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"the engine tuning bible"

Old 09-12-2010, 05:23 PM
  #241  
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I have done the research on these and I can tell you your last example is correct. For the first part with a Long needle you set the idle and LSN first and then the high.
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Old 09-12-2010, 05:35 PM
  #242  
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Originally Posted by Nesal
Thanks for the info grizz, great little guide. I have a question regarding the long needle carbs (thinking of getting a D5 precirotate engine but nervous I wont know how to tune the thing!)... when tuning a short needle carb I always begin with the HSN tuning for top end and then move on to the LSN for off the line performance. How does this differ with the long needle carbs? Do you start with the 7sec pinch test and adjust LSN accordingly and then simply tune for WOT max revs on the HSN and basically not touch the LSN any more?
I mean, do you start with the LSN and then go to the HSN instead of the opposite with short needle carbs?
What would happen if for example in a long needle carb I have set my LSN, then tune for max revs on the HSN and it lean bogs, my short needle intuition says richen LSN however grizz's guide says NO, common mistake, I richen the HSN and in theory I will have a smooth powerband and max revs?

Thanks again!
I tune both type carbs the same way, do bottom end and idle first with the pinch method, then top end for performance, "then revisit bottom end to fine tune (but only after I'v done 3 consecutive tanks to saturate the chassis in temp and check top is not too lean)".
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Old 09-15-2010, 04:56 PM
  #243  
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hey guys , had to take this down for legal reasons. cheers m

Last edited by MassiveMods; 05-14-2012 at 04:55 PM. Reason: copyright information pending
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Old 09-15-2010, 06:43 PM
  #244  
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Originally Posted by MassiveMods
Howdy all , Ive had a basic edit of the Grizz version here. This is the version we are putting out so there is no confusion between long and short needle carbs as we only deal with long needle carbs.

FYI no matter what carb you have Either the older Short needle or the more Modern Long needle you MUST ALWAYS TUNE LSN AND IDLE GAP FIRST ! tuning the HSN first will not optimise your carburation.

Cheers MM

GO GX & MG66 series tuning guide;

The carburettors on the GO GX Series and MG66 engines are fitted with a long taper Low Speed Needle (LSN).
The long tapered needle gives a very smooth power band and great economy, which is why GO and Massive Mods use it in their carburettors.
Be aware that the High Speed Needle (HSN) settings on these carburettors will be different from other common brands of motor on the market. They are more sensitive.

Here is a simple step by step tuning guide for the older GO Gen 4 and 5 Pro Series motors, and the newer GX Series and MG66 motors fitted with the long taper low speed needles.

We would like to acknowledge the help of Massive Mods Australia in the preparation of this tuning guide.

Required steps to properly tune your motor for racing

1. Return needles to factory settings:
This step is normally only required if you have completely "lost" the tune, and are starting again from scratch.
HSN (High Speed Needle) – Flush
LSN (Low Speed Needle) – Flush

2. Set the idle air gap and the initial LSN setting using the " MassiveMods 7 second Pinch Test"
The first and most important step is to ensure the idle gap is set correctly.
Because the LSN is directly connected to the throttle slide, getting the idle air gap set properly, so the throttle slide and LSN are correctly positioned before you start tuning is paramount.

Fill the fuel tank and start the motor. Let it warm up for 30 seconds on the starter box - no more.
If the motor will not idle pinch the fuel line to listen where the idle gap is set to, lean the low speed needle 1/8 of a turn at a time until the motor idles without stalling.
Now, fully pinch off the fuel line 1 to 2 cm back from the fuel nipple.
What you are looking for is a slow and steady rise in revs (only 500 rpm or so), which will indicate the idle air gap is correct.
If the revs rise high or "chirp up" quite high, this indicates the idle air gap is too wide.
Decrease the idle air gap a little at a time until you get the slow steady rise previously mentioned.

2a. Initial setting of the Low Speed Needle
Now that the Idle Gap is correctly positioned you can adjust the low speed needle so the motor will die from fuel starvation after 7 seconds when you pinch off the fuel line.
The length of time it takes the motor to die reveals how rich or lean the bottom end is.
If the motor dies at say 4 seconds that means its too lean , you need to richen the bottom end. If it takes 10 seconds for the motor to die, you must lean the bottom end.
7 seconds is the time we want to achieve for a basic tune on the motor.

NB: The idle air gap and 7 second pinch test procedures outlined above need to be carried out before the motor gets too warm - otherwise higher crankcase temperatures will not allow the correct results to be achieved. You need to be able to conclude this procedure in about 2 to 3 minutes. Once you get the hang of it you can do it in less than a minute.

