OT: Nitro-Powered RC Trucks

Howdy gang,
Anyone in here have experience with Nitro-Powered RC trucks? I got two of em' last week and they've been giving me fits in the tuning department.
Could use some help if anyone is knowledgeable.
Megatech Gladiator, powered by stock .16 (1 HP) motor, slide carb, running Trinity 20/12 fuel. The damn thing wants to stall out on me every chance it gets. If I keep it rich enough to not overheat at high speeds it bogs/stalls in idle and low-speed conditions. If I lean it out to run good at idle and mid-RPM it overheats when I mash it.
Slide carb has three adjustments: idle/low, high and throttle stop.
Thanks,
Doc
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On Sun, 01 May 2005 23:09:17 -0400, "Doc" wrote:

Doc,
I always had good luck with tuning the high side first, then the low side. Any adjustments you make to the high side also affects the low side. Open the throttle fully then adjust high side for top rpm. When that seems right adjust the low side. Careful with the break in of these little motors too. Take it easy for a few tanks of fuel.
When you say it overheats, is that checked with a thermometer? Or is that your gut feeling? If it is smoking mildly at WOT you should be ok temp wise. Good luck. I had a tower hobbies cheapy and it was a PITA until I figured it out. Patience and luck.
Brian
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Thanks for the reply Brian! I broke her in very carefully. Ran it at super rich idle with glow ignitor attached for a full tank. Then at low speeds, super rich idle w/glow ignitor, then at 50% throttle for another tank w/o glow ignitor.
Goddamn thing still wants to crap out on me every chance it gets and I'm afraid to lean it out any further. It is smoking slightly at WOT but seems to lose power after running it real hard for a minute or so and the head gets very hot (gut feeling, not checked with IR). Seems to run really good after it's just warmed up but before it gets to full running temp.
Any other suggestions?
Doc

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on my airboat (K&B.65) I've had zero luck with tower hobbies or K&B glow plugs.. it'd run like complete crap, however once I switched to OS (#8 for my application) plugs it made a world of difference. my carb just has one main needle adjustment, so I can't help you there.
hth, Bret
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The one that came with the motor, Megatech M3 Platinum.

I might try one of the Q series plugs, heard good things about them. Thanks Bret!
Doc

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procedure. Nearly all modern glow engines don'ty need the super rich break-in like the old ones did. Unless it's a ringed engine, it should be run for a tank or two leaned out just enough that it's breaking into two-stroke mode (out of really rich four stroke). That way the liner and piston get up to temp properly. It's likely ABC construction, aluminum-brass-chrome. Aluminum piston, brass liner that's chrome plated. It relies on the differing expansion properties for proper fit, which needs heat. That said, some engine need a half-gallon run through them before they get happy.
You should lean the engine out until it peaks, then back off a bit (~300-500 RPM). If you run it at peak, it has no room for further leaning as the tank gets low, , trash in the fuel, etc. You should be able to pinch the fuel line and it speed up a bit before it dies. If it just dies, it's too lean. If it picks up a lot then finally dies, too rich.
The idle adjustment can be made the same way after the high needle is done, and then fine tune both again.
Check for any air leaks, including leaks inside the tank, bubbles in the fuel line from the fuel foaming from vibration, air leaks from the needle valves and carb base are common as well. The engine backplate can leak, too. Tank carb and tank should be roughly on the same centerline, and no big loop of fuel tubing... short, straight runs.
Don't rule out fuel... it's hydroscopic (absorbs moisture), can't be left open for extended periods, and can cause all kinds of grief if contaminated with water. It screws up the combustion timing.
Hope that helps,
Jack
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I was just following the manual that came with the truck that instructed me to do just that.

You're correct, unringed ABC motor.

I think I need to continue leaning out the low speed adjustment to get a reliable idle/low speed throttle response. Right now if it sits for more than 15-20 seconds it loads up and will stall out if you don't tweak the throttle just right.

Damn instructions said to do the low first, then dial-in the high, which is likely why it took me so long to get it to even run!

Definitely bubbles in tank from bouncing around so much (off-road 4x4)

Brand new sealed quarts, Trinity 20/12, so I think we can rule out that one.

