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Fuel consumption is still too low

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My pig still running avg of 33 mpg (6,5l/100km).

How to improve this?

Main jet now 158, not running great changing to 160 ( had 165 in it)

Slow jet 62

Twin air filter

Std exhaust

102 mm je big bore

It should be doing at least 40 mpg (5,5/100km) I think

Help?

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But is there a rule of thumb or something?smaller jet size is more (fuel) efficient.. I can imagine there's an optimum, as the fuel air ratio is well defined..

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Yes, as a generalization the higher the RPM the greater the fuel consumption.  I've found that to be very true with these engines.  So I'd recommend changing your sprocket ratios to give the lowest acceptable RPM at your typical cruising speed.

 

You could pay a bike shop with a chassis dynomometer to tune your jetting, but the cost probably outweighs any fuel cost savings.  You could also get a wide band O2 sensor and guage for a continuous measurement of your jetting, but I don't think those setups are cheap either.

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higher average RPMs will of course cause the bike to use more fuel, but how you ride it will affect it more.

if you use the bike for commuting and do a lot of riding at static RPMs, then swapping the main jet will have no effect on fuel consumption since you are riding on throttle openings way below the main jets work range, on highway type riding you will be most affected by the needle.

if you ride in a city enviroment with a lot of starting and stopping, then fuel consumption will remain higher than average no matter what, you don't want to jet to lean if this is how you ride since lean jetting will make the bike run hotter, and getting stuck at a red light or something can cause the bike to overheat relatively fast.

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Clear, thanks. Can you tell me, is the mixture (with the needle in the same position) different when the main jet is changed? So, is the mix richer with a 165 main in stead of a 158, in the needle jet range?

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Yes, the main jet does affect the mixture somewhat in the part of the throttle range that is mostly associated with the needle.  The different parts of the jetting range have significant overlap.  Traditionally the main jet is regarded as influencing the carburettion from 1/2 to full throttle, but arguably it has some (slight) effect at ever smaller throttle openings. 

Edited by heart_of_darkness
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Gearing is huge for fuel efficiency and so are tires. While a bigger jets obviously lets more fuel through, a properly tuned carb also makes more power. In most cases( but not all) the increase in power and rideability will permit the use of higher gearing and can recover some of the fuel economy lost through power mods like Dave's mods.

There is definitely a point of dismal returns associated with this concept meaning as more mods are performed and power is gained there is always a point where economy is reduced.

My point is to jet your bike so it runs and rides best then try and recover fuel economy through gearing, riding style and appropriate tire choice for street riding. On my Drz I can get close to 60 mpg but I swap the 44 tooth sprocket for a 48 and throw on the knobbies and I'm down to about 40mpg.

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My pig still running avg of 33 mpg (6,5l/100km).

How to improve this?

Main jet now 158, not running great changing to 160 ( had 165 in it)

Slow jet 62

Twin air filter

Std exhaust

102 mm je big bore

It should be doing at least 40 mpg (5,5/100km) I think

Help?

your pilot is far too large....55 to 58 is all you should ever need....look too a combination of 55/160 or 58 /160....it appears you run way too rich. What does your plug look like?

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your pilot is far too large....55 to 58 is all you should ever need....look too a combination of 55/160 or 58 /160....it appears you run way too rich. What does your plug look like?

What elevation are you at? I live in the Netherlands which is a country partially below sea level, the spark plug looks ok.

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What elevation are you at? I live in the Netherlands which is a country partially below sea level, the spark plug looks ok.

I live and ride at 2-6k feet...but regardless...a 62 pilot seems far too rich IMO. I know you have plenty of air vol at your level but I can't see a 62 pilot.
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Installed a 58 pilot jet today. It runs, hopefully will be able to do a test run later today, but a/f mix screw is better

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Seems like you've modded your bike somewhat,  I would recommend you get yourself a o2 sensor.  They sell for $200 and after you've calibrated your carb then you can remove it and resell it recoup part of your costs.  I kept mine installed because it looks cool too:)  Nice to have with temperature and elevation changes.

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I kept mine installed not only because is looks cool but it's a nice engine early warning/diagnosing device, If your riding along and the AFR shoots rich and the bike starts stalling out your probably loosing spark but If it shoots lean then your either running out of fuel,developed a vacuum leak or jets are getting clogged, I'm sure there are other scenarios but that's just off the top of my head.

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Installed a 58 pilot jet today. It runs, hopefully will be able to do a test run later today, but a/f mix screw is better

you have to keep in mind that you cannot jet a bike with ONLY the best fuel consumption in mind, if you do this you will probably end up with a bike that runs hot, is hard to start and feels weak, you have to jet a bike so it runs cleanest and pulls the strongest, a strong, clean running engine is a healthy engine.

if you feel the bike is using to much fuel, there are other things you should look at first, proper tires for your use, proper gearing for your riding, keep the airfilter clean, clean oil and oilfilter and so on.

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Well I installed a smaller pilot jet 55, and a smaller rear sprocket 45t. It seems to be running good. It looks like it's going to take quite some time to get the tank on empty. Keep you posted.

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