It’s been a few weeks (at least) since I last had any significant progress to report on the custom Honda CB 350, but this weekend I finally did a few things worth mentioning.
First, the exhaust: I’ve never done anything like this before, but my housemate has a TIG welder, I found this website to order pre-bent sections of stainless steel tubing, and I figured ‘what can go wrong?’
So, I started out with a box of 1.5″ stainless steel tubing:
2 x 180 degree bends swaged at one end
2 x 45 degree bends swaged at one end
4 x 1′ straight swaged at both ends
1 x 1.5″x1.5″ Y collector
1 x muffler with 1.5″ input
I began at the exhaust ports on the engine. The original Honda CB 350 exhaust flange is a thicker diameter section of tube for the first inch or so of the header, which the exhaust nut pushes against when you bolt it down. I ‘carefully’ cut my 180s in half so I had 4 90 degree sections. Then I welded a 1″ piece to the two non-swaged ends, to be the exhaust flanges. Bolted those to the motor and just went from there, marking, cutting and taping the tubing together, until I had two headers coming together underneath the motor.
The “Y” collector was tricky. It was swaged to accept 1.5″ tube, but only about 1/16″ fit into the collector – not really enough to grip it. So I cut two short sections of tube (with swages) and tacked them into the collector, effectively extending the collector. Once I had the collector tacked onto the headers, it was just a matter of figuring out where I wanted the muffler, and using the two 45 degree bends to get there. The muffler will have a little bracket welded to it that will make it possible to bolt it to the passenger footpeg mounting spot. Also the headers are separate from the collector, and will be held on by the tight fit of the swaged tubes, as well as some slick stainless steel springs, that I ordered from Cone. I’ll post some more detailed photos on flickr to explain the process, but here’s what it looks like now:
It’s still just tacked together. Having looked at it a lot, I’m not quite happy with how low it is. I’d like it to hug the left frame tube a little more. Before I finish welding, I’ll see if I can separate some of the tack welds, shorten the headers a little, and rotate the whole thing upwards so that it fits tighter to the frame/motor. This will make the headers closer to vertical. The muffler is also awfully close to the left rearset, but I’m seriously considering moving the rearsets to the original footpeg locations; it just means a little engineering for the control linkages. That would leave more space for the muffler/center stand/passenger footpegs. It gets crowded back there!
After tacking together the exhaust, I was so pleased with my progress that I thought – hey, let’s see if it runs! There was only a very little bit of old gas in the tank, timing and valve lash haven’t been set since last summer, it’s got brand new untuned carburetors on it, and I’ve never tried out the dyna coils. Not to mention that since the exhaust is only tacked, it’s more like a sieve than an exhaust system.
But, bullheaded as I am, I quickly wired up a simple ignition circuit (don’t forget a fuse!), sprayed a dash of starter into the new air filters, and kicked it over.
HOLY s#*t! I’ve never been so scared in my life. Not only did the bike start, but it wound right up to about 5500 rpm! I was so panicked I forgot for a second where I had mounted the temporary kill switch, but quickly found it and shut it off. In the video below I started it up again and just let it run for a second – I don’t want to do any damage. Between air leaks, bad tuning (or lack thereof), oversized jets and maladjusted throttle cables, there’s a lot to do before it will idle properly. I’m just thrilled it ran at all, considering all the unrefined work I’ve done. Hearing that motor run, just for a second through the new pipes, was about all the encouragement I needed! So, next is to finish the exhaust and work out the control positions/linkages, which will include some welding on the frame. I hope to have another update after this weekend!