Carburetor setup - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-01-2019, 04:01 PM   #1
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Carburetor setup

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How do you know if the low needle is set too rich?????
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Old 07-01-2019, 04:02 PM   #2
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Re: Carburetor setup

Thank you for any input
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Old 07-01-2019, 05:11 PM   #3
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Re: Carburetor setup

Eh? When did you get a reply?
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Old 07-02-2019, 06:44 AM   #4
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Re: Carburetor setup

gas or glow carb ? . Most often you will have a slow transition , if it's rich enough you may even get smoke and not need much choke when cold, if it's too lean it will sag when throttled quick and may be hard to start or keep running when cold . I set the low speed to get the highest RPM then back it off a bit .On gas engines - I set the high speed last because the low speed effects the overall mixture of the high speed. The high speed will not have much if any effect on the low speed at idle unless you have a problem with the main jet pop off valve because the main does not or should not feed fuel at idle .With most glow carbs you need to work the needles back ad forth to get them correct because the low and high effect each other but you will get the same symptoms for rich and lean ..
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Last edited by RAMJET; 07-02-2019 at 07:13 AM.
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Old 07-04-2019, 11:52 AM   #5
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Re: Carburetor setup

This may be useful if you are talking glow engines - Dub Jett goes through his process for setting low end mixture on his engines here:
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Old 07-31-2019, 09:28 AM   #6
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Re: Carburetor setup

First; The low speed needle usually has no effect on high speed mixture! (explained in adjustment)
1. attach a clean piece of fuel line to to the fuel inlet.
2. close the throttle barrel on a "T" pin or something the same size.
3. Blow in the fuel line and adjust the low speed needle so a small bit of air jus starts to come through.
4. Open the throttle full and look down the barrel. Check to see if "the low speed needle" is clear of the end of the spray bar, on most engines it will be.
5. Remove the "T" pin. Open the throttle full and blow in the fuel line and adjust the high speed needle so I restricts about one third of the air flow.

You will find that the low speed needle is quite close and the high speed is quite rich.

6. Start the engine and set the high speed needle.
7. Completely peak the engine at full throttle. then richen it so it looses 200 - 400 RPM.
8. Now try the idle, what we are looking for is 2500 - 2600 RPM.
9. Adjust the low speed needle for maximum RPM then richen it up 1/8th of a turn. You might have to blip the throttle to clear the excess fuel in the base. If your RPM is not at a good RPM for that engine, adjust the idle stop screw and readjust low speed needle to get a reliable idle.
10. Every now and then give the engine a good burst of full throttle to clean out and heat up the engine. When you go back to idle it will probably go to around 2800 - 3000RPM, then it will loose several hundred RPM because of the slightly rich mixture which builds up a rich mixture in the lower crankcase which the engine uses to accelerate when you open the throttle.

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