"Homemade Air Thingy"

Here is what I was working on that Bridget referred to as some "home made air thingy for the bike" in the previous post. I have been considering making a new airbox for the Ural for a while as I continued to have problems with the stock airbox when it is snowing while riding. The stock filter would get soggy and clog up.

Before the Talkeetna road trip, I put in a new K&N filter and changed the main jet back to stock (122 main, 42 pilot) and gas mileage was decent at 28 mpg average even with the extra passenger and the mound of camping gear on the rear rack. The second experiment is this airbox known as the "Leftka 3, no metal" on SovietSteeds, a Ural forum. The attraction of this box is a larger air filter and reports of fuel mileage in the mid-30s. The main body is made from an 8" length of 5" PVC fence post which another SovietSteeds member generously sent for just the shipping cost. The air intake hole is offset since the airbox doesn't sit centered in the frame due to the 2WD shifter linkage.

I think it uses K&N filter from a Moto Guzzi that I ordered from Amazon. The aluminum flanges were ordered from Aircraft Spruce, the same vendor I had ordered the CHT (cylinder head temperature) gauge from. The plastic ends are caps were the hardest piece to get as they seem to be sold only in quantities of 1000+ units. I (guiltily) requested a couple of free samples which were happily sent. The assembly went together in one afternoon though the fit is pretty tight in the space used by the old air filter housing. Tight enough that I don't even have any mounting hardware holding it in place. The flanges were installed slightly off center because I wanted to try and re-use the one-piece branch pipes. Other installations used Ceet flexible hose which is hard to find anywhere besides Aircraft Spruce and they alway want a bunch for shipping.

Initial testing is good. At idle and partial throttle, no popping so the pilot jet isn't too lean. On the initial test ride, there was popping at mid-throttle indicating that the mixture was too lean. I installed the two shims back under the carb needles. No more popping. At wide open throttle, there was some hesitation so the 130 main jets went in. Now, it seems to run pretty well. No popping at any throttle position even when cold.

A long grade on the Parks Hwy towards Nenana which had required downshifting to third could now be taken in fourth at 55 mph. CHT are maxing out at 450°F/425°F (L/R) under heavy loads such as that grade and actually drop at wide open throttle suggesting that the main jet is on the rich side. I'll order a 128 main jet. Normal running on flat terrain is around 375°F/350°F (L/R). On the Talkeetna road trip, I regularly saw 500°F which I personally think is on the high side. And that was basically stock.

Between the last picture and this one, I cut a relief (i.e. hole) in the air box to clear the tank mounting bracket and allow the box to sit more forward and vertical. Now that the box it is fitting the way I want it to, I'll paint it. The original design had all this weather stripping to seal the box but since it is all on the "dirty side" of the filter, I didn't bother. The clearance cutout is also on the "dirty side" of the filter. In this position, the branch tubes don't exert any additional mechanical stress on the all too fragile compliance fittings.

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