Ninja EX500 carbs on an XS650?

Float height - 17 mm or with fuel level gauge .5mm above gasket surface

Checking with a piece of tubing would prove your float level is accurate.

Have you tried anything different than stock on the needles?

What do you call stock?
 
Could be your tank vent is blocked. What needles are you running ? Put a hose on bowel drain and see how much fuel drains out. If fuel runs out and stops tank not venting. You should at least put the JJJ in the stock don't work.
 
Week before last I ran a 4hr trip on my xs with my son on his zx-7 and the only issue I ran into was I ran out of gas (that is what I get for having no reserve) but at least I now know how far I can run on a tank of gas!! I agree with scabber sounds like you may have a poorly vented tank/gas cap and you need to change the needles. You can make them run but you will get much better performance from a jjj or one of the others that are being used.
 
well I was out on on the tail end of a trip when this all happened - which is why this is so confusing since it just started happening now - but I could only do so much trouble shooting on the side of the road. here's what I know, or think I do..

Not the gas cap because if I remove the hose and just turn on the petcock the gas rushes out - and I ran it with the cap open, no difference.

Needles are certainly a possibility and I have a set of jjj's - just have yet to get them in.

The vent between the carbs is open, might have got clogged though...? good suggestion there.

Thought about the filter too, I'll pull that out temporarily and see what difference it makes.

I'm back now though so I'll run through the list and see. It's just strange that I should get almost 600 miles in before this happened. Most of this trip was on 75mph roads so I was always at 3/4 and above. Only bit of info left is I was at 8,000 to 12,000 feet most of the time.. maybe atmospheric pressure is playing in to this? I only had it happen once down here in town, 5,280ft, and that was flat out on the highway. This trip it would happen anytime I had to pass someone or just maintain a high rpm for an extended period of time
 
Had a bike once where the bottom of the fuel screen inside the tank was gunked up. When you ran the tank down it would start running like crap because gas couldn't flow through the bottom of the screen. Put more gas in it and it ran well again because gas flowed fine through the top of the screen.
 
This thread has grabbed my attention, but I have a TX750 vs. the 650 and have a few questions. Has anyone used these carbs with a 650 taken to 750 (sorry, might have missed that reading the thread)? Perhaps more importantly, I know that switching from the BS38 carb holder to the BS34 is needed, but what is the spacing between the carbs? I'm concerned the intakes on my cylinders will be too wide to keep the EX500 carbs mounted together, opening up an additional can of worms for the conversion. And if the width is correct, is there a BS34 mount straight mount that would fit the early 650s that came with the BS38s? I only see angled ones available at the JBM site.
 
Brian902 said:
Sailor,
You just need to read this thread. That info is on the first page of posts.
Click to expand...

My bad, you're right, the info is there in post #13, 120mm. I'll claim brain fart, as I was looking to confirm the need for new carb holders to fit the 34s vs. the 38s and just dumped it.

Any word on the straight 34 carb mounts, or would putting the angled ones available from JBM work? I'm assuming that would tilt the carb body, possibly affecting the float level??
 
Sailor, you need the 34 mm carb holders but just about any make will do. The JBM's are great and a bit stronger but these carbs are so light that almost anything will do. So in this case even some of MikeXS will work. You will be amazed in the weight difference.
 
I have Mike's 750 kit on my 75, the carbs work great.
On the carb spacing does the TX750 run the same spacing as the XS650?
Is so they should work fine.
On the angled carb holders, the very early 650's had straight carb holders, these held the unlinked carbs pointing out at an angle. They changed the way the enricheners worked, early a metal strap hooked the two enricheners, one on each carb to one lever.
I'm not sure just what year they changed, 73 maybe, they used one enrichener one the left carb with a rubber hose to the other carb.
Once they made this change the carbs needed to point straight back, They angled the holders to accomplish this.
I don't know if the TX750 did the same.
Leo
 
Brian and Leo thanks for the information. The TX750 uses the single enricher on the left with the connecting tube, so the carbs point straight back, but it also uses the straight mounting flange the earlier 650s used. I have the straight JBM 38 mounts on at the moment, but don't see a straight 34, nor did I see a straight 34 at Mikes. Would this one work if I need a straight flange even if the bolt hole are 1.5mm larger? http://tinyurl.com/o2dsek5 I need to check the mounting distance to see if it's 120mm center to center for the carb. If it's not, are there other carbs that could work with the JBM 38s I have installed? I'm asking in part because I recently rode an '80 Guzzi 1000 on a nice loop and it got almost twice the mpg on a larger engine than I'm getting from my BS38s.
 
Well rats! It looks like the 750 has 125mm center to center so a ganged EX500 carb set won't work. It's too bad, since there is a lot of good information on jetting and set up for this combination. Rather than hijack this tread, I'll start another to see about alternatives.
 
What sort of MPG's are you getting. On my 750 kitted 75 on a ride poking around the back two lanes. averaging 45 to 50 mph I get around 55. Pick up the speeds to around 55 to 60 it drops to around 50.
Back and forth to work around 45.
If your mileage is much worse you need a bit of carb tuning.
Leo
 
MPG has dropped to 32 or so. The best it's been has been around 42. As documented here in other threads I've had the carbs off several times, replaced the butterfly seals, new jets and float needle, adjusted the floats, and tuned using the dead cylinder method. The needle and jets are stock size per the owners manual and shop manual, and the exhaust is stock. The only change is using two round Triumph air cleaners "ovalized" into the airbox. As I mentioned, the bike runs nicely with no surging or hesitation, just the MPG has dropped off. From reviews back in the day the low 40s sounds about right. It would be nice to have a little more range between fill ups which is why I was intrigued by this thread. I have noticed a bit of wetness in the overflow tubes, so suspect the float height or needles aren't up to snuff. I hope it's not the overflow tube failing as mentioned in the carb guide.
 
So I've got a good clean set on the way...I've read the thread over and over but want to be sure about what I'm getting. Here is my setup:

'78 xs with 700cc, shell #1, mac 2 into 1 with torque cones.

I've got a set of bs34 holders/gaskets/clamps from JBM.
Jets r us: 38 pilots, 138 mains, gjh needles.

I'll play with the throttle set up and enrichener. Am I missing anything? Any suggestions for a newb?
 

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