Differences between carbs

[Clumzi]

I am going to go against the grain here, but you can try the 650 carbs in the 550 and probably get it to run okay. I have both bikes and my 550 didn't run well with the stock setup. Pretty sure it was nearly stock with aftermarket main jets. Since I had an extra set of 650e carbs sitting on shelf, I decided to play around. First was replacing 650 carbs with 550 parts. Ran about the same, still pretty long warm up needed, excessive bogging until fully warmed. Then I went the other direction with 650e bits. No longer required the 2 minute warm up and seems to give a little more total zip. I haven't ran it more than about 15 minutes, but still doesn't run nearly as nice as my 650g at all speeds.

I will tell you that the 550 carb parts; needles, slide springs, are much different from 650s. The 650 shaft drive models also seems to be tuned a lot richer than 650 chain drive on main jets (110 vs 97.5). Conversely the main jets between 550 and 650e is similar 92.5 vs 97.5.

I find these changes interesting since there is only a 123cc difference in motor displacement.

One thing you may not consider with the carb body swap is that there are non replaceable air jets that are different between models. Likewise, the throttle butterflies are numbered different.

Here is compiled data from top link of tech section
GS 650 GZ/GLZ (82)

idle r/min 1100-+/-100r/min
carb mik bs32ss (4 seprate carbs)
id no 34300
bore size 32 (1.26)
float height 22.4.+/-1.0 (0.88 +/-0.04)
fuel level 5.0+/-0.5 (0.20 +/-0.04)
main jet #110
main air jet 2.0
jet needle 5C45
needle jet Y-7
pilot jet #42.5
throttle valve #135
by pass 0.8, 0.7, 0.8
pilot outlet 0.7
valve seat 2.0
starter jet #45
pilot screw pre-set (1.5 turns back (mixture screw))
pilot air jet #160
throttle cable play 0.5-1.0 (0.02-0.04)
choke cable play 0.5-1.0 (0.02-0.04)

GS550 (80-82) the specs are for the CV's

idle r/min 1100-+/-100r/min
carb mik bs32ss (4 seprate carbs)
id no 47160 (us) 47170 (can)
bore size 32 (1.26)
float height 22.4.+/-1.0 (0.88 +/-0.04)
fuel level 5.0+/-0.5 (0.20 +/-0.04)
main jet #92.5
main air jet 1.6
jet needle (4bel2 us model) (5f42-3rd notch canadian adjusable needle)
needle jet x-6
pilot jet #40
throttle valve #135
by pass (0.9, 0.7, 0.7 us model) (1.0,0.8,0.8 canadian)
pilot outlet 0.7
valve seat 2.0
starter jet #35
pilot screw 3.5 turns back (mixture screw)
pilot air jet (us model #150) (#120 canadian)

I can't copy 650e info, this link has it;

http://www.thegsresources.com/_forum/showthread.php?t=73723&page=5

Clean them up and give them a go, I would bet it won't run that badly.

This gets me real curious. Also, I hear people saying that with the 650 carbs the bike with run too rich. Makes perfect sense, I get that, but what about the mixture screw? Can you back up the mixture screw and adjust somewhat for the richness of the mixture? I'm not arguing that it is a better idea than using the original 550 carbs, but in the spirit of play... I dunno. I still don't know what I'm going to do. However the whim strikes me when I walk out to do it.

[waterman]

You most certainly can adjust the "mixture" screw. I call it the pilot jet screw. Its effect is mainly on idle and part throttle (1/4). I find that it will make huge difference in startup and low throttle response. After 1/4 throttle the needle shape and position plays a larger role. Here the mixture screw setting does have a slight effect, but usually not enough to make any real difference.

[Steve]

You most certainly can adjust the "mixture" screw.

That would be quite correct.

More correctly, though, it is the "idle mixture adjustment screw". You are correct in that it only affects idle and very low throttle openings. The idle mixture is pre-set by the sizes of the pilot air jet in the carb intake throat and the pilot fuel jet in the float bowl, next to the main jet. This adjustment screw only controls how much of that mixture gets to the engine.

Clumzi, if you plan on operating your bike with more throttle than that you will most certainly want to transfer all of the brass pieces (jets) from the 550's carbs over to the 650's carb bodies.

