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Old 08-23-2005, 08:26 AM   #1
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Default tuning the top end - keeps stalling

ever since the motor was finished breaking in, and i installed a new glow pug, whenever I pull the throttle to anything more than about 50% the engine dies. I can't figure out if it's too rich or too lean or something. i've tried making small adjustments either way and it seams to help leaning it out, but it still does the same thing. Can anyone tell me what this is? and this is the high end needle I should be worrying about right? seems to me that where it dies is right when the low end needle comes out of that hole in the carb (not sure if that made any sense!)
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Old 08-23-2005, 09:33 AM   #2
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Need some more info to go on. Does it acclerate well, or is it boggy with a lot of smoke. Lots of smoke would indicate a possible too rich condition. Not much smoke when it dies is an indicator of a too lean condition. It sounds to me like the low end needle is too lean. A too lean setting on the low end can cause flame outs in the early to mid-range with really snappy throttle response out of the hole. It's best to have the low-end a bit rich to start with until you get the top end tuned (flush is usually a good starting place on most engines). Once you can keep it running, you can assess whether the top end is too rich or lean and finish out with low end needle to improve throttle response. The pinch test is a good guideline to use on the low end needle. Just pinch the fuel line and inch or two behind the carb inlet and see how long it takes for the engine to die. If it dies immediately you are too lean. If it revs up immediately and then dies, it is about optimal but toward the lean side. Anything from 1-2 seconds before revving and then dieing is a good range with longer times leaning on the rich side.

Now you say it helps to lean it out which makes me wonder if it isn't loading up on the low end and too rich. This is where you need to judge throttle response. If it's boggy with lots of smoke it could be too rich both high and low, but a rich setting on the low end will not kill the engine unless the high speed is too rich as well.

I'll explain why this is and why you need to set high speed first. The high speed needle controls the primary flow of fuel. Kind of like the main water supply coming into your house. The low speed needle is like the faucet. So if you aren't getting enough pressure (high speed too lean) then the faucet (low speed) won't do much either. But if the water pressure is really high (too rich high speed) You can still sowewhat control it with the faucet (low speed needle). So it is possible to have the engine too rich on the top and make it run somehat by running the low speed too lean to compensate. This is what I suspect may be happening. This condition will have usually result in mid-range flameouts. Just make sure the low speed in not too lean and you should be able to chase it on the top end from there.

Hope this helps.
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Old 08-23-2005, 06:44 PM   #3
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When you replaced the glow plug, did you replace it with one that`s the same temperature?...if not it`ll certainly need retuning, but then again these engines need tuning from day to day to adjust to various temps/humidities.
If its a cooler glow plug and the engine is running quite rich, it may struggle to "burn" thru this richer mix....a hotter glow plug will burn thru a richer mix a little easier.
My suggestion would be to richen it out a couple of turns (main needle) and then work leaning it from this point (its always easier to work from richer to leaner than vice versa)....once the main needle is set, then you can go on and adjust the low end and idle.
Theres some good tuning info on Josh Cyruls website-
www.cefx.net
Cheers
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Old 08-23-2005, 09:35 PM   #4
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wow, thanks for that reply terry sturchio I think this may help

the engine doesn't bog down at all, in fact - giving it just a little gas makes the car pretty much rocket off from the start, spinning tires and all. it's just when I open the carb up past half way, it flames out. the analogy of the faucet makes sense, so I will try that, richen the top end and tune the low end from there then the top end right? the pinch test wors out good, 2 seconds and then the car revs and dies. that's why I think it was the top end needle out of tune. RD logics said to leave the mid range needle pretty much alone, flush with the housing. I did switch fuels as recommended by the manual - using 20% to break in and now switched to 30% nitro, and I realize I will have to retune the motor each time I go out, but no matter what I do it seams that the motor just dies whenever I open the throttle past 50%

again thanks for the quick replies and help
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Old 08-23-2005, 09:44 PM   #5
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Quote:
Originally Posted by NTC3Kitty
wow, thanks for that reply terry sturchio I think this may help

the engine doesn't bog down at all, in fact - giving it just a little gas makes the car pretty much rocket off from the start, spinning tires and all. it's just when I open the carb up past half way, it flames out. the analogy of the faucet makes sense, so I will try that, richen the top end and tune the low end from there then the top end right? the pinch test wors out good, 2 seconds and then the car revs and dies. that's why I think it was the top end needle out of tune. RD logics said to leave the mid range needle pretty much alone, flush with the housing. I did switch fuels as recommended by the manual - using 20% to break in and now switched to 30% nitro, and I realize I will have to retune the motor each time I go out, but no matter what I do it seams that the motor just dies whenever I open the throttle past 50%

again thanks for the quick replies and help
what is your motor?
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Old 08-23-2005, 10:06 PM   #6
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RD logics RRE R3SRT
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Old 08-24-2005, 12:47 AM   #7
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Quote:
Originally Posted by NTC3Kitty
RD logics RRE R3SRT
What glowplug are you using?
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Old 08-24-2005, 01:27 AM   #8
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First thing first : you need to open the engine and clean it first. After break in you need to clean inside the engine thoroughly. I'm sure the sleeve's ports and piston head got brown things. Don't forget inside engine wall and crankshaft.

Second, do this test at longest straight way in your track :

if the engine dies at full throttle at top speed = HSN too lean
if engine's sound rattles ( bogging ) at full throttle = almost there, so lean it
if the engine dies at within 1 or 2 second after full throttle = HSN too rich

IMO, your engine is still rich at HSN. Close HSN 15 minute (turn left ) and open LSN 5 minute (turn right).

Just tips, you can't throttle gas car like playing electric cars ( by squeezing throttle so smoothly and/or holding the gas at 50% range for too long ) the engine will be die.

Last edited by asw7576; 08-24-2005 at 01:44 AM.
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Old 08-24-2005, 08:58 AM   #9
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Quote:
Originally Posted by NTC3Kitty
RD logics RRE R3SRT
thats what i run on my R12 , i run mine rich on the low end and then i lean the hich end as i need to.
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Old 08-24-2005, 10:28 AM   #10
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asw7576 so you mean that the throttle should not be applied smoothly, and not be held at a 50% for a long time? I figured the opposite!

but also, after the engine break in, I did dissamble the motor and clean it up.
the engine does die at full throttle top speed, so I will try and richen up the needle, as you said it's best to start rich and go from there. thanks for the help once again
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Old 08-24-2005, 10:40 AM   #11
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Quote:
Originally Posted by asw7576
Just tips, you can't throttle gas car like playing electric cars ( by squeezing throttle so smoothly and/or holding the gas at 50% range for too long ) the engine will be die.
Correct me if I mis-interpret this comment, however I would disagree with it if you are saying what I thin you are. I throttle mine smoothly and hold half throttle for sustined periods all the time. Sometimes that is the fastest way through the mid-sections. Granted it isn't the same as electric, but just because the powerband reacts differently, not because my engine would die. If you can't do that your tune is off and it's leaning out after the residual fuel burns from the crankcase. This is usually the result of an engine that's overlean on the top, but rich on the low to compensate. Now I wouldn't depend on a engine to idle forever, because it will eventually load up, but as long as you are applying some throttle and cycling a fair amount of fuel (50% throttle should be doing that) then it should run for fine with smooth inputs. You should not have to blip the throttle or clamp it all the time. In fact, that driving style tends to upset the suspension and it makes for horrible fuel economy when running longer mains.
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