Engine Carburetor Tech Secret!?
[ratings]
What is engine carburetor? Is there a need for so-called techical secret in it? Honestly saying even after reading this articles twice, i still believe doing it practically is the way to go by trial and error. On the other hand, one still need to know the basic of engine carburetor function. Especially in RC 2 stroke engine.
For RC Nitro rookie or newbie, learning to tune the carb is like learning to ride a bicycle. Well, at least for me. Once you’ve got the hang of turning the needles clockwise & anti clockwise, you did it right and believe me, you will never forget it.
I quote from Dave Gierke:RCCA
In RC 2-stroke engines, either a rotary-barrel or slide-valve carb is used to control this vital air/fuel mixture; the valve controls the amount of air fed into the engine, and the fuel-mixture needle, or needles, controls the fuel delivery. As your vehicle’s transmitter trigger is pulled, the throttle servo either rotates the throttle barrel (on a rotary carb) or retracts the slide valve (on a slide carb) to feed more air into the engine to increase power and speed. Similarly, when the carb is closed, air and fuel intakes are restricted and, consequently, the engine slows down.
The articles is here for all to read…Feb 2007 RCCA
Listed as paragraphs:
a) How Carb type regulate air/fuel mixture
b) Single Needle Carbs and how to tune it
c) 2 Needles Carbs and how to tune it
*** Attention please: that low speed arrow indicated is actually the idle screw. The Low Speed needle is a bit on the left side of the arrow head. Sorry for the picture imperfection.
d) 3 Needles Carbs and how to tune it
A 3-needle carb’s high- and low-end needles are in the usual locations, and the third needle is on the valve side of the carb. Three-needle carburetors represent the ultimate in tunability but take more time to dial in properly. A correctly tuned engine with a 2-needle carb will outperform the same engine with an improperly tuned 3-needle carb, so let your skills and experience guide your carb selection rather than adopting a “more-needles-are-better” approach.
ENGINE TUNING TERMS
LEAN To lean an engine means to reduce the amount of fuel (relative to the amount of air) entering the engine by turning a needle valve clockwise.
RICHEN Richening increases the amount of fuel (relative to the amount of air) entering the engine, by turning a needle valve counterclockwise. Richening an engine to obtain the proper air/fuel mixture will generally reduce engine temperature and increase lubrication.
NEEDLE VALVES These are the small screws found on the upper portion and sides of the carb body. These are used to adjust the fuel-to-air ratio.
SPRAYBAR This is the metering jet inside the carb body that mates with the low-speed/idle needle (when equipped). They fit together like a tapered peg into a tapered hole.
ON THE PIPE A phrase that indicates an engine is running with an ideal tune and producing excellent power.
For more details, check here the original source: Feb 2007 RCCA online article
9 Responses to “Engine Carburetor Tech Secret!?”
By webmaster on Jan 29, 2007 | Reply
Thanks to CobraSVT from Middle East, Qatar, for the 2 Needle Carb picture error. It supposed to be the idle screw and a bit on the left of the arrow head is the Low Speed Needle. Thanks there mate.!
By horatio on Jan 30, 2007 | Reply
It seems like the 2 needle carb picture is actually a picture of a 3 needle setup, too. It clearly shows the mid-range adjustment screw opposite the ball-end. Regardless of mid-range adjustment, all slide carbs that I’ve seen have the LSN in the ball end side of the carb. In effect, both the LSN and Midrange control the same thing, but by adjusting the ‘midrange’, you actually control the point at which the LS jet is fully opened, as the throttle is opened.
By webmaster on Jan 30, 2007 | Reply
correct there. Good observation!
By mbogash on Apr 6, 2008 | Reply
how do you adjust a single needle carb.i’ve tried and cant seem to get it right.the car dies out at full throttle and i don’t know if it is to lean or to rich.
By webmaster on Apr 6, 2008 | Reply
if its single needle, the usual practice is to assume that is tuned lean. So with that, turn the needle counter clockwise from the top view. Opening it to make it richer. at full speed the engine got thirsty but not enough fuel to supplement it, so it dies. Try this first and let us know what happen. It always better to make it richer at first than to assume it is richer and you lean it.
By mbogash on Apr 7, 2008 | Reply
Thank you i tried it and it worked.I just have to fine tune it now.
By webmaster on Apr 7, 2008 | Reply
Great. Happy to help here. If you have picture or video of your ride, please supply us here. You never know we might post it up just for you
By Shawn on Jul 17, 2008 | Reply
I have an RB Concept S7 L2g .21 engine. I am in the process of tuning it and I am trying to figure out if richening the LSN will in any lower my engine temps. I have leaned the HSN to gain performance and my engine temps went from an average break-in max temp of 220f to 250f - 265f. I am definitely don’t want to damage my new engine but there has to be a way to maximize performance and speed without jeopardizing safe engine temperatures. I am using 20% O’Donnel nitro fuel.
By webmaster on Jul 17, 2008 | Reply
Hi there Shawn. Nice to see you commenting here. WE appreciate it much.
Now, the usual practice is to richen the HSN first then the LSN. Try that. I have no experience on RB engine but the basic tuning still apply here. You must start tuning by idle screw first, the HSN and LSN.. in that order. Others may object this but we never face any problem of getting the tune we wanted on a good engine.
In addition, some engine like it hot like the STS brand but still perform like others with no side effect. Of course bear in mind, it is good to have a little richer tuning than being hot and lean. Try opening HSN while closing a bit on your LSN.
Hope that help