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Old 06-07-2011, 08:30 PM   #1
nick_onelove
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Default New Truck Stalls Under Acceleration

I'm a heli flyer and I just got the Traxxas Revo 3.3, my first foray into nitro and cars in general.

Anyway, with the factory needle settings it would only stay running for about 2 seconds after I released the EZ-Start button. I richened the idle needle setting until it would stay running at idle, which I think is way richer than it should be. When I just let it sit and idle, it gradually gets louder and louder until it starts inching forward tiny bits. Then when I give it throttle it doesn't want to move, then it dies when I release the trigger. I can get it to move if I give it full throttle, but it still dies once I release it, and I'm not supposed to do that during break-in anyway, right?

I've tried richening the high-speed needle setting and it helps, but even with it like 3-4 full turns richer than factory settings its just not right. I looked through the Traxxas support site and the things their FAQ says could be causing it mostly don't relate to a new model (ie, bent shaft after a crash etc.).

I got this to help me decide whether I'm going to get my Trex 700 nitro or electric; I'm not very encouraged at the moment lol. Anyway, any help would be greatly appreciated, if I can't get it running in the next couple hours I'm going to have to do the after-run procedure without even getting to run it.
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Old 06-07-2011, 08:38 PM   #2
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what fuel and what glow plug?

sounds like the idle circuit is lean.. try turning low speed needle out untill its a RICH idle



Crank engine.. when its IDLE pinch fuel line.. does it rev up fast before it dies.. or just die?
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Old 06-07-2011, 08:40 PM   #3
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First of all a trex700 nitro is a much easier motor to tune than a traxxas truck. I would make sure you don't have leak in any of the fuel lines and check the fuel tank seal, then start from scratch on the needle settings, sounds like it to rich to me,
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Old 06-07-2011, 08:44 PM   #4
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QUOTE : "When I just let it sit and idle, it gradually gets louder and louder until it starts inching forward tiny bits"


that sounds like its LEAN
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Old 06-07-2011, 09:03 PM   #5
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I'm using Traxxas Top Fuel 20% and the stock glow plug. There's just one small sweet spot on the idle needle setting where it will stay running. If I richen it or lean it much more than 1/4 turn, it dies. When I pinch the line it does rev up before it dies.

There doesn't appear to be any leaks in either the tubes or the cap.
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Old 06-07-2011, 09:14 PM   #6
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maybe IDLE speed is incorrect.. when its Rich it will idle down... lean = rev up
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Old 06-07-2011, 09:17 PM   #7
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Car's are tricky to tune. SLOW tuning. 1/16th turns make a difference. Richen it a little, and turn up the idle stop screw to maintain idle. Also, is engine warmed up when you try to acellerate? They need time to warm up to operating temp. Lift car so wheels are off ground and slowly blip throttle to "clear out' engine. Cold engine will puddle fuel in crankcase at idle, even if it's lean, then you hit throttle and it gets a gulp of pure fuel and flames out. I also keep the glow igniter on for 30 seconds or so while she first fires, to help with flameouts untill warmed. No hard acellerations fr the first couple minutes too. Nitro car engines last best if they are warmed up gently before driven hard. They are a different animal than plane and Heli engines. I've beeen tuning and modifying Nitro cars for over 16 years now. They can still cause me greif at times too.
Golden rule, Adjust 1(ONE) thing at a time, and try it. give engine 30-45 seconds to adjust to the change beforfe making another change. If you change both needles at once, you can really screw yourself.

Also, To check if bottom end lean or rich, Once you do get her running, come in from a run, let her idle. She should idle high fro 7-15 seconds, then the idle should drop on it's own. The faster it drops, the richer the engine. For sport play, you want the bottom end richer. It's slower off the line, but when you chop the throttle from a WOT run, the richer mixture helps from running the enigne to lean.
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Old 06-07-2011, 09:20 PM   #8
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Quote:
Originally Posted by banditpowdercoat View Post
Car's are tricky to tune. SLOW tuning. 1/16th turns make a difference. Richen it a little, and turn up the idle stop screw to maintain idle. Also, is engine warmed up when you try to acellerate? They need time to warm up to operating temp. Lift car so wheels are off ground and slowly blip throttle to "clear out' engine. Cold engine will puddle fuel in crankcase at idle, even if it's lean, then you hit throttle and it gets a gulp of pure fuel and flames out. I also keep the glow igniter on for 30 seconds or so while she first fires, to help with flameouts untill warmed. No hard acellerations fr the first couple minutes too. Nitro car engines last best if they are warmed up gently before driven hard. They are a different animal than plane and Heli engines. I've beeen tuning and modifying Nitro cars for over 16 years now. They can still cause me greif at times too.
Golden rule, Adjust 1(ONE) thing at a time, and try it. give engine 30-45 seconds to adjust to the change beforfe making another change. If you change both needles at once, you can really screw yourself.

