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Old 07-03-2004, 12:56 PM   #1
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Default What does this mean..

I just got a used XXX NT sport and have since converted everything on the truck to a drake truck except the motor... It is still the Mach .15 which I was told had no more than 10 tanks through it. But my problem is that I can't get the motor to run good until it gets to about 250 deg. If I richen it up it will stall, hesitate, sputter and just run like crap. So my question is: Does this mean the motor is worn out, or are these motors really that hard to tune? I am pretty new to nitro cars/trucks, but have boats, and planes and have never had a problem tuning those motors?

Here are my current needle settings:

Low speed: 4 1/4 turns out
High speed: 2 1/4 turns out.

Recommended needle settings are:

Low Speed: 4 1/2 turns out
High Speed: 2 1/2 turns out

At these setting it runs horrible, very hard to start, and usually with a slight blip of the throttle it will kill the motor?

I am not far off of the recommended setting and the temp is reading right around 240-250 range. It runs pretty good at these setting, however the high speed still seams very rich. It has a lot of punch from the bottom and at about 25 feet it starts to sputter and loose the power.

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Old 07-03-2004, 09:58 PM   #2
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well, if i were you i'd ditch that mach .15 and buy a fantom .12 or a novarossi .12, but if u want to keep that engine, i'd try starting it with a heat gun, heat it up to 230, and then start it with the factory recommended settings, btw, did u check the glowplug? If it's anything short than a full glow, it will affect the performance of the engine, hope this helps.
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Old 07-03-2004, 11:04 PM   #3
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I would say that your motor is too hot (lean). Perhaps when it was broken in, it was broken in wrong, or ran too lean-Not enough fuel. No engine will last if it was broken in or ran too lean.
My gas engines-I've had (5) .15s in (5) different gas trucks and my engines never ran over 190 degrees unless the piston and sleeve was worn or wearing out.
If you wanted to stick with the mach then try replacing the piston,connecting rod & sleeve. If the piston, sleeve and connecting rod is going to be more than 60 dollars you may wish to consider buying another engine .15 for your truck.
Another recommendation in addition to the motor rebuild would be to purchase a cooling head designed for your engine depending on the engine you use.
Odonell, crazy nut, are companies that make them. These devices can help your engine run cooler (by as much as 20 degrees cooler or more) and your engine will last longer
I cant comment on the other .15 engines but I can comment on OS motors-They are reliable, you can buy parts for them almost anywhere (except for some hobby people stores) and the replacement parts wont cost you an arm and a leg. A piston and sleeve would cost around 35-43 bucks. Connecting rod should be around 10-14 dollars. Ebay (RcBoyz) is a good cheaper source for parts!
When you go to rebuild your engine (if you decide to) just take your time, read the instructions for your motor and follow it to the letter-and be patient. If you do it right your motor should run a few gallons (3-4) of nitro with no problems.
Dont forget..It doesn't hurt you to run your truck more on the rich side instead of the lean side!

RC Bucket
Team Holy Rollers

Last edited by threeEwes; 07-03-2004 at 11:10 PM.
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Old 07-04-2004, 09:51 AM   #4
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I had a very similar problem last week with my OS CV with rotary carb, RC10GT. Off the line was ok, but it was running very hot, and the high speed was very sputtery and slow. Very stubborn to start up, and while trying to start it up, lots of fuel would come pouring out the exhaust.

Through trial and error, I found out that my high speed needle was way rich (around 1 full turn), and my low end needle was way lean (I forget how much I adjusted it, maybe around 1/2 turn). I also had to change out a very new glow plug as well (around 3 tanks). So I slowly started changing the high speed and low speed needles incrementally by leaning the high end, and richening the low end, and now it works like a charm again. The giveaway was that I noticed my opening in the carb had to be set almost closed (the carb opening at idle was just a sliver) just to get a decent idle speed. As I started to make the corrections, I'd have to open up the idle to compensate, and now at the correct needle setting, the carb opening is where it should be.

Hope this helps.
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Old 07-04-2004, 11:24 AM   #5
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Dave - Any time you have a problem with a nitro engine running incorrectly, immediately change the glow plug. It is a very inexpensive variable to rule out right away by simply changing the plug.

The factory settings listed for virtually any motor are slightly rich and aimed for break-in; you should be able to tune much leaner than these recommended settings.

Take your air filter off (clean around the engine really well first!) and check the opening left by the throttle arm in the carb. It should be around 1/16 of an inch (more or less). You can adjust the size of this opening by using the idle screw. Making sure the idle is set correctly will help GREATLY in keeping the engine running long enough to tune it.

You were correct in adjusting the high speed needle before tinkering with the low-end needle. Make sure to use small increments at a time and see where that gets you.
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