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Old 10-06-2001, 09:22 PM   #1
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Default Serious gas engine question. pro engine tuners look here

last week another guy i race with has the same car same engine i do. he really smokes me out of the corners as far as power. when i looked at his engine settings the boot side carb adjustment (black one) was further out than mine and the brass one on the other side was further in.

here is my question will that give more bottom/midrange power or less?

MTX-2, MT12 Rossi engine.

i understand this. one side of the carb is the female jet and the other is the male jet so as you turn one side in you have to turn the other side in also. im talking 1-2 full turns. if i only adjust one side i will be way to rich or way to lean depending on what i do.

Question 2

say i back the (boot side) black one out 2 full turns and then brass one in 2 full turns will that create a leaner mid? or a fatter mid?

its seems that his car rockets out of turns and mine is slugish to wind up.

i have my low end about as lean as i can get it. any leaner it will flame out.
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Old 10-06-2001, 09:48 PM   #2
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are you running the same gearing as him? what about clutch settings? I think you should think about those other than just engine tuning..but hey, what do I know, i'm just some electric guy...
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Old 10-07-2001, 07:20 AM   #3
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everything is the same sept fuel and body. chassis,engine,gearing,clutch is all the same.
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Old 10-07-2001, 07:50 AM   #4
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ok then, im not good at engine tuning...so, sorry can't help you there
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Old 10-07-2001, 08:13 AM   #5
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Hello, I'm going to see what i can answer here then. It sounds like the only difference is who is driving, and engine tuning. I don't know how you drive, i've never seen you drive, but remember everyone is different, and i'll leave that subject where it is. Now on to engine tuning. How "seasoned" are you in nitro? You might have it running too lean. I know i used to like to run the bottom extra rich. I have never tuned a MT12 Rossi engine, so i don't know how far i can help you there. I would play with carb. settings and see how much that helps you.
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Old 10-07-2001, 08:56 AM   #6
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Quote:
Originally posted by TSR6
Hello, I'm going to see what i can answer here then. It sounds like the only difference is who is driving, and engine tuning. I don't know how you drive, i've never seen you drive, but remember everyone is different, and i'll leave that subject where it is. Now on to engine tuning. How "seasoned" are you in nitro? You might have it running too lean. I know i used to like to run the bottom extra rich. I have never tuned a MT12 Rossi engine, so i don't know how far i can help you there. I would play with carb. settings and see how much that helps you.
I second that.

A newbie with an ultra mod engine without proper tunning might get dust with a stock MT12 engine on an expert hand.
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Old 10-07-2001, 10:10 AM   #7
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From what I read in the Serpent Impulse manuel that comes with the kit with the rs12 engine I was reading there way of tuning the engine. I learned that the brass screw *mid end* is mostly used during races as a low end needle so you dont have to screw with the black screw on the oppsite side for 5 mins.
Find out whats his low end settings on the black screw.
how the brass screw works is the black screw say like you have the low end set at 3 turns in from the base of the carb
and you turn in the brass screw in 1 full turn from the base the low end will really be 4 turns in all it really is, is a faster way to lean out the low end also after the race fix the brass screw so its with the base and lean it out on the low end side.
i wish i had a brass screw on my mt12 but some one that screwed up my old c12 got me a replacment mt12 with a rotary carb
hope that helped
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Old 10-07-2001, 09:39 PM   #8
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looks like i may have to draw a picture. i dont think you guys understand the way the 3 needle carbs work.

if i screw one side out 2 turns (black boot side) and turn the brass side in 2 turns i should still be letting the same amount of fuel in (for idle) but as i open the slide this will change the way the air comes in.

but this is where im not sure.

now it seems that my bottom/mid is a little slugish so im thinking that when i open the slide more fuel is comming in and less air this will give me a fat (i think) bottom/mid. but if i move the whole jet over a few turns this should let mor air in before the fuel and give me more bottom/mid.

one other thing is his pipe. his pipe is different than mine. he is using a rossi style that has a faster taper then it stay large. my pipe looks like a baseball bat. it has a slow smooth taper till it gets to the end. and i think think this style pipe also give a smoother bottom wich also may be my problem.

Today was the last race of the season. but i want to work on this for next season. and i was hoping to get a reply before i raced today so i could fiddle around with the settings.

ill tell you it was a wild season. my first few weeks with the MTX-2 wasnt real good, i couldnt get this car to hook up and i almost sold it. i finaly let another guy set it up and i was on a roll i was winning right and left. but then everyone started running foams and my setup went down the tubes. i just couldnt keep up with foams. then i got foams now im having engine trouble. i think my car needs a break. im glad the season is over my car isnt doing to well.
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Old 10-07-2001, 10:18 PM   #9
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What you are seeing in the other guy's car is the position of the spraybar in the carb venturi.

As you know, the carb is somewhat hourglass shaped. It is so the air is sped up to draw it into the engine faster. The velocity of the air is different at different places in the venturi. The air flows at a different speed in the exact middle of the carb hole versus near the walls. (Think hourglass again)

When you turn the the brass spraybar in 2 turns and turn the lowend needle out 2 turns, this relationship stays the same as if the spraybar is flush and the lowend needle is screwed in 2 turns BUT.......... The position of the spraybar hole where the fuel comes out is now in a different location in the carb (Think hourglass again). The fuel might come out faster or slower (depending on the position) thus changing the engine performance. Most of the time most people will not notice a difference. Some will. This is an option to tune the engine. This is something I tell people to try and change when they absolutely can not get the car to idle well or if the car stumbles off the line and they have fiddled with the lowend needle.

Maybe you should try to tune your engine the "traditional" way first before messing with the position of the spraybar to get more punch?

Maybe his clutch is set up different than yours. His might engage a little later than yours?

Pipe shape and length has a significant effect on the powerband of the engine.

Ron you've been running gas long enough to know this.

Last edited by Sydewynder; 10-07-2001 at 10:23 PM.
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Old 10-07-2001, 10:29 PM   #10
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your right. i did stretch my springs a little so that it kicks in earlier that was when it was new and i couldnt keep the rear planted i hoped this would help tame the bottom some but i guess now i need it back where it was stock.

he may have a better clutch i dont know. Jeff what clutch are you running? (Jeff is the guy)

but that still isnt answering my question. it kida does your telling me it will change how the engine performs but i already know this. what im asking is how will this change affect the low/mid ?

like i said HIS (Jeff) his brass setting is IN more than mine and his black one is out more than mine. so his "spraybar" is in a different position than mine. and i think thats another reason why his bottom/mid is a little better than mine.

usualy i look at the other racers settings on their engines and i can usualy tell how they have theirs setup. ive had over 40 .12-.21 engines so i have a pretty good idea on the 2 needle engines but the 3 needle novas im lost.
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Old 10-08-2001, 09:32 AM   #11
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I have the same engine and basically the third needle just adjust when the low end needle completely disengages the main needle. This adjustment lets you adjust when the venturi receives maximum air flow. You can adjust it so it happens sooner in the throttle throw or later.
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Old 10-08-2001, 12:40 PM   #12
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ok so wich way is sooner? thats what im trying to get
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Old 10-09-2001, 09:04 PM   #13
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The further out the needle is the sooner the low end needle is disengaged, but if you go to far the engine will run too rich.
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Old 10-10-2001, 02:13 PM   #14
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the further out wich needle? and further out on wich side? there are 3 needles
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Old 10-10-2001, 10:09 PM   #15
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The third needle
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