1980 xs11 special dies with throttle

[darylcaribou69]

I can get the bike into the upper rpm ranges if I hold the throttle open. It'll stumble through the mid range and smooth out on the top end. The trouble is the transition from the pilot to main circuit.

[skids]

https://www.youtube.com/watch?v=yYeS0fyTQp8

video of the bike

I watched the video and it looks like it dies when you shut the throttle down(?)

[darylcaribou69]

That's just my hand going back to the off throttle position after it stalls. Those are some frustrated hand movements. I noticed after I posted it. I put excessive play in the throttle to make sure that wasn't getting hung up while trying to diagnose this issue. I can rev it very little. It'll give me hope it'll keep climbing then it just dies with half a hair more movement in the throttle.

[skids]

So did you find out what kind of carbs you do have? Early, transitional, or later model carbs? Is the airbox appropriate?

[motoman]

I would also suggest that fuel levels in bowls are to high or to low. May wanna check those float levels when carbs are off. That initial float setting should be 23mm.

[darylcaribou69]

Pulled the emulsion tubes got 300 x-2 on it with the genuine mikuni stamp in between 300 and x-2. Also no passage between main to pilot circuit.

[darylcaribou69]

When setting the float height do I measure 23mm from where the gasket sits on the carb (the aluminum carb surface itself)? Or do I put the gasket down then measure 23mm (from the gasket surface)? Ive read both on these forums.

[DiverRay]

I use25mm from the bare surface. Make SURE all 8 floats are the same! Sometimes you need to work on it to get them all the same. Also, before you button it up, rotate the carb bank so the floats are down and then back up. Look as yoou do this for anyplace a float may hang up on something.
I ALWAYS mount the bank upside down and try to put some fuel into it, just to make sure there is no seeping or leaks. Lift each float slightly until you see gas, let go and on to the next. Leave for about 3 minutes to verify no more fuel is escaping from anyplace, like the seat "O" ring on the new carbs.

[Radioguylogs]

No gasket.

[darylcaribou69]

Update. I moved the floats to 25mm The bike seemed to do better. The problem area was more noticeable. I would open the throttle slowly and it would climb to between 2000 and 2500 rpms and stumble. When it started to stumble if I opened the throttle wide open it would skip this rpm range and rev awesome. Bike sounds really great. Anyway, this tells me that the transition from the pilot circuit to the main cercuit is my issue. My question would be, will the 120 main jet do that to It? Won't transition but runs awesome up top. Either thats the issue or the "professional" who rebuilt them put in the wrong needles? I am going to order the 110 main jets. The place locally who sells them wants $4.50 each. Can they be had for cheaper elsewhere

[jetmechmarty]

I am going to order the 110 main jets. The place locally who sells them wants $4.50 each. Can they be had for cheaper elsewhere

These are genuine Mikuni jets for $4.50 each? I use Jets-R-Us and theirs are $6.50 each. Accept no aftermarket jet unless you want to endlessly mess with your carburetors.

http://jetsrus.com/a_jet_kit_street/...ECIAL_1980.htm

[motoman]

Update. I moved the floats to 25mm The bike seemed to do better. The problem area was more noticeable. I would open the throttle slowly and it would climb to between 2000 and 2500 rpms and stumble. When it started to stumble if I opened the throttle wide open it would skip this rpm range and rev awesome. Bike sounds really great. Anyway, this tells me that the transition from the pilot circuit to the main cercuit is my issue. My question would be, will the 120 main jet do that to It? Won't transition but runs awesome up top. Either thats the issue or the "professional" who rebuilt them put in the wrong needles? I am going to order the 110 main jets. The place locally who sells them wants $4.50 each. Can they be had for cheaper elsewhere

That float level(25mm as opposed to 23mm) makes a huge difference as to actual fuel level in bowls. From testing different actual fuel levels in bowls myself, I found that 1mm of float settings makes for 3mm of actual fuel levels. In that related sense, that IS a whole lot of difference and DRASTICLY affects correct operation of carbs, specially when throttle opens a bit. My Venturer had this issue when at the Colo. Rally in Canon City some four summers ago. When back at home I 'hosed' each of the four carbs, which having the actual set screw in the side of bowls of each carb and IS correct way of checking actual fuel levels with bike idling, and found fuel levels to be at 6mm(to low) instead of the factory specified 3mm measured from casting flange. Correcting that to the 3mm made a new running bike out of it through ALL rpm ranges! In your bikes carb case, it is criticly important that ALL eight floats are set IDENTICAL heights! Also, when floats are mounted on hanger, it is important that all eight are perfectly vertical and not cocked to one side or the other. Any, even the slightest angled float can and will hang up on side of fuel bowl.....not a whole lot of room in there at all once fuel bowl is attached in place! What happens as far as fuel drawn up through pick-up tube if fuel level in incorrect one way or the other, I could write a whole chapter about, but this site, the room needed in order to do that is not real feasible. Hope this adds to your aid in solving the ongoing issue. If and when solved, would like to know what solved your bikes running correctly issue. It would I'm sure be interesting to others here also. I would also remove the timing cover, unhook that vacuum advance, and check that advance assembly rotates extremely free with no resistance or dragging. If it does not rotate freely, that assembly has to be removed, sprayed clean with Brake-Kleen, lightly oiled and re-installed. This definitely affects the vcuum advance and smooth accelerating of motor thru ALL rpm ranges!

[dansmith65]

If it idles fine and runs at WOT fine, then it still sounds to me like the mid-range air/fuel mixture is off.



To me, that sounds more like the needle than anything else. Perhaps the needle has the wrong tapper on it? Do these needles have clips on them? If so, maybe it should be moved up or down.

[motoman]

If it idles fine and runs at WOT fine, then it still sounds to me like the mid-range air/fuel mixture is off.



To me, that sounds more like the needle than anything else. Perhaps the needle has the wrong tapper on it? Do these needles have clips on them? If so, maybe it should be moved up or down.

Float bowl fuel levels DRASTICLY affect what you describe. As I stated to daryl, spot on 23mm is where floats need to be set. Float bowl fuel levels, even a half a millimeter one way or another affect correct running thru ALL rpm ranges. Have made these changes so many times for testing correct running along with fuel levels at different settings I can't even remember how many times for testing along with many a different result fuel level wise. And BTW, I am a carb garu. Also, those float settings ARE sea-level settings, so at my elevation(5,000ft.) and most my riding goes UP from there, my bikes FUEL bowl levels are 1/2mm lower(3.5) than sea level setting(3mm).

[dansmith65]

Float bowl fuel levels, even a half a millimeter one way or another affect correct running thru ALL rpm ranges.

This is the part I'm hung up on. If it idles fine and runs fine on wide-open throttle, then it would seem to me like fuel level in carbs isn't the thing that's most out-of-whack, since that would affect the entire RPM range.