2 carbs insted of 4

Is this a mod that would be worththe time cause i have a guy here in town selling 2 Mikuni VM30-83 Carbs and i really want to make the bike look less full and more simple is this worth it for 60$ and the

 

Those are a single barrel carb, how would that work?

I thought maybe it was something like the two hole carbs the old KZ1300's ran or something...that might work...

 

i would build a splitter for it so each carb would feed two cylanders i just wondered even with big big jets would it flow enough to feed the bike cause one of the other members on here said he had switched from the four to the two but i dont remember who or what he had done that on

 

This idea has crossed my mind a few times. If they are seperate carbs you'll need to build a rack or something so the throttles operate synchronously. I'm no expert but I assume the VM30 is a 30mm carb, 2 should be more than enough to handle a 550,possibly too much. My 1000cc bike has a single VM38 running it.

 

I did it on my 700. Got 2 Mikuni 34mm round slides with homemade intakes. Took a while to get it all straight, works great. See my build thread in my signature. 8)

 

Considering the firing order - you'd want 1 carb to feed 1 & 4, the other carb to feed 2 & 3. That would be one heck of an intake.

 

My intakes feed 1&2 and 3&4. Works fine.

 

I dont think it matters with the firing order its not like carbs act like fuel injection

By the way black and orange your my hero now

 

Thanks Flyingseca, your right about the firing order. If you couple 2 cylinders that fire at the same time, it would require bigger carbs or at least bigger jets for more fuel mix. This mod works better if you close the YICS ports or you'll be robbing fuel mix from the next cylinder firing.

 

Thanks Flyingseca, your right about the firing order. If you couple 2 cylinders that fire at the same time, it would require bigger carbs or at least bigger jets for more fuel mix. This mod works better if you close the YICS ports or you'll be robbing fuel mix from the next cylinder firing.

 

Ummm, guys--- there really isn't a "FIRING" order as such; keeping in mind that both plugs on a coil fire together, one of the cylinders in the pair is getting a "wasted" spark (on its exhaust stroke.) "Firing order" in an XJ is determined more by which cylinder is on what part of its crank cycle than by the ignition.

It's more a case of "power stroke order."

However, I completely agree that YICS and this idea are counter to each other. YICS is designed to support four individual carbs via four individual intake tracts; "siamese-ing" the intakes into two pairs would create an imbalance in the YICS passages. It might still work if you could block it in the center and isolate each pair.

I'd like to see HP, torque and fuel economy numbers compared to a stock 4-carb system before I could believe any true advantage (other than effort required to maintain) to 2 carbs over 4 on an XJ motor; especially an originally YICS motor.

Interesting idea, though.

 

Fitz is right about the firing, really its more like compression strokes. Couldn't afford to do any dyno results, but from riding I can tell you it has better low end and mid range performance with a slight drop in mpg's. The mpg's went from 45 to 42. Couldn't say about the high end range because I didn't really get down on it but 1 time and that was after the mod so I can't compare to the original setup. Logical thought leans to the original setup as having better high end results, but since I just cruise around it doesn't matter to me.
The best things about this setup is the simplicity of cleaning and syncing(2 carbs instead of 4) and these round slides aren't as finicky with air and exhaust mods. 8)

 

I want it cause its simpler and it would give me a cleaner look i think and i can get the carbs and play with this while i wait to rebuild the rack.

 

Ok, first thing to figure out is what size carbs. My bike originally had cv33mm and I switched to vm34mm because they came in a kit made for a xs650.
If I'm not mistaken, your bike came with cv28mm carbs. So vm30's should work with the right jets.
Second, do you know how to weld. You'll probably need to fab some 2 into 1 intakes. You need the outside diameter of the carb throat(head side), the distance center to center of the head to carb boots. Then you can figure the overall length of each intake.
Third, you'll need some mounting boots to mount the carb to the intakes and make some flanges to attach them to.
Forth, filter choices: pods,velocity stacks,pvc air intake or airbox with intake boot mods.
Other things you need: 2 into 1 throttle kit(if you can't find 1 cyclex has them), the right size and length steel rod to block off the YICS, then you may need to mod the fuel delivery. I had to change the size of the lines, filters and petcock.
Material for the intakes: aluminum is the best choice but requires tig welding or use mild steel that is thin to keep the weight down and requires arc or mig welding. I suppose you could use metal plumbing pipe if you can weld it without blowing thru, if not you'll have to braise it.
If you have any questions I'll help. Are your valves in spec?