Gs550 carb on xj550 seca?

Hi guys,
My first post here, been reading the forum for a while though. I just bought a xj550 with plans to convert it into a cafe racer. My big question is after reading much about cv carbs and pod filters is can I find a 77-79 gs550 carb and fit into xj550? The whole reason for me to do this is to be able to tune the bike properly in the future after installing pods. I know I could use stock airbox to avoid the hassle but that's not my question.If I can't then I might have to consider flipping the bike and getting something that I could work with, I would hate to do that though cuz I kinda fell in love with the seca.I have searched the google and this forum but couldn't find an answer. If someone has dOne this or have the knowledge about it, please help me out. I appreciate all your help.

 

Has anybody attempted this or even thought or considered this? I'm the only one who wants to cafe a seca with pods and still have the bike running right? Or is it just a real dumb question?

 

All I can say is DO IT and let's see if it works.

Because if it does, I'm gonna do it and KEEP the airbox/exhaust; but that's beside the point.

IIRC, the carbs you're referring to are 28mm direct-slide carbs which SHOULD WORK FINE if jetted properly. It's a matter of rack spacing more than anything else; and I'll bet they're close. The Suzuki jetting will probably even be close because the engines are so similar, numbers-wise.

Do it do it do it and let us know.

 

Thanks bigfitz! I appreciate that. So I'll try to get more info on the rack spacing. It amazes me that nobody has tried it. I mean people here keep on resetting and tweaking the cv carb after installing pod filters. But never thought of swapping carbs? I assume it would be easier to jet the direct slide and get it to work better than our stock cv, right?

 

You would think. But "think" isn't all that common of an affliction, plus making a true swap like this involves spending some money and a commitment to doing it right. Most of the "pod-modders" don't want to be confused with facts when they've already made up their minds; and very few of them seem to understand what's truly necessary when re-jetting. There's even a certain faction that insist their bike runs fine on stock jets with pods. (Since nobody's running a tach, how do they know?)

I have both of my 550 Secas running like rockets with the stock setup so I gave up on it when gas got so expensive. I like the 52~56mpg with a sportbike personality. The CVs aren't so bad, but they reward meticulous precision. Anything less and they just keep biting you in the ass.

Do it do it do it and let us know!

 

I have seen it done on a Post classic (pre82) XJ550 race bike, however I dont know how much work it was, bike was no rocketship but seemed to go ok

 

I am watching......my friend has an 82 GS 550, those carbs are a pain. I might have to suggest to him an older carb swap.

 

Well, if somebody had the rack spacing measurement for 1977-79 gs550 that would help a lot.

 

46.9mm inner lip to the other is the carb spacing of gs550. Also the outer intake diameter on the carb to the engine is 31mm. I don't have my carb with me right now, it's at my buddies. If someone had their carb out and a caliper please measure and post. Thx. What do u think bigfitz?

 

Theirs a guy on this thread running GS750 carbs on his 550.
Al

http://www.xjbikes.com/Forums/viewtopic ... carbs.html

 

Hmm...

The intake port spacing on the XJ550s is assymetrical.

Carb pairs #1 - #2; and #3 - #4, are 68mm apart (on center.)

HOWEVER, carbs #2 and #3 are 82mm apart. The cam chain runs up the middle of the motor.

A quick check of references reveals that just like the XJ, the GS550s cam chain was in the center of the motor, so I suspect that a more careful measurement of the Suzuki will show that it is similar. If the Suzuki's intake ports/carbs are evenly spaced, they'd have to be adapted to the Yamaha's rack and the necessary linkage mods engineered.

The BS28's have an engine-side "spigot" OD of 34mm.

Upper carb-to-rack mounting holes are 35mm apart on each carb.
Lower carb-to-rack mounting holes are 28mm apart on each carb.

 

Unfortunatly Thrasher isn't here to explain how and why gs750 carbs instead of gs550. I noticed that spacing between #2 and #3 carbs also on gs550

 

The bike that Thrasher put the GS750 carbs on was a racebike with an FJ600 motor in a 550 Seca. You can't base this swap idea on that; I can't swear that the intakes are even the same size.

 

You cant swear or u can?

 

It looked the same to me

 

A lot of Yamaha stuff LOOKS the same. Thrasher's racebike with the GS750 carbs has an FJ600 motor in it. None of the North American market 550s motors came fully in black.

I DO NOT know whether the FJ600 intake ports/manifolds are the same size.

I do know for sure it's an FJ600 motor in a 550 Seca. THAT swap works easily; it's one of my long-term plans (I want an all-black mill in my '83 someday.)

 

XJ600 ports measure 3mm bigger that the XJ550 at the entrance

 

I hope they work out for you. If they don't, look into some Mikuni round slide carbs. They handle air and exhaust mods well.

 

Bad news, looks like gs550 carbs are evenly spaced out all through 4 carbs, unlike ours where 2&3 are spaced out more than the other. Those mikuni round slide carbs are over 400 bucks right?

 

Sometimes you can find them on Ebay for as little as 70.00 a piece. Just remember to get 2 right side and 2 left side. You'll also need a different throttle and cable. They will have manual choke levers you can reach from each side of the tank. (Hence the 2 right and 2 left) May seem like a big expense but they will save a lot of time and pain. If you keep the Cv carbs, try the velocity stacked pod method. Look for streetbrawler750's thread in XJ Modifications Forum.

 

If you look for the round slide carbs, look for VM32mm Mikuni round slide carbs.

 

So,VM32mm Mikuni will bolt right on? How about the racks? How will it all connect? If u could describe it a lil more that would be nice.

 

They just slip into the intake boots individually. No rack involved. I looked on Ebay, there are several to be had for 90.00 to 100.00 a piece. I bought mine from CycleX with the throttle, but I have 2 carbs instead of 4. I don't know where the throttle kit came from, but I think its a ATV throttle. The cable goes into the top of the carb and 2 carbs are usually paired, so you would need 2 paired cables that attach to 1 or 2 paired that attach to 2 for the throttle. The paired cable has a loop on the end that the throttle cable hooks into.

 

So basically the carb would just hang there with pod filters, I assume?

 

Yes, the clamp on the boot holds it in place. On another note, each carb will need its own fuel line. So you would need a fuel line splitter and some more fuel line. You may also need to increase the size of line to get adequate flow. I actually had to change out the petcock on mine, but I have larger carbs- VM34mm Mikuni Round slides. Don't think that would be needed since we are talking 4 carbs of the same size. It may seem a bit involved, but its actually a simple setup and the round slide carbs are easier to adjust/sync and maintain.

 

Yea sure does sound like, I get the fuel line, but not the throttle cable part. I imagine One cable running down then splits to two then they would connect to each pair like a upside down Y. If u have some pics u should put them up. I think we don't have a write up on this here. Thx for ur help.

 

I saw the one u have I think from cycleX. So u have 2 carbs splitting to 4 using that Y adapter? How much did u pay? 500? That looks cool!

 

Your getting it on the cable setup. I looked back at my build thread, but I didn't add pics of the throttle and cable setup.
http://www.xjbikes.com/Forums/viewtopic/t=26691.html

 

I thought we got 28mm stock carbs, so the vm 32mm will bolt right on? Or will I have to tweak around with the boots?

 

I thought they were 32's, my mistake. If you have 28's, go for 28's their probably cheaper too.