Quick carb question and notes...

[cywelchjr]

If it passed the ATF draw test it would prove my point. Try and stop me.
Over the years Ive watched all kinds of grief posted about those o-rings.

I guess the world would end if it was a fact they aren't necessarily. And the sky would fall. Galileo spent time in prison over that round world idea. I feel lucky.

I'm really surprised someone hasn't found a way to put them in the early carbs And scoffed if anyone questioned their efforts. I question pretty much everything, never been a good sheep i guess. When I'm wrong I admit it. Just don't follow well with my brain turned off.

My XS400 has the same carbs, and with the o-rings almost gone, it could NOT be tuned to idle properly no matter what I did. I replaced the o-rings (you can get them and the washer and spring from MikesXS as a kit, it in part I believe to keep water and stuff out as well since that's down in that well that stuff can get down into, but it WILL suck air, and not sucking ATF doesn't tell you anything about sucking air, as air will go through where ATF will not, being that ATF is far far far thicker than air. But I speak from experience when I say that those being bad does affect the tuning ability of the late model carbs. It's well known in the 650 and 400 circles, as it's one of the common causes of an inability to get a solid idle on those models with the late model Mikuni carbs.

[SFerinTEXAS]

o-rings almost gone, it could NOT be tuned to idle properly

Thanks for another parameter in the test.

[SFerinTEXAS]

How about another crazy notion I have that will stir the pot.Side bleed holes in the pilot jets. My puzzler started here when I cleaned the XJ carbs and found no holes. Suspecting wrong jets POed started checking and found most likely original. Been a lot said about those holes or lack of being an issue.Studied a 79 body on my desk and remembered the caveat under the jet chart at MikesXS

Note: BS 30/96 type Pilot Jets WITH Side bleed holes
holes and those without side bleed holes are
completely interchangeable.

and having sprayed, and cleaned the 79"s so many times with no evidence of any passage (nor obviously visible on the body)(nor any flow chart i've seen) to any area those holes could go to. I think they are there because these jets were used in some earlier design and have no function in fact in these carbs, Again untested theory but on my TO DO list someday. Just have to seal the tip of a holes jet and seat it and blow air in the tunnel under water.Am aware of the main tunnel passage and will deal with that.Guess I have an over active puzzler . Wonder if there's a med for that
I do agree as with those tiny O-rings that without a conclusive test all things should be replaced as originally installed.

[Ken Talbot]

I really doubt those o-rings are essential.I think they are mainly a by product of the stricter emission mentality of those years.

I think the 'potential vacuum leak' scenario is overplayed too. However, I do think the slight squashing of the o-ring around the screw gives a bit of friction to keep the screw where you set it. With heat and cool cycles and vibration, it seems to me the screw might tend to wind itself in or out a bit.

[SFerinTEXAS]

I think the 'potential vacuum leak' scenario is overplayed too. However, I do think the slight squashing of the o-ring around the screw gives a bit of friction to keep the screw where you set it. With heat and cool cycles and vibration, it seems to me the screw might tend to wind itself in or out a bit.

Good point I had not considered. The spring on the early screws is much stiffer and a completely different effect. Set my puzzler in motion again. You the man.

[cywelchjr]

I think the 'potential vacuum leak' scenario is overplayed too. However, I do think the slight squashing of the o-ring around the screw gives a bit of friction to keep the screw where you set it. With heat and cool cycles and vibration, it seems to me the screw might tend to wind itself in or out a bit.

Y'all are welcome to discount the experience of many riders with the same carbs on 650's and 400's and myself where those o-rings were damaged or very backly worn (almost paper thin) and the carbs were basically untuneable at idle, doing nothing more than pulling the mixture screws and replacing the o-rings caused the carbs to be easily tuned at idle. They DO suck air if those are not there as the screws don't seem to seal all that well, and need those o-rings being squished by the washer against the screw to provide a air tight seal. I don't know exactly what's happening, I just know that bad or no o-rings cause a problem that nice new o-rings fixes. It's a cheap easy fix, even from MikesXS the kits are only a few $ per carb, and you really only need the o-rings which can be had from several places, and I think can use several sizes as long as they fit over the screw and under the washer.

[petejw]

How about another crazy notion I have that will stir the pot.Side bleed holes in the pilot jets. My puzzler started here when I cleaned the XJ carbs and found no holes. Suspecting wrong jets POed started checking and found most likely original. Been a lot said about those holes or lack of being an issue.Studied a 79 body on my desk and remembered the caveat under the jet chart at MikesXS and having sprayed, and cleaned the 79"s so many times with no evidence of any passage (nor obviously visible on the body)(nor any flow chart i've seen) to any area those holes could go to. I think they are there because these jets were used in some earlier design and have no function in fact in these carbs.

the stock pilot jets for the aussie 81rh are 40 with no bleeder holes,
ive bought the aftermarket jets that have been discussed not only do they
have 8 bleed holes but i measured the centre hole and it was closer to a size 50 than the stated 42.5 thats stamped on them which causes them to run rich.

i tried searching to see what the actual differences are between the pilot jets that have bleed holes compared to the jets that dont, it was a late nite and i didnt save the page and my memorys starting to fade but it had something to do with the holed jets running leaner through out the later stage of the idle circuit, the rh is also fitted with adjustable needles and the emulsion tube is also different to the corresponding 81 us model, if that has anything to do with it, i dont know.