Carbs - Carburetors

[xjwmx]

What is the point of the plug for the pilot jet.

There's a drilled passage connecting the area behind the main jet to the pilot jet area. With the plug, gas goes through both jets before it comes out the pilot jet. Incidentally, I seem to remember there's a foot in the bowl that holds the plug up, no worries if the plug feels loose in the hole. There's a small flat on the plug that ought to be turned the right way. The bowl also blocks the float pin, so it doesn't really have to be in tight either.

There's a BS34 version that doesn't use the plug and there is no passage connecting the two places. I had one on an SR250 (a fun little bike!).

I have a 1983 Heritage Special (USA) it has an idle sync screw between the carbs. ...How do I adjust it so I can adjust both carbs idle from the carb on the left side?

Just read the vacuum from both barbs and adjust the screw between the carbs till the right matches what you read on the left. It's pretty critical..you can feel just a few degrees difference. If it's off it will feel like it does when it's starting to run out of gas. Your vacuum gauge might just swing crazy, because the vacuum isn't steady and isn't supposed to be. Tighten a little clamp (vice grip, etc.) on the hose until the needle barely moves, then allow it 10 sec. or so to settle down before you take the reading.

 

[xsjohn]

Make the right look like the left.......fish tank control valve to trim the vacuum.....when you are all done with everything including setting the mix screws correctly then connect the barbs with some 3/16" ID tubing....Pete reminded me of that and it works to relieve any imperfections in tuning at for a better idol and low and cruise speeds...

xsjohn

 

[xjwmx]

.....connect the barbs with some 3/16" ID tubing....Pete reminded me of that
xsjohn

Does he use a "T" to get the vacuum to the petcock then? Do the vacuums add together? Does it suck twice as hard? Will it blow the cock with that much sucking?

 

[xsjohn]

Forgot.........can't do that with the vacuum petcocks.....a small bit of the charge goes back and forth in the tubing ........yamaha had a model that this was built in .....can't remember it right off hand.......the vacuum petcock can be blocked off in the rear by removing the diaphram and cutting some inner tube or gasket witha hole in the center....(it's been so long Ican't remember all this)............no off then though or replace with manual petcock which is the best..........

xsjohn

 

[royxxx]

Mikuni BS38. book says each carb is fed by it's own petcock & the carbs are linked, these don't have a link, any info' on this? Bike IS '76 xs500. Thanks.

 

[mbvanhorn]

Hey guys, I have two 650s but am working on my 81 xs400... Cleaned the carbs but for some reason the bowls arent filling up. i tried three different tanks...which all gas flowed through each one but the carbs wouldnt fill. Floats all moved freely (cant say i set them to specs), blew air through the fuel receptor on the carb and it blows air through the float needle in the bowl. has new carb holders with the two vacum ports that i capped. racked my brain to no end. please...someone make me feel dumb. Im outta ideas.

 

[inxs]

- wasp built a nest in your fuel line?
- in line filter blocked?
- float needle valve stuck?
.......

 

[mbvanhorn]

nope, nope, and nope.

 

[Sundie]

you capped the vacuum ports? The ports that let air escape from the bowls so that fuel can fill them?

 

[bloodthirstysystem]

try it with the gas cap off. i have my vacuum barbs capped too but my gas cap lets air in while the fuel is flowing. when i turn the petcock to "off" the gas stops in the fuel lines.

hook up some clear hose so you can really see what's happening

 

[Sundie]

sorry, i just realized you were talking about your carb holders. My bad.

 

[mbvanhorn]

-tried gas cap open. no joy.

 

[XSLeo]

If your float level is set to far off the float valve may not be opening. Set the floats to what your repair manual calls for.

 

[Pyrobooster]

get vacuum gauges on them, run the bike, turn the screw until they match.

If it's backed right off, the bike must not run very well, and vibrate like crazy.

My bike vibrates like crazy, it will literally move feet backwards on the center stand, and runs like crap. I can only get the right side cylinder to fire regularly. I have a 1980 Special, where are the sync screws located? I used a spark tester so I believe I have spark, also the plugs are new, the bike only has 3500 miles (so I believe I have compression, I finger tested it) and starts up with little effort, but does not want to keep running, it needs constant throttle. Also when it is set to "PR" on the petcock gas leaks from the left side carb, even on center stand. Also I cleaned the carbs and I think I have it all clean and clear.

Any help would be greatly appreciated it's my dad's old bike, and I would love to ride before the Midwestern winter sets in.

Thank

 

[mrkil]

Sounds like the float is stuck on your carb.

 

[Pyrobooster]

It seems to move freely like the other side, but obviously I can't see inside to see if it moves when there is gas in there. How can it tell if the float is stuck? I did notice that when I took apart the left side carb that the slide and needle felt the slightest bit resistive when I removed it, but very very slight.

 

[retiredgentleman]

Pyrobooster;

The pilot circuit is partially blocked. Remove tha carbs to the bench. Turn the carbs upside down. Remove the float bowls. Remove the rubber plug that covers the pilot jets, then remove the pilot jets. If you view the pilot jet with a good light source, you may or may not see light through it. Spray some carb cleaner into the jets and then use a finewire to probe the jets until you can see light and a fully clear orifice.

With the carbs back on the bike, you should do an adjustment of the mixture screws using the "dead cylinder" method.

There is only 1 sync screw, and its located between the carbs where the throttle shafts meet. Use a u-tube manometer to accurately set the sync.

 

[Pyrobooster]

Great, that is a very clear explanation. I will try that right as soon as get my new brass fuel line carb connecter from mikes. Thanks a lot!

I am not aware of the "dead cylinder" method, would you enlighten me, or tell me where I can find it?

 

[retiredgentleman]

Great, that is a very clear explanation. I will try that right as soon as get my new brass fuel line carb connecter from mikes. Thanks a lot!

I am not aware of the "dead cylinder" method, would you enlighten me, or tell me where I can find it?

Click on "Tech" at top of page...............click on "Carb manuals'...........click on the first link. Lots to read, but read it all, maybe several times.When adjusting the mixture screw (with only 1 cylinder running), reduce the rpm as much as possible with the speed screw, so that you can detect a change in rpm.

 

[Pyrobooster]

Great thanks a lot, can't wait for my brass fuel linkage to come from mikes so I can give it a shot