Carb Question

[krakum1967]

So, I am trying to get my rebuild dialed in. When the petcocks are fully opened, the bike runs incredibly rich. When I shut the petcocks off, the engine balances out, runs fine, and generally gets better until the petcocks are turned back on to allow for more fuel. But when on, it chugs, it wil not idle, and runs choppy with thick fuel rich smoke. My air idle screw are at .75 turns out, I am running one size up on jets with pod filters. I went one up on the main and pilot jet.

My floats out of whack? What should I look at? They have been stripped and cleaned, but I cant get them dialed in.

Thanks

[Schming]

Sounds like your floats are set too high and your flooding the intake tract and may also be flooding the crankcase with raw fuel.

IMHO you need to remove the carbs and check/reset the float height at the spec for the specific carbs used.

Also there are no air idle screws on the CV mikuni carbs, the adjustment screws on top front of carbs control idle fuel feed

[motoman]

So, I am trying to get my rebuild dialed in. When the petcocks are fully opened, the bike runs incredibly rich. When I shut the petcocks off, the engine balances out, runs fine, and generally gets better until the petcocks are turned back on to allow for more fuel. But when on, it chugs, it wil not idle, and runs choppy with thick fuel rich smoke. My air idle screw are at .75 turns out, I am running one size up on jets with pod filters. I went one up on the main and pilot jet.

My floats out of whack? What should I look at? They have been stripped and cleaned, but I cant get them dialed in.

Thanks

Float needles not seating properly, floats not set right(x8) and idle mixtures set too lean trying to compensate for overfueling. Put stock jetting back in for a baseline plug reading BEFORE just asumming jumping up in jet sizes.......specially the pilot jets. If changing pilot jets, make sure replacements have same hole configuration and that ANY jet replacements are in fact GenuineMikuni, not wanna'be copies.

[krakum1967]

The crankcase is fine, but I agree on the intact track, I pulled a pod, there is moisture in the venturi (front part that should be dry). Jets are genuine, trusted source, and have used their OEM Subs before, they are good. But these are genuine. The stocks were rich too, I have been reading the baseline, this pattern has followed all the way through my tuning attempts. I have the idle cranked up as it will not hold idle, but I cant get it to settle in to synch effectively. But I will pull the bowls and recheck the specs. They lied up when I cleaned them, but that does not mean they are set correctly.

ButI think we are on track with the float height. A few seconds after shutting off the petcocks, it smooths out, idles, and revs great, runs like this for 15 to 30 seconds, and loses the fuel and dies.

So what is a good baseline setting for the idle adjustment screws. I have read that this circuit is different. How many turns out should the screws be out? My manual says don't pull them, but I need a baseline.

I am also doing the coils for good measure cause they are 30 years old, and the plug wires are crud.

[Ken Talbot]

...I have the idle cranked up as it will not hold idle, but I cant get it to settle in to synch effectively....

This says to me that your carbs are dirty, especially the low-speed circuits. Get them clean then start working through float settings, screw adjustment, syncing, etc. Lots of good articles available in the tech section.

...I am also doing the coils for good measure cause they are 30 years old, and the plug wires are crud...

One thing at a time - leave the coils alone until you get the carbs clean and properly sync'd. The more variables you mess with at once, the more you end up chasing your own tail.

BTDT

[BA80]

So, I am trying to get my rebuild dialed in. When the petcocks are fully opened, the bike runs incredibly rich. When I shut the petcocks off, the engine balances out, runs fine, and generally gets better until the petcocks are turned back on to allow for more fuel. But when on, it chugs, it wil not idle, and runs choppy with thick fuel rich smoke. My air idle screw are at .75 turns out, I am running one size up on jets with pod filters. I went one up on the main and pilot jet.

My floats out of whack? What should I look at? They have been stripped and cleaned, but I cant get them dialed in.

Thanks

Most definitely sounds like a float setting or float valve issue. too much fuel in the bowls.

Make sure none of those old brass floats are leaking and filling with fuel. I've been through that before, all it takes is one. I accidentally discovered it after the umphteenth time of tearing the carbs down and one sloshed when I shook it. Replaced that one float and it was golden.

[MPittma100]

Rich

After rechecking/adjusting everything, do not put the carbs back on the engine. Hook up a fuel source to the carbs while on the bench and wait to see if fuel is running out of any of them. Fix that problem if there is one, saving a lot of time and effort prior to installation on to the engine.

Note: you can use your tank and a tee to accomplish this.

