Friday, November 19, 2010
SU HS2 Carburetor
A few weeks ago I removed the carburetor from the Morris to rebuild it. Progress has been slow, mostly because I had no idea what I was doing so I didn't want to get in a hurry and mess anything up.
I have been doing a lot of reading and it is starting to pay off. I am beginning to understand how it all works, including why the gas vaporizes in a carburetor. After reading many many different sets of instructions on how to adjust it, and they seem to differ wildly, I hope to get it all figured out soon.
Last night, I successfully got the jet centered. It took several attempts, but once I got it right, it was dead on. Tonight I installed the carburetor back on the manifold. (I haven't hooked the throttle or choke cables yet.) After getting it mounted, I gave it a shot of starter fluid and attempted to turn the motor over. Unfortunately the battery was dead so after hooking up the charger I hit the starter switch again. It cranked up (and ran very smoothly) until all the starter fluid burned off. Two more attempts at cranking it before the bowl finally filled with fuel and the car started running off gasoline. I was fairly impressed with my efforts at this point because it was probably running smoother than I have ever heard it.
Tomorrow I plan to get back out to the garage and adjust the fuel mixture, idle, and fast idle. Hopefully it will all come together without much trouble.
(Dirty carburetor, before cleaning.)
Did you know that the reason fuel atomizes in a carburetor, is that when air passes through a venturi, the air speed increases thus causing the atmospheric pressure to decrease. (This decrease relative to atmospheric pressure is a slight vacuum.) The decrease in air pressure lowers the boiling point of the gasoline. The lower boiling power causes the gas to vaporize. Any extra fuel that does not vaporize at this point, will vapor due to the heat as it flows through the intake manifold.
My daughter would say this was "very interesting." This of course would mean she was not really listening.
Monday, November 15, 2010
Tuesday, November 02, 2010
The Wikipedia entry for 'British Standard Whitworth' had two interesting bits of info about Whitworth threads.
1) "The Whitworth thread that most people encounter is the quarter-inch thread on the bottom of most cameras for mounting on a tripod..."
2) "British Morris and MG engines from 1919 to 1955 were built in a factory that used metric threads but with bolts and nuts for Whitworth spanners (wrenches) and sockets."
Yes Morris, as in Morris Minor 1000.
The SU HS2 carburetor off the Morris Minor has been on hold for a couple of weeks. I had two problems that needed to be solved (without causing any permanent damage).
1) The brass jet was stuck in the jet pilot. This was keeping the jet from moving when the choke handle was pulled. I believe the strongest adhesive in the world is probably varnish made from dried gasoline. After soaking the pieces in carb cleaner for two weeks, they were still stuck. The solution to this problem turned out to be taking a propane torch to the brass for about 10 seconds and then dropping it in a bucket of water. Presto! The parts had separated.
2) The threads for the jet locking nut on the carburetor body had been cross-threaded at some point in the past. This made it impossible to put the nut back on correctly.
It was suggested to me that I could remove the first row of threads using a roto-tool. It would probably work but I was not certain I would improve the situation.
I checked the net for a tap and die set so I could clean up the threads. The problem here is that the nut has 3/8 Whitworth threads. (Three-eights of what? Not metric, not SAE. Whitworth!) I found a set online, but wasn't sure I wanted to throw $40 at the problem. I would if that turned out to be the only viable option, but I continued to search for other options.
I ended up borrowing a 3/8 Whitworth wrench from Lott. Using the wrench I was able to non-forcefully coerce the nut back across the threads. After a few twists back and forth, the threads were clean enough to hand tighten the nut.
The two problems are now behind me. Maybe I will finally get the carburetor put back together in the near future.