T-Maxx 2.5 Carb troubles!

[jay3]

Hello,
I'm not a pro at fixing and tuning RC Nitro trucks, as a matter of fact I'm quite new to the world of Nitro RC. Lately I have been having problems with my T-Maxx 2.5 . A month ago when I turned it on it would run great for about 10 minutes. After about 10 minutes or even less you could notice a huge difference in the acceleration and top speeds. It became extremely sluggish and kept driving faster and faster without me applying the throttle! My idle speed is to the lowest. Just before, it would shut off when you give it medium throttle. This model is under a year old and has only been driven gently (1/2 a gallon fuel). I finally decided to try and return the Carburetor high-speed needle setting to factory default. In the manual it says to turn it closed and than 4 turns out from there.

This must be where I went wrong. So, I tightened the high-speed needle (I tried not to overtighten. I gently tightened it until it wouldnt go in anymore, without applying very much force at all). I had done this once before without any troubles. After this I turned it 4 full turns loose and attempted to start the engine. I noticed that the fuel was dripping to the ground and found out it was coming out of the carb under the high-speed needle. I realized that the entire needle was loose. It no longer tightened.

After this I took out the high-speed needle and noticed that the entire thread came out with it!!! (Atleast I'm pretty sure, there was brittle coil around the needle threads which came off). I've read that turning any engine screw too tight can strip but I'm sure I didnt tighten it that hard its just common sense...

Now the high-speed needle no longer sits tight and fuel spurts out, this means i need to purchase a new carburetor right?

I may sound really dumb (maybe I am) but this really seems bad :S

 

[CharliesTheMan]

This is exactly what happened to me. It doesn't take much force to strip the composite threads. You don't have to buy a new carb. You can buy a new carb body for about 12 bucks and put your internals in it. I'll post a link to the great article on rebuilding one. I had an extra carb but I just sold it to another guy who had the same problem. I didn't think I had it very tight either and when I started it, the maxx was puking fuel everywhere.

It's a pretty simple process and should take about 30 minutes to an hour. When you buy a new carb, it will come with all new o-rings, as it's always good to change them once you take them out. This article can be invaluable at times.

http://www.traxxas.com/support/kb_search.php?action=artikel&cat=0&id=595&highlight=595

Here's the carb body that you will need.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDGA0&P=ML

 

[jay3]

Thanks!

Thank you so much for helping me out!
It looks quite complicated since I've never actually took anything apart yet. I have a friend who is very good with this stuff, I'm sure he will be able to assist me. I will have to run to my local dealership "Flight Craft" and pick up the body.

How exactly do you know how far to tighten the needle? Should I stop right after I can feel the change in force needed? I surely do not want this to happen again :LoL:
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By the way, my T-Maxx 2.5 is still stock, what do you recommend I should add/replace without spending much money to improve performance? A new tuned pipe? I've seen many "dual pipe's" that go out the back. I really dont like the stock one since it spits any excess fuel out onto the tire and shock area which really attracts the dirt.

Thanks once again!

 

[Rolex]

Go with the tuned side pipe. I don't know of any rear duals that improve performance unless you re-engineer them and are a tuning wizard.
You are correct as far as installing the needle valves in the new body. Just seat them. NEVER tighten them. Closed is only a starting point to back your HSN out from, so there's no need to have it tight.

 

[CharliesTheMan]

I have never heard anything positive about the rear dual exhaust. This would help you out a lot by redirecting the ehaust away from the tire and shocks. The way I bash, the rear exhaust would hang up and drag on things, and put parts in a bind that shouldn't be in a bind.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHT0&P=7
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHS6&P=7

 

[itsalifeworthliving]

good call charles!! i had the same problem as well.. it would just driblle out. i new i didnt over tighten it at all ever..but what i did notice was that my o-rings were lose in there and couseing it to vibrate, wich also threw my tuning off within minutes of running.. shortly after that, it just stipped out.. i thought it was a freak thing.. but i guess its more common then i thought..

 

[CharliesTheMan]

well I did over tighten mine. I didn't realize it was plastic and I was itching to use a new wrench that I got for christmas (electric crescent style wrench) and well you can just imagine how it turned out using a full size wrench on a plastic housing, I never felt it get tight.

 

[Mattyfats420]

do they have an upgraded carb you can get without the plastic HSN?

 

[CharliesTheMan]

it's not the HSN that's causing the problem in this case, it's the composite carb housing that the high speed needle screws into. The problem with a metal carb housing is that it heats up with the engine, and the warmer the fuel gets, the more performance drops off. It's amazing how much a few degrees less with the air/fuel mixture will increase the performance of an internal combustion engine.

 

[jay3]

I have never heard anything positive about the rear dual exhaust. This would help you out a lot by redirecting the ehaust away from the tire and shocks. The way I bash, the rear exhaust would hang up and drag on things, and put parts in a bind that shouldn't be in a bind.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHT0&P=7
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRHS6&P=7

I've never seen those before! I wonder if my hobby shop sells em... Any links on a recommended tuned side pipe to stick em on? By the way, the extention of the pipe wont decrease performance will it?

I have another question I'm sure someone could answer.

Anyone know why my truck doesn't shift into reverse and back properly? The servo moves in and out but when i try to shift back to forward the servo lever pulls out but still stays in reverse. I usually have to turn the engine off and fiddle with it by hand...

 

[CharliesTheMan]

I think it may because the truck is idling too fast. Try adjusting the idle speed to idle slower and applying the brake and see if it does any better. It could always be the linkage, but I would check the idle speed. Maybe you could try it without the engine running, and if it shifts you'll know that the idle speed could be causing the problem.

 

[jay3]

It must be something else because after about 8minutes of run-time the truck begins to drive faster and faster without any throttle applied. The idle screw it to the lowest and I have tried everything on the trim.
I think I need a professional to take a look at it while its running on the track... I had brought it into the shop a couple times and they just tune it up on the table while its running... They say its normal to drive forward a bit, but its not just a bit, its actually gets quite fast.

After I get my carb fixed up I'm going to get the tuning right somehow and purchase an exhaust deflector.

A good pipe upgrade by traxxas? (scroll down to resonator)
--> http://www.traxxas.com/products/nitro/maxx/tmaxx25r/trx_tmaxx25r_accessories.htm