Jetting mikesxs slider carbs

cmills83

cmills83

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I went ahead and picked up a set of these since I was having issues with the sliders and needles on my stock carbs but can't seem to get them dialed in. I checked the timing and charged my battery this morning.

The bike starts up but then seems to die, I think the longest it's ran for is 10 seconds. I didn't have this issue with the stock carbs when they were on a couple weeks ago. I'm running a Delkevic 2->1, +.25mm pistons, aside from the carbs stock everything else on a 1980.

I had a couple questions:
1. If anyone has a similar setup what jet sizes are you running? I am thinking about just buying some in bulk and doing trial and error to get this right. I tried 35 pilot / 105 main and now the 40 pilot / 110 main
2. Anyone know about how many turns in the idle adjustment screws should be? I backed mine out and went two turns in, but the bike doesn't run long enough to know if that's correct let alone try to sync the carbs
 
Based on jetting it looks like you have the "XS Performance" Keihin knockoffs of the PWK 28, punched out to 32 mm. in a futile attempt to get the 2-stroke atomizer/needle jet small enough to run at all on a 4-stroke motor. The best you can hope for is a lot of expense installing genuine Keihin bits and grossly excessive fuel consumption. The best advice I can give you is to return them if you can and use them for paperweights if you can't. The cheapest usable aftermarket carb for the XS650 is the Mikuni VM34.
 
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Seems everyone is running 40 pilot then 115 - 125 main. The threads are pretty old though and it seems like Mikes was in the process of making changes to the carb reliability. I'm not sure if just around the slides or elsewhere, can anyone say what jets the carbs used to come with? Mine included 30/35/40 pilot and 100/105/110 main. Or can anyone chime in with their current jets if you bought the kit recently?
 
Ok got it running, I adjusted the floats too far like a dummy. It was probably just a stuck float to begin with. It starts and idles ok but bogs down on the 40 pilot, but once that's over I definitely feel a difference with these carbs right away.
 
im running them, put them on a year ago, havent rejetted, well i did, but adjusted floats wrong, and put them back, finally got floats right and havent messed with it, they run good as far as im concerned, only seems too like choke when its cold, sometimes cant get it to start with choke at all, i got the idle set a 1500, sometimes just have to hold the throttle to keep it running on start up, but once it warms its fine, tho after i been riding idle is at 2000 or more, whatever, im usualy never sitting in traffic so havent messed with it more, tempted to see what happens if i cut mufflers off, maybe they will like running open exhaust who knows, but think im going to chilicothe next weekend and its running fine now
 
I have a set and they seem to work great for me. But I don't understand " I backed mine out and went two turns in". Mine are adjusted all the way turned in and then backed out 9 1/2 - 11 1/2 turns. I did just change to the 110 main today and it made a big difference.
 
copernicusdan said:
im running them, put them on a year ago, havent rejetted, well i did, but adjusted floats wrong, and put them back, finally got floats right and havent messed with it, they run good as far as im concerned, only seems too like choke when its cold, sometimes cant get it to start with choke at all, i got the idle set a 1500, sometimes just have to hold the throttle to keep it running on start up, but once it warms its fine, tho after i been riding idle is at 2000 or more, whatever, im usualy never sitting in traffic so havent messed with it more, tempted to see what happens if i cut mufflers off, maybe they will like running open exhaust who knows, but think im going to chilicothe next weekend and its running fine now
Click to expand...

I'm having similar issues around difficulty starting while cold. It won't start at all with the chokes on so the only way is to hold the throttle for a couple minutes while it warms up. Then the idle is around 1000 then 1600 once warm. I tried adjusting the mixture screw to increase the fuel at idle but even a half turn and the bike won't start. Tried backing out the screw a half turn and get the occasional carb backfire and difficulty idling at a consistent rpm I'm assuming from running lean.

If anyone has tips on tuning for a cold start that would be appreciated. It seems the jet is the correct size and I think the mixture screw is correct at 1 turn out.
 
yeah thats what ive been doing, unless its really cold out, no choke, just hold throttle awhile
took mufflers off cuz bike was acting funny, havent rejetted but it runs alright, have to be carefull in first, give it the right amount of gas
but when i took it out friday it was leaking fuel with petcock on prime when sitting, will start to die if you dont have it on prime
went to leave my freinds and had to roll down hill to gas station at bottom, but i ran it an hour and a half yesterday, ran fine, just tried not to stop
 
I increased the pilot jet size from #35 to #38 and it seems a little better. But there is still no way to really apply a choke to these carbs from a cold start, the bike starts with the choke on now but it doesn't seem to have any effect. I still have to hold the throttle at 2k for about 3 min in the morning before riding.

I tried the #40 pilot and it was too rich, the bike was bogging down and some smoke from the exhaust in the first 1/4 throttle
 
So this document actually help me out more than anything with the slide carbs.
 

Attachments

  • KeihinCarbJetting.pdf
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