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Help with nitro tuning/troubleshooting.

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Old 07-26-2014, 07:57 PM
  #1
ScotWithOne_t
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Default Help with nitro tuning/troubleshooting.

Recently pulled my O.S. .12 powered RC car out of the closet after 10+ years of storage. Did a complete teardown and cleaned all the old, gunky gas out of it. Everything went back togther just fine and it even started up almost imediately! yay!

BUT...

tuning is another story.

I can't seem to get it to idle at a reasonably slow RPM. I have tried several setting of the idle adjust screw. It's either so fast that it will overpower the meager brake on my ancient RC10GT and it will drive off, or it will go too slow an die.

I've tried playing with the mixture screw, and if I lean it out a little, it seems to at least not die when I give it throttle.

After a while, I started needing to trim the throttle all the way up for it to start, an a while later, I had to hold the throttle wide open to get it to fire. After tuning it for roughly one tankful, it would not start anymore no matter what I did. Did it just overheat? I pulled on the starter until my fingers got a blister and I gave up.

Needle valve was set per the manual at 2.5 turns open. But that should affect the idle speed and starting issue.
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Old 07-26-2014, 08:20 PM
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The end part about not starting sounds like it did overheat, or you kill your glow plug. Let it sit till tomorrow (works for me, lol) and try again. When you add more fuel to the mixture, it will idle higher. You can do the math from there.
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Old 07-30-2014, 03:39 AM
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Ok, we'll it's a good thing u can start it that makes it a lot easier.

Thing that hat could be causing it...
leak in the fuel system
incorrect LSN or HSN settings
wrong glow plug
air leak
low compression

did u replace the gaskets/seal on the back plate and carby? Did u remove the cylinder head?
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Old 07-30-2014, 09:49 AM
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Quote:
Originally Posted by phmaximus View Post
Ok, we'll it's a good thing u can start it that makes it a lot easier.

Thing that hat could be causing it...
leak in the fuel system
incorrect LSN or HSN settings
wrong glow plug
air leak
low compression

did u replace the gaskets/seal on the back plate and carby? Did u remove the cylinder head?
no. no. yes.

gaskets appeared to be in good shape.
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Old 07-30-2014, 05:13 PM
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I'd recommend replacing them. They might look ok, but I can assure you that they would be squished.

the idea of a gasket is to seal to mating surfaces, when they are bolted together it squishes the gasket between the 2 parts and fills in any imperfections making good seal.
and because the gaskets u have use are already squished, they won't be able to fill in any of the imperfections.

Im im not saying that's the problem. But it is very suspect.

I'd recommend replacing them regardless, then visually inspecting everything and turn the engine over by hand to see if u can feel good compression
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Old 07-30-2014, 05:16 PM
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Once u have replaced them and checked the compression we know the motor is good and if the problem is still there it's a fuel/carby/exhaust problem
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Old 07-30-2014, 07:21 PM
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Might have overheated....may have just killed the glow plug.

start with a fresh glow plug and go back to the base tune.

I could be wrong, but if you have trouble finding a "sweet spot" for the idle then the low speed needle could be to high/low....right guys? Seems like I have had a nitro in the past that would either idle to high...or die....I couldn't get the idle set screw to do anything else. then I tweaked the low speed needle some and that adjusted the idle just a bit.

So, maybe try setting the idle screw where it wants to idle a bit fast, and then try very small adjustments (either way) to the low speed needle.

But first, replacing the gaskets as mentioned above as well as a new glow plug are very good ideas.

It can be impressive what these small motors can go threw and still work. I once bought a used nitro rustler .15 for a few bucks....when I got it the motor was locked right up. couldn't start with with the starter motor or by turning the flywheel. Tore it down as much as I could and let it sit in a tub of PB blast over night. The next day I had the truck up and running! It had likely sat in a basement for a couple of years (if not more) but with the gunk removed it was still able to run decent.
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Old 07-31-2014, 06:34 PM
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It's hard, to get everything right
if the HSN is set incorrectly u will never be able to effectively set the LSN and idle screw.
if the LSN is off u will have idling issues that can not be resolved by the idle screw
if the idle screw is off it will have issues than con not be resolved by the LSN.

my recommendations, check the idle screw adjustment visually if its around 2mm open, don't adjust if the car start
recheck idle air gap with the radio and receiver on, make sure it does not close further with the brakes and does not open it further when the trigger is neutral
if the car starts and runs, ignore the idle (proving u can safely stop it) and set the HSN for max speed with a few speed runs. Once u find that speed spot for maximum speed, richen the mixture 1/8-1/16 of a turn

now tune the LSN, in small 1/8 increments untill u can hold full throttle with out it stalling or bogging down. But... If u tune the needle more than a 1/4 of a turn and it improves, stop and retune the HSN, then once that's done continue back on the LSN. Allso at this time it's worth fine tuning the idel and doing a pinch test...

tip, only drive it to tune it, don't play until it's tuned. Otherwise it can heat up effecting the tuning. And if it's been 5-7min or so and it's still got problem, stop
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