Air box/filter mod

Questions regarding the DR750

Air box/filter mod

Postby ladder106 » Sun May 24, 2015 6:07 am

Trying to improve air flow into the SR41 airbox and eliminate the silly paper "inside-out" air filter at the same time.

I built an adapter out of 60 thou. aluminium sheet and formed it into an oval shaped cone (after several tries) and then welded a circular cylinder onto the back.

Image

Image

It's attached with 4 countersunk pop rivets to be flush to the sealing surface and sealed with RTV silicone. A UNI foam filter will be used. There's a large(ish) spring inside the filter to keep if from collapsing but allowing it to squeeze into the airbox from the side.Not having to pull the side straight out will (hopefully) allow me to remove the 2 rear screws but only loosen the front screw and slide the metal insert toward the front. In this way I hope to be able to remove the filter without disturbing the right side fuel tank.

Image

Image

I cut a hole on the top of the airbox and will seal the side opening with an aluminium plate.

I'm hoping that there will be enough air flow under the seat and that keeping the original box will not damage the plenum effect. I'll remount the box tomorrow or Monday and have a go.

Results in a few days....fingers crossed.
User avatar
ladder106
Site Supporter & all round Good Egg!
Site Supporter & all round Good Egg!
 
Posts: 397
Joined: Sat Aug 27, 2011 6:02 pm
Location: Davis, California, USA

Re: Air box/filter mod

Postby BigBob » Sun May 24, 2015 9:05 am

What you are doing is essentially what Suzuki came up with for the SR43 800, with a top loading filter. I`m sure it will be successful.
Having to move the l/h tank to change the air filter was not a good design either, especially with the idiosyncratic plumbing.
Surely the most abysmal design fault on the Big has to be the way the beak is attached with the indicators that are virtually inaccessible from the back, where you can only get 1/6th of a turn on the spanner and guaranteed grazed knuckles as well. As for trying to connect the indicator wires in no space at all..... just what were they thinking? :crazy:
User avatar
BigBob
Admin
Admin
 
Posts: 3944
Joined: Sat Jan 23, 2010 10:46 pm
Location: ESSEX

Re: Air box/filter mod

Postby nug » Tue May 26, 2015 10:48 pm

Good job ladder. I am pretty happy with mine the way it is, but if I decide to get into the airbox again I will most probably use the rubber intake from a ccm 644. These will fit our carbs (I hope) & they will take a round tube to which you can fit a K&N or similar filter which is for the early Carb'd Range Rover. I would most likely make a new airbox as well for the hell of it.

Keep us posted on how it goes mate :tup:
User avatar
nug
Site Supporter & all round Good Egg!
Site Supporter & all round Good Egg!
 
Posts: 3379
Images: 14
Joined: Sat Jan 23, 2010 10:46 pm
Location: Lincoln

Re: Air box/filter mod

Postby ladder106 » Sun May 31, 2015 6:49 am

Aaaaannnnnnddddd....its done. Added an aluminium plate over an old air filter lid with the filter and screen removed.

Image

It runs. Runs pretty well also. At least no different than before I started.

Starts the same and no apparent lean condition or feeling like it's not getting enough air.

It pulls to redline in the bottom 4 gears but just to a bit more than 6500 in top. It's possible that the opening is too big and the carbs aren't seeing quite enough vacuum to open fully.

I'll try it again tomorrow with some duct tape over about 1/2 the top hole just to see what happens.

Happy to have a cleanable filter.
User avatar
ladder106
Site Supporter & all round Good Egg!
Site Supporter & all round Good Egg!
 
Posts: 397
Joined: Sat Aug 27, 2011 6:02 pm
Location: Davis, California, USA

Re: Air box/filter mod

Postby ladder106 » Wed Jun 03, 2015 5:46 am

Adding to the saga:

The hole I put into the top of the airbox measured 3 X 3.5 inches...about 7.5 X 9 cm.

Yesterday I taped over about 1/2 the hole giving a 2 X 3 in opening.

The bike seemed to run better and I got to 6800 rpm in top. I'm thinking I'll add a bit more tape down to about 1.5 X 3 inches and see what happens next. That should be about the size of the hole I had in the old side-opening filter. So far I'm having no problems with air flow into the airbox.

It's nice to ride in cross-wind and move my left leg around without disturbing the airflow. (NOTE: the prior setup had the hole on the left filter end enlarged and jetting richened to compensate. It worked fine but I could create very lean running by simply moving my left leg out into the airstream causing more air to be directed into the airbox. Crosswinds did pretty much the same)

More laters....if anyone it still interested.
User avatar
ladder106
Site Supporter & all round Good Egg!
Site Supporter & all round Good Egg!
 
Posts: 397
Joined: Sat Aug 27, 2011 6:02 pm
Location: Davis, California, USA


Return to DR750

Who is online

Users browsing this forum: No registered users and 1 guest

cron

x