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Old 03-28-2010, 01:25 PM   #1
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Default Tuning consistency questions

I've got a Kyosho DBX running Traxxas 20% fuel, and I've got 2 tuning issues that I would really appreciate tips with. It's still a blast to drive, I'm just splitting hairs with the tuning here:

(1) Consistency across a single tank of fuel. Assuming I tune it with 50% full fuel tank, then; If I start with a 100% full fuel tank, basically the first 10% runs very rich, the middle 70% runs just where I tuned it, the bottom 20% runs like a rocket bordering on too lean, though it still smokes. Is this typical, or is there some trick to getting it to run consistently across the entire tank?

(2) Very rich mid-throttle. No matter how much fuel is in the tank, from about 1/4 to 1/2 throttle it runs very rich. If I'm only wide open or idle then it runs perfect, but if I run from 1/4 to 1/2 throttle for, say more than 4 or 5 seconds, then when I go back to wide open I get lots of smoke and slow acceleration (it loads up). If I go leaner with the slow speed screw then it won't idle or idle will be unstable, and the high speed is definitely as lean as I dare go. Is this just a trait of a price-point (inexpensive) car? Any ideas on correcting this?

This car is a blast for the price, I would definitely buy it again, but if I could nail the tuning then I would be estatic.
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Old 03-28-2010, 01:34 PM   #2
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Your to fat on the bottom and lean on top. Fatten the top a couple of hours and then lean the bottom a couple of hours. Check to make sure your airgap is .5 to 1 mm. This should do it for ya.
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Old 03-28-2010, 05:52 PM   #3
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Thanks for the tips. I tried 1/8 turn richer on top and when the tank is full it won't rev out at all, so I guess it wasn't as lean as I thought on top. But going leaner on bottom did help it to not load up at 1/2 throttle, but the idle is very lean. It acts like when you pinch the gas line with your fingers; smooth idle for a couple seconds, then the idle races up and it stalls. If you blip the throttle then the idle will settle for a couple more seconds before racing up again. However the throttle response everywhere above idle is fantastic. I wonder if I've got an air leak somewhere?
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Old 03-28-2010, 06:16 PM   #4
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Quote:
Originally Posted by MattFL View Post
Thanks for the tips. I tried 1/8 turn richer on top and when the tank is full it won't rev out at all, so I guess it wasn't as lean as I thought on top. But going leaner on bottom did help it to not load up at 1/2 throttle, but the idle is very lean. It acts like when you pinch the gas line with your fingers; smooth idle for a couple seconds, then the idle races up and it stalls. If you blip the throttle then the idle will settle for a couple more seconds before racing up again. However the throttle response everywhere above idle is fantastic. I wonder if I've got an air leak somewhere?
You shouldnt have an air leak. With an airleak it will hardly run at all. Heres another way to do it. Put both needles flush make sure your air gap is correct. Start with the low speed and lean it till you have the idle you want. Then get out and drive it till its warm. Start leaning the top 1 or 2 hrs at a time until you get the top end performance you want. bring it in and check the idle if its to fast then fatten the bottom a little if its to slow then lean the bottom a little. Its kinda hard to explain but if I were there to help you we could do it in a couple of mins.
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Old 03-28-2010, 06:24 PM   #5
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,
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Old 03-28-2010, 06:25 PM   #6
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[QUOTE=MattFL;7198306]Thanks for the tips. I tried 1/8 turn richer on top and when the tank is full it won't rev out at all, so I guess it wasn't as lean as I thought on top. But going leaner on bottom did help it to not load up at 1/2 throttle, but the idle is very lean. It acts like when you pinch the gas line with your fingers; smooth idle for a couple seconds, then the idle races up and it stalls. If you blip the throttle then the idle will settle for a couple more seconds before racing up again. However the throttle response everywhere above idle is fantastic. I wonder if I've got an air leak somewhere?[/QUOTE


,

sounds like your still to rich on the bottom. Don't worry about the high idle just yet, keep leaning your bottom until it takes off with no hesitation and it's clean and smooth throught the powerband. At that point your idle will probably be really high and racing.

then reset you idle screw by turning counter clockwise until the idle gets back to normal.

basically your idle gap is too big. you are getting to much air at idle causing you to add more fuel. Thus loading the case.
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Old 03-28-2010, 06:52 PM   #7
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[QUOTE=dreaux;7198494]
Quote:
Originally Posted by MattFL View Post
Thanks for the tips. I tried 1/8 turn richer on top and when the tank is full it won't rev out at all, so I guess it wasn't as lean as I thought on top. But going leaner on bottom did help it to not load up at 1/2 throttle, but the idle is very lean. It acts like when you pinch the gas line with your fingers; smooth idle for a couple seconds, then the idle races up and it stalls. If you blip the throttle then the idle will settle for a couple more seconds before racing up again. However the throttle response everywhere above idle is fantastic. I wonder if I've got an air leak somewhere?[/QUOTE


,

sounds like your still to rich on the bottom. Don't worry about the high idle just yet, keep leaning your bottom until it takes off with no hesitation and it's clean and smooth throught the powerband. At that point your idle will probably be really high and racing.

then reset you idle screw by turning counter clockwise until the idle gets back to normal.

basically your idle gap is too big. you are getting to much air at idle causing you to add more fuel. Thus loading the case.
I agree I think that is his problem also to big of air gap.
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Old 03-28-2010, 07:13 PM   #8
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but he must be careful. once he resets his low end he might be to lean on top!

the best advice would be to reset everything set your idle gap at about 1mm. tune your high speed first, remember though, you might have a hard time idling at this point do to the rich low end and small idle gap. So if you have to lean your lsn just enough so it doesn't die on you for about 15 seconds.

