New Lungs for Phaedrus

This morning I tackled the latest modification to my motorcycle, removing the airbox and replacing it with a velocity stack.

Before and after: Left: Stock airbox.. Right: airbox removed and velocity stack.

The first task was to remove the original airbox. The process was pretty simple, Just three screws held the cover on. Behind that was the filter, and two more screws holding the box in place. Once the main box was off, the black plastic tubing that filled the space between the top of the cylinder and the frame came out easily, it was only held in place by a hose clamp and friction apparently.

Airbox with the cover and filter removed. Only the two screws top center hold it on.

With the airbox removed, no screws to hold the tube in place behind it.

With the whole airbox assembly removed, the carb is exposed. The mounting plate under the gas tank is easily removed after the tank is off. Only two bolts attach the plate to the frame.

Getting the carb off was pretty straight forward. The gas tank had to be removed, which meant taking off the seat and petcock knob, then the one bolt that holds the tank on. I'd done all that before, and its not technically difficult, just takes a few minutes.

Under the tank a lot of hoses to remove. Like a lot of motorcycles, this one has things that aren't necessary to make it run well. The white triangle is part of the crank case breather,, which is overly complicated.

Before getting to the carburetor, I removed some unnecessary hoses. TJ Brutal Customs has a great video about what can be removed safely from this bike. Mine didn't have quite as much junk parts as some, probably because it wasn't originally sold in California.

The airbox and assorted hoses which no longer reside on Phaedrus.

With all those hoses removed, you can see straight down to where the carb connects to the manifold. Those two black screws are the hose clamps that hold the carb in place. The hose, immediately above them in this photo, is a coolant line that goes to the carb, which I rerouted.

With the extra hoses removed, getting my hands and tools inside to remove the fuel lines, coolant hoses, vacuum lines and throttle cables was much easier. There was a set of wires for the throttle position sensor to disconnect, that was the only wiring to deal with. 

I disconnected everything and pulled the carb off. The biggest problem was just working some of the hoses loose. 

With carb removed and the coolant hose rerouted.

This carb had two coolant hoses attached to it. One leading out of the engine into the carb, then a second from the carb to the radiator. Apparently this is to help warm the fuel in the carb (in theory), but in reality doesn't really effect much. Both the hoses are under pressure, so simply capping the nipples would not work (Coolant spraying out of the engine is usually a bad sign.) 

One source recommends using a screw inserted in the end of the hose (cut short) and a hose clamp to hold the screw in place. I may do that eventually, but I couldn't find a small enough hose clamp. Instead I cut the longer of the two hoses and ran it straight from the radiator to the engine, simply removing the carburetor from the routing. This will keep coolant flowing through everything else.

The velocity stack itself simply slides over the open air intake of the carb, and attaches with three recessed screws. Because of the increased air flow, the carb needed to be re-jetted. Again, TJ Brutal Customs has an excellent video showing how to install the new jets, and everything went exactly as described in the video. Since he does such a good job, I won't go into details, just follow his instructions.

Once the jetting was done, I capped off a couple vacuum and coolant ports. I also added TJ's long handled adjustment screw, since accessing the pilot adjustment on this bike is a real pain in the ass, even with the airbox removed. 

Once all that was done, I put the carb back on, which was simple since several hoses didn't need to be attached anymore. 

Adjusting the throttle cables was the biggest issue for me, mainly because I'd never done it before. It took me a bit to figure out I'd switched the two cables. Once I figured out that mistake, I had too much free play, I went from having no free play in the throttle to having too much. But eventually I got it adjusted.

A few more minutes to put the tank and seat back on, then came the moment of truth... After about 20 seconds of cranking (to get fuel through the drained lines) it started right up! 

I let it warm up while I cleaned up my tools, then took it for a spin. It ran a little rough at first, but after giving it time to warm up fully, and adjusting the new long handled screw on the carb it came right into tune. It runs fine, and seems to have a bit more power. There's now lots of room under the gas tank to move electronics to when I get around to rewiring it. 

My only issue is that proper tuning has the adjustment screw all the way in (at least I think its all the way in?) Which should actually make it stall instead of increasing the RPMs. So I might need to pull the carb off and change one of the jets (the kit includes 2 main jets, and 4 pilot jets), but I'm going to ride it for a bit and see how it goes. I would like to have some play in the tuning so I can adjust for altitude in the mountains, but I'm not going that far until spring, so there's time. 

UPDATE:
I tinkered with it most of yesterday, off and on, and never quite got it running right. After some emails with TJ, I woke up today and pulled the carb back off the bike, swapped out the pilot jet for a size up and took it out.

After warming up, and a couple turns of the air/fuel mixture screw it settled in nicely. I rode it around neighborhood streets, then out onto higher speed city roads, and finally for several miles of highway. It works great in all gears, wide open acceleration, cruising, and no popping or sputtering when I close the throttle down.

Thanks again to TJ Brutal Customs for a great product, great support with both videos and email assistance!