GuyS
XS400 Enthusiast
I’ve torn apart and cleaned my BS34 carbs. I have found a multitude of problems so far:
1. The right side carb float needle was stuck. I changed both float needles (purchased from MikeXS) in a partial kit.
2. The right main jet tube was horribly dirty, greenish, crud all over it, and the pin needle was covered in crud too. I cleaned the needle and tube, as well as ultrasonically cleaned both of the disassembled carbs.
3. The left main jet was 127.5 and the right main jet was 120. I have a Seca service manual that says the jets are supposed to be 127.5 and 117.5. So I changed them back to the Seca Service Manual spec. with the brand new main jets from MikeXS
4. The right side “carb holder” boot, was damaged at some point in the past, and repaired. But not effectively repaired, I suspect the cause of a vacuum leak. So I bought a NOS boot I fortunately found on Ebay.
5. I been having a heck of time trying to find out the correct float height for my BS34 (there are variations of the carb which make this a challenging research project. Mine were set at 24mm.
Then I ran across this post from another Maxim owner from 2013. “Greg” had been trying 32mm on the float height but found at that measurement the floats actually were hitting the bowls!
“I fiddled with the floats to bend them inward (bent too much by common wisdom, but these aren't ordinary BS34s) and then get the height adjusted (for me it's 23-24mm) until I could hear them slam open and shut reliably, and can't blow through them even once upside down.
Yay, we have a working Maxim again!”
So I’ve decided to leave mine set as they were at 24mm, even though I have replaced the float needles. Once I get to the stage of running the engine I’ll post my results.
Oh and here’s another thing. The Seca service manual does not suggest the float height measurement method anywhere in the manual. They suggest the tube method of establishing fuel levels in the carbs!
1. The right side carb float needle was stuck. I changed both float needles (purchased from MikeXS) in a partial kit.
2. The right main jet tube was horribly dirty, greenish, crud all over it, and the pin needle was covered in crud too. I cleaned the needle and tube, as well as ultrasonically cleaned both of the disassembled carbs.
3. The left main jet was 127.5 and the right main jet was 120. I have a Seca service manual that says the jets are supposed to be 127.5 and 117.5. So I changed them back to the Seca Service Manual spec. with the brand new main jets from MikeXS
4. The right side “carb holder” boot, was damaged at some point in the past, and repaired. But not effectively repaired, I suspect the cause of a vacuum leak. So I bought a NOS boot I fortunately found on Ebay.
5. I been having a heck of time trying to find out the correct float height for my BS34 (there are variations of the carb which make this a challenging research project. Mine were set at 24mm.
Then I ran across this post from another Maxim owner from 2013. “Greg” had been trying 32mm on the float height but found at that measurement the floats actually were hitting the bowls!
“I fiddled with the floats to bend them inward (bent too much by common wisdom, but these aren't ordinary BS34s) and then get the height adjusted (for me it's 23-24mm) until I could hear them slam open and shut reliably, and can't blow through them even once upside down.
HOORAY!
I took it for its first test ride last night, and it was great. It revs, and slows, and goes fast, and goes slow. It doesn't backfire, it doesn't surge forward, it doesn't hesitate, it doesn't stall. It starts on the first try.Yay, we have a working Maxim again!”
So I’ve decided to leave mine set as they were at 24mm, even though I have replaced the float needles. Once I get to the stage of running the engine I’ll post my results.
Oh and here’s another thing. The Seca service manual does not suggest the float height measurement method anywhere in the manual. They suggest the tube method of establishing fuel levels in the carbs!
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