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  1. #41
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    Alright, got the engine rebuilt. Got it running, but it will just not want to idle. It'll only stay running if I hold the gas. I have the idle screw all the way in. Had needles at recommended settings, 4 out for HSN, and flush for LSN. I even had to adjust the throttle trim to hold the throttle out further.

    Any ideas?

  2. #42
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    Your idle screw should never be "all the way in". Check your servo setting at make sure it's at zero. Take servo horn off, turn vehicle on and then place servo horn back on at neutral position. Make sure throttle knob on transmitter is set to "0" first. If that is no help try dialing LSN in 1/8 turn until you find happy setting. You are over compensating for a bad tune with the idle screw. May also consider a Losi 3.4 carb mod. I was so pleased with this carb that I've put them in all my nitro vehicles. Makes tuning sooo much easier
    uh oh.... that didn't sound good

  3. #43
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    How am I supposed to tune it if it won't stay running? It seems like the idle RPM's are way too low to stay running. By compensating with throttle trim, I'm making the engine hover around the RPMs it should be at normally. Is it too rich to stay running? Too lean? Are the "factory" needle settings way off for an engine that's already broken in?

    The servos are fine, there's even a tiny bit of play between the horn and the set-screw thingy on the linkage.

    What's some "general" needle settings for an already-broken-in engine that I can tune from?

    There were a lot of gaskets, especially the two on each needle, that were in bad shape, so hopefully I solved my air leak. I saw a decent amount of smoke (a lot more than before) with mid to WOT, so tuning that won't be an issue, it's the idle I'm having issues with.

    Remeber guys, I'm new to Nitro, AND this is a garage sale T-Maxx. Probably a bad combination.

  4. #44
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    Again guys, thanks for the help. Tomorrrow I'm gonna have another stab at it. I'm gonna reset the idle so the carb has about a 1-1.5mm gap. Then I'm gonna mess with the LSN. Perhaps it's too rich at idle.

    I'm also reading about a possible compression issue with other people. Would changing to the .15mm gasket help? At WOT, it seems to have some decent power, although I'm having issues reaching second gear. (Obviously I haven't tuned HSN yet, so it may even have more power) I was on gravel, so no wheelies, but the power was there, which makes the compression thing seem unlikely.
    Last edited by JohnnyGrey; 07-14-2014 at 11:57 PM.

  5. #45
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    I would say at those settings its a bit rich and it's loading up causing the stalling .try leaning the hsn a touch until it idles and check your temps they should be lowish say around 220 then try to tune for power.
    if you had low compression it would stall once the engine got warm and wont restart until it cools down ,your issues lie in your tune ,I may have asked before but what plug are you running? for a 2.5/r I would recommend an os lc3 plug or the traxxas 3231 plug the 2.5's seem to like a hotter plug than the 3.3

  6. #46
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    Leaning the HSN? Does that affect idle? Or did you mean LSN?

    As for the plug, I think it's the Traxxas heavy duty one. I had maybe four or so that came in the box of crap with the truck, but I destroyed a few on that first tank a couple weeks ago. I'm down to my last one.

    I'll charge my nicd packs after work and give it another go this evening

  7. #47
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    haha typo ,lean the lsn a touch....
    you will need some new plugs if that plug you are running now was used in your old configuration it could possibly be damaged which would make tuning very difficult ,for the sake of 5 dollar grab a new plug before you try again.

  8. #48
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    I can't even get it started now. Tried leaning out the LSN a little. Doesn't even sound like it's igniting. Took out the plug, held it against the cooling head, couldn't get a good connection. It did glow against the exhaust manifold though.

    And now, the infuriating part: the hole that the HSN / fuel barb assembly is stripped. Spent all that time (thankfully not much money) and the whole carb is shot now.

    What's the difference between say a Losi 3.4 carb and this carb? Materials? Because they look identical, same layout and all.

    I do have two more carb bodies that came in the box of goodies, but I'll have to spend some time transferring the carb internals.
    Last edited by JohnnyGrey; 07-15-2014 at 05:42 PM.

  9. #49
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    The two carb bodies are garbage, one is cracked, and was able to break it a part. The second had a different plug that was stripped.

    Finally got it running, but with a Frankenstein carb that was on backwards, with no way to hook up throttle linkage. But it still refuses to idle. It's igniting, and almost wants to idle, but I have to hold the throttle open. I tried playing with the LSN, richer, leaner, etc.

    I'm to the point where I wanna give up. I'd be better off with a new engine.

  10. #50
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    Quote Originally Posted by JohnnyGrey View Post
    Alright, got the engine rebuilt. Got it running, but it will just not want to idle. It'll only stay running if I hold the gas. I have the idle screw all the way in. Had needles at recommended settings, 4 out for HSN, and flush for LSN. I even had to adjust the throttle trim to hold the throttle out further.

    Any ideas?
    Surprised no one said anything in response to this. The cut-out on the piston needs to face the carb. Remove the header and spin the engine and if you see the rod the piston is in backwards. IF you have rebuilt the engine and it will not idle unless throttle is applied and has poor performance this is your issue.

    Quote Originally Posted by JohnnyGrey View Post
    What's the difference between say a Losi 3.4 carb and this carb? Materials? Because they look identical, same layout and all.
    Same set-up and will take a little modification to fit but the throat is bigger to let in more air for the engine to breathe better.
    The Super Derecho

  11. #51
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    Well that's my issue then haha. The cutout in the piston is facing the exhaust header haha.

    Regardless I still need a new carb. Because I swapped the HSN and the plug, I have the carb in rotated 180 degrees, with no way to hook up throttle linkage.

    Now the question, do I get a new throttle body w/o internals and reuse mine ($15-20), a complete trx 2.5/3.3 carb ($25 or so), or the Losi 3.4 carb (one on eBay right now for $32.

    What needs to be modified with the losi carb? I think I read that the ball joint for the linkage needs to be sanded down or something. I have a dremmel if that's needed.

    Thanks for the tip about the piston, I could have sworn I had it right when reading the Traxxas rebuild guide.
    Last edited by JohnnyGrey; 07-16-2014 at 07:56 AM.

  12. #52
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    I haven't personally tried a 3.4 carb on a 2.5 I got one on a 3.3 and its great ,holds a tune and idles like a champ so I would say go for a 3.4 carb and never look back.
    it is very easy to install on a maxx you just need to lightly sand the carb where it goes into the block some fit without needing to be sanded , once installed just rotate the carb in the base until you get the carb to open at full throttle.
    I have a 3.3 carb that's good just need a new rubber boot ,I'd be happy to give it to you if you pay the ship.

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