Also, To check if bottom end lean or rich, Once you do get her running, come in from a run, let her idle. She should idle high fro 7-15 seconds, then the idle should drop on it's own. The faster it drops, the richer the engine. For sport play, you want the bottom end richer. It's slower off the line, but when you chop the throttle from a WOT run, the richer mixture helps from running the enigne to lean.

could not have said it better!!!
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Old 06-07-2011, 09:25 PM   #9
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Quote:
Originally Posted by banditpowdercoat View Post
Richen it a little, and turn up the idle stop screw to maintain idle.
Whoa wait, isn't turning the screw how you richen/lean it? What do you mean "richen it, and turn up the screw"?
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Old 06-07-2011, 09:31 PM   #10
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find your Low speed needle.. its different then IDLE screw

look in manual
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Old 06-07-2011, 09:40 PM   #11
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see page 25 of the manual..http://www.horizonhobby.com/ProdInfo...ers_Manual.pdf
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Old 06-07-2011, 10:17 PM   #12
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Oh wow, what an oversight on my part. What I've been adjusting is the low-speed needle, it was the idle screw that I didn't know about. Sorry about that.

But I've managed to get it running without even touching the idle screw. I think the problem was that I wasn't letting it warm enough, like bandit said. I'm used to plugging in a battery and taking off, the engine warm-up alone is as long as an entire battery flight lol.

When I come in from a run, the idle drops down almost immediately, it only idles high for like a second or two. I guess that means I've got it running really rich? I'm OK with that though, I'm much more interested in making sure the engine is lubricated enough than getting higher performance.

Thanks for the help guys, its really fun even just breaking it in! Its nice not having the stress of having $1000+ hanging in the air.
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Old 06-07-2011, 10:38 PM   #13
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yeah I am eyeballing a BajaSC. to kick around.. or an OnRoad Racer InfernoGT2
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Old 06-07-2011, 10:50 PM   #14
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Quote:
Originally Posted by nick_onelove View Post
Oh wow, what an oversight on my part. What I've been adjusting is the low-speed needle, it was the idle screw that I didn't know about. Sorry about that.

But I've managed to get it running without even touching the idle screw. I think the problem was that I wasn't letting it warm enough, like bandit said. I'm used to plugging in a battery and taking off, the engine warm-up alone is as long as an entire battery flight lol.

When I come in from a run, the idle drops down almost immediately, it only idles high for like a second or two. I guess that means I've got it running really rich? I'm OK with that though, I'm much more interested in making sure the engine is lubricated enough than getting higher performance.



Thanks for the help guys, its really fun even just breaking it in! Its nice not having the stress of having $1000+ hanging in the air.
Ya there is a lower stress level fro sure. But less adrenaline too. Thats the rush I get from heli's now and why I stopped cars. And sounds like your bottom end is fine for tune. Just remember, if you idle for a little while, you won't be able to just punch it. It will load up and you will have to feather the throttle to clean her out again.
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Old 06-07-2011, 10:56 PM   #15
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Quote:
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When I come in from a run, the idle drops down almost immediately, it only idles high for like a second or two.
I'm wrong, I wasn't being patient enough again. It idles high for about 8 seconds before dropping to a slightly lower idle. Is that still alright? And I get what you're saying about not being able to really take off from low idle; for a while I thought something was wrong because the acceleration seemed inconsistent.

That Baja SC looks pretty cool, I was considering a short-course truck myself before I decided on the Revo. And that Inferno looks like it'd be badass if I had pavement nearby, but I live on a walnut orchard with a gravel road.

Thanks again guys, you REALLY helped me out today. I just finished my third tank, I'm almost done with break-in! Its getting dark though, time for my first after-run maintenance.
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Old 06-07-2011, 11:11 PM   #16
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You should be fine there. One tool you NEED with Nitro is a temp gun. You need to tune the top end by glow plug temp. To cold, and the piston/sleeve is not expanded enough, and it wears faster, To hot and the fit is to loose, and the piston rocks around and wears too. 220-240*F is where I run my 1/8th engines. Leaner is more power, but more heat. You can't have great power and hold it Wide open for extended periods of time either. It will get to hot. On Off blips and shorter bursts help the enigne cool while having the top end needle set lean enough that it does make good bursts under power. Your play area/driving stile will dictate and with the temp gun, you will be able to see yourself and adjust needles and driving habbits.

Ever notice Nitro Helis put out WAY more smoke than car's? cause they are setup richer, because they are run WOT the whole time. You can almost double the engine power by leaning it out, but would have to blip the throttle and have cooldown periods etc. That wouldnt work so well when your inverted 3ft off the deck...
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Old 06-07-2011, 11:21 PM   #17
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Quote:
Originally Posted by banditpowdercoat View Post
One tool you NEED with Nitro is a temp gun. You need to tune the top end by glow plug temp
Hah, I've thought about picking one of those up for cooking before anyway, this is a perfect excuse. Is there anyway to know that the high-speed is at least within safety margins until then? Should I just set the high-speed needle as rich as it will go and still run?
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Old 06-07-2011, 11:32 PM   #18
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SHould be good smoke upon acelleration. And you can do the spit/water test. A drop of water or spit n the glow plug should just bubble away. not fast and not sit there. Water boils at 217F isn't it? so 220-230F It;s a crude, but effective test for time being
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Old 06-08-2011, 12:23 AM   #19
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Gotcha. I do get good smoke, but I might try the water drop test; I believe boiling point is 212, so that makes sense.

Thanks again bro, you've been super informative.
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Old 06-12-2011, 11:43 AM   #20
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How's it goin? having success?
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