SOHC 750s have suffered an intake problem with non stock air cleaners from day one. They seem to suffer from what I call a cross draft problem across the front, or intake, side of the carbs. Some say they don't experience this all the time. Personally, I've noticed the problem on every one I've built. It seems to be an issue when you directly open up the breathing. It usually starts to make the bike stutter a bit at about 50-55 mph, no matter what the rpms are. This, of course occurs with relatively normal riding. If you are on full acceleration at that point, it will go right through that range un-noticed. When you are riding and get to the point that it starts to stutter a bit, you can move you legs in towards the carbs to shield them and it will level out.

A couple of setups will cure this problem for most. The K&N pods that are oiled seem to work fine, but fairly costly. The Ram Flows work fine as well, but again, costly and hard to find. For the Ram Flows to work well, they have to have the factory type foam filters in them. Another system that has worked for me is the longer velocity stack. Stacks that are at least 100mm long, possibly longer. But, they are hard to find and spendy when you do. Also, they don't offer the filtering you should have.

The cheapest and easiest to find chrome, accessory type, air cleaner available now days, is the Breadbox Style Air Cleaner. This type of air cleaner is only available used, but there are thousands of them out there. Without modifying them, they will suffer from this cross draft problem, same as the others. So, I'm going to show you an easy way I've found to make one work well.

The fist photo shows the two types that I know of. The thinner and longer one is made to fit the 73-80 KZ900/1000s and early GS 1000s that had Mikuni non CV type carbs. Notice the carb holes have a larger spread. The thicker one is made to fit the 69-76 SOHC 750s. There were a number of companies offering these back in the 70s and 80s. Drag Specialties, Amen and Henry Abe to name a few. There were many others too. More than likely one company actually made most of them and sold them to various suppliers or vendors who trademarked them. Therefore, many dimensions and combinations have  surfaced. Also, over these 30 or better years, many owners have switched and swapped parts of them... So, no one knows for sure what they have ended up with . No matter though, this is still the easiest setup to use and solve the problem. Just make sure it will line up with your carbs when you buy it.

The second photo shows what you should do first. Disassemble and see just what you have. This one is relatively complete except for a Z shaped support that would hold the center of the screen from possibly dropping.. One you're at this point, its a good time to clean as best as you can. Be sure to get all of the old foam and grit off of the screens and give the two covers a good once over as well..

The third photo shows how I block the cross flow. I apply duct tape on the outer surface of the inner screen. When this is assembled, the tape will be sandwiched between the screens and the foam filtering. I leave about a six inch opening in the bottom of the screen. It's important that you bring the duct tape around those bottom corners a couple of inches as I have.

The fourth photo shows the mounting screws and spacers. Most of these don't have these spacers anymore because previous owners over the years have lost them and not bothered to replace them. These are very important include. The keep you from over tightening the screws and denting the area of the top and bottom cover around the screws. When that happens it really looks bad with the divots in the middle of the covers. If they are missing it's to just cut a pair out of any tubing larger than the screw. I always have a chunk of car brake line here to make stuff like this.

The fifth photo shows the material I use for filtering.  I use foam designed as actual filter foam for motorcycle applications. You can probably use any number of foams available, but I figure this stuff is designed for this use and probably the best bet.  Its not all that expensive at about $10 for the sheet shown in the picture and a sheet of it is more than enough to do two breadboxes. I cut and link strips together to go around the filter completely, even though most of its blocked off. I do this basically for cosmetics so it looks even all around. This stuff is a little thick, but worth the effort to get it in there. I put the foam inside of the outer screen first and then put the inner screen in place, having to bend it a little and force it to squish the foam  I always make sure the seams are placed at the bottom of the filter, out of site when it's mounted. It just looks better that way.The sixth photo shows the finished Breadbox, ready to use.

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