PaulH
08-30-2006, 09:49 PM
In the year or so that I have been a member here, I have seen many people ask similar questions about setting up and maintaining their gas engine. I asked Will if I could start a Gasser tuning FAQ. He was gracious enough to allow me that opportunity. This thread will be a living discussion. I will modify this first post as people post their questions and answers, similar to how Finless Bob has been handling some of his threads.
I am not the final authority on much of this. There may be innaccuracies. Please let me know what they are so that I can fix them. The hope is that this first post will become a "living document" with one-stop information for new and experienced gas engine owners alike.
A. FUEL SYSTEM
A1. What type of fuel should I use?
Many people have good luck with Coleman camper fuel and its counterparts. However, due to the inconsistancies in its octane rating, most of the vendors and tuners recommend plain-vanilla 87 octane gasoline from the pump.
A2. What type of oil should I use?
Again, most people have good luck with a wide variety of oils, from Mobil-1 to Amsol. The engine vendors and tuners recommend Blue Marble (http://www.bluemarbleoil.com/) even though it is not a synthetic. You can go to their web site to find a dealer near you. At the time of this writing, Hanson and Bergen R/C resell Blue Marble. That being said, these oils will prolong your break-in period. You should use an ashless dino oil, like Lawn Boy Ashless for the first gallon or two before switching over to Blue Marble.
A3. What gas/oil ratio should I use?
25:1 Seems to be common. This translates into 5 ounces of oil per gallon of fuel. People use more and less oil than 5 oz with success, but this is a good starting point.
B. ENGINE TUNING
B1. What should my initial needle settings be?
This depends on the carburator used. The Walbro 64x series are the most common on our G23 and G26 engines. For this model, both needles should be closed all the way, then opened to 1-3/8 turns.
B2. I'm used to tuning nitro engines. How do I tune my gasser?
You can't tune by the amount of smoke coming out as with a nitro engine. Gas engines burn quite clean once they're up to temperature. Two years ago, John Garst made a wonderfully comprehensive post in this topic that explains tuning about as well as can be done with mere words. Here is what he said:
To initially set up the low needle, make it purposely rich (the tail will kick as you apply power). Then take the low end in a bit at a time listening for the motor to clean up and the tail to stop kicking. The low needle commands the mixtures through hover-range where the high needle picks up nearer wide open throttle. Listen and watch the machine. A burble accompanied by a tail twitch is still rich. As you adjust leaner and this goes away, stop. A lean bottom end condition will show up first in the skids as a vibration. Once set, you can then work on the high end needle.
High needle: Once again, start from rich and do powered climbs and listen for a rich condition at wide open throttle. A sag or bog could be taken as either rich or lean (this is why you make it purposely rich). Richen up the top and see if it gets better, if worse go leaner and then try again. What you are looking for is a good hard "pull" without a sag and as always err to the rich side (take in mind the gas needles have a much narrower operating window). Do not mistake the motor "loading" for a bog (this is where the ear comes in). The high needle is hardest to get right so take this in small steps and develop an ear for it.
C. TRANSMITTER PROGRAMMING
C1. I have heard that gas engines do not work with a linear throttle curve. What should my throttle curve look like?
A gas engine uses a butterfly for the intake, which means it does not have a linear response like a nitro engine. Half throttle (hovering speed) is around 25% or so on your throttle curve. Assuming that you hover at 3/4 stick, you curves will look something like these:
N (1550): 0, 20, 22.5, 25, 100
ID1 (1650): 100, 30, 27.5, 30, 100
ID2 (1750): 100, 32.5, 30, 32.5, 100
D. OPERATION
I am not the final authority on much of this. There may be innaccuracies. Please let me know what they are so that I can fix them. The hope is that this first post will become a "living document" with one-stop information for new and experienced gas engine owners alike.
A. FUEL SYSTEM
A1. What type of fuel should I use?
Many people have good luck with Coleman camper fuel and its counterparts. However, due to the inconsistancies in its octane rating, most of the vendors and tuners recommend plain-vanilla 87 octane gasoline from the pump.
A2. What type of oil should I use?
Again, most people have good luck with a wide variety of oils, from Mobil-1 to Amsol. The engine vendors and tuners recommend Blue Marble (http://www.bluemarbleoil.com/) even though it is not a synthetic. You can go to their web site to find a dealer near you. At the time of this writing, Hanson and Bergen R/C resell Blue Marble. That being said, these oils will prolong your break-in period. You should use an ashless dino oil, like Lawn Boy Ashless for the first gallon or two before switching over to Blue Marble.
A3. What gas/oil ratio should I use?
25:1 Seems to be common. This translates into 5 ounces of oil per gallon of fuel. People use more and less oil than 5 oz with success, but this is a good starting point.
B. ENGINE TUNING
B1. What should my initial needle settings be?
This depends on the carburator used. The Walbro 64x series are the most common on our G23 and G26 engines. For this model, both needles should be closed all the way, then opened to 1-3/8 turns.
B2. I'm used to tuning nitro engines. How do I tune my gasser?
You can't tune by the amount of smoke coming out as with a nitro engine. Gas engines burn quite clean once they're up to temperature. Two years ago, John Garst made a wonderfully comprehensive post in this topic that explains tuning about as well as can be done with mere words. Here is what he said:
To initially set up the low needle, make it purposely rich (the tail will kick as you apply power). Then take the low end in a bit at a time listening for the motor to clean up and the tail to stop kicking. The low needle commands the mixtures through hover-range where the high needle picks up nearer wide open throttle. Listen and watch the machine. A burble accompanied by a tail twitch is still rich. As you adjust leaner and this goes away, stop. A lean bottom end condition will show up first in the skids as a vibration. Once set, you can then work on the high end needle.
High needle: Once again, start from rich and do powered climbs and listen for a rich condition at wide open throttle. A sag or bog could be taken as either rich or lean (this is why you make it purposely rich). Richen up the top and see if it gets better, if worse go leaner and then try again. What you are looking for is a good hard "pull" without a sag and as always err to the rich side (take in mind the gas needles have a much narrower operating window). Do not mistake the motor "loading" for a bog (this is where the ear comes in). The high needle is hardest to get right so take this in small steps and develop an ear for it.
C. TRANSMITTER PROGRAMMING
C1. I have heard that gas engines do not work with a linear throttle curve. What should my throttle curve look like?
A gas engine uses a butterfly for the intake, which means it does not have a linear response like a nitro engine. Half throttle (hovering speed) is around 25% or so on your throttle curve. Assuming that you hover at 3/4 stick, you curves will look something like these:
N (1550): 0, 20, 22.5, 25, 100
ID1 (1650): 100, 30, 27.5, 30, 100
ID2 (1750): 100, 32.5, 30, 32.5, 100
D. OPERATION