|The Trials and Tribulations of riding a
CJ750 in China Part 2 by Dave Vella
Fixing a leaky set of Mikuni knock-off carburetors
Shortly after I arrived in China I saw my first CJ750. I knew immediately I would end up with one. Initially, I thought I might just buy it and ship it straight home to the US, but then I started reading about some of the reliability problems folks were having. I decided it would be a better idea to get it while I was in China. I am here on a long term assignment so I have plenty of time to work all the bugs out; and there are piles of spare parts here, all of which are just a phone call and a couple of days shipping away.
My first bug was a fuel leak. I had stopped at the local supermarket to stock up on some groceries, and when I came out of the store I noticed a great puddle of gasoline running out from under my bike. I discovered the source of the leak was the overflow tube on the port side carburetor. I had turned the petcock off when I went into the store, but I played with it again anyway and banged on the float bowl too, but neither trick managed to stem the flow. Eventually I pulled the feed hose off and stuck a plug in it.
Fortunately the supermarket is only a hundred yards from my apartment. I pushed the bike home, and since I was now a tiny bit angry, tired, and covered in gas, I thought it best to grab a beer and tackle the problem the next day.
I sent an e-mail to the shop where I bought the bike. They apologized about the petcock not holding and promised to ship me a couple of new ones the following day. While I was waiting for those, I took the carburetor off so I could clean it out. A new carburetor shouldnt leak like that; and past experience has shown these leaks are most often caused by a little trash under the seat of the float valve.
Try as I might, I could not manage to stop the leak at the float valve. No matter how many magic words I uttered, the little rubber tip on the needle just would not do its job. I was a bit disappointed, but needles go bad all the time so I just thought Id go get a new one. Every carburetor kit Ive ever bought had a new needle in it; should be simple. Much to my surprise, there are no new needles for these carburetors. I even got on the internet and tried to find some back home in the hope I could get them shipped here. No Luck; Sorry. The guys at the bike shop in Beijing even said they just throw the carburetors in the scrap pile when they act up like that.
I guess Ive always been a little too conservative to just throw away perfectly good stuff. I liked those little carburetors. The bike ran good with them and I just couldnt see buying a whole new set over a five-cent valve needle. So I determined to fix them.
While all this was going on, the new petcocks I was promised came. Not surprisingly, they were just as bad at leaking as the original one was. So I took a note from Tony Salvatores Toolbox and ordered a new Honda Petcock. It works perfect. Thanks Tony!!
I know Im going to show my age here, but I remember a time when carburetor float needles were made of brass. Every carburetor kit came with a new needle and seat. One of my friends from the office has a little hobby machine shop set up in his apartment; so how hard can this be?
It took a little measuring to come up with the correct dimensions; but after that it didnt take long at all to transform a few bits of scrap brass into two perfectly operational float valves. To assure a better seal, I cut the bevel in the bottom of the seat with a center drill, turned the needle to match then lapped them together with some fine polishing compound.
While I had the carburetors in the shop, I put manometer connections in them following the advice in Bill Taylors Toolbox; except that I used a rubber cap as a seal instead of a screw. I never would have thought about using a grease fitting as a vacuum port; thats a great idea, so thanks to you too Bill!!
Since the new valve needles and seats were installed, floats adjusted, carbs tuned, fuel filters replaced and a brand new Honda petcock installed; weve been running great and not one drop of gas has hit the pavement.
Life is good again.
Take care, ride safe, and have a great day!!