Originally Posted by nsxshogun
............... I'm still trying to get the LSN right though. Also the colder plug really made this thing fly.
Obtaining a good carburetion of the engine could appear as a hard obstacle even if in reality is quite simple. The most important thing while carbureting is to well understand how a carburetor works and having a good feeling with the sounds produced by the engine.
All carburetors are factory set on a flow bench. For this reason it is recommended that you count the number of turns on the low and high end needles before you use the engine. All carbs are not the same, but are set to flow the same amount of air and fuel. Up to a one half turn difference can be had on factory carburetor settings on each needle. A two micron difference in the needle taper can make the setting up to 1/2 turn different from another carb.
It is also not recommended not to adjust the mid-range needle setting until you are completely comfortable with carburetor adjustment.How big is a micron? There are 25,400 microns in one inch. This dot (.) is approximately 1/64 of an inch wide and equals 615 microns. It doesn't take much to off set a needle setting.
First you have to warm up the engine for a couple of minutes with a very light acceleration. Adjusting of the minimum speed: when the engine is at about 85 - 100 C°, keep the carburetor at the minimum rpm (with the throttle completely closed) and adjust the minimum needle screw (air needle) so that the engine reaches a regular RPM (.5 to 1mm slide piston open).
The carburetor has two main adjustments (leave mid range needle untouched):
1. The needle of the throttle (low needle) which adjusts the engine when you start it up in static position and at a low speed up to its medium rpm.
2. The top needle (high needle) that adjusts the engine to medium - high rpm, at the maximum speed level and acceleration ADVISEAlways adjust the high speed needle in a way that the engine, with the carburetor opened at a maximum produces smoke while driving straight. This means that you are doing a "rich" carburetion.
If you use the engine in a "lean" condition you can damage the engine due to a lack of oil.
Now you can start giving much more power to the accelerator in order to hear the engine at a higher rpm. If the engine grows up very quickly or sobs (before you reach the maximum gas), the carburetion is "lean", the volume of fuel you introduce in the combustion chamber is not up to the request of the engine.In this case you have to screw off the full speed needle till you hear a more regular noise coming from the engine and a good quantity of smoke has to come out from the pipe. If the engine has difficulties in going up with the rpm, sobs and a lot of smoke together with oil comes out from the exhaust, the carburetion is "rich", which means that too many fuel goes into the combustion chamber and the engine is not able to burn it.Screw in or fasten the screw of the high speed needle till the quantity of smoke coming out from the exhaust is more balanced and the rpm’s are higher.
Carburetion in movement:
At this point you have to make the carburetion with the car driving on a racetrack. The behavior of the engine is the same but now you have one more help: the engine reflects its behavior on the car and due to that the carburetion is now simpler. Make a couple of laps in order to reach the working temperature always taking care that at full gas a good quantity of smoke comes out from the exhaust.
Carburetion of the low speed needle:
Try to stop the engine for 2-3 second and then start quickly. If the engine sobs and presents difficulties in starting, the base speed goes up, and no smoke is coming out from the engine, the carburetion is lean of low speed. In this case you have to screw out the needle till the starting and the sound of the engine improves.If on the other hand the engine has difficulties in increasing the rpm, a lot of smoke comes out or stops, then it is "rich of low speed". In this case you have to screw the needle till you reach a progressive sound of the engine, a hiss and a some smoke comes out. Overall, your engine should idle nice and consistent for at least 45+ seconds before the idle slows enough to stall the engine.
Carburetion of the high speed needle:
Make 2 or 3 laps in this condition and adjust the high speed needle so that the engine produces a constant acceleration till the end of the longest straightaway of the track with a hiss for all the length. Making other 2 or 3 laps you can check if the engine keeps the performances all over the track under the maximum power. If so, then the carburetion is OK!In case it looses power and decreases rpm, screw out the full speed needle about 1/8 th (richen the carburetion) and try again and again till you reach stable performances.