Going to attempt a carb swap for my XJ700X

I'll start off by saying that if anyone has any tips, please chime in!

A couple of years back I bought my XJ700X from a coworker. I rode it once (barely) before it refused to move again. I knew this at the time, hence the $300 price. Since then I've replaced all fluids and filters, coils (Dynacoil conversion), plugs and wires, brake shoes, airbox boots, a couple of cables, and some wiring connectors, along with doing the valve shims.

Also, another coworker helped me mess with the carbs. I'd known they weren't in the best shape, but they were worse than feared. In two of them, at some point the main jets had come loose (!) and rattled around in the carb bore, taking aluminum chunks with them. The pilot circuit seems to be a mess too, and at least one diaphragm has an ill-repaired hole. We tried it anyway - it bogged badly from idle and, once it did start to rev higher, would get stuck at 4000 and not drop down. So we said screw it - he has years of experience with bikes and agrees they're pretty much shot.

However, he did have a rack of Mikunis from an '86 Suzuki GSXR 750, in very good shape after having been fully cleaned and rebuilt. The engine was a similar configuration breathing-wise, and the carb bore is close as well. The OD of the carb's output matches that of the XJ700X's Mikunis, and the spacing from 1-2 and 3-4 is close enough to work. The one issue is the spacing between carbs 2-3, which is ~6mm too large. However, the more I looked, the more doable a reduction appeared.

So I'm going to give it a shot - not much to lose at this point. I pulled the rack apart last night to start planning. They'll need some new brackets and trimming here and there, but the only difficult part appears to be getting the idle adjustment screw to work on the shortened linkage.

Here it is shortly after I bought it:



Some pics from a few days ago, messing around in the garage:





Dyna Coils:



Donor carbs vs. originals:







I'll have to trim the spare mounting holes in the body/bowls through the red lines, and move the linkage over as shown.



Shaft has room to be trimmed & rethreaded:



Wish me luck!

 

i think you might have more problems then you think if you look at the suzuki carbs they sit at an angle vs stright for the x carbs float levels will be way off not sure if they will work flat you say the x carbs are messed up on the inside show us a pic of whats wrong someone might have a good diaphram on here for you

 

also im not sure about the compatibility but when i bought my bike(yesterday) i got a second carb free lol....needs to be scrubbed and its for a 750 instead of a 700. pm if ur interested.

 

the carbs have to be off a maxim x water cooled they are mikuni not hitachi not sure if yours was a maximx 750 or an air cooled one

 

They're angled a bit, but my coworker says that the angle is nearly identical to that of the X. The angle on the float bowl was not horizontal as they sat on the bike.

I'll have to take the X's carbs apart at some point again. One diaphragm is bad, the rest might be ok, but the bodies are chewed up inside. It would basically need two completely new ones (maybe three), and that might give enough to rebuild the rack. This is less work and is much cheaper, and I won't have to modify the bike itself.

 

Worked on them a bit this weekend. Shortened the throttle shaft, extended its threading and keyways, ground off the unneeded bowl/body holes between the sets, cut the throttle return spring down, and cut off the fuel drain nipple from carb 4.

Just need to put together some new brackets now, and fix the cable throttle actuator to work with the idle adjustment screw.

To test them I'm going to fire 'em up with some pantyhose "filters." If they work ok I'll either go with EMGO or Uni pod filters - we're hoping that the increase in air will go well with the slightly hotter jetting in the GSXR carbs.











They fit together great now!

 

Man, ... you are a DieHard!

I hope this works-out for you.
This if the sort of Guerrilla Fabrication that's an adventure if you have all the right tools.

Good luck.
I hope nothing doesn't fit right and you succeed.
I never seen this done.
What people on this site do is amazing sometimes.

 

Thanks! Honestly, if Maxim X carbs were cheaper and easier to find, I'd have gone that route. Since these were free I'm not out any cash other than a couple of screws, so I don't have much to lose! Plus I enjoy messing around with stuff like this. I just hope the bike will run now.

Speaking of Guerrilla Fabrications, the guy who's helped me and gave me the set of carbs is tooling around on his own crazy creation at the ABATE Boogie, a big biker gathering here in IN. It's a cheesy minibike he shoehorned a 14hp V-twin lawn mower engine and torque converter into. He had to fabricate all brackets/mounts, jackshaft, shorten the wheelbase, raise the top of the frame, change the headtube angle, etc. He threw a rusty old Sportster tank on top for good measure, too - calls it the 2010 Hardley-Ableson Murdercycles Death Trap!

 

Getting them to fit is going to be one-half the battle.

Coming attractions:

The right Jetting of the Carbs you are working-on to get to fit is Phase Two.

That the Carbs are Mikuni is a blessing. Mic's are easy to Re-Jet.
Getting the Jets OUT of the Old Carbs might be a fight.
Before you get involved inn that fight, ... have the right weapons.

Screwdrivers that FIT the Screw SLOTS of the Jets with GREAT Precision.
Have a tool that fits with such great precision that the Whole Jet Body HAS to turn ... Not just the Slot's Wings.

Swap all the "Exchangable" Jets.
Fuel, Air, Vents and Pilot Air and Breathers on the Horn at 3 and 9 O'Clock.

 

Initially I'm going to give them a shot as they are now. Like I mentioned, hopefully the increased airflow will offset the increased fuel metering. Either way I may as well establish a baseline to go from, and I might luck out.

 

Let the craptastic bracket creation begin! I finished one today and started working on the pattern for the second. It's definitely not perfect but should be just fine where it matters, strength and mounting holes.

I also got the rest of the hardware in that I needed - some new socket head capscrews to attach the brackets, and a shortened nylon washer for the throttle shaft. The latter was turned down on a lathe at work thanks to our machinist.

 

yowza!

 

It might be easier to construct a PVC pipe airbox instead - especially if you will be taking the carbs out repeatedly for re-jetting. Probably would let the carbs work in a broader RPM range too as it would provide some "velocity stack" air to the carbs.

 

Sorry for the bump, but figured I'd follow up in case someone found this later. I gave up after realizing that the #4 carb's float bowl hits one of the water pump cover's mounting screw bosses that sticks out of the engine case. So it's temporarily on hold, I'm looking for other carbs I could use or for some spacers to get the carbs just a bit further away from the engine.