Pesky Carb on 2.5 ???

[Rolex]

First day on this forum, but I've had my Tmaxx for almost 2 years. I just swapped out the stock .15 for the 2.5. The .15 was flawless, but I got an irresistible deal on the 2.5 at cost. Now I'm hearing stories that it's a real pain to keep tuned. Any truth to this?
Someone said there's an OS carb that works well.....set it and forget it. I checked one of my airplanes today that has an OS engine, but it's a narrow throat on a .40.
My new engine has only had one quart run through it, and that includes the 6 break in tanks, and so far it starts almost instantly and idles well. A little warm up time, and it WANTS to rip. Temp runs between 220 and 240 depending on the surface it's running on. I'm very patient and picky about tuning engines, and I've tweeked my needles after break in. I always prefer to run slightly on the rich side, and prefer to trade off wheelie power for better high end. After break in and tweeking, it hasn't stalled once.
Is it possible that the complainers just don't have their's adjusted properly, or am I just lucky because it's new?

 

[slodsm]

No, your not lucky, 90% of the complaints come from noob's who don't know how to tune yet. I have never had a problem with my 2.5 but I have been tuning nitro motors for a long time so it comes easy. When someone is brand new, they don't know what they are looking for or hearing and they make to large of an adjustment. The same people who thing 2.5's are garbage should give a real picco motor a shot, they would think they were the biggest peices of crap ever since you have to tune them by 1/16th of a turn.

 

[Chevy-SS]

It sounds like you are really breaking the motor in properly. I tried to do the same with my 2.5. Mine runs pretty good, but was sensitive to air temp and low fuel in tank, things which will affect all nitro motors anyway. Plus my 2.5 motor gets hot quick, even when running rich.

My LHS owner says the 2.5 T-Maxxes are his best seller, but the worst for returns due to engine tuning issues. He says the break-in for the 2.5 motor is critical and many people simply don't spend the time doing it right. He recommends 10 tanks to break in. One of the most common complaints he gets is that the engine gets hot, then stalls, and won't start til it cools down. He says once that starts happening, it's time for new piston and sleeve.

I like my 2.5 engine, but was a little disappointed in the power. I ended up installing the Picco P2 .21, and now it really flies. I plan to start racing it this summer. I was going to use the 2.5 engine to race, but the LHS owner (he also owns the race track) says the 2.5 engines simply don't do well (tuning, overheating issues) in races. According to him, virtually everyone upgrades to a .21 to race.

Good luck with yours. Sounds like you are treating it right.

 

[SavageRockS]

Nitro engines are like you said "pesky" in general. It takes a lot of patience and know how to tune one, ones tuned though, they are a delight to run and lots of fun. I agree with slodsm that most of the complaints are from newbies who have not mastered tuning their engines yet. If you are flying planes, you must know how to tune your nitros.
:smoke:

 

[StrechM]

No problems with my old 2.5. Nothing that a screwdriver and temp gun wouldn't take care of.

 

[30%NitroBoy]

Well,

I've got three 2.5 Mills now. One of the works great and is consistent and holds a tune relatively well. The other two are a nightmare. IMO you definitely have to be an experienced tuner to run the 2.5 properly. It's sad really how many in this hobby can't properly tune their engines and aren't realizing their full power potential.

 

[Domination]

I've had my maxx for a lil over 1/2 yr and i havnt had any problems with tuning but tuning come relitivly easy to me since i used to always tune weedwackers and chainsaws which also use needle to tune with that may be why. The 2.5 also holds the tune pretty good IMO

Chevy-SS your shop owner is wrong if the engine get too hot and dies out then wont start up untill it cools down you dont need to get a new piston and sleeve just put the piston to BDC let it cool and start it up. The only reason it stalls ouyt is because it over exspands and looses compression. If you keep running in these consitions for a extened period of time then you would need a piston sleeve but if it only happen a few times it shouldnt hurt anything dramatically

 

[HumboldtBlazer]

Originally posted by slodsm
No, your not lucky, 90% of the complaints come from noob's who don't know how to tune yet. I have never had a problem with my 2.5 but I have been tuning nitro motors for a long time so it comes easy. When someone is brand new, they don't know what they are looking for or hearing and they make to large of an adjustment. The same people who thing 2.5's are garbage should give a real picco motor a shot, they would think they were the biggest peices of crap ever since you have to tune them by 1/16th of a turn.

You really couldn't be more wrong here imo. 2.5 compared to an italian engine. Now I have not owned a Piccio but I have owned Sirios, and a 2.5 and will it was a good engine, and fast for a .15 but it was hard to tune and way more sensitive than ANY engine I have ever owned. Sure there were some great ones but even they ran hot. I really like that with the Revo they got it through their heads as me and everyone else said the cast head was cheap and did not dissapait near the amount of heat it needed to. The reason it got hot was they squeezed more power out of the block by giving it more ports in the right places. But just like overclocking a computer you can't do it safley without a better source of cooling. That said happy to see the CNC's head and I hope it works out. Also you can't deny the hundreds of OS carbs that were swapped out by owners and suddeny fixed the touching settings and made the engine easier to tune. All of this said I do not doubt that you have a trouble free experience with the 2.5 that you owned. The one I owned was one of the good ones too. It ran hot but good. 280-290 is just not to my liking of the engine temps. IT had a big vehicle to push under harsh conditions with a cast head I say under those circumstances it did great, better than average even. But to totally say it is just because people don't know how tune was a scapegoat used by the dasdardly duo on the TRX forum and the company stonewalled everyone that complained and made them to feel inatiquit (sp)?:hypno:

I have to also have to say my customer support with Traxxas was probablly the best I have seen in the industry. I am sure one on one they took care of everyone that had a bad product, but publicly the stuck to there guns that there was no problem with the engine whatsoever. Just had to be real about as the went above and beyond with me when I had a problem.

 

[Domination]

i run around 210 with the ACNCM head and it runs like a dream with a dynamite exhuast on it also

 

[HumboldtBlazer]

Originally posted by Domination
i run around 210 with the ACNCM head and it runs like a dream with a dynamite exhuast on it also

I also had success with an aftermarket head made by Hardcore Racing. It ran 220-250 after that.

 

[Chevy-SS]

Originally posted by Domination
Chevy-SS your shop owner is wrong if the engine get too hot and dies out then wont start up untill it cools down you dont need to get a new piston and sleeve just put the piston to BDC let it cool and start it up. The only reason it stalls ouyt is because it over exspands and looses compression. If you keep running in these consitions for a extened period of time then you would need a piston sleeve but if it only happen a few times it shouldnt hurt anything dramatically

All I can tell you is this LHS owner has six T-Maxxes himself. He sells a ton of them and works on them every day. He also owns and runs an outdoor race truck with a T-Maxx truck class, so he sees firsthand how Maxxes fare in receational, as well as racing environments. I would consider him a qualified expert on T-Maxx tuning issues, and it is his opinion that the 2.5 engine is difficult to keep tuned and is easily susceptible to damage from overheating. The 2.5 is only a modest .15, and has to work too hard to make all that power. I only own one T-Maxx, but I basically agree with him.

Keep your eye on Traxxas, I will bet a million bucks (wish I had a million) that they come out with re-make of T-Maxx sporting a .21 engine (or bigger).

 

[SkyMaxx]

I'll take that bet, and I'd like payment in the form of a cashier's check please.

They did indeed come out with something, only they redid the 2.5 and dropped it in a totally new design for an MT and tagged it as REVO. Check out our homepage for information or go to TRAXXAS for more info.

 

[slodsm]

Originally posted by HumboldtBlazer


You really couldn't be more wrong here imo.

