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  1. #1
    RC Racer
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    2.5 air leak from carb slide maybe???

    Only place it has a leak is.from here. I noticed fuel in the boot...


    Would this.be.normal? Should the rubber boot complete seal it? Thought it was.leaking from Carb base but its from that groove ...

    Thought I had air leaks because it will idle fine and run fine at.half throttle, but dies at full throttle.... even at factory setting. Fuel drips out of exhaust at idle....

  2. #2
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    well I will tell you that is not an air leak as when at WOT you have much less Vacuum, you would notice a air leak much more at Idle or off idle and after it warms up a bit ( I had a front bearing leak only showed up after running for a min or two.
    I think the Groove there is to put the boot under vacuum to help to get it back to the idle position as without that the boot would Ballon when coming from WOT to idle not to mention it would be harder to go from Idle to WOT without some way to Vent the boot either allowing air in or out ( I am sure Someone can correct me if i am wrong about the groove it just seemed logical to me)
    If I were you I would check to make sure you have no kinks in your fuel lines/Pressure lines and your tank is sealing well.
    I found I had a leak in my fuel system ( as it is kinda a closed Pressure system when running) as I was having some weird Issues kinda like yours Dying at WOT even at 5 Turns out and at Idle and some times running like it was lean etc, I used my Vacuum Tester I have for my Full Size Vehicles and found my Cap seal was leaking if I spun the O-ring a little about 1/16th on the cap it quit then after opening and closing the cap it would return so I replaced the cap and have had no Problems since. I also run a Fuel filter between tank and carb to keep stuff out of it.
    I would also remove the HSN and fuel inlet and blow it out and ensure there is nothing in it causing you to have fuel flow issues.
    I can also tell you I can have my HSN set way lean to where the Engine Boggs out at WOT but spews fuel at Idle due to having my LSN set rich.
    SO you have HSN set at 4 turns out from seated and LSN out Even with Ledge or out about 1-1/2 or 1-3/4 Turns from seated?
    Just so you know I ended up running my T-Maxx at I think at 4 or 4-1/2 Turns out on my HSN and 2 Turns out on my LSN must be due to cool temps running 20% Nitro and since I am about 1 foot above sea level ( J/K I think we are 40' above sea level)
    I have found It changes about 1/4 Turn on either Needle depending on if it is sunny or raining outside but thats about all teh Fine tuning I have had to do after Break-In and the cap Issue.
    I hope this helps you fix the issue.

  3. #3
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    Oh I totally forgot to mention I was having a Problem with my O-Rings on my Carb the 13mm and the 10mm ones had accidentally been sliced when I removed and installed the carb. The 10mm is the one on the carb itself and the 13mm is the one in the engine block groove, actually the 10mm one was not sliced but I replaced it anyway. That was prior to the fuel cap and actually on the engien that ended up loosing teh front bearing seal, now I am running a New 2.5 with new carb O-rings, body etc. have no Vac leaks now ( that I know of) you can try spraying wd-40 around the carb O-rings etc to see if it changes your idle locate any vac leaks.
    I took some sand paper of 800 grit and rounded the Very end of the carb Shaft that slides into Block a Minor bit to keep it from Slicing the new oring as well as lubed the ring with Marvel Mystery oil to allow body to slide over O-ring easier too.
    Last edited by spudler_t; 11-30-2012 at 01:18 PM.
    T-Maxx 3.3 :)

  4. #4
    RC Champion
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    I think a good ole fashion carb rebuild will take care of the leak. Check the housing near the high side screw and plugs for cracks while you're in there. Hairline cracks will wreck havok with your tune

  5. #5
    RC Racer
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    Well I replaced the o ring for the exhaust manifold and cleaned up the rubber boot on the carburetor. Set every thing back to factory and it started and ran great. Had no problems from it at all.... only ran about a tank through it. Hsn is set at about 4.25 turns lsn is still flush. I think the fuel line to the carburetor was leaking so I trimmed the end off and reattached it....