Now we have the idle air gap set correctly, and the low speed needle close to where we want it, run a full tank of fuel through to warm the motor and saturate the chassis with engine heat. Depending on the chassis this can take up to 3 consecutive tanks.
You must always fine tune a motor when it is hot - this is very important.

If the motor chokes up and will not run cleanly unless you keep blipping the throttle to clear it out, lean the LSN a little more at a time until it runs cleanly - DO NOT ADJUST THE IDLE TO COMPENSATE FOR A RICH BOTTOM END.

3. Setting of High Speed Needle
Refill the fuel tank and go for some high speed runs.
Adjust the high speed needle so you achieve a nice clear exhaust note with good exhaust smoke evident right through the rev range. This will depend on the fuel you run , some smoke more than others so bear that in mind. Good high performance fuels dont smoke as much as RTR fuels. Indeed watching the top drivers you will notice barely any smoke out the pipe.

NB: The HSN is very sensitive and only requires very small adjustments. 1/12 th of a turn WILL make a considerable difference to performance.
It is best practice to adjust the HSN in terms of "Hours" (ie hours of the clock face).

Going on our experiences, you shouldn't need to lean the HSN any more than 2 - 3 hours from the factory setting of flush for peak performance (although differing fuel, plug and pipe choice may dictate otherwise).

4. Re-visit Low Speed Needle
Because the HSN setting has a direct bearing on the fuel flow to the LSN, after adjusting the HSN it is necessary to re-check the LSN again.
Adjust the LSN as required for a crisp clean take off from a standing start after letting the buggy sit for 5 - 7 seconds.
If the motor coughs and falters with excessive exhaust smoke, lean the LSN 1 hour at a time until a clean take of is achieved.
If the motor hesitates with little or no exhaust smoke before pulling away, richen the HSN 1 hour at a time until a clean take off is achieved.
Once you have both HSN and LSN set correctly, fill the tank again and run this entire tank through at race pace.

5. Check for Lean-Bog
While running this tank of fuel through the motor, the power should remain constant all the way to the bottom of the tank - if at any time during this tank of fuel (particularly below half a tank) you get lean bog off the mark, or out of corners, this is what you need to do -

Richen the High Speed Needle 1 hour at a time until the lean bog is cured.

YES THE HIGH SPEED NEEDLE ! NOT THE LOW SPEED

Here is a quote from the Massive Mods web site to explain what is happening:
"As the tank pressure gets lower as a result of the fuel being used, the pipe has to pressurise a larger space. When you accelerate off the mark, that’s when the engine has the least amount of pressure in the tank. So for a split second the engine appears to have lean bog, because there is a lesser amount of pressure to push the fuel through the line.
The only needle regulating this is the HSN, because it is the first needle in the fuel system to offer resisitance to the fuel flow of a low pressure tank. If you richen the HSN at this stage, you will allow fuel flow to the engine with the lower tank lower pressure. Then when you go to accelerate, the lower pressure can force fuel through the HSN to the LSN and you won’t get lean bog.

If your motor performs well from full, right down to the bottom of the tank - you now have a basic tune.

Realise that this tune will be good for this particular surface and ambient temperature.
If the surface or tyre choice changes the tune will change.
If the ambient temperature changes more than 5 deg C, the tune will change.
If you change plugs or pipes the tune will change. "

OK Peeps i hope this is informative. The full version is on the LRRCC site for those who want to read the whole shebang.

http://www.lrrcc.com/phpBB3/viewtopi...=1151&start=30

Cheers MassiveMods Australia
very nice guys!!! that is a very useful tuning guide
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Old 09-25-2010, 08:26 PM
  #245  
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more tuning tips added to original post
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Old 09-27-2010, 03:16 AM
  #246  
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G'day houston,

I have a ? for you

If an engine is designed to run on 25% Nitro fuel (.21 off road engine)

Can i run 16% nitro fuel if i wanted to with out harming the engine, if i tuned it correctly to suit it.

Or are these nitro engines like real high performance 1:1 car engines, that will ping/pre detonate from fuel with a lower ron/octane rating???
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Old 09-27-2010, 05:55 AM
  #247  
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Originally Posted by LOSI123
G'day houston,

I have a ? for you

If an engine is designed to run on 25% Nitro fuel (.21 off road engine)

Can i run 16% nitro fuel if i wanted to with out harming the engine, if i tuned it correctly to suit it.

