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Opening up the 'box

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Guys,

Were looking at opening dads 03 DR650 airbox to get it to breathe better.

So far we have removed the snorkel, ground out header welds and added an aftermarket slip-on.

So we rang the local DR expert, Vince Strang ( www.vincestrangmotorcycles.com.au ) and asked what they do.

Apparently on their dyno, the dr made the most power with a Staintune full system ( www.staintune.com.au ) and with the airbox snorke IN! completely opposite from what we thought.

We removed the snorkel and it seemed to make more power, so we were going to drill more holes in the top of the box, but we dont know now!

What do you guys do with your airboxes and jetting at sea level to about 2500 feet.

Thanks for your help:thumbsup:

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Whether or not the snorkel is in the tiny hole of the stock air box is nearly moot by comparison of a fully modded air box. To know just how restrictive the stock air box opening is to performance, with or without the snorkel in place, just remove the air box cover and run the machine. It will start and idle. You will be able to turn the throttle maybe to 1/4 open... maybe. Not that you could but make sure not to ride the machine without removing the plate nuts for the side cover or they will remove themselves. The stock opening is extremely restrictive. If you want to get the full potential out of the DR650's engine you have to open the air box and allow the engine to breathe along with the requisite jetting to handle the extra air. The side cover removal is just a test... do not run the machine with it off on a permanent basis. It creates a noisy echo chamber that is unbearable to put up with IMO and the filter gets trashed in very short order. The air box top mod is far and away the better choice. :smirk:

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+1 on what Rob said.

But a few other points;

So we rang the local DR expert, Vince Strang ( www.vincestrangmotorcycles.com.au ) and asked what they do.

Apparently on their dyno, the dr made the most power with a Staintune full system ( www.staintune.com.au ) and with the airbox snorke IN! completely opposite from what we thought.

And completely opposite from my experience. I admit I do NOT have a dyno but I do have an AFR meter and wide band O2 sensor. When I pulled out the snorkel, there was a very noticeable increase in off idle to mid range power. I could easily lift the front wheel in first gear where I could not before. But I can't verify if it made more power on top or not. I can say that for reasons I do not pretend to understand, my bike got richer with the snorkel out. :shocked:Others report that they needed a .030 shim to get it to run well, but my bike did best with the stock needle and jet when I pulled out the snorkel according to the AFR meter.

As Rob points out, it should give the most power with the top cut out. I chose the "Drill holes" method because it is reversal and tunable. And because I don't expect that the difference in power between full opened and the 4 1" holes I drilled is significant, but that is just my theory. YMMV

One thing I feel sure about is that if you open up the box beyond removing the snorkel, you will need a larger main jet and a different needle. The Dynojet needle is working great for me but you have to avoid the installation pitfalls. As always YMMV.

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thanks for the replies!

Being the Australian model, it has a adjustable needle with clips, and afaik its running the stock jetting (140, 42.5).

How does the australian needle compare to the US needle?

if i drill 2 one inch holes how many sizes do you suggest going up on the main & pilot and where should i set the needle?

ive been researching these mods and there are many different opinions about how to work the carb, im hoping someone can point me in the right direction.

Thanks Again,

Coopz

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thanks for the replies!

Being the Australian model, it has a adjustable needle with clips, and afaik its running the stock jetting (140, 42.5).

How does the australian needle compare to the US needle?

if i drill 2 one inch holes how many sizes do you suggest going up on the main & pilot and where should i set the needle?

ive been researching these mods and there are many different opinions about how to work the carb, im hoping someone can point me in the right direction.

Thanks Again,

Coopz

Although your Aussie needle may have clip positions you still have a restricted air box and therefore and very mild taper on the needle. Modding the air box with that needle is asking for a range of issues from lean to rich in different parts of the throttle depending on where you put the needle. In a nutshell the needle taper must match the air flow characteristics of the air box. At lower engine speeds and throttle openings the mild taper and root diamter of the stock needle is fine..... even for the modded air box but as speed and throttle opening increase the air flow potential becomes exponential in the modded box and the mild taper of the stock needle can not provide the required fuel. I wouldn't do any more than remove the snorkel with your stock needle and leave both your pilot and main jet stock. If you want to let your engine breathe you have to get a needle that can provide the required fuel in the mid to upper throttle range (much sharper taper) :smirk:

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thanks for that Rob :smirk:

What needle do you reccommend using?

Ive read the dynojet needle is a better taper, but may be too rich?

Also the KTM needle you used, it seems it might work better with my setup?

which one would you reccommend with 2 1 inch holes?

and do you suggest leaving jetting stock?

thanks mate :smirk:

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+1 The DJ needle is not rich unless you set it up that way. It has the taper required to match the modded air box flow. That being said 2 one inch holes will not provide the required air for the DJ needle so you will have a richer mid to upper mid (or a lean 1/8 to 3/8 range depending on what height you hang the needle at) even if you do figure out what main jet to run. The DJ kit is designed to run with the air box cover off... two one inch holes will not supply the same type of air flow. The established tried and proven top mod provides the needed air and eliminate the horrific echoing noise of the removed cover. Seriously, once you get the air box modded properly and the jetting correct for the additional air supplied you will not want to go back to a strangulated air box. :smirk:

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+1 The DJ needle is not rich unless you set it up that way. It has the taper required to match the modded air box flow. That being said 2 one inch holes will not provide the required air for the DJ needle so you will have a richer mid to upper mid (or a lean 1/8 to 3/8 range depending on what height you hang the needle at) even if you do figure out what main jet to run. The DJ kit is designed to run with the air box cover off... two one inch holes will not supply the same type of air flow. The established tried and proven top mod provides the needed air and eliminate the horrific echoing noise of the removed cover. Seriously, once you get the air box modded properly and the jetting correct for the additional air supplied you will not want to go back to a strangulated air box. :prof:

sorry for the late reply guys,

where we ride is usually dusty as hell, or the next weekend it'll be wet and there will be bog holes :smirk:

How does the airbox mod go with this sort of stuff,

And river crossings? on one of our loops there are 6 decent crossings (like just above footpeg) in a 5km sectiom :lol:

Has anyone had any troubles with the mod letting any water or mud into the airbox?

because as i said before, it used 90% offroad.

and who said the dr couldnt be ultra competitve in the bush :smirk:

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sorry for the late reply guys,

where we ride is usually dusty as hell, or the next weekend it'll be wet and there will be bog holes :smirk:

How does the airbox mod go with this sort of stuff,

And river crossings? on one of our loops there are 6 decent crossings (like just above footpeg) in a 5km sectiom :smirk:

Has anyone had any troubles with the mod letting any water or mud into the airbox?

I got it up to the bottom of the seat once. Must have been about a gnats whisker away from sucking water.

Opening up the airbox top lowers the safe water level about 3-4mm but if you do go over it, then it'll flood the airbox more quickly.

Water to top of wheels is no problem as long as you've T'd the carb float bowel vent.

20101003-160130.jpg

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