  6. #6
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    Spelling Issues again

    Cool, I bet maybe the exhaust was leaking and not giving you proper Pressure to the tank to push the fuel needed at WOT.
    I will go recheck my HSN setting just to be sure I was correct, I noticed today though or about 4 hours ago I had to richen the HSN about 1/4 Turn and for some reason The Idle was really High and then it started acting funny at idle and just off so I Richened LSN about 1/16 and then did the Pinch test and it did perfect 2 seconds then reved up and died at about 3 sec so it is set ok.
    That was weird as I was just talking about it and had not had to change it in last 3 days then today LOL.
    But normally I never have to go more then 1/4 turn on HSN and Normally never more the 1/8 on LSN so if all of a sudden you find you are adjusting more the 1/4 on either without a Huge change in weather Like say going from 50 and rainy to 60 and sunny then I would be looking for some other issues. Not sure where you live but I found today that when it is 50 or less outside the Engine really does not like to fire unless Pre warmed. I usually use my G-Friends old 1500 watt Hair dryer (since I do not use a Hair Dryer and from 1994-2009 I had No hair to Blow lol.
    I set the dryer on low and let it blow on the Exhaust/Engine while I gather up EZstart unit, fuel, get TX, plug in RX then I hit High and blw straight down on Head for about 15 seconds and usually it will fire without primming in about 3-5 seconds.
    Today though I took the truck to a field with a steep hill and had to use my weedeater to clear hillside and I (being retarded as I sometimes get) Was impatient as I was running out of daylight and did not fire up truck and drive it around unti warmed up so it was cold and took about 10 minutes to start up.
    Last edited by spudler_t; 11-30-2012 at 10:21 PM. Reason: OOPs spelling issues again was suppose to be here
    T-Maxx 3.3 :)

  7. #7
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    The weathers been nice and been running great. Leaned it out more. Seem to run better. should I lean the lsn if fuel drips from the exhaust? But could it be the lubricate in the fuel dripping out?

  8. #8
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    The best way to do the LSN and Surprisingly it is exactly the way they explain in the manual ( I say that because like you I had some fuel or should I say fluid coming out when Idling and off Idle so I fiddled with it ALOT) Which is once you have HSN set do a couple HS passes then pull it up to you (works best for me with Body off) and Pich off the Fuel line and if it runs 2-3 seconds revs and dies you are good, if it dies instantly you should richen the LSN if it Runs Longer the 2-3 seconds you shoudl lean the LSN) I actually had mine run up to about 6 seconds at one time lol.
    I mention the instructions in teh manual the way I did because No Mattter what I did I woudl have Idle issues it would some times Idle way to High then turn around and Die when I let off throttle to idle and was coasting, when I did the adjustment exactly like the manual said I have not had any Idle issues and a matter of fact it it idles amazingmy low and always seems to be the exact same speed have not had to mess with it at all, but I still see "fluid" coming out of exhaust so I am starting to think maybe it is Castor Oil building up as I do not think teh castor oil burns completely if at all. It is a bit messy but I have started to get used to it now and Since I finally got the hang of tuning and the whole Nitro engine concept etc I would rather have that minor issue to worry about then running to lean and burning up an engine.
    T-Maxx 3.3 :)

  9. #9
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    When I pinch it off it does die 2-3 seconds after so lsn probably OK then. Ive been using traxxas fuel and i hear it has high lube content so it may be just unburnt oil. I bought some byron fuel so ill see how that goes. Thanks for all the info.
    Last edited by ausher1880; 12-04-2012 at 01:26 PM.

  10. #10
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Quote Originally Posted by ausher1880 View Post
    When I pinch it off it does die 2-3 seconds after so lsn probably OK then. Ive been using traxxas fuel and i hear it has high lube content so it may be just unburnt oil. I bought some byron fuel so ill see how that goes. Thanks for all the info.
    Pinch test for the TRX engines should be 3-4 seconds with only 1/2 a tank of fuel in it, no more and engine up to operating temps when you do this....

    I'd says it's close but a wee bit lean....
    Robin Williams
    He will be greatly missed...

  11. #11
    RC Competitor
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    Check ur orings on carb throat. I was fighting an off idle bog an it turned out the oring that sits in carb base of block was bad.
    revo 3.3 tmaxx 3.3 ofna hyper 7

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