for a couple of seconds, then begins to lose RPM's.
(and if you quickly advance the throttle it will likely quit)
an engine that is too lean at idle will have an RPM that increases pretty quickly and usually quits while still at idle.
(and if you quickly advance the throttle the engine may also quit)

if you're unsure about the low end, try to pinch the fuel line with the engine at idle. if it quits immediately it's almost surely too lean.
if instead it continues to run, and even sounds better at idle it's likely rich, (or right on target if it continues to run, just not as well)

these are not 'absolutes' but rather rules of thumb.

one other item..again, Typically: if the engine runs "HOT", it's too lean (or doesn't have enough cooling airflow).

hope that helps!
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Old 03-18-2014, 12:13 PM
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[QUOTE=SushiHunter;

the engine is a .65. .[/QUOTE]



Exactly what is this engine? Is it an OS .065AX or perhaps the old K&B .65 Sportster?



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Old 03-18-2014, 01:18 PM
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Thanks for all the input. I'll try that fuel line pinch technic and see what that does.

The engine is an OS Max .65AX

Another question I have is, the range of props for this specific engine range from 11's all the way up to 14's. The hobby shop I purchased the engine from said 14's are way to big for this engine though. I've run 11x8s, 11x7s, 12x5s, 12x6s and 13x5s. Out of all those, which would anyone suggest be the best match for this engine?
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Old 03-19-2014, 05:40 AM
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You choose the prop based on how it makes the plane fly. That's why the manufacturer gives you a range to work with. If you need more straight line speed, you go with more pitch and less diameter. If you need better vertical performance, it's the opposite.

As mentioned above, oil or smoke coming out of the exhaust tells you nothing about how good your tune is. It's all about the RPM you are running. A properly set high end gives you a noticeable jump in RPM when you pinch the line. That tells you that you are rich, which allows for the higher RPM the engine will turn in the air versus on the ground. How rich it needs to be depends upon how much the engine unloads in the air. My Ugly Stick with a Super Tigre G90 is good with about 400 rpm rich of peak, while my Kaos with a Thunder Tiger .46 needs 1000 RPM to give me the best power in the air. Get the high speed needle set a bit rich, then set the low end. Your low end is set right when you get a steady idle and strong transition from idle to full throttle.
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Old 03-19-2014, 06:25 AM
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yup, Jester has it exactly right. (As does John... )

the 'pinch' for me is a great technique ... at full throttle or at low throttle, pinching the fuel line simulates closing the needle valve (turning it IN a couple of clicks)
if the engine is already running too lean, the engine will immediately run even worse when the line is pinched.
OTOH, if the engine is already running rich, pinching the fuel line will make the engine immediately begin to run (and sound) better.
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Old 03-19-2014, 06:43 AM
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Oil out the exhaust. Remember, that oil does not burn. It will accumulate, wherever, and run out.

Les
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Old 03-19-2014, 08:33 AM
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When talking about stoichiometric ratio of fuel to air, you are talking about the METHANOL to air ratio in glow fuel. Glow fuel also includes oil and nitromethane. So, the adjustment needles have to be set to get the right methanol to air ratio and allow the extra flow through the needles for nitro and oil. If you change the fuel to a different ratio of nitro or oil, the needles will have to be re-adjusted to maintain the correct methanol to air ratio.

I also use the fuel line pinch trick as all mentioned. Very helpful. Also, make sure (I learned this the hard way) that you are using the correct glowplug temp range for you engine/fuel. Lower nitro needs a hotter plug, higher nitro, cooler plug.
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Old 03-19-2014, 08:37 AM
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[QUOTE=SushiHunter;

The engine is an OS Max .65AX

QUOTE]

Ah Ha now were getting there. First of all let me congratulate you on your choice of engines. The AX series are my all time favorites in a general purpose sport aircraft. I have and actively operate multiples of the .25, .35, .55, .65 and one lonely .95. Now the .65 in particular is a favorite and with that one I have completed several long distance flights including one down the Colorado river and even a static non stop flight at the home field with that lonely little .65 chugging along for 6 hours and 12 minutes.

I apologize for the long preamble but it helps to know that I am not just talking in generalities and actually wish to share some very specific points about the .65 AX and that I do love that engine.

Ok now first you have have considerable high quality imput in this thread including Jim B. and Jester as well as others. I also wish to stress also just how much learning the pinch tunning method can be of great benefit to any flyers. That is specifically for two stroke glow engines. Which requires easy access to the carburetor fuel line while the engine is running even when cowlings are used. There are variations of the technique but in general it is superior even to tachometers in my opinion.

Now to the specific of your engine. All the AX series except the first series 1 .46 use a very different carburation and fuel metering system than most other two stroke glow engines. And there does seem to be one peculiar trait and this is I find more often than not that I have set the main mixture too rich! Perhaps this is because this condition (too rich) seems for whatever the reason sounds and acts like it was too lean.

