RobH
Gone - bye bye.
- Messages
- 1,958
- Reaction score
- 0
- RC Driving Style
I think one of the hardest things for a nitro newbie is tuning his carb. I'm not a expert so read on at your own risk. I would, however, like to share my experience on the topic so that maybe you wont make the same mistakes I did.
I thought i was doing everything right. I tuned my HSN first and the LSN needle second and the idel set screw last. The temps were always good (230-250). When I took my R/C out to the track, i got a pretty stiff wake up call. My engine seemed to lack the bottom end found in the other engines on the track. I say "seemed" because, as luck would have it, I re-tuned my engine a week later and found a drastic error my tuning methods.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
RobH's Carb Tuning HOW-TO:
The first thing you need to do if get your RC to stay running under rich conditions. Start with the low speed needle (LSN) and high speed needle (HSN) rich enough that the engine bogs down constantly, but lean enough that it doesn't die. You need your RC to run before you can tune it.
Next, as we've all read before, get the engine up to temp. Under rich conditions, the engine won't get that hot. The warmer you can get it, however, the more accurate the tune.
Before we start on the needles, let me point out that it's important that you never let the RC have less than a 1/2 tank of gas at any time during the tuning process. If you run the tank to the bottom, you will get a false since of lean / rich as the RC will naturally lean out as it gets to the bottom of the tank. As you tune the engine, be sure to top off the tank each time it hits the half way mark.
Now you can finally start turning needles. Again, as you've read before, you adjust the HSN first. The HSN directly effects the engine's performance and temperature while it’s at WOT. When the HSN is too rich, you will hear an odd noise at WOT. The engine looses speed and can be best described as bogging down. That noise is an indication that the HSN is too rich. Make a couple of WOT passes and listen for the noise. Continue to lean the engine in small increments after each set of passes. Eventually, the noise will go away and you will notice an improvement in the speed at WOT.
You're not done with the HSN yet. You should still see lots of smoke coming out at WOT. That smoke means health. The smoke is made by the oil in the fuel and if you don't see smoke, you're damaging your engine because it isn't lubricated enough. SMOKE SMOKE SMOKE SMOKE! Did I say SMOKE enough? Continue to lean the HSN and pay close attention to the smoke at WOT. If the smoke is gone, you need to richen it up until you have a visible stream of smoke at WOT.
The HSN is all about WOT. You're looking for smoke at WOT and you're listening for bogging down at WOT. At this point, we don't care about acceleration and smoke and bogging during acceleration. The HSN only pertains to what you see and hear at WOT.
If you tuned the HSN correctly, the RC should still be slow and it should still bog down during acceleration. At WOT, however, you should see a visible trail of smoke and you should not hear any sort of bogging engine noise.
The LSN is next, but we need to talk about "loading up" and "cleaning out" first. The best way to test a LSN setting is to mash the throttle down and "gun it". If the RC bogs down and acceleration poorly, you know the RC is too rich. There is something you must that that will mess you up. If your RC sits at an idle for any amount of time (10 or more seconds), excess fuel will build up in your carb. When you hit the throttle, that excess fuel gets pushed into the engine and makes it look like a rich condition. To avoid this, you need to "clean it out" before you test your acceleration. If you RC has been idling for some time, pick up the RC and put the hammer down. Just mash it and let the wheels spin up to full revs then let go. The blows out all that excess fuel and you're now ready to test your LSN setting.
From a stand still, mash the throttle all the way down. At this point, the RC should bog down and really sound unhealthy during acceleration. Do this a few times before making a small clockwise turn on the LSN. Repeat the process by mashing down on the throttle a few times and listening for the bogging down. Eventually, the bogging will go away. At this point, you're getting close to the "sweet spot". It's now time to take your temps. Run the RC a few passes accelerating quickly and hitting top speed. Afterwards, take the temperature (point your temp gun squarely at the glow plug for the most accurate reading). At a full tank, you should not exceed 230-240 degrees. If you run the tank out, you can expect temps as high as 260-270. In my book, that's fine. You wont run for very long on an empty tank anyway.
The next setting is the idle set screw (ISS). This is a real no-brainer. There is no prize for the guy that can idle at the lowest RPMs. The goal of the ISS is to keep the engine at a low enough RPM that the clutch does not engage, but high enough that it's doesn't die. Find someplace in the middle where you think it sounds good and you're done.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
The first time I tried this, it felt like I had bought a new engine. I now had a ton more speed an acceleration than before. I had seen this speed before, but it was at unsafe temps. Now, I run a sweet 230-240 with ton's of acceleration and top speed.
As it turns out my biggest problem was incorrectly tuning the HSN. I saw the RC bogging down under acceleration and figured the HSN was still too rich. By the time the low-end stopped bogging down, the HSN was way too lean and the engine wasn't producing any smoke at WOT. Furthermore, I had to compensate by leaving the LSN very rich. This kept the RC at a stable temperature but at the cost of bottom-end performance.