It does Jack, thanks. Fron the sounds of it I'm still running too rich and not getting into the powerband of the motor. The reason I'm so confused, the manual said to start with high-speed 4 turns out and low-speed 3 turns out, then move in 1/8 turn increments until stoichiometry was acheived.
I couldn't even get it to run at those settings (would flood out 3 seconds after starting) and am currently 1.5 turns out high, 3/4 turn out low.
Doc
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On Sun, 01 May 2005 23:09:17 -0400, "Doc" wrote:

I should have mentioned that also.... Change that glow plug. When I had drivablity problems the glow plug would look fine, but changing it made a world of difference. A friend of mine has a Savage .21, chews up a plug every few tanks.
Brian
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I'm going to do that Brian. The plug "looks" fine, not that I'd know the difference either way, and gets red hot nice and fast with the ignitor attached to it.
I sure hope it doesn't eat plugs like your buddy's truck. I only get 10-15 minutes of run time per tank (100cc) and at that rate the glow plug expense would get a little steep!
How do the plugs look or act when they're shot? Any way to troubleshoot a shot plug based on looks?
Any ideas why the truck looses power the longer I run it? If I take a long run thru the grass by the end of the run it's down on power and I have to take it easy for a few minutes before the power comes back.
These things are a pain in the ass!
Thanks,
Doc
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The plug is worth a try. You can't tell by looking... it's platinum, and relies on a chemical reaction for combustion, which needs heat, but that's not the sole source. If the platinum is worn off or gets coated by something, it doesn't work as well as usual. If a motor "eats" plugs, it's usually an indication of something else... bad fuel, too much nitro, too much compression, etc. The only plug damage you could see is a broken or collapsed coil.
It seems to me that it is overheating at full throttle from your description. Look closely at the airflow over the engine. Make sure it's sufficient and all the air ducts are opened up in the body. Get the idle adjusted and get some more run time on it... it sounds like it's not broken in yet.
FWIW, most glow engines are very easy to handle and adjust. They are really very basic engines, and once you get the hang of tuning them, require little maintenance. Every so often one comes along that can be a real pain!
Check in with one of the online forums for some help, or rec.models.rc.airplanes or one of the other model derivatives (maybe a car one exists?). You will probably find someone who knows that exact engine and carb. Good luck!
Jack
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Thanks a bunch Jack, I appreciate the information. I kinda thought the same thing, that the motor was overheating at WOT, but there is still some blue smoke coming out of the exhaust at WOT so I know the mixture isn't too lean. I'm gunna keep playing with it till' I get it right.
It's a Parma Silverado body, I have the head hole cut out as well as all the windows to increase airflow, but I'm going to run it with the body off and see if I have the same issues.
Will keep y'all posted.
Doc
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Check for binding in the drive-line, and seal up every screw and joint in the carburetor. Make sure your foam air filter is clean and not overly oiled. You shouldn't be able to squeeze drops out of the filter after you oil it.
Beware that running with the body off will damage the body posts and anything else that's on the topside of the chassis when you roll the little bastard over.
These monster trucks aren't designed to run at full speed for long periods of time. I also noticed on my old T-Maxx and my new Revo that if the 2-speed is set to engage too late, my motor will over-rev and heat up. You can lower the shift point by lining up the holes in the 2-speed gears and turning out (lefty) the adjustment screw 1/16 to 1/8 turn at a time.
Justin
"Doc" wrote:

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Well, one out of three ain't bad I guess. Got two trucks and parts on E-Bay with this whole mess. One engine/truck runs fine, the other two are shot I think.
I have an extra chassis so I rigged it up to my bench vise last night and tried to bench-run both of the trouble motors using my drill as a starter to give higher starting RPM's. Both engines have compression, both have a nice healthy pop on the exhaust stroke, both are moving fuel thru the engine, but neither will fire. I used the same fuel and glo plug that runs in the other one just fine, nothin'! Even tried switching carbs around etc., still nothing.
Arrrgh. Shoulda bought a Traxxas!
Doc
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"Doc" wrote:

if they're shot. Try the webpages for the engine models and see what the default needle settings are. Oh yeah, and swap glow plugs with the good engine to rule that out.
btw we should start a new thread in rec.models.rc.land
There are much more knowledgeble people there.
Justin
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Gotta ask: 1. How old is the fuel? and 2. Have you tried a new/different plug ignitor? I used to have maddening problems with an old Kyosho GS-11 which could later be attributed to old/incorrect fuel and a lousy ignitor (aside from the fact that it was known to be a HORRIBLE engine all around). After leaving nitro for several years I eventually threw a new (then) Tamiya/OPS .15 in that lil Kyosho Rampage ZR-1, new fuel, new ignitor, and it hasn't given me a moment's trouble since.
Oh and 3. You're not using airplane fuel by some odd chance are you? I had a couple of shops sell me a jug of airplane fuel when I was a kid claiming that it'd work fine in a buggy. It doesn't.
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the tubing to the carb. Learned the hard way on take-offs/intermittant dieing. The thing can run perfectly then a little piece of crap can get in the carb and make it run bad or just kill it. GL
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GL, I'm running a Dubro in-line on both trucks.....................will still blow out the carbs through and see if that's the issue!
Doc

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