New to r/c few problems with project rc car

[truggy83]

I have bought my first nitro powered r/c car. It is a Traxxas Nitro Stampede in need of some tlc. I got it for a good price with a Futaba transmitter. It is missing the body and muffler otherwise everything is there. It has the electric EZ start and has been sitting for at least two years before I bought it. I got it last Friday and got it to start. I wanted to run it for a little to get an idea of what I will need to get this coming Friday when I go to the hobby store. The car took awhile of cranking but did eventually start. It ran pretty good but was loud because of the missing muffler. I noticed that unless I held the trigger forward on the transmitter that the car's tires would spin rapidly.

Now I have seen that the clutch shoes being worn may cause this. I removed the clutch bell and the clutch shoes appear to be in decent shape. I did not remove the spring that goes around the clutch shoes however it looked to be intact and was not bent or deformed. I am not sure what clutch shoes look like when they are worn out but mine appeared to look ok. There was a very small amount of material on the inside of the clutch bell. I cleaned it off with brake cleaner and a rag.

Another possible reason for the car taking off by itself that I read was the idle is adjusted to high. I started the car letting it run at normal opperating temperature. I had to remove the air filter in order to access the idle screw. I turned the idle adjustment screw to slow the idle while holding the brake on the transmittor. It seemed to decrease the idle when the brake was on but once I released the trigger back into the neutral position the tires started spinning fast. No matter how many times I turned the idle adjustment screw the tires still spun fast once I released the brake.

Would not having a muffler on somehow cause the car to accelerate on it's own? Any ideas what may cause this? I tried turning the trim on the transmitter and it only increase's the idle even more. Please help me figure out why the car is accelerating out of control when the brake is not on.

Thank you for any help that you can give me.

 

[beason]

the trim on the transmitter should be the issue. with the rig off, and the electronics on, take the filter off and turn the trim until the carb closes. if its to far off center, you may need to take the servo horn off, set the radio to center, then put the horn on correctly.

the muffler can cause the truck to run lean, which could cause it to idle high. there is a return pressure line from the muffler to the tank that acts like a fuel pump. without this, you get very little fuel pressure to the carb, and less fuel = lean.

 

[truggy83]

the exhaust manifold has the fuel pressure line on it. As far as I know the muffler doesn't have any kind of pressure line on it. When the throttle is closed there is a small gap in the throttle butterfly. Is it supposed to be completely closed at idle? I will wait until I get the muffler on and see if that changes anything. I am thinking it might help but I believe maybe the servo needs adjusted. It takes off at almost full throttle when the brake is released.

 

[beason]

there should be about 1mm gap, or the thickness of a credit card. if you have the connection for the return hose, then that is the "muffler" or pipe.

a picture of the rig would help a ton.

if you turn the trim all the way down and the carb still doesn't close, the servos are out of adjustment. first set your idle, by taking the linkage off the carb. lightly press the carb closed and turn the idle screw untill you get the 1mm gap.

then put the linkage back on the carb, and take the horn off the servo, set the trim to center, then put the horn back on where the carb is closed or or really close to it (closed as in against the idle screw, still having the 1mm gap.)

if it is still revving after that, your carb settings are out of wack and your running super lean. look up the proper factory settings for your engine and carb on traxxas website, and set them to that, then tune from there.

there is a tuning flowchart on here that will help greatly.

 

[truggy83]

i am at work right now so I can't take a picture of the car but I found this online. http://www.rc-trucks.org/traxxas-stampede.htm If you scroll down to the last picture on the page with the body off and it is a overview shot of the car you will see the blue fuel line comes from the top of the fuel tank and goes to the exhaust manifold at the rear of the engine which has a little nipple sticking out for the fuel pressure line. There is a clear fat tube which goes to the rear of the car and goes into the muffler which is the round cannister which has two duel outlets on the back. I am missing the muffler with the duel tips on my car. Everything else is there including the manifold with nipple and fuel pressure line and the clear fat exhaust tube. The car runs as long as you let it so I know the fuel pressure line must be providing adequate pressure to keep the car running. Just wondering if the lack of a muffler would not help my idle problem. I plan on ordering a muffler on friday to install in the car either on ebay or the local hobby shop.

I will make a video when I get home of the current setup that way you can best see what is going on. I am pretty sure the carb has more than a 1 mm gap though. Also I believe the throttle linkage is missing a part. It has a round stop which hits the servo which thus pulls the linkage opening the throttle however when I got the car there was no stop on the other side of the servo to push the throttle back closed. When you would pull the throttle open and release it, the throttle would stay open as there was nothing to push it shut. I rigged a makeshift throttle stop with zip ties and tape until I can make it out to the hobby shop on friday. I will show you this in the video when I make it. Hopefully from the video you will be able to tell me what needs adjusting. I am a little nervous to start making adjustments on the carb unless I absolutely have to.

