drewr33

Hi all.

I have just bought a TMAXX 2.5.. Running 10% nitro.

I have gone throught the break in procedure and was running fine.

Now I go and tune it for porformance and get it running good. Then it would cut out at high speeds, usually when changing to 2nd gear. So i richen the HSN up and then still running lean. So I end up riching it about 6 turns out from all the way in. Which should be reallly really rich. But its not it runs good again. Then after about 5mins it just runs rich. So I lean it (only small amounts at a time) and get it to run good (this is about 4 and a half turns out form tight). And it does the same thing again.

I am also having problems with the low end (kinda bogging down but no smoke). Does the low end effect some of the high end tune? The LSN looks to be richer then the stock setting by about a turn.

The thing is i can get it to run good but then it goes out of tune again.

Please help!!.


Thanks.

driveit

hi there did you try setting it back to stock settings

125cchyperman

As stated above reset the needles to the original setting and then go from there. Do small increments about 1/16th turn's clockwise on the HSN first. Then once you get that tuned then go for the LSN and start to tune that needle. Plus if you can try and put in a new glow plug as the glow plug tends to want to foul out after break in or arrund there and that eliminates that if that would be the problem.

Try and return the needles and if it's fine then, then it was just bad needle setting's. If it still continues then you may have an air leak somewhere and that could be the problem. But since it was running fine before you started to tune it it makes me think it was just bad needle setting's.

drewr33

Thanks for the replys.

I have resetted the needles to stock setting. HSN at 4turns out and low end. But at the stock settings the engine is too lean. Usually runs good at 4 1/2 out but then the tune just changes. EG. cuts out at high speeds. So to get any sort of change in the tune i wind it out like 2 more turns. The factory LSN setting is to lean also.

One thing is just driving it around slow in 1st gear, I can get through a tank of fuel with no problems.

I have change plugs.
Engine temp seams ok (i have a bigger head coming)

I have noticed small (small) bubbles in the fuel line... would this effect it?

dan1970

Hmmm...I am running a T Maxx with a 2.5R right now, and the factory setting of 4 turns out is rich yes, but not overly. I cannot believe you are running lean at 4 or more turns out, as I am currently slowly leaning mine down to about 3 turns out and it's running pefectly.

I would have to say you may have something wrong with a fuel line, blocked, kinked, or something where it is causing a lean condition. Check out your fuel lines and tank and be sure everything is clean and clear.

Also, I am running 20%, not 10%. Don't know how much of a difference that will make, depending on what glo plug you are using with that fuel.

HTh
Dan

legbuh

If you have to go that rich I assume you have an air leak or a blocked HSN or fuel line. Check these things out. It's most likely a blocked HSN.

Take the HSN needle all the way out and clean it out good with carb cleaner and compressed air.

Meziked

I chased the same problem for around 3 weeks now on a 2.5r revo. turned out to be the back plate leaking air causing a lean condition. i had some thin rubber gasket material that I cut into a make shift gasket and installed it between the back plate and the e-z start system. Problem solved. I also had a carb leak due to a bad o-ring where it seats in the engine. I have the 2.5r up and running now, but I got so use to the power that i had with the way lean engine..... correct tunning seems slow to me. I leaned her out today to the point of heat stalling and backed her back in 1/8th of a turn. Runs decent, not tire spinning or blistering speeds, but she will hold a 240 degree temp and run tank after tank with no stalls. Now that I have the 2.5r it running shape......time to get rid of it. It taught me to tune and troubleshoot, but now it on to bigger and better things. So I have ditched the 2.5r and I now have a O.S 18tm on the way. 2.5r is for sale, gallon of 20% ran thru her and sleeve and piston look great.

BTW the monster cooling head I got did nothing for the problem. you probably are chasing an air leak, it will making getting it tunned impossible and it wil not matter how much you tinker with needles, it wont run right intill the leak is fixxed.

The 2.5r seems, you either get a good one and the world is great, or you get a leaking one and life sucks till find the leak and get it plugged. Spray WD-40 while running around parts of your engine...look for either bubbling or idle change.... Mine was leaking so bad as soon as i hit the back plate with the wd-40 it died instantly. if it wasnt for someone clueing me in on the wd trick i would have never found the leak or even thought the backplate has to be sealed tight with the ez-start plastic.

Meziked

You can also flush it by pulling the HSN all the way out, remove the blue wire from the glow plug, hold your finger over the tip of the stinger (like you do to prime) and use the e-z start box to spin the engine.... This will push fuel though the carb and out the HSN hole, flushing the HSN completely.

Also if you have played with the idle screw, make sure its 1mm out or you will be in tunning hell, seems to affect eveything

drewr33

Thanks guys for your help.


Over the weekend I will do the things you guys have said. Ive got some new fuel tubing coming and glow plug. and ill do the WD40 test. If flushing the carby doesnt fix it.

For the LSN how many turns out is the factory setting???
Also why would the Idle screw effect the tuning???

Thanks again.

Meziked

The factory setting for the LSN is about 2 turns out. Its where the srew head is level with the ring that it sits in (about 2 turns)... As afr as the idel screw, when you set the LSN via pinch test, your not gonna get a true runtime befor stall with a car that is idleing higher then normal. Kinda like math, cant do algebra unless you know how to add first....

Meziked

I just wanted to add. Im pretty new at this too. If anyone see's that I am giving information that might not be correct, please tell me. The only info. I offer is things i have tried myself or problems I have had to tackle myself. I am still learning and I dont want anyone to think I am trying to be a know it all out of the box. Like I said, I have had my car down to the frame and back up sevral times already just to clean and see how everything works. Had a hard start with this wonderfull traxxas power plant and search this site and 4 more trying to figure out what I was doing worng. I post because it took me weeks to find one trick that solved my issue, and Id hate to think I knew something that could keep other people from doing the same.

drewr33

Meziked where you refering to the IDLE trick?

