Help Find A Cure for Crazcnuk's bike?

[Hawkins]

you can get intermediate needle settings by moving the washer to the other side of the clip. It only has an effect on the lower side of the clip (raising the needle). On the upper side it's for storage only. Worked for me.

[Crazcnuk]

I put the needles back in the middle spot, for now. Haven't had a chance to take it out on the road, to see what difference it made.

Right now, around town the bike is purring. It is smooth from idle to 4500rpm or so. It starts better than it has in quite a while, and it now likes the choke when cold, again.

Hopefully, I will get to do a road run in the next few days.

I also put the HID headlight conversion on, holy mackeral, what a difference THAT makes!!

Oil consumption is down, but still higher than I would like. I used about 1/2 liter in 350kms.

[egsols]

Craz,

FWIW, I just checked the needles that came in the kits for my 79, they are 52.5mm

Kits were 14.95 for mains, air jets, pilot jets, float valves, seats, bowl gasket and idle mix screw, spring and washer.

[Crazcnuk]

Mine are 50.5mm (according to the chart). So what does that mean as far as running is concerned?

I did arun today, 150km (93m) used 10.5liters (2.76g) for 33.7mpg (US), 40.3mpg(imp)

This is with everything in stock configuration. Moving the needles to thier middle spot, everything stock except the K&N filter (recently cleaned).

Bottom end bog is back, feels like taking off in 2nd gear. mid range runs good, no top end. Bike can hit 140kph fairly easily, but struggles to hit 160kph (100mph). Loses speed on hills, and passes a little slower than my Neon.

[psycoreefer]

Originally posted by egsols
Craz,

FWIW, I just checked the needles that came in the kits for my 79, they are 52.5mm

Kits were 14.95 for mains, air jets, pilot jets, float valves, seats, bowl gasket and idle mix screw, spring and washer.

Not sure what kits you got but make sure you compare your new needles to your old ones. The kits I got the new needles were slightly longer and had a visibly different tapper. I could not get my midrange right with the new needles.

[egsols]

Hey psyco,

I got the kits from carbkitcapital.com

I really only wanted the float seats, valves and bowl gaskets but at 14.95 for all of it..I ordered them. I tried the floats and seats and didn't like them..poor quality in my opinion...definitely not NOS.

I never compared the needles to what I have but maybe next time I take the carbs out I will. I might use the mains as I'm running 140's right know and I think they are causing me to be slightly rich.

Craz,

Don't know what it means....all the specs I see for fixed\adjustable needles are for either US or UK models. The last US model for adjustable was the 79's, however, the UK models E, F and G used adjustable with the SG(UK) using a fixed needle. That is also when the models changed to the cross drilled towers where the pilot circuit and main circuit are shared. (IIRC)

I'm running the same tubes as you on my 79sf with a blanking plug in the pilot tower. On your 80 carbs is your tower capped or open?...that might make a big difference as well...I thinking out loud right know, but if the 79's are running the tower plugged with the 300 tubes could having it open cause way too rich???

[egsols]

Okay....I think I screwed that up....I'm running the 266 tubes in my 79 with towers plugged. My 80 carbs are running the 300 tubes with fixed needles and the tower open.

So...if you are running the 300 tubes I wonder if the adjustable needles match those tubes. I think the adjustable needles were only designed for the 266 and 301 tubes. The 266 and 301s have more holes (leaner) so they run with the larger mains 137.5s as opposed to the 300 less holes (richer) and smaller mains 110-120s.

My 2 cents worth.

[psycoreefer]

holes and rich/lean....

Maybe someone who knows a lot more then me will chime in here but I've never understood how the number of side holes in the Emulsion tubes could effect lean/rich.

My Understanding:
The holes are there to mix air with the fuel as it travels up the tube, emulsifying the fuel so that it will burn better and more completely. From this I could see the argument that more holes = leaner. BUT isn't the air that is mixing with the fuel already metered before it gets to the tubes. We have a "MAIN" air jet pressed into the front rim of the carbs right? And all the air has to pass through that jet before it can get to the emulsion tube, and if I remember correctly the holes in the emulsion tube are equal or larger to the size of that main air jet, so any one of those holes could flow more air then the jet will allow.

Summary:
I don't get it. At least with FI you can say an injector is open for x time with y flow, and know how much fuel is getting in there. Carbs are powered by magic!

[Crazcnuk]

In the spec sheet mine calls for the adjustable needles and the 300-x2 tubes.

However, the needles I have are not the ones that the spec sheet calls for. No idea why.

MikesXS says that 1980 Canadian model year BS34s used the adjustable needles for XS650s, but thier part number(s) are different that mine.

[Crazcnuk]

"I don't get it. At least with FI you can say an injector is open for x time with y flow, and know how much fuel is getting in there. Carbs are powered by magic!"

No magic involved, unfortunately, as that could explain the goofy way they work sometimes.

1720's technology, though, so you'd think we would have it mastered by now!

Basically, the carb allows fuel through the mains into the carb throat metered by the main jet.

Now, fuel needs air, but you would think that the air going through the air cleaners would be enough, as this is the air we are actually burning the fuel with at somewhere around 12-14:1.

Why they feel the need to add more air via the tubes is anyone's guess. Mixing the fuel/air should be accomplished by the air coming through the carb throat at 60mph. I can only guess that trickling raw fuel into the carb throat doesn't give it enough time to mix.

Having holes in the smulsion tubes would make it harder for the incoming air to draw the fuel up the tube. Picture putting holes in your soda straw.

So now, With the holes, the bike has to draw a lot more to get the same fuel. This means they would have to put bigger mains in every time you added more holes in 'the straw'.