[Clumzi]

Ahh, see, that is news to me . Cool.

And I want to make sure people know I'm not ignoring people's advice for the sake of thing, that I'm not listening to what you're saying. I just have VERY little in the way of resources and need to get creative if this bike is going to run again. -nick

[Steve]

Ahh, see, that is news to me .

Which part is the 'news'? Moving all the jets over? Nessism mentioned that back in post #4.

To get the 650 carbs to work on a 550 you will have to move over all the jets from your 550 carbs and install them over.

[Spyder]

I have a 650 with single disc front brake. That means nothing. ALL of the jets in the 650 carbs are bigger than your 550 carbs. This MIGHT work. It more than likely gonna run rich. Get some pods, you should be ok.

[Spyder]

Why are you so set on the 650 cars anyway? Rebuild your 550 carbs (properly) and ride...
I don't get it...

[Clumzi]

No, the "idle mixture adjustment screw" is the new bit. Most people just seem to refer to the thing as the "air" screw. When folks were talking about it being the "mixture" screw, I figured it played a role in the air fuel mixture not just at idle but straight through the rev. Now I know .

The pod comment is interesting. To flesh this idea out, are you saying that if I removed the intake and exhaust bottlenecks, ie pods and aftermarket 4 in 1, that the richer fuel mixture might be beneficial?

[Steve]

No, the "idle mixture adjustment screw" is the new bit. Most people just seem to refer to the thing as the "air" screw. When folks were talking about it being the "mixture" screw, I figured it played a role in the air fuel mixture not just at idle but straight through the rev. Now I know .

The pod comment is interesting. To flesh this idea out, are you saying that if I removed the intake and exhaust bottlenecks, ie pods and aftermarket 4 in 1, that the richer fuel mixture might be beneficial?

On the earlier VM carbs ('79 and older Suzukis), there is a 'fuel' screw and an 'air' screw. As detailed above, the BS carbs have a 'mixture' screw. Too many people get confuzzled with their terminology and call them by the wrong names.

Yes, if you removed the bottlenecks, you will need a richer mixture than the 550 jets could provide, but based on the jet sizes listed in the carb sticky (quoted in post #12) the 650 jets would make it too rich. For example, the 550 main jet is a 92.5. For just pods, you might want a 97.5. For just a header, it might be a 100. For both of them, maybe a 105. The 650 comes with 110 jets, two sizes too large. All the other jets tell the same story. Please accept the idea that stock is not so bad. If you want other than stock, you will need to be buying different jets than you have in either set of carbs.

.

[Clumzi]

Alright, so we add pods, header and a turbo! How about then?

lol, I've no doubt you're right, I'm just being lazy. I'ma have a clean set of 650 carbs on my hands and I'm gonna want to throw those right on the bike instead of ripping another set of carbs apart. Right and wrong's got nothing to do with it. I'm a broke grad student, time and money are in short supply and doing things that are less than bright with a motorcycle two years older than I sounds like a good idea .

BTW - thanks a bunch again. I don't want you think I'm not listening. I'm just curious.

[Steve]

Alright, so we add pods, header and a turbo! How about then?

Ahhhh ... HORSEPRESSURE.

There again we get into problems. Are you doing a blow-through-the-carbs install or a suck-through-the carbs install? Yeah, it makes a difference. Either way, pods are out, as you will only need one filter. With a blow install, you will only need one filter for the turbo, which will then blow through all the carbs. You will also need to make a sealed box to house the carbs so the float bowl vents see the added pressure, too. With a suck install, You will only need one (larger) carb on the inlet of the turbo, therefore only one filter.

Header is another issue here, as standard 4-into-1 headers won't work. Depending on whether you mount the turbo in front of the engine or behind, you need to get all four cylinders into one pipe as quickly as possible and route that to the turbo, then you will have a single exhaust from the turbo back. The more-common location is behind the engine, where the carbs and airbox currently live.






Yeah I figured that was a facetious question, but I just thought I would take it and run with it. Just shows that your problems still would not be over.

.

[Clumzi]

you, sir, are a nut. But I've gotta say, you are my kind of nut! -nick