Or are these nitro engines like real high performance 1:1 car engines, that will ping/pre detonate from fuel with a lower ron/octane rating???
Check with the manufacturer about head shims. You can run anythingd from 10% to 30% assuming you add or remove the proper number of shims. This prevents pre detonation when running higher nitro content race fuels. You can run 16% but for best results check with the manufacturer about whethee or not your engine is shimmed and you need to change that.
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Old 09-27-2010, 07:30 AM
  #248  
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So with the pinch test, the idle screw controls the rise in pitch?

And the lsn controls the length of time the engine idles when pinched from 1-2cm away from carb?

What would happen if the idle gap when set using the above method doesn't maintain a high enough idle? or should that not happen given things are set correctly?
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Old 09-27-2010, 02:00 PM
  #249  
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Originally Posted by AndyF
So with the pinch test, the idle screw controls the rise in pitch?

And the lsn controls the length of time the engine idles when pinched from 1-2cm away from carb?

What would happen if the idle gap when set using the above method doesn't maintain a high enough idle? or should that not happen given things are set correctly?
Well, the idle is set after you have the engine tuned. Usually because the idle will go up when you lean the low speed needle. More air = more power in the combustion chamber to a point. SO set your HSN and LSN first, then adjust idle down so the vehicle still runs reliably. It should not start sputtering, puttering, choking or anything like that.

When the LSN is set correctly the idle will be consistent and also you will have good power at low throttle usage. When you ease into the throttle it should not stutter or bog at all. To get close the pinch test is used as an easy guide. Remember though, the pinch test means you're close to the right tune. Many people leave it at that which is fine.
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Old 09-27-2010, 06:08 PM
  #250  
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Originally Posted by Dredd
Check with the manufacturer about head shims. You can run anythingd from 10% to 30% assuming you add or remove the proper number of shims. This prevents pre detonation when running higher nitro content race fuels. You can run 16% but for best results check with the manufacturer about whethee or not your engine is shimmed and you need to change that.
I've tried low nitro percent A LOT!

Even with modified combustions chambers, less shimms, hotter plugs etc. etc. the magic point is about 16% nitro. At the moment I use 16% in my NOSRAM .21 engine and a O'Donnell 77T plug. The engine perform well, but you need to drive it rather hard. If you let it idle for approx. 5 sec or blib the throttle for one lap or so, the gas respons ins't perfect, and you need to let the engine come up in full speed, to make the combustion hot enough (so I think ).

I tried 7% nitro and the middelrange was terrible. Impossible to drive with.
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Old 09-28-2010, 03:51 PM
  #251  
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Originally Posted by Lille-bror
I've tried low nitro percent A LOT!

Even with modified combustions chambers, less shimms, hotter plugs etc. etc. the magic point is about 16% nitro. At the moment I use 16% in my NOSRAM .21 engine and a O'Donnell 77T plug. The engine perform well, but you need to drive it rather hard. If you let it idle for approx. 5 sec or blib the throttle for one lap or so, the gas respons ins't perfect, and you need to let the engine come up in full speed, to make the combustion hot enough (so I think ).

I tried 7% nitro and the middelrange was terrible. Impossible to drive with.
Usually it's because lower nitro content fuel has more oil. More oil is harder for the engine because it keeps temps low, sometimes too low and with Nitro engines it's heat that creates power (until a point). I use 20% nitro generally. In both my touring car an buggy despite having a .12 in one and .21 in the other. I don't race the buggy so it's not imperative to have high nitro.
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Old 09-29-2010, 10:39 AM
  #252  
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The post above state that during the pnch test your motor should run about 7 seconds. Is that for all motors or were you being specific to Go's ? I've always been told about 3-4 seconds is where you want it to die at.
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Old 09-29-2010, 12:14 PM
  #253  
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Originally Posted by Madbrad
The post above state that during the pnch test your motor should run about 7 seconds. Is that for all motors or were you being specific to Go's ? I've always been told about 3-4 seconds is where you want it to die at.
Mostly for the GO motors is what GRIZZ1 AND MASSIVE MODS ARE TALKING ABOUT!
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Old 10-04-2010, 07:45 PM
  #254  
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Originally Posted by deadmancourt
Mostly for the GO motors is what GRIZZ1 AND MASSIVE MODS ARE TALKING ABOUT!
And the 7 sec only aplies to a cold engine, only been running for a minute or so.
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Old 10-04-2010, 07:56 PM
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Originally Posted by Flanno
And the 7 sec only aplies to a cold engine, only been running for a minute or so.
+1 that too...
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