Happy Tuning,
RobH
I thought i was doing everything right. I tuned my HSN first and the LSN needle second and the idel set screw last. The temps were always good (230-250). When I took my R/C out to the track, i got a pretty stiff wake up call. My engine seemed to lack the bottom end found in the other engines on the track. I say "seemed" because, as luck would have it, I re-tuned my engine a week later and found a drastic error my tuning methods.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
RobH's Carb Tuning HOW-TO:
The first thing you need to do if get your RC to stay running under rich conditions. Start with the low speed needle (LSN) and high speed needle (HSN) rich enough that the engine bogs down constantly, but lean enough that it doesn't die. You need your RC to run before you can tune it.
Next, as we've all read before, get the engine up to temp. Under rich conditions, the engine won't get that hot. The warmer you can get it, however, the more accurate the tune.
Before we start on the needles, let me point out that it's important that you never let the RC have less than a 1/2 tank of gas at any time during the tuning process. If you run the tank to the bottom, you will get a false since of lean / rich as the RC will naturally lean out as it gets to the bottom of the tank. As you tune the engine, be sure to top off the tank each time it hits the half way mark.
Now you can finally start turning needles. Again, as you've read before, you adjust the HSN first. The HSN directly effects the engine's performance and temperature while it’s at WOT. When the HSN is too rich, you will hear an odd noise at WOT. The engine looses speed and can be best described as bogging down. That noise is an indication that the HSN is too rich. Make a couple of WOT passes and listen for the noise. Continue to lean the engine in small increments after each set of passes. Eventually, the noise will go away and you will notice an improvement in the speed at WOT.
You're not done with the HSN yet. You should still see lots of smoke coming out at WOT. That smoke means health. The smoke is made by the oil in the fuel and if you don't see smoke, you're damaging your engine because it isn't lubricated enough. SMOKE SMOKE SMOKE SMOKE! Did I say SMOKE enough? Continue to lean the HSN and pay close attention to the smoke at WOT. If the smoke is gone, you need to richen it up until you have a visible stream of smoke at WOT.
The HSN is all about WOT. You're looking for smoke at WOT and you're listening for bogging down at WOT. At this point, we don't care about acceleration and smoke and bogging during acceleration. The HSN only pertains to what you see and hear at WOT.
If you tuned the HSN correctly, the RC should still be slow and it should still bog down during acceleration. At WOT, however, you should see a visible trail of smoke and you should not hear any sort of bogging engine noise.
The LSN is next, but we need to talk about "loading up" and "cleaning out" first. The best way to test a LSN setting is to mash the throttle down and "gun it". If the RC bogs down and acceleration poorly, you know the RC is too rich. There is something you must that that will mess you up. If your RC sits at an idle for any amount of time (10 or more seconds), excess fuel will build up in your carb. When you hit the throttle, that excess fuel gets pushed into the engine and makes it look like a rich condition. To avoid this, you need to "clean it out" before you test your acceleration. If you RC has been idling for some time, pick up the RC and put the hammer down. Just mash it and let the wheels spin up to full revs then let go. The blows out all that excess fuel and you're now ready to test your LSN setting.
From a stand still, mash the throttle all the way down. At this point, the RC should bog down and really sound unhealthy during acceleration. Do this a few times before making a small clockwise turn on the LSN. Repeat the process by mashing down on the throttle a few times and listening for the bogging down. Eventually, the bogging will go away. At this point, you're getting close to the "sweet spot". It's now time to take your temps. Run the RC a few passes accelerating quickly and hitting top speed. Afterwards, take the temperature (point your temp gun squarely at the glow plug for the most accurate reading). At a full tank, you should not exceed 230-240 degrees. If you run the tank out, you can expect temps as high as 260-270. In my book, that's fine. You wont run for very long on an empty tank anyway.
The next setting is the idle set screw (ISS). This is a real no-brainer. There is no prize for the guy that can idle at the lowest RPMs. The goal of the ISS is to keep the engine at a low enough RPM that the clutch does not engage, but high enough that it's doesn't die. Find someplace in the middle where you think it sounds good and you're done.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
The first time I tried this, it felt like I had bought a new engine. I now had a ton more speed an acceleration than before. I had seen this speed before, but it was at unsafe temps. Now, I run a sweet 230-240 with ton's of acceleration and top speed.
As it turns out my biggest problem was incorrectly tuning the HSN. I saw the RC bogging down under acceleration and figured the HSN was still too rich. By the time the low-end stopped bogging down, the HSN was way too lean and the engine wasn't producing any smoke at WOT. Furthermore, I had to compensate by leaving the LSN very rich. This kept the RC at a stable temperature but at the cost of bottom-end performance.
Happy Tuning,
RobH
Last edited: