Bs32ss 550 carbs on 650 head.

[Kara25]

Hello i am looking for opinions or knowledge om what carbs can be used on a 550/673 swap. Right now i have a set of my 550 bs32ss with an DJ stage 3 in them and the option of 2 mains. 150 amd 155. The 550 works very nice with the 150s and the needle on the 4th spot(one lower than DJ instructions).I am using on the 550 and plan on swapping to the 650 my marving racing 4-1 and my K&Ns RC-2382 dual lunch box like filters. The question of course is are those carbs capable to fire up the 550/673 and make it drivable??? The concern here is that a newly built engine with new rings etc will not be very drivable and not seat its rings properly.. i am sitting here with a rebuild 650 top end hesitant to tear down my 550 to start the process..want to have an idea of what might work or not to save myself from grief down the road. 650 CVS are out of the question used sets go about 350+ euros not counting rebuilding kits etc etc.. tried sourcing at least 650 cv internals but no luck either all i get are float bowls and tops.. Thanks in advance!

[wraith]

The gs650gt has the same 32mm CV type carbs they only went to 34mm on the katana gs550/650

So have a look at what the pilot jets and screws are set at with the 650 carbs and set you 550 ones to that

[Kara25]

Mr wraith thanks for the reply. Yes i know the mikuni bs32ss are identical on both bikes only the guts are different. Pilot on the 550 Cvs is 40 - 650 Cvs is 42.5 . The only reason i think my 550 carbs might work is the DJ stage 3 kit that i have installed on them giving me the adjustable needle. There are other variables including a pressed air jet not removable on the 650 cvs from what i gather... any more info from anyone will be appreciated

[TonyGee]

its a case of putting them on and see how it runs,  doing a plug chop at different throttle openings will give you a good idea. 

I once put a set of 600 bandit carbs on a 1200 bandit, ran great with no re-jetting. 

[Kara25]

Yep it was more of a question targeting people who already did the swap and maybe have played around with both 550/650 CVs on the setup bcs i know THIS is the place for all kind of crazy zook swaps besides the gsresources

[Gixer1460]

Finding peeps who have done the swap is likely a REALLY small number - we tend to play LARGE LOL! It is very likely the carbs will work fine and will run sufficiently well to allow 'break-in' running - changing the pilots isn't the end of the world, neither is mains after a bit of loaded running!

[wraith]

Did this years ago gs550 bottom end and 650 top end but I can't remember what carbs I used or the settings, as it was well over 20+ years ago 

Sorry

 

[DAZ]

This is just me thinking out loud,but if you were to swap to the 42.5 pilot jet that would help the low end as it's the 650 size, now your going up 20% ish in capacity try the 155 mains,although not hugely bigger than what your using as a 550 would the increase capacity and subsequent vacuum cause more fuel draw from the main jet? I fully accept that I maybe wrong and am quite happy for someone who knows better to explain why, but if that's what you got then try it and see like I say just thinking out loud and willing to learn

[Kara25]

Digging around the web actually found some people who did the swap and figured out that people who went all stock on the 650 conversion using the 650E airbox had better results using 650 carbs (makes sense). But another guy who ended up with a similar setup like mine(4-1 550 exhaust and K&N dual filters) got the best results with 550 CV carbs WITH a dynojet stage 3 like mine. Obviously when you are ditching the airbox and oem exhaust all is going out of the window and you need the more fuel that you can get. Weirdly enough the 550 dynojeted carb user also used the stock pilot (mikuni 40) like i am running now as a 550 bcs the 42.5 that he upjetted in 650 specs made it run rich even as a 550/650 hybrid. Oh and trust me when you put the 150 and 155 mains from dynojet side by side they are CAVERNOUS in comparison to the 92.5 mikuni main a stock 550 has

Edited January 5, 2023 by Kara25

[Gixer1460]

You can't compare std jets to DJ - different written sizes. Stop over thinking the problem, just swap them over, monitor the result and act on that rather than speculate with internet tuning!

[DAZ]

57 minutes ago, Gixer1460 said:

You can't compare std jets to DJ - different written sizes. Stop over thinking the problem, just swap them over, monitor the result and act on that rather than speculate with internet tuning!

 

16 hours ago, TonyGee said:

its a case of putting them on and see how it runs,  doing a plug chop at different throttle openings will give you a good idea. 

I once put a set of 600 bandit carbs on a 1200 bandit, ran great with no re-jetting. 

@Gixer1460do you think, that it is the greater vacuum draw of the bigger motor that causes the bigger motor to run ok on small carbs? This is all hypothetical obviously each engine needs individually tuning,but does stronger airflow signal (as in @TonyGee600 carbs on a 1200) pull more fuel from a given jet size ? Would this enable a reasonable enough mixture ? Up to the airflow limits of the 600 carbs, obviously 32's wont have the top end of 36-40mm carbs, just want to learn/ get my head around the theory  thanks DAZ

[Gixer1460]

You are only increasing capacity by about 15% and yes the faster gas speed over the venturi jet will give greater depression to draw more fuel. This only works so far unless you increase the jet orifice to allow much greater flow. Bear in mind Suzuki fitted 34mm, 36mm & 40mm carbs to the 1100/1200 engines so a carb bore will work with lots of capacities . . . . . hell, one of the 750's got 38mm carbs! Smaller carbs will produce excellent rideability due to increase in torque low down but trim the top end due to airflow restriction.

[TonyGee]

Suzuki also fitted 32mm carbs to a 1200 oil cooled engine,  when i did mine the increase in bottom end and mid range was much better just where i like it and spend most of the time in, it still pulled 120 + mph and that wasn't full throttle so i would of thought 130 is possible. more than fast enough for me.