hello guys,

its been two years since I have touched my r/c cars and finally broke them out this past weekend and had a blast. I have:
RS4 3 rtr
RS4 3 SS
Tmaxx .15

Well the next day I went to the hobby shop and bought my first buggy the ultra lx comp by OFna.

Well my problems are after 5 tanks of fuel is that I can seem to keep the engine running. After a few minutes of running it will die. The most runtime I might have had is half a tank of gas before cutting off. I kept the needle at 3 turns and then tried to tune it to 2 1/2 to 2 but still did not make much of a difference. What is the problem with these engines? Are they harder to tune? Or am I doing something wrong?

thanks in advance.

Check the OFNA forums [link=http://ofna.com/forum/viewforum.php?f=27]OFNA Force Engine forums[/link]

First thing I would do after breaking a motor in is change the glowplug.

I have the same buggy and it has a force 26 like yours and I had the same prob. and thats what I did was change the plug and its running fine, a little sluggish but I have not fine tuned it yet.

Canzures, I hope it is ok with you that I piggyback on your thread instead of starting a new one. Thanks in advance.

I have the same exact problem with my Ultra LX Comp! Just now into the 5th tank and the most it will stay running is 3-5 minutes. Can easily get it restarted but again, it will only run for about 3-5 minutes. Factory glow plug is still in, for the time that it does run, I am seeing anywhere from 220-225* with a good amount of smoke from the exhaust. I noticed you guys mentioned changing the plug, would an OS A3 work ok? I have a few extras of those laying around that I have as spares for my Tornado (they are brand new) or should I use a medium plug? I have been reading the forums about the Ultra LX and seems a lot of members say the A3 may be too hot of a plug for it. Can you all tell me what kind of plug comes with it from the factory.

Thanks for any help you all can give this newbie.

im not sure about the a3 bbut ive had many engine problems after new front engine crank bearing os #8 ive got rid of all my problems and i only got it up to 300 degrees with alot of hig hpeed runs and before the top speed advertised was not able to be reached but today it sure looked like 50 so my adcice seal the back plate with rtv sealent loosen the carb push it down tightly with your thumb and re tightem if that dosent work replace the front bearing and expirement with diff glow plugs it says in big bold letters in my manual do not run the #8 but icant get over the preformance


the stock plug med long #50017 not sure about that number but the package saya for .12 engines

Here is an image of a three needle carburetor. If your carburetor doesn't have a middle speed needle, your low speed needle will likely be where the middle speed needle is:


Here is what I would suggest:

1.) Adjust your throttle linkage so that you can get the carburetor to open fully. Also, disconnect the linkage and close the carburetor by hand until it hits the stop screw(idle speed needle in picture). This is so you can get a feel for where you currently have your idle stop screw set to.

Re-connect the throttle linkage and make sure it pushes the carburetor slide all the way to the stop screw when you let off of the trigger on the transmitter. A common mistake is to have the linkage adjusted wrong, such that the carburetor slide isn't actually all the way to the stop screw, but is instead just being held in place by the linkage. If the stop screw isn't touching the slide at idle, then adjusting your idle screw won't do anything to change the engine's idle rpms.

2.) Set your needles to factory. If you don't know what those settings are, I would suggest:
High speed needle - Close needle all the way, until you just barely feel the threads bite (just getting snug). Back the needle out 3.5 turns.

Middle speed needle (if you have one) - Set the head of the needle flush with the carburetor housing.

Low speed needle - 3 turns out from fully closed (using method above)

Carburetor idle gap - .5 to 1mm

3.) Fully charge ignitor batteries. Make sure glow plug glows. Try to start car as normal. Try again with brand new plug even if current one glows (a glowing plug doesn't mean that it will work in the engine). If new plug doesn't help, start tuning. Once the engine is tuned from steps below, try old plug to see if it is still ok or not.

4.) Attempt to get car warmed up. If it is blubbery and spitting fuel, lean the high speed needle. Ignore what anyone says about how many turns it should be tuned to, engines are like fingerprints, nobodys are the same. Once the engine is warmed up, and about half way through the tank, keep leaning the high speed needle (clockwise) until maximum performance is reached. You will notice a point when performance no longer increases (car won't go any faster in high speed runs), you have gone too far. Back the needle off slightly (1/12-1/8th turn counter clockwise) to allow for the fact that the engine leans out at the end of the tankful.

5.) Once peak performance with the high speed needle has been reached, move to low speed needle. Run car around for a minute or so after warmed up (again around half tank level) bring the car in and immediately pinch the fuel and hold the fuel line until the engine dies. It should die within 5 seconds, and should only increase slightly in RPMs before dying. If it takes longer to die, and increases considerably in RPMs, and has difficulty dying, it is too rich. Lean the low speed needle. If, on the other hand, it bogs down and dies immediately, and does not increase in RPMs, it is too lean, and you need to richen the low speed needle. Note that your low speed needle setting has an effect on the idle of the car. The leaner the low speed needle, the higher it makes your idle and vice versa. Once you have your low speed needle roughly set, pick your car up off the ground, and adjust the idle screw to make the idle as high as possible without making the wheels move. Once you have the low speed needle roughly tuned by the pinch test and your idle set, tune for maximum performance by running around the track, stopping for 15 seconds or so at the beginning of the longest straightaway, and doing a full throttle takeoff. Lean the low speed needle until you get maximum launch (judging by acceleration and wheelspin).

Note: A common mistake is to run these engines too rich. Find a video clip of a race, such as the recent ROAR 1/8th buggy nationals (perhaps here, or Neobuggy.net or the Grid). Listen to just how whining-screaming-high-pitched these engines are when tuned properly (it surprised the hell out of me when I first heard it, they sound like they are going to explode compared to how rich I was running when I started out).

Many people run their engines blubbery and spitting fuel (as you mentioned above) and that puts alot of stress on the engines being in near hydrolock conditions, not to mention robs all your performance, and makes keeping them running (and keeping your glow plugs working) a nightmare. These engines shouldn't even really be rich during break in, just heat cycled in a couple minute intervals with cooldown in between.

Troubleshooting (allow 30 seconds of runtime between changes for needle settings to take effect):

1.) From starting, the engine blubbers and dies when gas is applied
- check plug, if no effect then
- lean high speed needle 1/12th turn, if no effect then
- lean low speed needle 1/12th turn

2.) Car takes off slowly, tons of smoke
- lean high speed needle 1/12th turn, if no effect then
- lean low speed needle 1/12th turn

3.) If engine dies immediately when applying throttle (no blubber)
- richen high speed needle 1/12th turn, if no effect then
- richen low speed needle 1/12th turn

4.) If engine dies immediately when letting off the throttle
- richen high speed needle 1/12th turn, if no effect then
- richen low speed needle 1/12th turn

5.) If engine idles down extremely low right after letting off throttle
- lean low speed needle 1/12th turn

whoa....that's a lot of good info.

Tommy.

thanks Kx250...there was alot of info there. I'm off tomorrow(sunday) so I will be able to tinker with it and go from there.. I just need more plugs.

OFNA Force .25 / .26 / .28 / .32

mccoy mc8 plug for < 25% Nitro fuel

mccoy mc9 for > 25% nitro [probably need to add a head

OS plugs are for OS engines ... regardless of what the goobers behind the counter of the LHS say. Hobby People usually only stocks OS plugs - so thats why they WORK in so many engines .. if you consult hobbit peeps.