GS550 carbs on GS650 head?

[Chuck78]

Mike, what jetting and needles are you running now???? I wonder if I got a set of 33's, if the jetting would still be pretty spot-on if I started out with your combination? I also wondered if I could squeeze the BST31's into the BS32 intake boots???? Maybe worth it for performance to go bigger rather than smaller and just buy some GSXR BST33 or BST34 intake boots

 

[boontonmike]

I'm using 110 Mains, stock idle jets, idle mix screws at 2 turns out. I have a 4 into 1 and K&N pods as well as dyna coils and dyna iginition. I have the dyna stage 3 needles at the 2nd clip form the bottom. I still need to do some tweaking when riding season starts. MY AFRs are looking with a half point of where I want them and the bike starts up in 1-2 kicks and idles like a champ.

As for boots I kept buying different katana and GSXR boots, I'm not sure which I ended up with. But i did use 2 of my stock BS32 boots aluminum plates as spacers. I want to buy some more because I am almost positive I could make 4 work if I had the time.

Check out my build thread:
http://www.thegsresources.com/_forum/showthread.php?t=183707

 

[Chuck78]

Well I am watching some carbs on ebay now. I see rebuilt/reman sets for $400-$500, but used sets needing rebuilt starting around $50-$150. I think I will probably pick up a set and deal with delving into the unknown and try your jetting and intake boot suggestions. If all else fails, I can rebuild them and re-ebay them.

The local vintage japanese mc junkyard has a whole giant drawer full of intake boots, so maybe I could come up with something. I think in your build thread, you may have listed exactly what models you had to combine boots from to get the wider carbs to fit the narrower spacing on the 650 head. I thought I reposted that info somewhere here but maybe it didn't go through.

 

[Chuck78]

http://www.ebay.com/itm/200856086897

That is a KILLER deal as it includes $60 worth of Emgo pods that I'd need and $60 for the carb set and free Katana throttle grips and cable etc. They are BST31's though. I was hoping for 33's.

What do you guys think, Mike in particular? BST slingshots flow better than the original GS650 BS32's, so maybe going with the 31's would still be an improvement? The BST33's are cheaper than the 34's, and they are the same casting, so same boot and filter sizes. Not sure about the 31's on that note. So I am leaning towards the 33's.



I can get the flat oval pods for $60 a set, or what would be really beneficial to tuning and cross breezes at speed would be K&N dual oval filters so that you have more filter area and you have two carbs sucking from one filter plenum that won't suffer from carbs 1&4 running rich due to cross breezes, and more dirt ad moisture accumulating on cy's 1&4 pods. I'm doing this style on my VM26'd GS750.

 

[cowboyup3371]

The Emgo pods are crap. If you are going to use them, go to the K&Ns

 

[Chuck78]

I had heard that they don't filter well, and have heard other people just saying they weren't as good in general.

The intake boots needed to fit the wider spacing GSXR carbs is still somewhat of a mystery, but Mike had enough info on his build thread that I think his parts matching can be duplicated. I am most likely going to buy the GSXR BST33SSS carbs, although I might be able to find a set off of an older GPZ, as I had read that the older they are, the less plastic parts there are in them and the more aluminum. Not sure if that goes for the 90-97 GSXR models I'm looking at, as they may be the same through the whole run.

I can snatch up the carbs that came off the head that I bought, 81 GS650G BS32's, for $150, but I am really leaning towards getting these slingshots and trying to one up everybody else (except boontonmike's sick build) and make my wife a really happy girl, as she always wants to go faster faster faster, speed demon... She is short (5'6") with shorter legs, so the GS550 fits her perfectly after we lowered it an inch, so going bigger to a GS750 or 1000 for more speed is not an option, making this the raddest fastest and best braking GS550 based bike IS the only option!

 

[Chuck78]

I had accidentally reposted this on Mike's build thread when I meant to copy and paste it to here, oops:

From your build thread, thanks again Mike! Between you and 49er, our two bike builds here 920cc GS750 with VM26's, and 673cc GS550 with hopefully BST33SS flatslide CV's will both end up being nearly dead on with the first set of jets and needles we put in them!

I got these 88 GSXR 750 intake boots which I though would line up with the two 92 GSXR750 ones I already had. Turn out 2 from each set did line up spacing wise and in a nice horizontal line. Only problem was the 88's were 1/4" shorter then the 92's.

Luckily I had the stock 650 boots which are an aluminum base moulded into rubber. An hour of cutting filing and drilling on 2 of the 650 boots turned into perfect spacers (well within 1/16th" which should do just fine). The final step is to port match the head inlet to the carb boots (as seen on other members 650 head projects).

I think I finally narrowed the carbs down to BST33SS (or 32 ) Mikuni flatslide CVs off of late 80s GSXRs.

 

[Chuck78]

Well, I picked up two complete racks of 1990 BST33SS Carbs off of a Suzuki GSX600 for $75 off ebay shipped, and two dual oval K&N air filters like I pictured above for $50, now I just need to do some searching for intake boots until I find at least what boontonmike has, if not a set that can be adapted that doesn't need the 1/4" or so extra spacer. The spacing on these carbs is wider than the GS650, and I suspect that it would be tough to find any compatible carbs other than the BS32 setup with the spacing to fit a GS650 head.

Any other tips on intake boots that will make this fit as good or easier than Mike did?

 

[Chuck78]

Several years later, I realized KZ1000 late 1970's VM28 carbs have the exact same spacing as the ports on the gs650 heads! Same spacing as GS750/1000/Kz750-4/Z1/Z900. The boots for those models are straight, no offset. Only problem is the heads for those applications have the intake port extended as a spigot beyond the head a bit, the gs650 intake boot surface is flush with the head and the boots are taller or longer to get the carbs past the cam chain tunnel.

The gs400/425 2v models have a spacer between the head and intake boots that would solve most of this problem. The vm28 kz1000 boots have a bit shorter distance between the mounting bolts, but I think I could slot the ends of the boot bolt holes and use a couple of larger washers to distribute the torque inwards more. Then we have manual slide carbs that have a diameter that matches up really well to the bs32 intake ports!

I'll be trying k&n rc2222 dual oval filters to see how they fit in the compact gs550 frame as well. Not much room for even standard size pods on the 550 frames.

Also we can run these more kean in the cruising throttle range as Kawasaki did on the late 70's for EPA/Emissions standards, as they added an accelerator pump to eliminate the throttle roll on stumbling that was a byproduct of the leaning out the mixture

 

[tkent02]

I think if I rode mostly at one elevation or a narrow range of elevations like on the eastern half of the US I'd go with VM26 from a 750, 850, or 1000. Yep, it might take some doing but I'd make them fit. Better throttle response, easy to tune, the larger size would flow plenty of air for a 700.

Where I typically ride I could go from 2,000' to over 14,000' in a day, and sometimes up and down 6,000' or so many times a day, the CVs work much much better for that. I'm happy with them, at least I will be once I get them dialed in.

 

[Chuck78]

Well my wife is now looking at KZ1000's, a bit long and heavy for someone 5'2", but I figured I needed to step up the game a bit to make her GS550 exceptionally apoealing to ride. 740cc 10.25:1 Wiseco pistons, 650 head and cylinders, Megacycle .380" lift cams, and vm28 carbs. The vm26 would work quite well I'm sure.the intake ports are about 27.## mm inside diameter, but I believe it's best in performance terms to not let the air/fuel mixture expand too much, as that may lead to some of the fuel condensing on the port walls. Just a tidbit I read on here somewhere about performance engine carb sizing. It outlined drag race vs road race scenarios, talking about RS34 and/or vm33 carbs. I believe for road race applications, the poster said port diameter 1mm larger than carb venturi diameter is best. For drag racing, I believe the poster said larger, but I cannot recall exactly.

 

[tkent02]

Unless all I had to ride on was interstate highways, I would MUCH rather ride the 550/700 from what I've seen so far.

 

[Chuck78]

As compared to a kz1000? Yes, I'd agree! My 920cc GS750 is down to about 480lbs after a major diet but adding much wider (heavier) tires and dual disc front brakes. The 920cc with advanced cams is a BLAST to ride, plenty plenty fast enough acceleration even far above legal limits. It's still a bit hefty when pushing around the yard and on uneven surfaces, but riding, only the tightest of low speed turns does the weight seem noticeably heavy. Carefully revised rake and trail helps out substantially, but racing around the neighborhood on my buddy's CB200... helps put the middleweight gs750 in perspective.

If I had it to do over again, I think a GS650E engine and frame would have been my top pick for a project base. The kickstart 550 bottom is something else though that I desire, but the later 650E frame and the 550 kicker, 650 top, Wiseco custom batch 740cc GS650 pistons, megacycle .380" lift cams... GS1100E swingarm, wire spoke wheels. 3.50 or 4.00x18 rear DID or Excel alloy rim, 2.50x18 front... racetech fork mods or CBR600F4 forks in VMAX1200 triples. $500+ YSS rear shocks. Pirelli Sport Demon or Bridgestone Battlax BT45V tires...