Get a long stretch of land or parking lot get it decently warm and leg it out at wot and lean the hsn a hour at the time. As long as performance improves and there is smoke visible you are doing right. when you get to the point where you turn it a hour and performance decreases you have gone to far. back it out 2 hours. That should basically be you hsn setting then work on the lsn. Lean it out (remember your gap is small so it steadily loading up, that is why you need the long straight to get a good reed on the hsn), like i was saying. Lean the lsn out a hour at a time until it takes off without hesitation and there is no puff of smoke and comes up to rpms rapidly. You really have to know the sound and when you hear it and the temps are right you got it.

Then richen it a hour and this is your final setting. When you get better at it you can tune them both at the same time, but this is how i had to learn and it has worked like a charm for me.
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Old 03-30-2010, 05:42 AM   #9
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Just an update: I think I might have an air leak so I removed the carb and sealed it. I'll try again tonight to see if that makes a difference.

That said, here's where I'm at before sealing:

HSN - 2.25 turns (factory baseline 2.5)
LSN - 3.75 turns (factory baseline 2.5)

My air gap is teeny tiny (see image below). Sorry for the hacked up link, the site won't let me post images yet (I'm too new):

h t t p :// w w w .vortexsprockets.com/images/dbx/air_gap_dbx.jpg

At these settings I get great throttle response, no loading up at mid-throttle and strong power bottom to top, the only down side is idle is very very lean. At idle it will rev up then stall, exactly like it ran out of gas, even though the LSN seems to be obscenely rich and the air gap is tiny. I'll try again tonight after the sealer dries and post back what happens.
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Old 03-30-2010, 06:29 AM   #10
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Are you preheating your engine? It sounds like the first part of your tanks are spent "warming up" the engine. That's why it's so rich early.
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Old 03-30-2010, 06:41 AM   #11
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Reset all needles to factory, start with the high end needle.
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Old 03-30-2010, 04:40 PM   #12
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Quote:
Originally Posted by MattFL View Post
Just an update: I think I might have an air leak so I removed the carb and sealed it. I'll try again tonight to see if that makes a difference.

That said, here's where I'm at before sealing:

HSN - 2.25 turns (factory baseline 2.5)
LSN - 3.75 turns (factory baseline 2.5)

My air gap is teeny tiny (see image below). Sorry for the hacked up link, the site won't let me post images yet (I'm too new):

h t t p :// w w w .vortexsprockets.com/images/dbx/air_gap_dbx.jpg

At these settings I get great throttle response, no loading up at mid-throttle and strong power bottom to top, the only down side is idle is very very lean. At idle it will rev up then stall, exactly like it ran out of gas, even though the LSN seems to be obscenely rich and the air gap is tiny. I'll try again tonight after the sealer dries and post back what happens.
I checked the pic of your airgap. It looks fine. If your 3.75 turns out on the bottom your probably way fat, just like I said in a previuos post. Go back to 2.5, out leave your hsn where its at. Drive it untill it gets to 200 degrees. Then adjust your bottom. If its idleing fast fatten it 1 hr at a time. Blip the throttle after each hour and see how it idles. Keep doing this until you get the idle you want and you should be good to. After that you can adjust your high speed to the race tune you want.
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Old 03-30-2010, 04:57 PM   #13
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Default Got it!

Firstly thank you to everyone for your tips, I really appreciate it!

I think I got it. I warmed it up, went back to factory settings, got the HSN right then worked on the idle and LSN. In the end my HSN is about the same (2.5-2.25 turns) and the LSN is close to factory (2.5-ish) and the idle is very lean and goes up and down a bit, but doesn't stall at idle anymore.

How lean is too lean on idle? Currently if it idles for say 10+ seconds, then I floor it, I get instant response but basically zero smoke. If I keep driving it then the smoke returns a few seconds later. If I keep driving I get continuous good smoke so I'm assuming I'm not too lean up top?
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Old 03-30-2010, 05:08 PM   #14
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I checked the pic of your airgap. It looks fine. If your 3.75 turns out on the bottom your probably way fat, just like I said in a previuos post. Go back to 2.5, out leave your hsn where its at. Drive it untill it gets to 200 degrees. Then adjust your bottom. If its idleing fast fatten it 1 hr at a time. Blip the throttle after each hour and see how it idles. Keep doing this until you get the idle you want and you should be good to. After that you can adjust your high speed to the race tune you want.

I did basically just what you said, and you had it right; fat on bottom. The only thing that bugs me is I adjust for a really solid smooth slow idle (idles the exact same RPM forever), then the mid-throttle is waaay to rich. If I adjust for great mid-throttle response with no loading up, then the idle is lean and a little unstable but usable, and the drivability is much much better. I guess with this carb I just can't have both a nice solid idle and great mid-throttle response, but I don't idle that much so I'm satisfied.
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Old 03-30-2010, 05:30 PM   #15
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Quote:
Originally Posted by MattFL View Post
I did basically just what you said, and you had it right; fat on bottom. The only thing that bugs me is I adjust for a really solid smooth slow idle (idles the exact same RPM forever), then the mid-throttle is waaay to rich. If I adjust for great mid-throttle response with no loading up, then the idle is lean and a little unstable but usable, and the drivability is much much better. I guess with this carb I just can't have both a nice solid idle and great mid-throttle response, but I don't idle that much so I'm satisfied.
Matt put your Idle back to where it idles good your flat spot is past half throttle thats top end . Now you get to have fun. Try leaning the top an hr at a time and see what it does. If it gets worse then start fattining an hr at atime until it gets better and then best. Ive been doing this for about a year now. and have it figured out pretty good. But the no smoke thing when you take off and the flat spot in the middle sounds like your starving for fuel . I say put it back to where it idles good with a good take off and fatten the top a couple hours and see what happens
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