Both of my cubs have Zenith carburetors, one has a short oil fill tube, and the one I just rebuilt has a long one. I wanted to make a fuel line that would pass behind the oil filler, so it would work on both of them, and since the hood was still off Aunt Jessie, I used the 49 for a trial run. Took a couple tries, but this was the result.
Once I got the hood on the 48 I made one like it for her, and was pretty pleased with myself
After a couple hours of running in the shed I ran her up the road, then put the flail on and got some work down. I had been mowing heavy thick grass between 6 and 8 inches tall for a little over an hour when the cub suddenly stalled. It would restart and idle, but the only way it would run faster was to pull the choke about 2/3 way out. No big problem, I figured it was a piece of dirt in the main jet which it was, but while checking it I could hear a bubbling noise, softer and higher pitched than an engine boiling, but otherwise similar. It even sounded as if it were coming from the rear of the engine. After doing some listening and checking I pulled the gas cap (new safety cap), and got a slight whoosh, it was pressurized
. When I looked in the tank i saw bubbles coming up in it. I then loosened the fitting at the carb., and was getting gas and vapor mixed coming out there. The line was clearing the manifold by what I thought was plenty of room, but apparently when i really worked the cub hard on a hot day it was getting enough heat blown back on it from the manifold to boil the gas so hard in it that the vapors were coming out faster than they could escape out the cap vents. Yes, I checked, the vents are open, but as you may have noticed, they are very small. I drove it back to the shed, and cleaned the load jet, which fixed the running problem, then I made one more gas line, staying well away from the manifold.
I went out and mowed for 2 more hours with no more trouble. Apparently the gas line was ok under light duty, but when I put it under a hard load for an extended period it was too close to the manifold. I can see the potential for a real disaster with it pushing fumes out the cap that bad.