 

[truggy83]

the car doesn't slowly start creeping forward either it floors it and takes off, well it trys to take off because the one gear is stripped and needs replaced.

 

[truggy83]

alright. I adjusted the throttle so there is only a little tiny gap at the back of the throttle now. It seemed to help it. Once I get one of the throttle stop (round things with the set screw in it) I should be able to get it more dialed in. I also may need to adjust my servos like you said. How far should the throttle open when it is all the way at full throttle? I am asking this because now that I adjusted the throttle and the throttle linkage on the servo, I see the throttle only opens about to half way. Should it open all the way under full acceleration? Here are my videos that I made showing how it was before I adjusted it and afer I adjusted it. I may also need to adjust the brakes as one I apply the brakes fully the servo makes a slight buzzing sound and shakes like it is trying to put the brakes on even more but they cannot move anymore as they are all the way on. Let me know if you think this is better. Because the spur gear is worn down so much the car won't move at all but it seems like the other gear is not spinning as much. Tell me what you think and thanks for the help so far.

 

[alien13]

Read this: https://www.rcnitrotalk.com/forum/showthread.php?t=87194

Your spur gear is stripped, most likely due to bad mesh. There's a video in the link above that will explain how to fix that when you put the new one in.

Just a bit of advice, if you break it once, you'll break it again, so by two. Plus you save on shipping.

 

[Rolex]

You HAVE to have a muffler to develop the proper back pressure. Until that's replaced, you'll never get a good tune.

 

[broken_civic]

first off, inside that carb looked nasty, you have no air filter and that motor is prob. already screwed. around the carb should be cleaned as well.

secondly, replace the spur, secure the receiver and get a exaust

 

[beason]

when you hit the brakes the carb is closing further then at idle. this is wrong.

your linkage needs some flex to work right. its not solid stops, but stops and springs. you need to get the proper stuff for the linkage, then adjust the servo horn so that at idle, with the transmitter trim set to center, the carb is closed. (like it is with full brake).

the spur, as stated before is shot, they are designed as a weak link in the drivetrain and can go with a hard tumble. grab a few just in case.

the muffler needs to be on there for a proper tune, but you need to fix the linkage first.

looks like you got a pretty rough rig, but dont get discouraged. we can help and get you going.

try this http://rcdocuments.com/ go to the traxxas area and download the exploded views and manual for your rig.

 

[truggy83]

some of the parts are removed or loose because of me. I unfastened the receiver to clean the frame out, the gas tank isn't fastened because it is leaky because of a mistake I made and I will be getting a new one this weekend, there is an air filter for it I just had it off so you could see inside the carb and so I could easily access the throttle adjustment screw. It does need a lot of work which is mainly why I got it. I love fixing up things and making them better.

Thank you for the links about setting gear mesh. I was planning on getting atleast two or three spur gears at the hobby shop this weekend since I know that cars go through them fast. They don't happen to make an aluminum spur gear do they? So from the looks of the picture it appears that the throttle linkage is supposed to have a spring which would go between the carb and the servo horn where I have my rigged up twist ties? I am trying to figure out how this works in my head. I guess the spring pushes the throttle closed by pressing against the carb and the servo horn. How would I set the throttle so it doesn't close anymore when the brakes are applied?

Thanks for the help. I will more than likely be back on here this weekend hopefully with all the parts needed to get this thing back in tune.

 

[beason]

the spring allows for the setup to move when you apply the brakes, while still keeping the throttle linkage tight.

the idle screw stops the carb from closing to much. it should stop the carb at the idle setting (1mm or so)

the servo closes the carb, the spring doesn't. it just allows for movement past the stop point of the carb so the brakes will work.

a metal spur is a bad idea. the spur is plastic for a reason. its better to smash a $5 part then replace a diff, shafts, or whatever the next weakest point is.

you have to re-adjust that servo horn.(after you get the proper parts) At center the carb should be closed and the brakes should be loose.

pull the trigger, horn should turn, pushing against the solid stop, and opening the carb all the way.

press the brakes from center. horn should turn the other way, compressing the spring and pulling on the brake linkage, applying the brakes.

it will make more sense when you have the proper parts on there and cycle it.

 

[truggy83]

I think I understand. One I get all the parts on the table it should be clear. I will let you know how everything goes once I get all the parts. Thanks again for all the help you have offered.