Rejetting for mileage???

[jsb223]

I bought a used 2001 DRZ400S and though I'm only put a few tanks of gas through it, I was hoping for better gas mileage.

Currently hitting reserve at 90 miles which puts me at 45mpg.

And I have not hit the dirt yet.

I read post of people getting 60 mpg and was wondering if I should carry the bike to a dealer and have him check the jets and revert to stock if they have been changed.

The bike has an FMF Q exhaust and has PLENTY of power for me mostly commuting.

Am I barking up the wrong tree?

[Kidder]

Nope, you're on the right track. With the aftermarket pipe, they changed to bigger mains to pump more fuel based on the freer flowing exhaust. So, if you have the stock exhaust you can rejet which will increase your gas mileage. In fact, I'm sure someone here could help you with that.

[jsb223]

So, if you have the stock exhaust

And if I don't have the stock exhaust???

[Kidder]

Then you may be stuck. If you put a smaller main in, you'll be running too lean more than likely or the bike won't run quite right. You could try moving the clip up one notch on the needle to try and eek out some more mileage. Or, you could buy a stock exhaust on e-bay or ask around if anyone has one.

[WoodButcher]

Have the other common mods to a DRZ been done? 3x3 opening of the airbox, dynojet needle and slide spring? I still have the stock exhaust on mine, but when I opened the airbox and did the dynojet kit and new jets my mileage went from the low to mid 40's to low to mid 50's. Just a matter of getting full power out of the engine.

Take off the seat and look to see if the opening down into the airbox has a snorkel in it, or if that is gone, see if the hole is a large square or as small rectangle. That will be a clue if any of the intake/carb work has been done.

The PO may have just put on the pipe and upped the jet, but the bike is still choked down on the intake side so you aren't getting full benefit of the exhaust.

[jsb223]

Take off the seat and look to see if the opening down into the airbox has a snorkel in it, or if that is gone, see if the hole is a large square or as small rectangle.

Snorkel is gone but the hole is still oval...

[WoodButcher]

Sounds like there is still some work you can do. Have you read on Thumpertalk about the DRZ? definitely the best forum around for our bike.

DRZ info (http://drz.info/drz/) Good link for basic info.

Pictures of airbox and carb (http://www.trailpilgrim.com/forums/showthread.php?t=1474) From another forum with pics of doing the carb and airbox.

more pics (http://mr-cob.smugmug.com/gallery/5955/1)

jetting info (http://drz.info/drz/dynofaq.htm)

Hope that helps. If you end up in the Austin area with your bike I can help you do the changes and also figure out what has been done so far.

[jsb223]

Sounds like there is still some work you can do.

Okay please be patient with this newbie...

I bought the bike used so I know a previous owner installed the FMF Q
but IF by chance, they did a rejet on the carb, and removed the air box snorkel but DID NOT do the 3x3 air box mod, my bike could be running rich?

I dunno?

[bushwhacker]

The bike has ..... PLENTY of power for me mostly commuting.



How much of that power are you using.

If I keep mine down around 65 top end and stay away from the rabbit starts I am getting mid to upper 50's but if I start the way I like to and hit 75-80 on the Highway then I am down in the mid to upper 40's.

My gas mileage on the DRZ is very "Right Hand" sensitive!

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[letsride]

If the change in exhaust is just the silencer then I doubt if it has been rejetted, rejetting is common if pipe + silencer are changed. There is a range of adjustments and within that range you can adjust to get better gas milage and throttle response. First of all you need to understand the components that affect fuel delivery at various throttle openings. I might be slightly off here but it goes like this,

Idle to 1/4 throttle opening is controlled by the pilot jet. You can lean out the pilot screw and reduce the amount of fuel in the mixture. Tighten the fuel mixture screw 1/4 turn.

The jet needle clip position controls the fuel delivery from 1/4 to 3/4 throttle opening. The clip has 5 adjustments. If the clip is at #3 notch from top, move it up to #2 from top. If at #2, move it to the top most position.

The main jet controls 1/2 to full throttle opening. If satisfactory results are not obtained from the above adjustments then the main might need to be tightened by 1# but leave that as a last resort.

Offcourse change plug + clean air filter and check the new plug insulator color (after a ride) before making these adjustments, if it is whitish then do not perform the above adjustments but chances are that it will be dark and sooty. In this case go ahead with the above adjustments and ride on with better gas milage and throttle response :)

[racerxr650r]

I agree with BushWacker. The way you are riding the bike and type of roads (city or highway) effect the mileage much more than your jetting. Do not re-jet a bike motor to improve mileage. Re-jet a motor to improve performance such as idle quality, throttle response, and power delivery at various throttle openings. Then put a little sprocket on the back and ride like an old lady (start in second gear and short shift) to get better gas mileage. Your motor will last a lot longer.

Also remember the numbers reported by all of us are not scientific. You always have to factor in the method in which the results were collected and the tendancy to exaggerate.

The guy reporting 65 mpg may have been riding the highway all day in 5th gear and you may be measuring on city streets in second and third gear all day. Those numbers will not be comparable.

- John

[racerxr650r]

Oops, I forgot a couple of things. There is no rule that a bike needs to be re-jetted only when you replace this part or that. There are a ton of factors such as altitude, air temp, specific gravity of the fuel, and stock jetting quality effect the need to re-jet a bike. I have never bought a new Japanese bike that was jetted optimally for my conditions and riding. They almost always jet them too lean to improve emissions quality.

Even worse, every used bike I have purchased has had the jetting messed up even worse. My favorites were a '96 CR125 and '99 XR400, both had been taken to local shops to be jetted by "experts". Both bikes ran like crap until I changed the jetting to values suggested in the user's manuals.

My suggestion is to go to the FMF webpages (http://www.fmfracing.com/jetting_center.aspx). I always use their numbers as a baseline even on bikes without FMF exhausts. They are usually spot on.

- John

[XR650Rocketman]

Good advice all around....John mentioned gearing.....Very important.....Check what sprockets are on the bike vs stock.

The other comment re. throttle use is very important.....I've ridden with guys with identical XR650Rs that have used almost half as much fuel over the same ride and distance....The only difference was the amount of throttle used!!!

Maybe the grin factor was a little different too...

On a recent ride I used 3.6 gallons to go 130 miles there and 4.6 gallons to get back.....Only difference was the throttle use!!!!

45MPG sounds pretty good to me....

Steve

[bushwhacker]

PS - My DRZ is stock exhaust with x3x mod and rejet.

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