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Thread: Carb Upgrade?

  1. #1
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    Carb Upgrade?

    At 12+ pounds of rolling chassis, I'm looking to make a little more power, I've heard a high quality carburetor can make improvements. If so, could somebody recommend the best carb upgrade for the TRX 3.3 engine? Should it also be easier to tune or is there a compromise factor? I don't want a carb that's a pain to tune.

    ***Or should I be looking at a big block conversion? If I see an after market engine block that cost twice as much as a TRX 3.3 replacement, could I expect it to last twice as long?***

  2. #2
    Marshal Double G's Avatar
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    Properly tuned a 3.3 will last around 8 or so gallons. Same with comparable engines or ones twice as much.

    A very common carb change is the Losi 3.4 carb. I had it and it was pretty nice. Coupled with a THS pipe and the 3.3 screamed.
    The Super Derecho

  3. #3
    RC Racer Nitrocrazy66's Avatar
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    As double g stated losi carb and THS pipe it's the shiznit
    "Drive it like you stole it"

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    I ran the same setup .ran great easy to tune. My problem was the 3.3 blow a piston around five gallons.

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    Ok, just got the losi carb. What's with the extra ball joint extension on the end of the throttle linkage? Can this be removed forcefully? If i pull on it any harder i think im gonna break something.

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    It should pop off like a ball cup. All I did was twist it back until it popped off.

  7. #7
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    delete me please
    Last edited by DMackVB757; 01-05-2017 at 06:05 PM.

  8. #8
    RC Champion olds97_lss's Avatar
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    I tried the losi carb on my revo and it started binding really badly after about the 5th tank. Then I just got an OS21Tm. lol

    I don't have patience to fiddle with things anymore. I just want it to work how it should work!
    Expert rigging at it's best!

  9. #9
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    I have an upgraded pipe (nothing crazy) and upgraded my carb to the Lost 3.4 carb. Honestly, I didn't notice any difference. Also, the Los carb started having that stupid throttle lockup that people report where the carb locks up because it slightly twists and binds and thus it either sticks open or closed (luckily, mine has only ever gotten stuck closed). I tried EVERYTHING to fix the sticking throttle including springs, got a ball bearing throttle rocker, filed down the little carb pin, twisted the carb to try and line the pin up better, etc. As soon as I took it off and stuck my stock carb on problem solved and still screams!

  10. #10
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    I just replaced the stock carb with a losi 3.4 carb, and I cant be happier. It runs the way I thought the 3.3 should run, in fact I wish I would have done the same thing on the revo that I had 2 years ago.
    I can totally tell the stock carb is to small for the displacement of the engine because tuning adjustments are at 1/16 (stock carb), were as the losi 3.4 is done in 1/4 turns. All of this of course is due to Venturis effect and Bernoullis law. As gas, in an open space, passes through a constriction it picks up speed and decreases pressure. Just like a car at high speed little movements in the wheel correspond to huge changes in direction, stock revo only adjust 1/16. Where as a carb with a larger opening decreases the speed of gas going through the carb and maintains the pressure better with more control.

    As far as having the losi carb stick..... Haven't had that problem yet on my Jato.
    Last edited by ericglover46; 05-06-2017 at 12:59 PM.

  11. #11
    RC Champion olds97_lss's Avatar
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    Quote Originally Posted by ericglover46 View Post
    As far as having the losi carb stick..... Haven't had that problem yet on my Jato.
    The jato has different linkage geometry than the revo. I had issues with that carb sticking bad after a few tanks on my revo.
    Expert rigging at it's best!

  12. #12
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    OK, the upgraded Losi carb tunes well, however, I accidentally needle-filed the uni-ball linkage down too far and it failed over time. The TRX 3.3 carb uni-ball linkage doesn't fit on the 3.4 carb throttle pull. Losi doesn't sell the uni-ball as a single part; have to buy the entire carb over again. Is there a compatible uni-ball linkage out there? Metal? What's the best ultimate solution to connect the throttle servo to the 3.4 carb pull? As it relates to the Traxxas REVO 3.3:

    Last edited by DMackVB757; 05-23-2017 at 05:19 PM.
    Experience is what you get just after you need it.

  13. #13
    RC Racer Nitrocrazy66's Avatar
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    Take the little set screw out and slide the collar with the ball stud off and try the one from your traxxas carb. May or may not fit. I
    "Drive it like you stole it"

  14. #14
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    Quote Originally Posted by Nitrocrazy66 View Post
    Take the little set screw out and slide the collar with the ball stud off and try the one from your traxxas carb. May or may not fit. I
    Doesn't fit.
    Experience is what you get just after you need it.

  15. #15
    RC Champion olds97_lss's Avatar
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    Take a 3mm screw that is a little longer than your current throttle arm, put the tip of it in a dremel, then use a file to mill down the threads and use the screw instead of the set screw.

    I had to do a total hackjob on mine once. I installed a big block, but the stupid throttle arm was way too short. So, I found a reasonably thick walled piece of aluminum tubing, drilled opposing holes in it, tapped them, then put a milled down screw in it for the throttle arm and a normal screw on the other side to lock it onto the carb.


    I made sure to screw the "throttle arm" in far enough so the threads stuck through to the inside a bit so when I tightened the actual screw, it put pressure on it so it would have been less likely to work itself loose and fall out.

    Worked fine for a long time.
    Expert rigging at it's best!

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