I know this seems counter intuitive to most but if you use the pinch tuning method this is soon discovered. It is very possible that you actually may have had the main needle far too rich which one single momentary pinch of the carburetor line would soon indicate. This is why I strongly would suggest you find someone who understands pinch tuning and can demonstrate. I teach this to all my students who use two stroke glow engines and their tuning skills soon excel.

John

Edit, I neglected to mention that I found that the OS #8 is the best glow plug choice for the .65 in my opinion.

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Old 03-19-2014, 08:48 AM
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Thanks John, I have an OS 55AX with an OS#8 plug. Runs great. How does your 65AX compare to the 55AX? weight, power?
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Old 03-19-2014, 10:24 AM
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Keep in mind also that if an engine begins to overheat, it will go lean as well. So if it is properly tuned, but in a bad cowl situation, you will start to lean out as the flight goes on. Adding nitro, adds heat as well, so that could have been a factor. If you do not have a cowl, then it sounds like the increase in nitro caused you to go lean. Is the increase in nitro the only change? By that I mean is it exactly the same fuel otherwise? Same oil percentage, same kind of oil, all synthetic, some castor etc. This matters a lot. Keep in mind that the fuel flowing through your glow engine is as much of the coolant as anything. If you increase nitro, and there is a reduction in oil, then the temps could have increased. Then you could go lean from the heat.
I think the simple answer though, is to just make sure you get the needle set right, and the pinch is the best way to do that. You should note a slight increase in RPM, If it sags, and then comes back, you are lean and you need to open a couple of clicks, then try again.

Interesting, I have a brand new one of these .65 AX engines that I have not run yet. I will be flying it for the first time within a week hopefully. It is mounted on a new Bridi, Sun Fli 5 model. I am going to try 11-7, 11-8, and 12-6 props. I can report back which I like the best. I have also added a Macs one piece black muffler, as I hate those fragile 2 piece things that come with them stock. Not sure how that effects power, but I am going to guess I may lose a little.
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Old 03-19-2014, 10:31 AM
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More great information, thanks. I also am running the #8 glow plug in the engine. Would it be recommended to change that to coincide with the greater nitro (15%) content that I switched to recently? I did notice that the engine run temperature did jump up a bit running the higher nitro content fuel. Would changing the plug lower the run temp? That would also be something I would need to do, as I think it was running a bit on the hot side, which may have been contributing to the issues it was having last Saturday.
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Old 03-19-2014, 11:01 AM
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Originally Posted by hsukaria View Post
When talking about stoichiometric ratio of fuel to air, you are talking about the METHANOL to air ratio in glow fuel. Glow fuel also includes oil and nitromethane. So, the adjustment needles have to be set to get the right methanol to air ratio and allow the extra flow through the needles for nitro and oil. If you change the fuel to a different ratio of nitro or oil, the needles will have to be re-adjusted to maintain the correct methanol to air ratio.
It's been a long time since organic chemistry, but I think that I remember nitro-methane requiring just a little oxygen in order for complete combustion. Without a little oxygen, I suspect that there will be a little hydrogen left over.

In any event, if you make any change to the nitro-methane, methanol, and lubricant ratios, you will have to tweak the needles to get the mixture right.

Blue skies
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Old 03-19-2014, 11:19 AM
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Originally Posted by SushiHunter View Post
I also am running the #8 glow plug in the engine. Would it be recommended to change that to coincide with the greater nitro (15%) content that I switched to recently? .

No, the #8 is entirely satisfactory with 15% which is my normal fuel, stick with that plug. I suspect much of your perceived problem is just due to needling and maybe because of a lack of educated ear regardless of the tuning method used. Some of which may not be a problem at all. Their is no way any forum can completely supplant a hands on mentor.


Hsukaria

Actually I can give you a direct comparison and on the same airplane. I did use a .65AX on my river running airplane which needed to carry itself and 72 ounces of fuel as well as floats. The sixty five did a wonderful job and got of the water in a reasonable way with plenty of power in the air. Now with the four fuel tanks removed and just a ten ounce in the nose I am sport flying the same airplane with a .55AX on the water and its perfect but there is no way The 'Soilent Green' would have ever got off the water with the .55. The engine (.65) was switched out to go to even a heavier XC airplane Which is the one that maid the six hour flight.

Vertical Grimmace

Hmm I think you get a kick out the airplane I described above the 'Soilent Green' is actually started life as one of Mr. Joe's airplanes and very close to your Sun Fli 5 as my ship was a Sun Fli 3



John
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Old 03-19-2014, 11:54 AM
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Originally Posted by JohnBuckner View Post
No, the #8 is entirely satisfactory with 15% which is my normal fuel, stick with that plug. I suspect much of your perceived problem is just due to needling and maybe because of a lack of educated ear regardless of the tuning method used. Some of which may not be a problem at all. Their is no way any forum can completely supplant a hands on mentor.


