Stalling After Part Throttle (Another tuning Q...)

[aberg12012]

As if there arn't enough tuning threads already... =devil

I have a new T-Max 3.3, has roughly 3/4 gallon of fuel through it so far. The main problem I have with it is that it stalls after idling down from part throttle. Seems to do it much more after it's good and warm. Getting a temp guage today before doing anything more w/ it... I know this is vital information. (How accurate are those laser pointing infrared temp gauges??)

Without knowing the real temp, it seems to me this would indicate it's too rich at part throttle, that it's flooding out? It also seems to bog down every now and then going from part throttle to WOT. But as soon as I go WOT (clean it's throat) it idles fine. WOT seems just right, I run slightly leaner than the stock 4 turns. (About 3 3/4 turns out.)

Trouble is that as I lean out the LSN, the idle screw is already backed out as far as it affects the slide... so I've been just letting the clutch chatter so it stays running after part throttle. (And it's an Integy clutch, so I'm not expecting it to last long anyways... lol)

Another thing is the idle isn't very consistant. It tends to reve a bit higher after a good full throttle run, and then if I "blip" the throttle it will idle down a bit more... some times (depending on idle screw and LSN) dies after this "blip."

It's quite annoying having it die every time I do a part throttle turn, and bring it to a stop. Especially when I'm on the other end of the soccar field. :LoL:

 

[aberg12012]

Just a note...

Through searching I've discovered one thing that could be my problem:

The bottle of filter oil that came with the car is MIA, so I've been using K&N "spray on" oil from my cars and bikes. Too much oil=choking affect. Wouldn't this also be causing problems with WOT as well though? Thoughts?

(I'll be putting far less oil on today...)

 

[danketchpel]

IMO you're experiencing the typical issue with the TRX carb. It's lousy at getting a good tune around idle, especially if you're running Top Fuel.

I'd recommend two things, first change fuel. I changed to O'donnells 20% race blend an it tunes WAY better, I'm talking night and day. If you can't find O'd fuel I'd try Byrons or maybe Sidewinder. There are lots of opinions on fuel out there, do a little research. I went with O'd because I read lots of good opinions on it and I can get it locally, plus it's ~$10/gal cheaper than Top Fuel. My first choice was Byrons but I can't get it in my area. I've been so happy with O'd that I won't change now.

Second, the idle seems to work best at a slightly rich mixture. The problem is that it will load up pretty quickly and will run pretty rich from about 1/4 - 1/2 throttle, which I hate. If you keep the motor cleared out and use a blip type of throttle application it will be very responsive and come on power quick. But, it will load up quick if you drive around at less than half throttle much and it will die when idling for more than maybe 20 seconds.

If you lean out the LSN more you can clean up that lower throttle range "some" but the idle will be typical of a lean mixture, it won't idle down smoothly (will tend to hang on the rpms), it will be a bit more erratic, plus it won't start as easily. It comes down to a balance between the two. Use the pinch test to make sure you're in the ball park. With the motor idling, pinch the fuel line about 1.5" inches back from the carb, it should take about 3-4 seconds for the motor to die. Shorter time = too lean, longer time = too rich. The aspect of the LSN setting is that it can dramatically affect running temps. I find that if you run a bit lean on the LSN temps will rise up quick, a bit richer and they seem to stay down. Once again, a balance. Mine seems to run about 240 - 280 depending on how I'm driving and the ambient temperature.

Double check you're idle stop (speed) setting, there should be about 1mm (.025") of gap between the bottom of the slide and the carb throat when the throttle is closed. This is mostly to see that you're in the ball park.

After running other engines my opinion is that the stock carb seriously needs a slide needle to control the mixture in that mid range. My other engines have that needle (you can see it when you open the throttle) and they tune really excellent. I truly believe that many Traxxas owners would not have the tuning agony if Traxxas improved their carburetor. That's one of the reasons so many people change their engine, so the tuning is easier and more stable.

My other engines will run cleanly through out the throttle range and will sit and idle nicely for long periods of time. They also hold a tune very well. I almost never have to retune them unless the weather changes dramatically. I run the same fuel in all my vehicles.

BTW, I use motorcycle foam filter oil (Bel Ray) and it works fine.

 

[aberg12012]

Ok yea, what you described pretty much fits my situation to a T. And yea, the change in filter oil dosn't seem to make any difference.

Today I put about 6 more tanks of fuel through it, and just learned to deal with the sacrafice of a high idle so it wouldn't die every time I idle it down from part throttle. I still think I've got an air leak somewhere, possibly the front bearing as I see the flywheel is slinging a bit of oil/fuel around. I'll be investigating that more this week some time when I tear everything appart for a good cleaning.

EDIT: Forgott to mention, I did find a temp gauge today, and discovered my temps are actually a bit cold... around 200 at the glow plug, about 180 around the outside of the heat fins.

 

[danketchpel]

I still think I've got an air leak somewhere, possibly the front bearing as I see the flywheel is slinging a bit of oil/fuel around. I'll be investigating that more this week some time when I tear everything appart for a good cleaning.

I was convinced I had an air leak because of the way mine acted at idle. I did the check where you plug up the exhaust/intake, then blow air into the car fuel inlet and check for bubbles, no leaks.

EDIT: Forgott to mention, I did find a temp gauge today, and discovered my temps are actually a bit cold... around 200 at the glow plug, about 180 around the outside of the heat fins.

That's pretty cold. I run mine from about 240 - 280 for the most part. If you're running slow and just blipping the throttle alot (short course, dinking around, etc.) then the temps will be lower maybe 210 - 220. I run pretty close to a race tune for the most part. Those ~280#s are after doing LOTS of WOT type driving in large areas.

I personally find Nitro engines run better once they're above 200-210 or so.

 

[aberg12012]

To update, I called Traxxas a few days ago and they said this bearing SHOULD NOT be slinging oil/gas like that, and they are sending me new bearings. I'm hoping the new bearings are a tighter fit around the output shaft, (this is where mine leaks) but I'm kinda guessing it's more of a design flaw, rather than that I just happened to get the rare odd-ball loose fitting bearing. We shall see...

As for temps: Mine does run pretty cool with the body off. Usually about 200 at the cooling head. With the body on, it gets up to about 220, max. I'm pretty sure it's related to me having the air leak, since I have to run it very rich. (Richer than stock...) And yea, she's suckin' the gas. I've barely had this thing a week, and already through my first gallon. And most of that is just trying to get the thing to run right. Due to the idling problems, I haven't been able to have much "play" time with it yet.

That's one of the reasons so many people change their engine, so the tuning is easier and more stable.

Danketchpel,

Since you seem to have a decent knowledge in the subject, would you suggest the Picco .26? I've come to realize that sooner or later, I will probably be getting a different motor, anyways... so if it will also save me some tuning trouble, I will do it sooner, than later.

 

[danketchpel]

Since you seem to have a decent knowledge in the subject, would you suggest the Picco .26? I've come to realize that sooner or later, I will probably be getting a different motor, anyways... so if it will also save me some tuning trouble, I will do it sooner, than later.

The Picco is one of the engines I'm strongly considering for my T-Maxx. For me it's coming down to either the Picco .26 Maxx or the O.S. .21TM.

I believe the O.S. will be a easier motor to tune and O.S. seems to have an excellent reputation. I've read a few complaints with the Piccos, mostly front bearing leaks and finicky tuning. Other's have said the tuning is a breeze and no problems at all. A friend of mine has the Picco .26 in his Revo and loves it.

I haven't completely decided yet. My "plan" is to try an O.S. .18CV-RX in my Associated NTC3 1/10 road car, an LRP Z.28r Spec 3 in my Kyosho Inferno GT road car, and probably the Picco in my T-Maxx. I'm set on the motors for the road cars, the only one I haven't settled on is for the Maxx.

 

[jerry7007]

hi

change the glow plug or richen it or both!

 

[aberg12012]

change the glow plug or richen it or both!

K, thanks. :bow:

 

[dracbec]

hey aberg iam having the same probems, how did you makeout with the bearing swap i was thinking the samething about mine having an air leak

cheers

 

[danketchpel]

The Picco is one of the engines I'm strongly considering for my T-Maxx. For me it's coming down to either the Picco .26 Maxx or the O.S. .21TM.

FYI, I went with the new Picco .26Max "JL Red Dot". I'm very happy with this engine. It's much better behaved (ie tuning) than the TRX motor and makes lots of torquey power, 1/2 throttle wheelies are normal. It has a nice stable idle and almost never stalls out. It also starts very quickly, like almost instantly.

I geared my Maxx up to work better with the power band. I with with the 24t clutch bell and the standard ratio gear set in the tranny. This setup works very well for most off-roading.