RB Concepts TM523 Carb The Real Info you need to know
I just recived my RB Concepts TM523 carb. You have to cut off this plastic sleeve around the base of it. Becareful not to cut your self it's very tuff to get off. You need to be carefull not cuting into the carb when trying to remove the plastic cover. It could possible create air leak and make it hard to slide into engine case. Once you do this the carb aclty fits nice and snug as it should be. Then you need to grind a little bit off the front of the carb to alow for it to sit flush on the base of the engine case and also to clear the fly wheel. It just fits with the stock fly wheel after you do a little grinding. Theres no way a 40mm fly wheel will fit. Now You have to remove the stock throttle lever thats on the carb and replace it with the stock traxxas unit. Next you need to move the throttle horn thats on the engine motor mount and move it out to the next hole. Next to get wide open throttle you need to remove the throttle and brake horn off the servo and turn it one spline towards the front of the truck and re-adjust your set screw coller. With a little tinkering you will get it to go wide open.
I added a Motor Save Air filter Part# RT80
Running Traxxas 33% fuel
Traxxas Glow plug
Engine temp 245
Stock gear ratio 15/36
Wide ratio trans
My opinion there needs to be a heaver gauge wire for the throttle, it's to thin and flexible. I watch it flex when it's going wide open.
The Test: it's too fat out of the box but that's a good thing. I leaned it out a little bit and all I can say is WOW Mission control we are ready for take off. It has silly power now. That little hesitaion bog or bobble off the line is gone. When I got it dialed in and cracked the throttle it would just rev to the moon, I thought I broke something or the clutch was bad or even the slipper was bad. None of the above It was just spinning the tires out of control. I never laughed so hard in my life. It was like electric truck or like hitting nitrous button.
Caution: slide the carb down as far as it goes and see were it needs to be clearanced, it just needs to be grinded a tiny bit. If you grind to much you will cut into the base of it were the O-ring goes and it might not seal and creat a air leak and ruinon the carb.
I have more testing to do but it was alot of fun and nite and day difference in throttle response and performance.
carburetors compared technically on paper / found stock carb issue
This is a lengthy post on this carb subject, but I've turned up some interesting comparisons.
Comparing the three carburetors that we've mentioned:
I measured the throat diameter of the standard TRX 3.3 carb and it is .227" (about 5.75mm) ($45). The OS 11KR carburator ($85) has a throat diamter of .35" (9mm). The TM523 has a throat diameter of 8mm ($123). But what is important is square area of the throat. Doing area calculations in mm:
TRX 3.3 throat area = 26.95 sq mm
OS 11KR throat area = 63.59 sq mm (2.36 times larger flow area than stock)
TM523 throat area = 50.24 sq mm (1.86 times larger flow area than stock)
Slayer17 made a keen observation, from an engineering persective. Consider that the 63 sq mm carb is what is designed to be on an OS .21 displacement engine.; the 50 sq mm carb is designed to be on a .23 engine, while the 27 sq mm carb supposedly designed to be on a .20 displacement engine. Hmmm. My engineering sirens are going off. How can this be? The .23 and the .21 carbs are relatively close in size, yet the .20 engine carb is tiny in comparison. How can engines that move about the same amount of air per stroke use carburetors that are so grossly different? Physics are physics. It would appear that the TRX carb is an afterthought for the TRX 3.3 engine and from an older and smaller engine design, as pointed out by Slayer17.
It would seem to be apparent as to why the 11KR and TM523 carburetors let a TRX 3.3 engine have so much more power and low end snap. Lower flow velocity & less pressure drop = greater possible air volume into engine. Lower flow velocity also mean less change in flow velocity occurs from one RPM to the next, so throttle response should feel quicker. There is a "sweet spot" with a carb's throat area where velocity and pressure drop is optimal for still good atomization with the lowest drop and enough fuel. (Not enough fuel is not normally an issue with Nitro engines however, since nitro is its own oxidizer.) A carb can be too big. Is the 11KR past that point and the TM523 what is optimal? That could be argued to the end of time, as there are too many variables to be able to answer this. But clearly based upon several's experiences (including Slayer17's here) and comparison with OS and TM carbs, I suspect the stock TRX 3.3 carb is well undersized.
I may have to buy the 11KR carb and give it a try. It's price point seems fair. I hope it doesn't take too many mods to make it fit.
I've torn apart the TRX carb on my Revo and made sure everything was OK. Found a couple suspect leaky point and a rough edge on the sleeve's seat that seals the o-ring against the engine. Carefully cleaned that up and made sure the carb was well seated with the o-ring. Put some fuel tubing to it and held it underwater with the ends capped and blew hard into the tubing enough to expand the bellows. No air leaks in the carb. Reinstalled and the engine now idles well. But frankly, the base of the carb where the o-ring seats and the seat area on the engine are not very good. The chamfer in the engine where the o-ring seats isn't concentric with the bore. Some RTV would have been good as well. So I had some bad tolerancing on the engine's carb seat and faulty base of the carb at the sleeve's o-ring area causing air leaks. Not very impressive QC. But any company can make errors and this carb is just an injection molded plastic part, so I can excuse that.