posted
I know there are a million tuning questions on this forum. I just want to know if my situation is "normal".
Here's what I'm running. It's in a Mugen MBX-5T:
Stock RB C6 BBT Stock carb Insert O.S. 203 Air Filter RB #6 glow plug TQ Fuel 30% Additional .1 head shim About a gallon and a half of fuel through the engine.
I was having horrible tuning issues for a while. Then I went back to the factory settings of 3 1/2 out on the top end needle and 5 out on the low end needle. I tweaked both needles about 1 hour leaner and now it's running good with temps peaking around 250 degree F. The mid-range is a little rich still but I'm afraid to lean out the bottom anymore because the temps soar. My question is: Is that normal for it to run well at near factory settings?
I've been pulling my hair out with this engine as it seems very sensitive to small needle changes (unlikes my previous engine) and just want to know if I'm on the right track.
Scarab
-------------------- Let's put the Laughter back in Manslaughter! Posts: 6 | From: Hampstead, Maryland, USA | Registered: Jul 2008
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posted
Well there can be several issues going on here. My first suggestion is to ignore that temp gun for a little while. I have an odonnell temp gun that always temps my engines between 250 and 280. I then put a drop of water by the glow plug and it slowly boils off telling me the engine is nowhere near 280 degrees. Try tuning the engine to run good and make sure it has a decent trail of smoke and ignore the temp gun for a little bit. If the engine is lean your going to hear it lean bogging and it will not run correctly. Another thing I am wondering is what pipe and header are you running and how do you have it geared? Last what is the altitude where you race most of the time? It's possible if your above sea level you may not need the extra head shim.
Posts: 348 | From: Colorado, usa | Registered: Apr 2005
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Darn! The one thing I forgot to put was my pipe! LOL! It's the 2045 pipe that came as a "box set" with the C6 BBT. The smoke trail does seem very nice in all the RPM ranges of the engine with just a little bog I assume is due to mid-range richness. I'm running a 14T clutch bell instead of the stock 13T clutch bell. I'm just north east of Baltimore in Maryland so I can't be too much above sea level. I'm an experienced engine tuner as well (8 years racing nitro) and try not to go by temps too much, but when your temps are pushing 280 I started to second guess myself.
Scarab
-------------------- Let's put the Laughter back in Manslaughter! Posts: 6 | From: Hampstead, Maryland, USA | Registered: Jul 2008
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posted
Turn the HSN one half turn (6 hours) richer and drive your truggy up and down the street in front of your house. Do this for 2 minutes! Is it to fat? If not richen it one quarter turn more. Find the point where it is to rich, then start leaning the top. Give it time, needle changes aren't always 'instant'. About 30 seconds to a minute should be good enough. Once you find the 'sweet spot' on the HSN you are half way there.
LSN- rev the motor and listen to how it transitions from high rpm's to low. If it wants to hang either your carb isn't closing all the way or the motor is a tad lean on the low end. You can also try the 'pinch test'. Pinch the fuel line near the carb count '1-2-3'. It should rev up after a 3 count.
Your mileage may vary.
Posts: 34 | From: Kansas City, MO | Registered: Jun 2004
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posted
I'm lucky enough to have a C6T7 and C6L2G, both broken in the same and both with about 2 gallons on them.
First thing I will say is that I've only raced nitro a year, so I'm no tuning expert. However I have found that the C6 is a very sensative motor to needle changes which has caught me out a lot.
My C6 is a pain to tune, I find tuning it to be a nightmare. The 'window' where it runs well seems so small, ad it flames out a lost. But when it runs well it flies so I forgive it!
The L2G is a different matter. That has run well from day one and for some reason I found it much easier to tune... I don't know why as they are basically the same motor as far as I can tell.
For reference my tune on the L2G is HSN just in (1 - 1 1/2 turns) from flush, LSN about 3/4 in from factory. However on the T7 that's too rich, so I'm more like 2 1/2 in from flush on the HSN.
Posts: 26 | From: Southampton, UK | Registered: Nov 2007
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