Help Find A Cure for Crazcnuk's bike?

[Crazcnuk]

I've checked all the advance mechanisms, just replaced the coils, wires, caps. Checked the connections to the TCI.

[egsols]

The only other peculiarity is that my idle screws are only out about 1/4 turn on 1 and 4, and 1/2-3/4 on 2 and 3. This should be a very lean setting, I would think

I would think that as well. Mine are 1 1/2 to 2 and I thought that was somewhat lean as most carbs I find are out 2 1/2 to 3.

The new tubes may help and once in, I would go back to the 115's or even possibly the 110's to start the testing.

Nothing new on the oil burning?

[psycoreefer]

I hope your perpared to do a fair amount of carb tinkering because the tubes/needles from Mikes xs are not for our bikes. I would have warned you earlier but you never said where you ordered the new tubes from.

Yes they will fit the carbs but they are like 10 steps richer then our stock tubes and needles. They can be made to work though. I read a thread some time ago before I ordered new tubes about someone who had gotten the Mikes tubes to work. You may want to search for that thread and use his setup as a starting point if your bikes are "close" in modifications.

[egsols]

Further to what psyco said, here's one link worthy of a read.

http://www.xs11.com/forum/showthread...s&pagenumber=1

[psycoreefer]

Thats the one...

I just glanced over it but I didn't see any mention of what jets he ended up using.

I'm not trying to rain on your parade or anything but you will have to fiddle with it. I can say that my midrange and top end improved 75% when I put in new tubes, however mine were NOS so I didn't have to re-jet. I'm sure most with higher mileage XS have tubes that are no longer round and leaking a bit of fuel.

As for your 7k issue it almost sound to rich, I've heard that if it pulls harder when you let out a bit on the throttle thats an indicator of too rich. Doesn't really matter because you'll have to start over with the new tubes and needles.

Any progress on where the oil's escaping at?

[Crazcnuk]

I think that it is running rich too. But I think that is because I have the 120's in it right now.

It almost seems that, originally, it was weak at the top because of the coils, but now I have created almost the same problem with too large jets.

I was thinking of going back to the 115's and putting in the new tubes as a starting point.

These tubes/needles ARE NOS for my carbs. This is what my carbs came with originally.

I am hoping the orignal poor economy is due to the tubes being oval, and these will (help) cure it.

I would assume that these needles being richer are one reason this series of carb uses such small mains?

I could also replace everything and go back to the 110's as a start, but with my K&N filter and 4-2 aftermarket exhaust, I was thinking the 115's would be a better start point.

[dbeardslee]

Craz - The way you describe it getting to 7k and then getting flaky sure sounds like fuel volume to me. Had similar problems with mine that wound up being petcock related. Do you notice any difference in the way it runs when set to 'prime' or with the filler cap cracked open? Carbs may need attention also, but I'd make sure your gas is flowing like it should.

[psycoreefer]

Have you pulled your tubes and checked the numbers on them? I was speaking from my experience with my 79 which has x2 tubes. I've just looked on the cross reference site and I now see that the 80 and later models use a different tube then the earlier but it still doesn't match the numbers for the 650 tubes. I also don't know what differences there are between Canadian and US models. If your tubes are 366-Y0 then I'm sure you'll see some improvement after the switch.

I'd also like to tell you that you lucked out because at 12.00 each you got a steal. I had to pay more then double that for the NOS ones for my carbs, which are discontinued.

I always thought the later carbs used smaller mains because the pilot got its gas directly from the float bowl vs the earlier carbs that had the pilot getting gas through the mains.

[Crazcnuk]

Ok, tooke the carbs apart, again.

Mine has 300-X2 needle jets w/4 large holes, 2 small holes.

The new ones are 336-YO with 18 small holes in them.

The needles are 5GLZ18 w/ 5 adjusting steps.

should be fun

[3Phase]

Needles and Jets

I hope this helps instead of adding to the muddle.

I was looking for jet needles and needle jets this morning and I found a Excel spreadsheet XLS file somewhere in Hungary with a list of Mikuni Jet Needles . You need the Excel Viewer to look at it, but it has your needle and its dimensions listed.

Motorcyclecarbs.com shows your Y0 needle jet. Their application part number is for a 1978 XS750. That's probably not the only bike that uses a Y0 jet, but there it is.

I have not yet found a list of Needle Jet dimensions to compliment the Jet Needle dimensions so they're just alphabet soup to me until I find them.



Regards,

Scott

[3Phase]

Oddly enough, Motorcyclecarbs' applications/part numbers seem to list a Type B (bleed) Y0 and a Type P (Primary) Y0. Our bikes are supposed to use Type P, and I could very well be misreading the list so take it for what it's worth.

Cyclewearbles.com has an image showing the difference between Type B and Type P but, wouldn't you know it, I can't find the link now.


Regards,

Scott

[Crazcnuk]

Ok, went back to my supplemental service manual (G, SG).

It states that the 3J6-00 carbs are from a 1980 SG Special.

These carbs SHOULD have : What I DO have:

110 main jets 1-4 : 110 mains 1-4
42.5 pilot jets : 45 pilot jets
#25 starter jet : ?
#140 Air Jet, main : ?
#185 Air jet, pilot : 185 Air Jet, main
#135 Throttle Plates : #135 Throttle plates
X-2 Needle valve : X-2 Needle valves
5GL16 Needles : 5GLZ18


So, if you notice the pilot jets are bigger (45), but the mains were stock?

I am wondering if these carbs weren't rejetted somewhere back in prehistory, and then ended up on a different bike, where they put the stock mains in but left the oversize pilot jets in...

Keeping in mind that the bike has always run best in the mid range (3500-5000). What difference is having these pilot jets in there, as far as fuel economy is concerned?

I also dropped the floats from the 25mm std setting to the 23mm Special setting.

[DiverRay]

The pilots will cause a rich running condition at low RPM, and the mains take care of the mid to high. If the bike starts with no or just one click of the "choke" when COLD, you need to go down one on the pilots.
JMHO

[3Phase]

I also dropped the floats from the 25mm std setting to the 23mm Special setting.

There is no Standard or Special float setting. What type of floats did you have in your hands when you set the float height?

1978-1979 rounded brass floats with threaded needle seats, a washer, and solid metal needle are set to ~25mm

1980s and later rectangular black plastic floats with press-fit needle seats, o-rings, and a rubber-tipped needle are set to ~23mm

Unless you tried to set black plastic floats to 25mm or brass floats to 23mm both types of floats allow the same fuel level in the float bowl.


Regards,

Scott

[Crazcnuk]

These are the black plastic floats, and I got the 25mm from one of the other few hundered posts on this.

Basically, right now it is back running like it used to, no bottom end bobble, good through the mids, and then it runs out of power at about 7k in 4th. 5th has no power up there either, all it does is frop the rpms when you shift, it will not accellerate.

I don't know why they would have put 45 pilots in and left the stock mains, that one just baffles me.

I won't know if there has been any change in fuel mileage until I can go somewhere.

Funny part is when I first got it on the road, it would pull right to redline in all gears. I could keep up with Derwat's Special within a length or two.

Only problem is it was getting less than 20mpg at the time.