As you may remember, I decided to design and make spacing tubes for carburetors to place pod air filters behind the frame central tube of Honda CB750 Seven Fifty cafe-racer.
I decided to model these tubes from PVC pipe because it looked like 50mm PVC pipe should fit quite easy. Then I cut them off and formed dents on internal pipes to round the central frame tube.
I had some thoughts about using PVC pipes not only as models but as parts themselves. I tested these pipes for durability and found more than satisfying their strength to mechanical loads. I even designed special aluminum washers and bracket to join all pipes together (to avoid unintentional tube slipping from carburetor). The only question I didn’t solve theoretically was how I can coat PVC pipes into black colour.
But I set a level of my projects high and I couldn’t lower it even on a dime. Even if PVC pipes look good, work good and someone may install them like real, there surely should be someone another who’ll poke a finger on them and be shouting about inadmissibility of using plastic water pipes in custom builds.
So using of PVC pipes was not my way. Yet one friend of mine helped me to find exhaust workshop which specialized on making stainless steel exhaust components. This workshop is on some 500km from Kiev, but I easily explained by phone that I need four custom exhaust pipe reducers, they took my order, we checked out dimensions and in a few days after prepayment my parts where ready.
Still there was a lot of work to do: to align lengths and cut tubes off, to treat the carburetor side ends, to make quite accurate dents on inner tubes so they could round the frame tube (this part of work was quite tricky, I also had to avoid both superfluous tube deformation and lose of roundness). That’s not to mention new mounting system designing, making, aligning and welding, tubes polishing and farther rubbers modifying .
I even had no time to shoot any photos in progress, so that’s how parts looked after I finished my work:
Tubes installed on spare carburetors I had at hand:
And all battery together:
I think I’ll made additional mounting point on frame and mount central plate to it through rubber mount.
Now about filters. This time I wished to use some special pod filters and found such items on Webike: Kijima pod filters with foam filtering element and very interesting design:
That’s how setup looks on Seven Fifty.
As this article will be uncompleted without general view of motorcycle so I am forced to show it, even if I prefer not to do so because of some experiments with exhaust header.
by 
Best intake I`ve ever seen yet!
Neat job , have you re-jetted the carbs yet
Thank you.
Yes, I re-jetted carburettors but only initially. I installed #125 main jets, #38 pilot (slow) jets and upped needles a bit. After engine running-in bike will be tested on Dyno and carburettors will be readjusted according to wideband oxygen sensor reading.
Hi , I look forward to the dyno runs . I have same CB seven fifty and struggled with jetting , 125 mains still ran lean and wouldn’t pull through all gears .
I nearly gave up , but numerous runs later I eventually got it dialled in.
Sick job!
You guys have an update about the carb setup?
Cheers!
Hi, Tim
Unfortunately no. Now I am waiting for the engine paint arriving. And even after cases painting there will be a lot of work to do before carburettors final adjusting…
Hi, I am about to build a cafe-racer based on a Honda sevenfifty. The project is going into the final stage. But I am still looking for a competent solution for the intake system; particularly for the tubes. I saw your solution and was very impressed !
Now my question: can you provide the tubes as a kit ? what were the criteria for the sizing of the tubes (length)? For experimental purposes only I would try out to build the tubes from PVC (trying out different lenngts…). How did you build them exactly?
I would appreciate your answer very much.
Kind regards
Rainer
Hi, Rainer
Sorry for late answer, I was working in my garage and completely forgot about time.
I am sorry to say this, but it is mostly next to impossible to replicate those intake pipes. It took huge amount of time and efforts, I was really glad to finish set for my CB and don’t work on it so if I decide to manufacture such kits firstly I shall solve the question of process formalization and simplification, hence decreasing the price. Now in high season I just have no time for that, but I’ll return to it in the Autumn.
Kind regards,
Nazar
Hello, can you make this steel intake for sale, because I have the same cafee racer from Honda cb 750 seven fifty and I have big problem as you now with frame tube and space to air filters. If it possible how cost it. Thanks.