Unfortunately that is your opinion and you are entitled to it although as you stated in your own post, YOU have never owned a picco engine. I have owned 2 of them and they made enormous power but were the most finicky engines I have ever owned. The 2.5 is a simple engine to tune as long as you are not a temp obsessed person. Tuning by temp is a huge downfall in nitro racing. Tunes come from sound and site, not temps simply because (short version) temps vary from engine to engine off of variables like manufacturers tolerances, head size, fuel mixture and brand, glow pug temp and brand, altitude, humidity, outside ambient temp, and so many others. I have owned many many nitro engines from Japan, Italy and France and found that they will all run at a different temp to run perfect. My RB motors have run perfect from 200 to 230 depending on the day where some of my picco's would not run at all under 280. When you actually learn how to properly tune a motor, a temp gun is obsolete.

 

[HumboldtBlazer]

Originally posted by slodsm



Unfortunately that is your opinion and you are entitled to it although as you stated in your own post, YOU have never owned a picco engine. I have owned 2 of them and they made enormous power but were the most finicky engines I have ever owned. The 2.5 is a simple engine to tune as long as you are not a temp obsessed person. Tuning by temp is a huge downfall in nitro racing. Tunes come from sound and site, not temps simply because (short version) temps vary from engine to engine off of variables like manufacturers tolerances, head size, fuel mixture and brand, glow pug temp and brand, altitude, humidity, outside ambient temp, and so many others. I have owned many many nitro engines from Japan, Italy and France and found that they will all run at a different temp to run perfect. My RB motors have run perfect from 200 to 230 depending on the day where some of my picco's would not run at all under 280. When you actually learn how to properly tune a motor, a temp gun is obsolete.

Spoken like a true traxxas employee. Trouble was I was tunning for performance, and whne it was optimal or close to it my engine was cooking @ 280-290. I guess I will go back to the Traxxas forum because I need to take another engines tunning course. Piccio must have gotten it under control if mr. Degani is signing up.

 

[Chevy-SS]

I can't believe I missed the REVO announcement. I get all the RC magazines. This is brand new?? It looks great, kinda like a truggy, such as the Storm SUT. :clap: However, I think the SUT would beat this REVO badly because of power.

I also can't believe they are still sticking to a 2.5. How can they possibly be so out-of-touch with RC fanatics? Traxxas is clearly asleep at the wheel. :sleeping:

We all want maximum power with minimum headaches. The easiest way to get that would be a mid-range performance .26, or maybe something using the clever design of the "mid-block" Picco P2 .21 that drops right in place of a 2.5.

Oh well, two things will probaby happen here:
1) I'll get one, and,
2) I'll put in a real motor

I need a beer. :beer:

You know, this reminds me of why I am no longer a completely dedicated Chevy fan like I used to be. I mean, I still have my '68 big-block Camaro with fuel injection and all the goodies. But Chevrolet (and GM itself, for that matter) just doesn't seem to get it. This is the heyday for muscle cars, perhaps the last gasp for true power before the oil crisis really hits home. What does GM do, they come out with Chevy SS truck......... wtf, who really wants a hot-rod truck??? Gimme a retro Camaro or Chevelle with massive power and new-tech handling. Oh, I forgot, GM did make a GTO. ROFLMAO.... What a joke. The GTO looks like a Taurus or any other car.

Now, look at Ford.... They listened to public and did a great retro job on T-Bird, then Mustang. The 2005 Mustang is awesome, modeled after the '67. I think I'm gonna change my name to "Ford-SS", and then go buy one of those supercharged Mustangs.

Sorry for rambling on, point is: Traxxas should have used bigger motor.

 

[Rolex]

Thanks

WOW, lot's of responses.....Thanks, guys.
Before I upgraded to the 2.5, I got 2 of them running for a couple of guys who had made so many adjustments that they lost track of where they should be. They would sputter as long as the starter was turning. Without having the info available at that time for the factory settings, I had them hold the start button while I adjusted the LSN till it would idle without the starter turning. At that point I started to lean or richen the HSN while they held the car down on the table as I gave short bursts on the trigger. It's all in the sound. When it pulled hard on short bursts, it was ready to run. Only then did I start doing checks with the temp gun just to know it was on the safe side.
Speaking of engines, the airplane with the OS .40 that was in one of my planes, had sat for over a year against the wall, on it's nose. When I picked it up to see if it had the same size carb throat THICK oil poured out of the prop spinner (nosecone) all over my hand and the floor. I hadn't emptied the tank, and a lot of fuel had seeped out of the carb and evaporated leaving the synthetic castor oil behind. I took the plane outside, drained the rest of the tank, changed the glow plug, filled it with fresh fuel and fired it up. It started instantly. Idled perfectly, and throttled up like it was brand new. I've always had great luck with all my plane engines, both 2 stroke and 4 stroke, so I expect to have the same luck with this 2.5.

