Beginner - trouble tuning idle so car will sit still
 

Hi,

I'm a beginner when it comes to gas powered R/C. My best friend gave me his RS4/2 that has some upgrades. One of those is the OS Max CV-15 engine. It has both high (which I believe they refer to as a needle valve) and low (which they refer to as the mixture control screw) idle adjustments as well as the throttle stop screw. I've been fooling around all day trying to figure out how to get this thing to idle low enough that it will stay still if I put it on the ground. As it stands the wheels are turning way too fast.

Right now I have it such that *I think* the low speed idle adjustment is about perfect. I'm using the pinch test to determine this. If I pinch off the fuel the rpm's increase just slightly and then engine shuts off. The low speed adjust is just under a full turn open from full closed. I hear this is wrong though, as most sites advise this screw to be flush.

The high speed is 3 full turns open. There's about a 1MM opening in the carb (per the OS Max instructions).

What do I adjust as this point to get the RPM's low enough to set it down?

Thanks in advance.

Maybe your idol postion in the carb is too open. Also, you may not have the brakes engaged enough. If you pull full brakes does it stop? Im just throwing stuff out there, i had the same problem at first. Turns out i had to set the minimum carb opening, which youve done, adjust the carb at neutral, half way open or less is what i use, and set the brake engagement where i want it. To do that, on the long stem from your throttle servo, turn the little knob on the end of it clockwise. Hope any part of this helps.

first off- how long does the engine run after you pinch the fuel line? Should be around 2- 3 seconds before it stalls.

Is your carb linkage set properly? If you hit the brake does the idle lower or the engine stall? Make sure your linkage is not holding the carb open a little. If the linkage is causing the carb to hang open a little, adjust the linkage so there is a slight movement of the servo before the carb barrel starts to open.

If your linkage is OK try these possibilities....

It may be that your low needle is too lean and the idle is very high because of this. If the car dies quickly with the pinch test, open the low needle 1/8 turn at a time.

The other possibility is that the idle screw is just open too far. If the pinch test is lasting 2- 3 seconds, then just lower your idle screw by turning it out till the idle lowers to where you want it.

I had a similiar experience after finishing a main. I was running out the last of the fuel in my tank and fuel lines but noticed the wheels were spinning... checking the clutch, I found the clutch nut had come loose... so this may be a place to start if you're drivetrain is engaged and moving...


J

Welcome to the forum,

I figure 1mm is hard to eye sometimes. Just turn your idle screw down a bit. Richen the low-speed a bit as well. These two together should help some.

Also check this article. This is where you can read about the fuel line pinch technique. But dont always rely on this , you also want to listen to the motor and feel the power out on the track. This is where you will fine tune the low-speed needle, if need be.

http://rcnitro.com/rn/articles/ht_tunengine_01.asp

See attached for carb opening at neutral and carb opening at full throttle.

As an update, today I tried some re-tuning based on advice from another forum thread. 2.5 turns on the high speed needle, 1 on the low speed with the carb full open and then turn the throttle screw for the 1MM opening.

It's REALLY weird now. It runs, but it runs very fast and after about 15-30 seconds it gets so fast the 2-speed tranny shifts. This is without touching the throttle!

No clue now :(

Yeah that looks more like 2-2.5mm. Close that puppy till its like a slit, about half should do.

Also yeah sounds like your running lean on the low-speed and high-speed possibly. Either way if the car is just sitting there and gets warmer and warmer and is able to rev high enough to shift into second. Thats gotta be lean...but try the 1mm carb opening first.

Ok tried to reduce the gap, no change. Tried to open the HSN a bit (richen), no change. I did notice something interesting: it looks like fuel is coming up through the glow plug. So I tightened it down and now it seems like it's running much more consistent, but I have to open the gap to get it started and running. As soon as I started to close the carb so it will idle at a reasonable speed the engine cuts out.

Crappy glow-plug , but shouldnt cause problems. Youll want to replace that when you can afford it. Get a different model or type all together. If its an A3 and its leaking , dont get anymore a3's they tend to do that anyway as they are a cheaper plug. (os a5 or a8 would work better if the a3 is leaking).

Did you try richening the low-speed thats probably the main cause of the high-revving at low-speed.

The low-speed needle is meant for fuel tuning of the lower rpms to idle. If your car is at idle and revving high that means more air than usual is coming in...

This can be from:

1. The carb is open too far , which we see... and you now say thats been fixed.
2. The low-speed is lean.
3. The throttle is open further than the idle is set. You can set the idle close, but if your throttle is keeping it open youll get high-revving.

Hi Artificial, I actually made a revision to my previous post after you replied.

It's idling much better now that I tightened down the plug. But I can't close the carb all the way or it'll cut out. IOW it's taking 2MM to keep it running so it's running too fast to set it down.

Odd stuff. Also yeah make sure the glow-plug is finger tight. If its bubbling fuel from the side that would mean that its loose. If its bubbling from the glow-plug top , that means the glow-plug itself would have been bad...at least seal wise.

But it seems your good in that area and it did calm the rev so thats good.

What you say now though confuses me. If you got less than 2mm it dies. It should be just fine at 1mm so that makes me believe that your low-speed is rich.

How long does it take for your engine to die when you pinch the fuel line now?

Also, a quick way to make sure your throttle isnt the culprit , grab it by hand and push the carb closed just via the throttle linkage or carb itself. If that gets it to idle down then thats your problem.

Let us know.

So far everything I have been doing has been completely by hand. I haven't used any of the electronics, so I've been opening and closing the throttle by hand (with the linkage attached). At neutral, it's 1mm. Car will absolutely not start like that. I have to open it up to 2mm, it starts and runs. As soon as I start closing it and it approaches 1mm, it dies. So far I haven't been able to get it to idle low enough to set it down. CRAZY! You'd think something like this shouldn't be so complicated :) All I wanted to do this weekend was drive it sheesh!

I just tried it with the linkage detached. As soon as I get to 1MM and it sounds like it might start reasonably idling it shuts down,

Lean your low-end a little bit , see if that allows it to get to 1mm.

i really dont think he should lean his low needle any more man...........he said its only like 1 turn out from close..............i personally think the low speed needle atleast has to be 2.5 turns out from close.....put ur high and low speed needles back to stock setting and go from there...............or just bring it to ur LHS and im sure they would help you set it up....


Mike