Does anyone have tips on carb adjustments on gas engines?
05-11-2002, 04:17 AM
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Does anyone have tips on carb adjustments on gas engines?
I am new at using gasoline engines. I own 2 Brison 3.2's and 1 Brison 6.4.
I am not familiar with how to identify if I am running too lean or rich on the high and low needle setting.
Any suggestions on what I should be listening for and whether I should lean out or richen up???
Thanks,
C&B
I am not familiar with how to identify if I am running too lean or rich on the high and low needle setting.
Any suggestions on what I should be listening for and whether I should lean out or richen up???
Thanks,
C&B
05-11-2002, 10:30 AM
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Does anyone have tips on carb adjustments on gas engines?
Okay, I'll be the first! I'll start off by saying you really want to invest in a good tach; I use the TNC ('bout $100) which is a lot less sensitive of ambient light than cheaper units... Take your time to set the needles; it's very time-consuming but once they're set, you really don't need to mess with them. Low speed adjustments will also affect the top end.
Hi speed- adjust for max rpm, then richen by approx 300 rpm. Too rich and the engine gets blubbery, too lean and the engine will sound a little "flat" and have a slight misfire. Hard to describe, but pretty distinctive when you hear it. When you get close to max rpm, make adjustments in 1/8 turn increments.
The low speed needle is actually easier to adjust, in my opinion... too rich and the idle speed will gradually decrease, and transition to full throttle will sputter; too lean and you will get a cough when you advance the throttle, then immediate high rpm.
I think it's easiest to set the hi speed needle, then set low speed for best (slow and smooth) idle, then reset the hi speed needle. That's how I do it, which quite possibly may be totally wrong, so others please jump in here! Happy flying; gas is fun!
Hi speed- adjust for max rpm, then richen by approx 300 rpm. Too rich and the engine gets blubbery, too lean and the engine will sound a little "flat" and have a slight misfire. Hard to describe, but pretty distinctive when you hear it. When you get close to max rpm, make adjustments in 1/8 turn increments.
The low speed needle is actually easier to adjust, in my opinion... too rich and the idle speed will gradually decrease, and transition to full throttle will sputter; too lean and you will get a cough when you advance the throttle, then immediate high rpm.
I think it's easiest to set the hi speed needle, then set low speed for best (slow and smooth) idle, then reset the hi speed needle. That's how I do it, which quite possibly may be totally wrong, so others please jump in here! Happy flying; gas is fun!
05-11-2002, 12:30 PM
#4
Does anyone have tips on carb adjustments on gas engines?
Beyond what the other have said---
The gas engines with carbs mount on the side of the engine, in general, are sensitive to air flow over (past) the carb inlet and or regulator vent hole. If you have trouble beyond what the other guys have mentioned, you might try a venturi extension. (sometimes called a velocity stack) They typically have a slant cut on the outer part of it. You may have to experment by turning this different directions until you get the response you want. Also the little vent hole on the carb body gives trouble sometimes. You can try turning the plat around to a different quadrant if you can. Or put a piece of tape in front of it or something to change the airflow around it. Do not plug it up. The engine will quit if you plug it up.
Most of these engines have a pressure wave that stands just ouside the carb or very near the outside. Air flowing past the carb inlet will blow this fuel mixture down the side of your plane. One solution is to use the velocity stack.
Good luck
Jim
The gas engines with carbs mount on the side of the engine, in general, are sensitive to air flow over (past) the carb inlet and or regulator vent hole. If you have trouble beyond what the other guys have mentioned, you might try a venturi extension. (sometimes called a velocity stack) They typically have a slant cut on the outer part of it. You may have to experment by turning this different directions until you get the response you want. Also the little vent hole on the carb body gives trouble sometimes. You can try turning the plat around to a different quadrant if you can. Or put a piece of tape in front of it or something to change the airflow around it. Do not plug it up. The engine will quit if you plug it up.
Most of these engines have a pressure wave that stands just ouside the carb or very near the outside. Air flowing past the carb inlet will blow this fuel mixture down the side of your plane. One solution is to use the velocity stack.
Good luck
Jim
05-11-2002, 12:56 PM
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Another solution?
Originally posted by w8ye
Beyond what the other have said---
The gas engines with carbs mount on the side of the engine, in general, are sensitive to air flow over (past) the carb inlet and or regulator vent hole. If you have trouble beyond what the other guys have mentioned, you might try a venturi extension. (sometimes called a velocity stack) They typically have a slant cut on the outer part of it. You may have to experment by turning this different directions until you get the response you want. Also the little vent hole on the carb body gives trouble sometimes. You can try turning the plat around to a different quadrant if you can. Or put a piece of tape in front of it or something to change the airflow around it. Do not plug it up. The engine will quit if you plug it up.
Most of these engines have a pressure wave that stands just ouside the carb or very near the outside. Air flowing past the carb inlet will blow this fuel mixture down the side of your plane. One solution is to use the velocity stack.
Good luck
Jim
Beyond what the other have said---
The gas engines with carbs mount on the side of the engine, in general, are sensitive to air flow over (past) the carb inlet and or regulator vent hole. If you have trouble beyond what the other guys have mentioned, you might try a venturi extension. (sometimes called a velocity stack) They typically have a slant cut on the outer part of it. You may have to experment by turning this different directions until you get the response you want. Also the little vent hole on the carb body gives trouble sometimes. You can try turning the plat around to a different quadrant if you can. Or put a piece of tape in front of it or something to change the airflow around it. Do not plug it up. The engine will quit if you plug it up.
Most of these engines have a pressure wave that stands just ouside the carb or very near the outside. Air flowing past the carb inlet will blow this fuel mixture down the side of your plane. One solution is to use the velocity stack.
Good luck
Jim
05-11-2002, 01:04 PM
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Does anyone have tips on carb adjustments on gas engines?
On gas engines, it is easier to adjust the low speed mixture first. The reason is that the low speed jet is operational over the entire throttle range. The high speed jet is operational only from about half throttle to full. This is very different from the standard 2 needle glow carb.
Set the low speed needle for good acceleration from idle to about mid throttle when you snap the throttle open. Once that is set, check the high speed needle by running the engine at full throttle. Adjust the needle only about 100 rpm down from the peak rpm on the rich side.
Now test fly it. Make sure the engine doesn't sag in the vertical- that's a sign of being too lean on the high speed needle. If it does sag, richen the high speed needle by about 1/8th turn and fly it again.
If you chop throttle to idle and the engine dies in the air, that's a sign that your low speed needle is too lean.
Engines never quit from being too rich. If it quits, it's too lean.
Set the low speed needle for good acceleration from idle to about mid throttle when you snap the throttle open. Once that is set, check the high speed needle by running the engine at full throttle. Adjust the needle only about 100 rpm down from the peak rpm on the rich side.
Now test fly it. Make sure the engine doesn't sag in the vertical- that's a sign of being too lean on the high speed needle. If it does sag, richen the high speed needle by about 1/8th turn and fly it again.
If you chop throttle to idle and the engine dies in the air, that's a sign that your low speed needle is too lean.
Engines never quit from being too rich. If it quits, it's too lean.
05-11-2002, 01:27 PM
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GREAT TIPS!!
I am very happy to have you guys giving me an education in the gas engine game.
I have already printed out the entire BME owners manual, which I believe has a far better carb adjustment section that the Brison manual.
I also already own the TNC tach.
I will be flying later today and will try these tips.
I do not believe have an airflow problem at this point. I just need to fine tune the carb.
By the way, I have not had a dead stick with either engine. So I believe I am still on the rich side.
Thanks for your tips so far!
C&B
I have already printed out the entire BME owners manual, which I believe has a far better carb adjustment section that the Brison manual.
I also already own the TNC tach.
I will be flying later today and will try these tips.
I do not believe have an airflow problem at this point. I just need to fine tune the carb.
By the way, I have not had a dead stick with either engine. So I believe I am still on the rich side.
Thanks for your tips so far!
C&B