[D0wn5h1ft]

Do the "upside down test" too. With the float bowls off, turn the carbs upside down and blow into each of the lines. The weight of the floats should shut off each float valve and no air should pass. If it does, it means you're leaking and it's going to run incredibly rich. (I just went through this with my bike).

[Schming]

The crankcase is fine, but I agree on the intact track, I pulled a pod, there is moisture in the venturi (front part that should be dry). Jets are genuine, trusted source, and have used their OEM Subs before, they are good. But these are genuine. The stocks were rich too, I have been reading the baseline, this pattern has followed all the way through my tuning attempts. I have the idle cranked up as it will not hold idle, but I cant get it to settle in to synch effectively. But I will pull the bowls and recheck the specs. They lied up when I cleaned them, but that does not mean they are set correctly.

ButI think we are on track with the float height. A few seconds after shutting off the petcocks, it smooths out, idles, and revs great, runs like this for 15 to 30 seconds, and loses the fuel and dies.

So what is a good baseline setting for the idle adjustment screws. I have read that this circuit is different. How many turns out should the screws be out? My manual says don't pull them, but I need a baseline.

I am also doing the coils for good measure cause they are 30 years old, and the plug wires are crud.

Pull your carbs, read this: http://www.xs11.com/forum/showthread.php?t=36017 and follow all directions, don't take any shortcuts cause We'll be eyeballin' ya, and you should come out with a fine running set of carbs

Also 1 1/2 to 2 turns out from LIGHTLY SEATED on the idle mixture screws

[D0wn5h1ft]

Pull your carbs, read this: http://www.xs11.com/forum/showthread.php?t=36017 and follow all directions, don't take any shortcuts cause We'll be eyeballin' ya, and you should come out with a fine running set of carbs

Also 1 1/2 to 2 turns out from LIGHTLY SEATED on the idle mixture screws

They will too, trust me. You'll get all sorts of flak, like I did, if your stuff isn't ship shape and bristol fashion. Worst thing is to find out that your carbs were dirty after you've asked for help...

[TopCatGr58]

Hey there Krakum,

I reviewed your other posts, and saw that you have had quite a bit of work done on the bike. When you start a new thread about a new problem, we don't necessarily remember stuff about what you might have told us in previous threads. SO...it would be good to recap the work you've done to the bike, along with the intake and exhaust mods.

IIRC, you said you did a big topend job, new pistons, rings, head/valve job, that you have those fancy 2 into 1 intake filters, and a 4-1 kerker exhaust.

I disagree with Mike regarding not doing the coils. Many on here have found that their low rpm stumbles and poor idles were actually IGNITION problems, and cleared up once they had good strong sparks! I don't believe that the problems you are having are related to the spark, but having good strong coils can help remove that as a possible fault.

I didn't read all of your previous posts, so I can't recall if this bike is relatively new to you or what the history of it is? The folks have mentioned a few of the more common problematic areas we have in trying to get these carbs tuned and working right,ie. incorrect float height, leaking floats, the possibility of broken pilot screw tips that start at 1.5 or so turns out from the "gentle seat", as well as possibly not as thoroughly cleaned carbs....the pilot jet circuit, as well as true Mikuni pilot jets.

Another thing I'll point out is to be sure that the upper carb T's are connected to OPEN vent tubes, not capped off, they are the float bowl vents, and if clogged/capped, the floats will not "FLOAT"/equalize and the carbs WILL flood.

From your description, as others have said, sounds like the floats are NOT set to the correct height because they are running rich, until you shut the fuel off, and it runs down to a more proper level then it runs right! Be sure you're measuring from the carb body surface, not the gasket, and at the top portion of the floats, the 25.7mm height. Keep at it!

T.C.

[krakum1967]

Carbs are off, I am painting the skins too, and I have to make some base gaskets for the petcocks. I like them, but have a very small stubborn seep.

Anywho, one cylinder was running grey the other are black, one is fouled, the oil is fine, but its due for dropping as it is the break in oil

[Newbee]

What jets to adjust

http://www.youtube.com/watch?v=y836ZPjvoMI Thought this was a good video what jets to adjust.

[krakum1967]

Yea my pilots are way out of spec, Ordering correct ones, recleaned and scrubbed and took brass gun bore brushed to the jet seat and main venturi, replaced the slide springs, checked the needles settings and set the air hole on the slide to have a clear passage on each slide, cleaned the slides, etc....

So now I wait for new pilots and paint, will post pics soon. Going to do some tail trimming and light replacement....ahh, 6 more weeks till riding season.

[MarkD]

Not sure of all the reading of posts you've done, Krak, but only order genuine Mikuni pilot jets. Long story short, it's the only way to get correctly operating and designed jets. Been there.