BSW30SS Carbs

[jimbo1364]

I have some observations, thoughts and a question or two about the BSW30SS carbs.
I own a 1985 GS550E. I want to “rebuild” the carbs.
I have 3 sets of carbs. All three have a different body number, 43410, 43560, and 43570.
Looking at all of the carbs, I only notice a difference in the following;




The angle of the vacuum nipple, the number stamped on the butterfly plates and the amount of “holes” in the top of the venture on the engine side of the butterfly plate.



The 43410 numbered carb body has;
1) 4 “holes” just behind the butterfly plate within the venture opening .
2) 1 “hole” in front of the butterfly plate that the idle air screw inserts into .
3) 1 vacuum nipple on the right side carb, angled back.
4) The butterfly plate is stamped “120”.




The 43560 numbered carb body has;
1) 3 “holes” behind butterfly plate.
2) 1 “hole” in front of the butterfly plate that the idle air screw inserts into.
3) 1 vacuum nipple on the right side carb, NOT at an angle.
4) The butterfly plate is stamped “110“.

The 43570 numbered carb body has;
1) 3 “holes” behind the butterfly plate.
2) 1 “hole” in front of the butterfly plate that the idle air screw inserts into.
3) 4 angled vacuum nipples connected to the backside of the butterfly plate (assumed to be for the smog attachment), 1 angle vacuum nipple on the right carb.
4) The butterfly plate is stamped “110“.
Looking at the specifications of the individual carbs, I have determined;




The 43410 carb is for a 1983 GS550E model.
The 34560 carb is for a 1985 GS550F model.
The 43570 carb is for a California 1985 GS550F model.




While searching the websites for parts, I noticed that different models (E,F,G) were listing different part numbers, depending on the year and model.
The main differences were in the needle jets, main jets, jet needles (emulsion tubes) and butterfly plates. Looking at the other items of the engine (cams, heads, cylinders) I can’t seems to understand the difference in jetting needed!
SO! Any suggestions as to the differences and proper jetting for my 1985 GS550E model bike?

[Nessism]

Can't imagine the difference between them is enough to cause problems. Maybe error on the side of richer is better, but I'd pick the best set and rebuild those.

[Beerman73]

Sigma 6 jet kit

I have an unused sigma 6 jet kit I bought for my 1983 gs550es I think this has the same carb setup as yours , 50$ shipped through USPS for the lower 48 states

[jimbo1364]

Difference in Diaphragm

I looked a little closer at the parts of the spare cabs that I have referenced in my first message. I noticed that there are two different weights to the diaphragm assemblies. One of the diaphragms had a plastic top "ring" that sandwiches the rubber bellows. The other diaphragm has a steel top "ring". There is a BIG difference in the weights of the two assemblies. The plastic topped assembly weighs 78 ounces and the metal topped assembly weighs 110 ounces!

This raises a question about the amount of vacuum needed to raise both valve pistons/needles that are attached to the bottom of the assy. I would think that it would take MORE vacuum to overcome the added weight of the heavier diaphragm assy. And, if this holds true there would be a longer time before the carbs came out/off of the idle circuit.

All of the diaphragms are in very good shape. I plan to use the lighter units for the above mentioned theory.

Although my model 550 is an "E" version, I plan to set it up with the factory designated jetting for an "F/G" model.

The cabs that I am prepping are body #43560 (1985 F model) with a #110 butterfly.

Anybody have any thoughts on the two different weight diaphragms?

[JEEPRUSTY]

Can you show us a pic?
I have 4 raks but all have platic in the diaphraghms.

The weight you quote sounds crazy high.

[jimbo1364]

steel and plastic diaphragm covers

This is a a picture of the two diaphragms. On the left is the plastic topped unit and on then right is the steel topped assembly.

[koolaid_kid]

This is a a picture of the two diaphragms. On the left is the plastic topped unit and on then right is the steel topped assembly.

Hey jimbo, just thought you might want to know that there is no picture.

[skreemer]

The weighted diaphragms may be from a jet kit set. When I put in my dynojet kit there was a weight for the diaphragm, drill for a few of the airways, shims for the needles, and two sets of main jets. (Stage 3 set didn't need to change the pilot jets) Also instructions for a suggested number of turns for the air mix screws(after I dug out the solder.)

There's no springs on the topside of these diaphragms, so there are weights instead.

The 83 and 85 ones should work, the 85 cali set I might be wary of. There were some changes made to make things cali compliant even back then.