Meziked

Nope, wd-40 trick....traxxas handbook will teach you the idle and tunning....

125cchyperman

Needles and how they are set will be different for every engine along with other factor's. There are just to many factors to go off of what someone else has for there needle setting's. Now it gives you a start but more then likely you will have to tune it a little to your liking.

Now saying that it sounds as if your having an air leak. An air leak can happen at several places and not just the engine. Now someone said about the wd-40 method and thats fine but I personally like the soap and water method. But if you have a primer on your fuel tank look at this first as these tend to have a lot of air leak problems for some reason. You can also get some new fuel lines as this is very cheap and is easy to replace. But before you start replacing things I would make sure that the carb nut is tight, the glow plug is tight, the head bolt's and the exhaust bolts along with the backplate bolts.

If you find an air leak on the fuel tank just replace it with a none primered tank, replace the fuel lines if they have an air leak. As for the engine you can go and get some RTV silicone, your local auto parts store should have some. Then where the air leak is you can apply some of the silicone to the base od the item that has the air leak. You can use it on the exhaust, backplate and the carb but I would suggest against yousing it on the head.

As for the idle screw take off the air filter and look down at the carb opening. There will be a opening at the left side when looking down. Then turn on your trucks electrics without the engine running then turn on your transmitter. Make sure all the trims are set to 50/50 and then see how large the carb opening is. For a any slide carb it should be about .5 cm, Then when you have this set your idle should be about right. If you have any other questions you can just get back to me.

Dil

i had similar problems with my old trx 2.5, well its definetely caused by air leaks, but my leak happened to from a cracked carb,!!

nitrorcjunkie

.5 cm????? that's 5 mm, the ID of the carb itself! the opening between the slide and the carb body should be around 1mm, or .01 cm. Use a 1mm hex driver as a guage. But this setting is only a ballpark figure.

drewr33

Ok guys I have been playing around with the tmaxx.

I can get it to run perfect when driving on the local car park. But only reaching top speed occasionaly.
When I take it onto the grass oval and sand, it starts to play up. Seems when its under more load. I have replaced fuel lines. plug, air filter and a bigger head.

Just this morning I started it up to do the wd40 test. I sprayed on everything. Now I did noticed that a couple of times when I sprayed on the front bearing that the engine stopped. It happend 3 times. So I took it for a spin to warm it up more. And this time it didn't do anything when I sprayed it. May there be a leak?

I cant drive it now. There was a funny sound from the gear box and now the speer gear wont turn in one direction?? (is this a common problem)

drewr33

Tested it again. This time with soapy water. Poored a whole bucket onto it. No bubbles and engine stayed running.

125cchyperman

Sorry I ment .5mm thats for a slide carb accidentally typed cm. This has been a common occurance for the 2.5 and 3.3 for some reason. This has come up on several other threads and I dont think we ever did find the reason for it to tell you the truth and if we did I cant remember. To tell you the truth I think Traxxas had a bad production run for a little and let some lemons out and they just dont know about it yet. As your not the only one with these type of problems so dont think thats your doing something wrong there's just something wrong with there engine's. I think the last guy just went out and bought a O.S engine and that fixed it.

But when I get back if nobody has figured out what the problem is I will do some searching for you and see if I can find and pin point exactly what the problem is. If I cant find the solution I'm more then sure with everybody here that we will be able to solve this problem.

125cchyperman

Sorry I looked and looked but couldnt seem to find what I was looking for. But never the less I'm sure we can find what the problem is.

02KLX300

I am currently having the same problem with my REVO 2.5R. Exactly what you have descreibed, It's in peices right now for cleaning while waited for a new gas Tank to come in (got the whole tank cheaper then the rebuild kit from shop). The one thing i dont think had been mentioned is that check you seal around your tank lid. Mine had been worn out and had actually been holding it open the slightest bit causing no the tank not to pressurize. When Running WOT there is enough exhaust pushed in that is doesn't have to be sealed When just putting around or slowly letting off the motor can suck the fuel through the lines enough to keep running. But when at WOT then Suddenly cutting off to nothing there is no time for the motor to bring in enough fuel to keep up with itself without it being pushed through the lines. That is best i can explain what I am trying to say and hopefully it makes sense.

drewr33

Sound like a good thing to check. My seal looks ok and is tight to close. I was thinking of strapping a model plane fuel tank on, as they have no lid, and see if that helps.

I cant drive it now, striped a gear in the gearbox already.

drewr33

Just found this on another thread. Will do this test tomorrow

"take off ur fuel tank and pressure check it... the oring on the top of the tank is extremely ****ty. mine leaked within 5 tanks. anyways if u dont know how to pressure check, hold the tank underwater blow into the pressure line from the exhaust and put ur finger over the fuel to carb fitting. blow as hard as u can, NO BUBBLES SHOULD BE RELEASED! ive had this problem multiple times. it was like i could not tune the motor, no matter how many turns i richen up the carb, it still runs like it is lean. if there is a pressure leak, not enough fuel is being pushed into the cylinder, therefore creating a lean mixture setting. this should fix ur problem. that situation is very familiar, and i would be surprised if that wasnt it. lemme know if thats what it was. "

drewr33

I have tested the tank for leaks and there is none.

Does the easy start plastic housing parts have to be fully sealed??