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"Radio" Issues - Maybe?

 
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theknight571



Joined: 27 May 2010
Posts: 3

PostPosted: Thu May 27, 2010 12:09 pm    Post subject: "Radio" Issues - Maybe? Reply with quote

My son has a Ultra LX One. It is about a month old, has been broken in properly, and has almost an entire gallon through it already. Mostly racing up and down the street and not much off-road.

We've been through 3 pull starts, rebuilt two shocks, and replaced a front support bracket (I forget what it's officially called).

All of which we were able to fix... it's nuts and bolts stuff... no biggie.

However, now he seems to be having a "radio" problem. The car will start, and initially respond appropriately to the controller, then it will just take off. The engine will race to the point it would probably explode.

Once that happens, on restart, the car may or may not respond to the controller again.

We took apart all of the electrical connections, made sure they were clean, re-connected them... problem still occurs.

We replaced all of the batteries in the controller and the car... problem still occurs.

The local hobby shop did the same thing and the car worked for about 3 minutes before it just took off.

They were really busy and asked if we wouldn't mind coming back later... which we haven't had a chance to do yet.

In the mean time I thought I'd ask here to see if anyone has had this happen and how to fix it.

Thanks for your help.

-TK
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Eggbert



Joined: 27 Jan 2006
Posts: 331
Location: Nova Scotia, Canada

PostPosted: Fri May 28, 2010 2:50 pm    Post subject: Reply with quote

It could be glitching. Metal to metal contact, typically the brake rods and loops touching each other, or even a loose glowplug, but your description sounds more like a more consistent problem.

Possible outside interference, but I suspect your throttle servo may be at fault. Try swapping the steering and throttle servos and see if the problem moves ot the steering.
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MotionMachine999



Joined: 20 Oct 2005
Posts: 1721
Location: Land of Oz

PostPosted: Fri May 28, 2010 5:07 pm    Post subject: Reply with quote

Ofna radio's are notorious for glitching and run aways, not fun. I'd suggest upgrading the radio system ASAP...
Until then, avoid operating in interferrance prone areas~ around large metal structures, around overhead or barried utilities, chain link fences, etc etc etc.
Make sure the crystal is fully seated, both in the RX and TX. Make sure the antenna isn't damaged, cut, or chaffed.
Make sure all metal to metal fasteners are tight.
Also, check the header gasket isn't torn, rip'd, or crushed read make sure the header isn't in direct contact with the exhaust port or engine block..
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theknight571



Joined: 27 May 2010
Posts: 3

PostPosted: Tue Jun 01, 2010 4:54 pm    Post subject: Reply with quote

Did a little more testing and here's what it looks like...

I ran the car, keeping it stationary (propped up on a board) and watched what was happening with the accelerator servo.

The servo appears to respond as it should, however, after 2 or 3 minutes of running the engine just starts to rev faster and faster... during this time the accelerator appears to remain in the "neutral" position. (the position it takes when the throttle is not in use).

If I brake, it stops until I release it, at which point it assumes the constant acceleration.

With the car not running the controls work as they should... no sticking, no hesitating... just smooth operations.

I dunno if this helps or not... but if it does I'll take any advice you may have.
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Eggbert



Joined: 27 Jan 2006
Posts: 331
Location: Nova Scotia, Canada

PostPosted: Wed Jun 02, 2010 2:02 am    Post subject: Reply with quote

If applying the brakes slows the engine back down, the carb must be open too much. It doesn't take much carb movement to accelerate an unloaded engine, so the servo may be moving, but not enough to notice it.

An enigen will speed up a bit as it warms up. Use your radio transmitter throttle trim to bring it back down. (It helps to have it up a bit when starting a cold engine)

Sidenote: When you apply the brakes, does it stall the engine? If so, turn in your idle stop screw a bit.

If in fact, the servo is not moving the carb, and the engine is speeding up, it could be tuning or an air leak.

If the LSN (Low Speed Needle) is set too lean, the engine will accelerate for a bit, and then stop at the point it no longer has enough fuel to support continuous running. Richen the LSN about 1/4 turn and try again.

If you have an air-leak, the leak may open up more as the engine heats up and parts expand. Remove the carb and put a little RTV (the red oxygen sensor safe stuff sold at auto-parts stores and Wal-Mart) around the upper carb O-ring. Re-install the carb, and holding it down firmly, tighen the carb pinch bolt. Cover each end of the carb pinch bolt with RTV as well.

Other air-leaks are actually exhaust/fuel system leaks. Make sure the fuel tank lid is closed tight, teh tank isn't cracked, there are no cuts or tears in the pressure line from the exhaust, and the exhaust system is properly assembled and tight. Any of these problems can result in an overly-lean fuel mixture and the engine will speed up.

Engine backplates have been known to leak, but I've never had it happen. But it may help to check the backplate screws are well snugged down.

Also check the head bolts are tight and the glow-plug is tight (don't over-do it or you'll strip threads).

Oh...make sure the stop collars on your throttle linkage are tight as well. Those pesky set-screws can loosen up and the collars may be slippig on the rod. Blue-Loc-tite (just a very small drop) can help keep them tight.
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theknight571



Joined: 27 May 2010
Posts: 3

PostPosted: Sun Jun 13, 2010 3:19 am    Post subject: Reply with quote

In case anyone was wondering... we took it to the local hobby shop and finally figured out that the crystal in the receiver was broken.

They said it was probably loose on the inside of the housing, and rattled around when the engine was running causing the problems.

New crystals... problem gone.

Thanks for everyone's help.

-TK
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