Hsukaria

Actually I can give you a direct comparison and on the same airplane. I did use a .65AX on my river running airplane which needed to carry itself and 72 ounces of fuel as well as floats. The sixty five did a wonderful job and got of the water in a reasonable way with plenty of power in the air. Now with the four fuel tanks removed and just a ten ounce in the nose I am sport flying the same airplane with a .55AX on the water and its perfect but there is no way The 'Soilent Green' would have ever got off the water with the .55. The engine (.65) was switched out to go to even a heavier XC airplane Which is the one that maid the six hour flight.

Vertical Grimmace

Hmm I think you get a kick out the airplane I described above the 'Soilent Green' is actually started life as one of Mr. Joe's airplanes and very close to your Sun Fli 5 as my ship was a Sun Fli 3



John
Good to know. I'll continue using the same plug for now.

BTW, interesting rudder setup on the float plane. The rudder of the plane itself isn't sufficient? I never thought about the additional drag that a float plane has cutting through the water on takeoff. Funny because there are some guys that won't mention that when trying to get new & inexperienced r/c pilots to try sticking floats on their land plane and attempting at water take-off. Probably not an exactly simple maneuver with the added drag so low below the thrust line. Not sure if that would be enjoyable experience to me, well, while training for it.
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Old 03-19-2014, 01:03 PM
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OOO and on the other hand, it hardly dawns on me to mention having a water rudder...
(I'm sure John will chime in with his thoughts as well )
imagine a tricycle gear land airplane.... without a steerable nosewheel. (or a taildragger with nothing but a fixed skid)
they're not a whole lot of fun, especially with a crosswind.

a floatplane is also more likely to 'weathervane' ... if you've got a hard crosswind from the left, that crosswind hits the big surface of the vertical fin and tries to turn the airplane to the left (into the wind).

if you're trying to turn the airplane to the RIGHT, (and without a water rudder) you've got little chance of success.
(and even if you decide, oh heck, I'll just turn to the left instead... the airplane will begin to turn left, till it's pointing directly away from you, and then the wind won't let the airplane turn further)
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Old 03-19-2014, 01:37 PM
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Originally Posted by AMA 74894 View Post
OOO and on the other hand, it hardly dawns on me to mention having a water rudder...
(I'm sure John will chime in with his thoughts as well )
imagine a tricycle gear land airplane.... without a steerable nosewheel. (or a taildragger with nothing but a fixed skid)
they're not a whole lot of fun, especially with a crosswind.

a floatplane is also more likely to 'weathervane' ... if you've got a hard crosswind from the left, that crosswind hits the big surface of the vertical fin and tries to turn the airplane to the left (into the wind).

if you're trying to turn the airplane to the RIGHT, (and without a water rudder) you've got little chance of success.
(and even if you decide, oh heck, I'll just turn to the left instead... the airplane will begin to turn left, till it's pointing directly away from you, and then the wind won't let the airplane turn further)
Sounds fun
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Old 03-19-2014, 01:46 PM
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[QUOTE=JohnBuckner;11763406]
Originally Posted by SushiHunter;

The engine is an OS Max .65AX

QUOTE

Ah Ha now were getting there. First of all let me congratulate you on your choice of engines. The AX series are my all time favorites in a general purpose sport aircraft. I have and actively operate multiples of the .25, .35, .55, .65 and one lonely .95. Now the .65 in particular is a favorite and with that one I have completed several long distance flights including one down the Colorado river and even a static non stop flight at the home field with that lonely little .65 chugging along for 6 hours and 12 minutes.

I apologize for the long preamble but it helps to know that I am not just talking in generalities and actually wish to share some very specific points about the .65 AX and that I do love that engine.

Ok now first you have have considerable high quality imput in this thread including Jim B. and Jester as well as others. I also wish to stress also just how much learning the pinch tunning method can be of great benefit to any flyers. That is specifically for two stroke glow engines. Which requires easy access to the carburetor fuel line while the engine is running even when cowlings are used. There are variations of the technique but in general it is superior even to tachometers in my opinion.

Now to the specific of your engine. All the AX series except the first series 1 .46 use a very different carburation and fuel metering system than most other two stroke glow engines. And there does seem to be one peculiar trait and this is I find more often than not that I have set the main mixture too rich! Perhaps this is because this condition (too rich) seems for whatever the reason sounds and acts like it was too lean.

I know this seems counter intuitive to most but if you use the pinch tuning method this is soon discovered. It is very possible that you actually may have had the main needle far too rich which one single momentary pinch of the carburetor line would soon indicate. This is why I strongly would suggest you find someone who understands pinch tuning and can demonstrate. I teach this to all my students who use two stroke glow engines and their tuning skills soon excel.

John

Edit, I neglected to mention that I found that the OS #8 is the best glow plug choice for the .65 in my opinion.
John, one quick note....When he changed to higher nitro, the engine started to die. If it was too rich, then the higher nitro should have helped
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