Fuel consumption question.

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Old 09-10-2007, 05:24 PM
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Default Fuel consumption question.

I have a nova mega sx12 ss. The engine runs well but i can't get 5 minutes out of a tank. The temps have been staying around 230 to 250. My plug is has a ring of oil and the wire is grey.

We tried leaning out the top end a little more and after 3 laps (the thing ran like a bat out of hell) - it hit 280f. I stopped that right away and brought the needle back 1/8 and it dropped right back to 250 after another 3 laps.

One of the guys at the track told me to add a shim or even 2 shims (.002) and i should be able to lean out the needle more, get more fuel economy and not have the engine over heat like it started.

I'm no engine guru and i've heard different things on this. Can someone confirm if adding shims will infact add fuel economy?

Thanks
Charles.
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Old 09-10-2007, 05:38 PM
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i tried that and no
it went slower and used the same fuel.
how old is the motor anyway.
i know a guy that runs his nova mega sx12ss at 280 i run my ninja about 260-270
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Old 09-10-2007, 06:02 PM
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This thing is old. It doesn't have much wear, probably one gallon but it dates back to 2003. (hasn't been used much).

I didn't run on road back then so i don't know if it's because 5 minutes on a .12 was normal 4-5 yrs ago. I can usually get 5 1/2 to 6minutes out of most of my engines but this one has got me beat.

I guess i'll be pitting at 4 1/2 minutes. Either that or i'll pull one of my huge 1/8 off-road fuel filters to try and gain the extra 30 seconds. Local club racing so we are flexible on the rules for this sort of stuff -- i would never do that at a sanctioned event.
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Old 09-23-2007, 06:50 AM
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Once apon a time my Novarossi's were getting 5.35 min per tank. I changed fuel and plugs and now I can get 7 min per tank. Tornado!!

I would check the manufactures original head clearence. I'm running 25% with a cold plug (Nov #7). Get a really good tune. Tune everytime you run your car. Remember to tune only after the engine gets warm. Run the motor for 3 min then set your needles. I see many many people try to tune engines a min after starting. Their run times are very low and their temps are not consistant.

Get some good fuel (2. Get the correct plug for your fuel. (3. Tune after your motor has heat in it. You will see a difference.

On the other hand......

Add 11 inches of fuel tubing from your tank to your motor!
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Old 09-24-2007, 06:44 AM
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you can also try different style pipes? and also gearing combinations
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Old 10-15-2007, 10:51 AM
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If you loosen up on the clutch spring 1/2 of a turn you will get a lot more run time.

In 1/8th scale I have a setting for the clutch in qualifing and another setting for the mains. I make 5 min in the qualifiers then I tighten up the spring for the mains and pit at 4 and a half minutes.
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Old 10-15-2007, 08:36 PM
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what I will do here is.


add a another 0.1mm shim. The effect is reduce compreassion, reduce heat, reduce power. To get back the same output power 230F~250F you need to lean to top a litle bit. When you lean the top you save more fuel. Retune the engine and try to get back the same power and tempareature.

If you satisfied the output power and temperature. add another 0.1mm shim. do it again see if you can get back the same power output. If you can get back the same power by this time I am sure your runtime should be more then 5 min.

Now if you add another 0.1mm I doubted if you can still get back the same power because the compression is too low. You may get back the same power but you need to lean alot and that may cause too lean and not enought fuel to produce the same power.


hope thats help...
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Old 10-16-2007, 12:58 PM
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Try to lower the tank pressure as I did:



This is just an empty fuelfilter with on the side a nipple for the flow of the overpressure.

You have to retune the engine but can give you up to 15 secs
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Old 10-16-2007, 01:55 PM
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Originally Posted by Roelof View Post
Try to lower the tank pressure as I did:



This is just an empty fuelfilter with on the side a nipple for the flow of the overpressure.

You have to retune the engine but can give you up to 15 secs
How does that affect your power? I am assuming you must lose something right?
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Old 10-16-2007, 06:51 PM
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Originally Posted by Roelof View Post
Try to lower the tank pressure as I did:



This is just an empty fuelfilter with on the side a nipple for the flow of the overpressure.

You have to retune the engine but can give you up to 15 secs
Lowering tank pressure will lead to unsufficient fuel supply on full trottle and that will cause too lean and overheat. To counter that effect you need to open up more on the top and the whole process goes back to the same cycle.
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Old 10-17-2007, 04:17 AM
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Yes, you have to retune the enging but the pressure is making less a role in the adjustments and for sure when you let the thottle go while normally the pressure still puts fuel in the engine.

With less pressure the engine does not need a rich setting from the bottom which will save you some fuel and also give you a bit more bottom power.
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Old 10-17-2007, 07:23 PM
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Originally Posted by Roelof View Post
Yes, you have to retune the enging but the pressure is making less a role in the adjustments and for sure when you let the thottle go while normally the pressure still puts fuel in the engine.

With less pressure the engine does not need a rich setting from the bottom which will save you some fuel and also give you a bit more bottom power.
Some old driver told me higher tanks pressure, it pushes the fuel out from the needle sharper and faster. When the high fuel pressure hits the closing needle (where you turn the LHS screw) it atomise better. Futhermore if you are using venturi ( smaller crab opening) high air flow, the effect is even better and that leads to fuel comsumption.
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Old 10-18-2007, 04:33 AM
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Originally Posted by thamjk View Post
Some old driver told me higher tanks pressure, it pushes the fuel out from the needle sharper and faster. When the high fuel pressure hits the closing needle (where you turn the LHS screw) it atomise better. Futhermore if you are using venturi ( smaller crab opening) high air flow, the effect is even better and that leads to fuel comsumption.
how to promote or establish higher tank pressure??
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