 

[bhwilder]

My brother and I both have a T-maxx and he's been through 2 carbs for his 2.5 and I was about to be on my second thanks to a crack underneath the hsn. Both never ran right with the composite carbs traxxas put on them, seems that they have a composite body with metal parts inside, everyone should know that metal and composite doesn't expand under heat at the same time or temps, so I did some research and found one heck of a carb.
The O.S. 10d or 10j carb!! both will fit the 2.5 both of the throats on the carb will fit perfectly just slide it in.
This will take care of alot the problems with stalling and idling, etc.
Since I put one on mine it's a screamin demon and not one problem. Idles all day, will run the tank out gas if you let it and won't just up and die, unless you run to high or low on lsn or hsn.
Don't think this doesn't have to be tuned, It does, but takes out alot of frustration of trying to tune the 2.5 piece of crap carb traxxas has.
If you want a worth while hop up, I highly reccomend the O.S. 10d or 10j (10j has a bigger venturi, I have the 10d). No complaints and fixed alot of the probs the stock carb on the 2.5 has.
It's a screamin demon and it ain't to perfection yet!!

About the composite and metal parts expanding at different temps, I've seen alot of people complaining that there 2.5 runs and then just dies, well, when the metal expands and the compostie doesn't it blocks the fuel from getting to the carb and shuts down the engine, that was one the reasons we switched to the O.S. 10d carb, it's all aluminum and all the parts heat and cool at the same time so the parts can't expand and block the fuel.
Once we swithed to the o.s. from the stock carb, that solved the problem and runs perfect every time.

 

[Chevy-SS]

From bhwilder
well, when the metal expands and the compostie doesn't it blocks the fuel from getting to the carb and shuts down the engine,

How is the fuel getting blocked in this scenario that you describe? The fuel (under pressure from exhaust gases) is coming straight to the carb through the plastic fuel line, where it goes into a metal HSN/LSN assembly to get metered out. There is some composite material in the carb, no doubt, but how does that block any fuel flow?

 

[bhwilder]

Think about it chevy ss, if the metal in the carb swells and the composite does not, how does the fuel flow throughout the body of the carb? If this does happen, then the 2.5 isn't going to have the pressure to push it through!!!
Now this is just what I've been reading on other forums and switching to the os 10d carb did solve my probs that the stock carb I had.
I tried alot of different things to get the stock carb to work right and never did. (as with several other people did) they all switched to the os carb and haven't had any probs whatsoever.
if you want to see for yourself go to the traxxas community and search on: os carb, sticking carb, etc. I think you get the point.

 

[Chevy-SS]

Metal typically expands when heated, I'll give you that. However, I have a hard time seeing how the metal carb parts could expand enough to choke off fuel flow. On the other hand, since the piston/cylinder fit is such tight tolerance, then I can see how a little extra heat can dramatically affect compression.

I have only owned one 2.5 engine and it was a pain to keep in tune. Since switching to a Picco P2, it is like night and day difference. Now it needs hardly any tuning.

As I said earlier in this thread, the LHS owner in my area owns six Maxxes, plus he sells a ton of them, races 'em, fixes 'em, etc, etc. He says the hot engine stalling condition is fixed with new piston and sleeve. He's way more of a qualified expert on that issue than me, so I am inclined to believe him.

Perhaps your new carb is helping the engine run cooler, which is helping to keep the compression up in the engine, which keeps the engine running better.