Originally Posted by uDi_MP7.5
I have a tuning question since there are a lot of novarossi experts here.
I recently bought a 35PLUS21 LC (hot mods - seen 2 gallons), and am having a little trouble getting it tuned. Basically my problem is, when I drive around at medium speeds for a while, and then try to hit full throttle, it flames out.
I've had this problem in the past with other novarossi engines and am not really sure how I fixed it.
I am running 18% nitro (9%s+4%c oil) and a C6-TGF plug which has been a good combination for me in the past.
My other concern is, on WOT passes, it blows only a very small amount of smoke, but if I richen the highspeed needle it makes the above problem worse.
Also, any tips on how to check whether my lowend needle is too rich or lean? I recall something about doing a few passes and timing how long it takes to idle down after coming to a stop.
Tuning tips from Ron Paris:
HOW TO SET CARB NEEDLES
New racers often ask where to set the needles on their carb. There is no such thing as a definitive universal setting for any engine. Every application will have its own unique requirements. Even two identical set ups can (and most likely will) have at least slightly different settings.
Some racers make the mistake of setting the idle speed opening to wide (high idle) and set the bottom end too rich. This will give a false normal idle speed even though the speed is set to high because it “loads up” the engine with excess fuel causing the idle to be lower than set. The end result is a very unstable idling engine that surges and may cut out as full throttle is applied because the over rich bottom end can disguise a too lean top end setting!
It is possible too set the idle screw adjustment in to far, but yet the idle speed is not high! Even though the air regulation (carb barrel or slide) may be set to a position that would normally equal a vary fast idle, the idle is low because the low speed mixture adjustment is set so rich that the engine loads up with excess fuel, and the engine goes into what’s commonly called a four cycle idle. One tell-tale sign of this is if after revving up the completely warmed up engine, it tends to idle fast for a few seconds, then drops to a lower idle speed. In other words, it’s something like da..da..da..da..da..da..da..da then it drops to da….da….da….da. If you start leaning the bottom end a little at a time (then repeat the revving up and idle test) and it takes longer before the idle drops, you’re going in the right direction. Eventually as you keep leaning the bottom, the idle will stay too high. Now it is time to lower the idle to where it belongs by re-adjusting the idle screw. Now that you have the idle set correctly, the top end may be too lean! Keep in mind the fuel does not directly enter the cylinder area like a 4 stroke engine; it enters the crankcase area first, then is transferred or pumped up to the cylinder area by the piston movement. Simply put, the crank case volume can hold much more capacity than the cylinder, so it takes some time to burn off the residual fuel. If the bottom end is too rich, the engine will be supplied by this residual fuel briefly, and depending on the demand you may be actually be experiencing a lean condition on the top end that can range from:
1 - Seems to run well, but engine life is short
2 - Seems to run well, but car continues to get hotter the longer you run to the point of overheat!
3 - Seems to run ok on the bottom, but sputters starves or strains to gain rpm
4 - Seems to run ok on the bottom, but when you give full throttle it cuts out or stalls
An overly rich top end can act the same as 3 & 4, but excessive smoke and oil are usually present with a distinct blubbering sound.
There is no reason for an engine to continually get hotter unless the tune is wrong (classic #2 symptom) or there is a mechanical problem causing more load or drag on the engine as the run continues. An exception is if the weather or track conditions change dramatically - for example, a light drizzle starts and the off road track goes from a very dry loose to high traction condition, or during a race a rapid weather front happens, causing something like a ten degree change in temperature.
It is very important to fully warm up your engine, clutch and chassis before making final adjustments. The chassis in most applications also works like a heat sink to the engine so it is important to fully saturate the chassis!!! I like to start the engine at least three or four minutes before the qualifier to get some heat in the engine. If you don’t yet have your radio, you can operate the throttle by hand. Remember though, it will still take at least two to three minutes of hard running on the track to fully saturate the chassis!
There is a series of restrictions to control fuel flow at different throttle/air flow positions called needles These are the five basic parts of the carb to concern yourself with.
The slide or barrel regulates the amount of air that can enter the engine. It is controlled by the servo. It simply blocks off the airflow to the engine, proportional to how far it is open or closed.
The idle/air speed screw sets the absolute minimum air the barrel/slide can control to maintain idle speed. It simply is an adjustment screw that comes in contact with the side at the nearly closed/idle position.
The high speed needle regulates maximum fuel flow allowed to enter the engine at any throttle position. It is simply a tapered needle that screws into the fuel flow orifice (an adjustable restriction). This maximum fuel flow ideally is adjusted to the correct mixture ratio for the surrounding conditions when the throttle is wide open.
The low speed needle regulates fuel to engine at idle. The low speed adjustment simply restricts the flow at idle speed. If you look down the bore of the carb you will usually see a long tapered needle. When the carb barrel/slide is closed the larger part or diameter portion of the long tapered needle is inserted into the spray bar, this is what’s adjusted when you turn the low speed/minimum adjustment. It literally moves either the tapered needle or the spray bar farther in or out, changing the restriction independent of the barrel/side position. This leans (more restriction) or richens (less restriction) the flow from the spray bar at idle. On some carbs the spray bar is moved and on others the needle assembly is moved. Both have the same effect.
The mid range needle regulates fuel to the engine after idle and before full fuel position. As you open and close the carb the tapered needle (mentioned above in item 4) enters into a small tube this is called the spray bar/jet. This spray bar is where ALL the fuel enters the airflow stream regulated by the high speed, mid range and idle/minimum adjustments! Normally at somewhere between ½ and ¾ throttle open position the needle is completely out of the spray bar, This is what is called full fuel position or FFP. At this point 100% of the mixture is controlled by the high speed needle. On many carbs the low speed and midrange are not independently adjustable, so the mid range is a factor of the needle taper and is engineered by the factory.
If there are adjustments on both the slide and the carb body, one is an adjustable mid range, and the other the low speed!!! Check with the engine manufacture before attempting to adjust these types of carbs! It is very important not to use the mid screw to adjust the low end by mistake; it is very easy to get the carb way out of sync, and the gains are VERY small and mostly limited to minute midrange drivability/economy changes that only the most sophisticated driver will recognize. If you do this wrong, you might end up with a carb that is so screwed up only an expert can get it back in tune!
HOW TO “READ” YOUR GLOW PLUG
When a new plug wire just goes slightly gray after a 5 or 10 minute hard run it means your very close to an optimal horsepower tune, but be careful - the next step is TOO LEAN!
If the wire and surrounding bottom of plug is wet, with like new shiny wire, you’re on the rich side of optimum power.
If the wire and surrounding bottom of the plug is starting to dry and the wire starting to gray, you’re very close to optimum power.
If the wire and surrounding bottom of plug is dry, and the wire is totally gray but not distorted, you’re at optimum power.
If the wire and surrounding bottom of the plug is dry, and the wire is distorted, you’re slightly lean.
If the wire and surrounding bottom of plug is dry, the wire is broken and distorted or burnt up, your engine is extremely lean and there’s the possibility of engine damage.
You can only “Read” your plug in a nearly new state (wire like new and shiny). A gray plug can still operate well. After it has totally gone gray, performance can start to fall off. To test, just put in a new plug. If there is no difference in performance, save the gray one or put it back in. If your engine does not feel or run right, try a new plug before making major tune changes.
Hope this helps!