(Cutting) Open Airboxes

[woods]

Looking at some carb swap options on the DR.

I guess one of the go-to requirements is cutting open the airbox. I'm very hesitant on doing it. I've dumped my bike before on water crossings. More recently, on a group ride my cousin hit some water on his KTM500 that required pulling the plug and cranking out the water followed by an oil change.

few days after that, I was alone on the bike bunch of mud holes up ahead, I'm riding the berms around them in 2nd, bike jumped down off the berm, into the mud, and up over the bars I went with a nice splash into the water. bike is on its side, water to the headlight, bar end sticking out of the water, and I kill the ignition. lift the bike up, crank it over for a moment, it kicks over, and away I go.

I'm thinking with an open airbox, I'm really risking getting water in place I don't need water. how major of a concern is this?

 

[skibum69]

It was a mod on the 640 too but I'm with you in keeping it whole as I too have been through some deep water! It's only a DR how much more performance do you want?

 

[woods]

It was a mod on the 640 too but I'm with you in keeping it whole as I too have been through some deep water! It's only a DR how much more performance do you want?

Looking at a new carb (FCR) and to get the full benefits of it, requires cutting the box.

 

[FLrider]

That’s a risk reward debate only you can really answer…. Yeah, I know doesn’t help much, but here’s my 0.02cts.. Does it really matter how fast you can ride yourself into trouble On a DR?….

 

[woods]

That’s a risk reward debate only you can really answer…. Yeah, I know doesn’t help much, but here’s my 0.02cts.. Does it really matter how fast you can ride yourself into trouble On a DR?….

Eh, that's a fair point too. Not a race bike. I feel like the BST40 in there could perform better. There still is a bit of surging. Rolling off the throttle then back on, it hesitates. I've shimmed the needle and stuff. But it still feels like something is missing.

Just doesn't feel right cutting open the airbox. Almost feels like doing a hack on something.

 

[Oldtrialer]

Find the carb settings for a country that doesn't have emissions regulations. I used Greek settings for my Super Sherpa. Got rid of the lean condition below 3000 rpm. I got my info and parts from Derek at Moto-Lab.

 

[skibum69]

Derek at Motolabs is a bit of a BST40 guru, he knows about all there is to know regarding tuning etc. He also sells all of the parts for rebuild etc.

With 640's he typically advises not to go to an FCR.

He's been very generous with his time with me walking me through my rebuilds etc over the phone.

Now all I need to do is figure out how to do the tuning on my 525 carb.

 

[Stormdog]

Years ago I swapped my BST for and FCR on my 640, results We’re good, but only because I didn’t know how to tune the BST.
My vote would be to tune the bike as is, and enjoy the bike for what it is. There just isn’t much upside potential in that bike without throwing more money at it then it’s worth.
After the carb swap you will be tempted to spend money on the exhaust to take advantage of the carb, then might as well look into some flow work for the head, maybe a big bore kit……..
Then if you spend enough to get power there is the suspension to throw more money at.

 

[woods]

Years ago I swapped my BST for and FCR on my 640, results We’re good, but only because I didn’t know how to tune the BST.
My vote would be to tune the bike as is, and enjoy the bike for what it is. There just isn’t much upside potential in that bike without throwing more money at it then it’s worth.
After the carb swap you will be tempted to spend money on the exhaust to take advantage of the carb, then might as well look into some flow work for the head, maybe a big bore kit……..
Then if you spend enough to get power there is the suspension to throw more money at.

Heh, so this is my DR650. Carb and exhaust is the only stock thing left. Its got waaaaaaay more money in it than its worth.

Actually, a built 790 is sort of on the table for next year or the following.

Its already got Cogent front and rear.

 

[Stormdog]

Well if you are that far down the rabbit hole, it might be easier to go all the way to bottom rather then turn around now and never know what could have been.🤣

 

[woods]

yea, I just about 80 miles today after lunch. bike runs perfect. idles fine. starts fine. cruises at 80 fine. bumbles along dirt roads in first fine.

I'm going to leave it. I can see myself kicking myself for starting to mess with this. bike runs well. I'm going to leave it.

 

[skibum69]

Sensible.

 

[matty]

Looking at some carb swap options on the DR.

I guess one of the go-to requirements is cutting open the airbox. I'm very hesitant on doing it. I've dumped my bike before on water crossings. More recently, on a group ride my cousin hit some water on his KTM500 that required pulling the plug and cranking out the water followed by an oil change.

few days after that, I was alone on the bike bunch of mud holes up ahead, I'm riding the berms around them in 2nd, bike jumped down off the berm, into the mud, and up over the bars I went with a nice splash into the water. bike is on its side, water to the headlight, bar end sticking out of the water, and I kill the ignition. lift the bike up, crank it over for a moment, it kicks over, and away I go.

I'm thinking with an open airbox, I'm really risking getting water in place I don't need water. how major of a concern is this?

Glad it as worked out ok for you, but just to say with carbs air boxes are a mine field at times and to move away from stock can on present you with a whole heap of problems that can be a pig to fettle.
Any CV carb is critical on the boxes volume and restriction of flow to function to its optimum.
The flat slides / straight forward slide carbs tend to be a little more forgiving. But the CVs i hate straying far from stock, my thoughts and experiences over years of bike murdering are that manufacturers dont waste time working air box designs out for fun and that big black box is not just that shape for fun.
If you got a lot of jets and time and patience you can get a bike to run ok and perhaps a bit bigger pilot curcuit jet or a neddle swap or a bit bigger vent hole in the slide will stop the bike falling on its face at just above tickover etc etc. Andd you might just get it running so as a bit richer adjustment masks the less than perfect air box pressure, but getting it to perform smoth reliable and ecconomical is a lot for a bloke in a shed to sort out and depending on the bike could just be a path you wish you never ventured down. just sayin. Think long and hard and do your research as best you can prior to cutting or driling any factory air box esspecialy with cv carbs ,