Originally Posted by Ladder106
Thanks for sending the photos....it's very helpful. I kept trying to imagine what your air cleaner modification would look like.....I failed miserably.
I quess I'm a "visual learner".
In any case, I'm happy to see you back here and also happy that more photos are being posted now. Your bike is very nicely done.
Thanks to everyone that's assisted this DR "noob" so far. I'm still finding the bike quite amazing. Rebuilding the front brake caliper today. It looks like the front pads are the same as those on the early (pre 96) DR650, so I can easily replace pads.
I plan on sending an e-mail to Herr Hessler today to inquire about brake discs and stock air filters.
A few people have said that the stock air filter frame might be used and modified with foam from a Twin-Air or other foam filter. I'd like to do that but am a bit confused about how to go about it.
Unlike my other bikes that take air fron the interior of the filter straight into the engine (air flows into the airbox - through the filter - then into the intake) the DR 750 (SR41) takes air into the center of the filter first then the air goes through the filter and clean air fills the entire airbox. I assume this is due to the large "gulps" of air the the engine takes.
The air filter element is unsupported on the inside and supported by expanded wire mesh on the outside. This makes sense since the element is supported against the air flow.
It appears that to modify the filter with foam I would have to remove the rubber "snorkel" and cut open the sheet metal on the outside of the box as shown in other posts....then remove the paper element and reline it with air filter foam.
This is not beyond my abilities but I would like to know if I should change jetting to accomdate this modification. Does the air-flow increase enough with the increased opening to require a larger pilot jet and raising the needle one notch?
It also seems that a potential "weak point" in the stock system is that the seal between the sheet metal part of the filter and the plastic airbox is critical. If this seal is bad, dirt just flows directly into the carbs. Adding more sealant here (grease, foam, etc) would probably be a good idea.
For airflow scheme - you got it spot on. Close to ideal scheme is filter into laaaaarge airbox for big twins and singles.
As for fuelling - no way you can know it prior to modifications. Just go ahead - jets are standard mikuni jets, worst case you will have to spend 10 bucks to change them to suitable size.
For foam filter - here is photo to help you - one of variants...
The GURU of DR Big Stefan Hessler did that