Now. Which needles you have, ie longer shorter, should really make no difference to HOW the bike runs/pulls, but rather a difference as to WHEN, ie at which hand grip position. Raising or lowering the needles may make some difference at idle and maybe at wide open, but that's about it. Everywhere in between is dependant on where you hold the throttle.

Then we add in the effects of vacuum in the engine.

When you crack the throttle, it opens the butterflies, and drops vacuum to near 0, this in turn must raise the slides and needles opening the mains and allowing full fuel.

However, one would think that as the rpms go up vacuum would start to rise and let the needles back down? Or does the vacuum stay at near 0 as long as the butterflies are wide open?

Unless, all of this is predetermined, and, just like with a mechanical connection, every position of the hand grip is tied to a set amount of vacuum, possible governed by the main air jet, because there is no mechanical connection between the hand grip and the needles, the entire mid range is governed by vacuum?

It also seems that these carbs use a supplemental system. That is, each range supplements the range before it.

For example: In these carbs there is no shut off for the idle circuit. So the idle circuit is flowing full bore the entire time the bike is running, even at wide open throttle.

The pilots do not replace the idle circuits, but rather ADD (supplement) the already flowing idles. Then the mains do not shut off or replace the pilot circuit, but just add on to the lower systems, so that at full throttle you are running:

Idle on full +pilot Jets on full+ mains at what ever throttle opening you are holding.

This would explain why these carbs have to be tuned backwards. You have to get the mains right, then the mids, then the idle.

So when tuning, you test for mains, which is the combined flow of all systems. Then you set the needles, which just changes WHEN the throttles come on, ie; faster or slower, to get around flat spots. Then you just set the idle screws for best idle.

[psycoreefer]

Thats a good run down of how it works. I guess what I mean by magic is that there are so darn many overlapping variables involved that tuning is reduced to a bunch of WAG's that hopefully result in a good running bike.

Having holes in the emulsion tubes would make it harder for the incoming air to draw the fuel up the tube. Picture putting holes in your soda straw.

So now, With the holes, the bike has to draw a lot more to get the same fuel. This means they would have to put bigger mains in every time you added more holes in 'the straw'

While this is true for your "soda straw" its not the same because the air sucking in through the hole in your straw isn't metered first. Imagine one hole in your straw can suck in X amount of air requiring you to suck Y amount harder. Now put 5 holes in your straw but each can only draw X/5 amount of air (because X is constant, metered by the Main air jet). You should still only have to suck Y amount harder to get the same fuel flow as with no holes.

[Crazcnuk]

That's why I added 'possibly governed by the main air jet'.

The carb can only draw so much air from around the tubes.

I didn't write that whole thing to explain how they work, exactly, I was more asking if that IS how they work.

I am trying to understand how they function to better aid in what I try next for tuning.

I would like to take the airbox off, put a video camera in there and see how my slides react at various speeds.

Since wide open throttle is governed mostly by the mains, with the residual from mid and idle circuits, I assume I am either not getting enough fuel, or the slides are leaking and not going up where they should on one or more cylinders.

I still have to figure out why I have no top end power. I assume 'top end' as the mid range seems fine, but chances are I am low there too, and just don't realize it.

I have tried bigger mains, and it made no difference. Usually fuel starvation issues (from the tank) are accompanied by surging which I don't have.

Not sure what to try next.

My oil consumption seems to be a 2 factor issue; #1 how fast am I travelling, and #2 how much gas am I using.

The worse the mileage, the worse the oil usage.

I got my new electronic flashers, so now my LED signals and 4-ways work, whether the bike is running or not.

I had to remove my RLU, as it didn't work with my HID headlight conversion, but that was expected.

[egsols]

Since wide open throttle is governed mostly by the mains, with the residual from mid and idle circuits, I assume I am either not getting enough fuel, or the slides are leaking and not going up where they should on one or more cylinders.

Yes....I believe I read, in one of the mikuni sites, that the needles and tubes only have an effect between 1/4 and 3/4 throttle. Based on that they should not bear on idle or WOT.....UNLESS they are not going either all the way down or up. But.....and this is only a thought...if the needle is all the way up the fuel is still coming through the tube (via the main) right? If so then the tube should still have an effect on WOT, regardless of the needle.

Please keep in mind I am no expert, and like you, Craz, I am constantly trying to grasp at a better understanding of the antiquidated fuel delivery system incorporated on our 2 wheeled time machines.

[Hawkins]

My understanding is, when the needles are down, the tube is effectively sealed and the mains aren't contributing anything at all, it's only the pilot circuit providing fuel. As the needles rise, more fuel is able to flow from the mains. The transition from fully lowered to fully raised needles is the midrange. The taper profile of the needle combined with the geometry of the tube will determine how fast the midrange comes on. If either the needle or tube are worn, I would expect a rich idle mixture and maybe a boggy transition to full power, but WOT should be ok. If the needles aren't rising enough, then you wouldn't have a lean mixture at WOT. If that's the case then I would think you would see that on your plugs, and you would have les and less power on tap as you increased throttle.

You can check your needle diaphragms by pushing them all the way up then blocking one of the holes on the inlet horn of the carb - top oval slot i think.

The pilot circuit is always contributing fuel to the mix. Not sure at what point that becomes insignificant compared to the flow from the mains.

If it were me I'd be doing compression and leakdown tests to make sure the engine is sound.

But, I'm no expert either. One thing I do know though, if I keep this bike for another year I'm getting a set of those keihin cr33s.

hawk

[Hawkins]

..would have lean at WOT

sorry, typo.... if the needles aren't rising enough you would have a lean condition at WOT.