XS2 Carb problem

Tim L

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Hi,

I have just started re-assembling my XS2 after a full strip down and a few modifications and have got a problem setting idle speed.
The manual says the best way is to run the engine, remove one spark plug cap and set the desired idle speed then reconnect and do the same on the other side. I have done that, setting idle to about 1000 rpm, but as soon as I put the second spark plug back on the idles races off to about 3000 revs.
I have repeated it a few times and it always does the same thing. On one cylinder it will run around 1000 but as soon as the second one is reconnected it revs away.
I have stripped and cleaned the carbs, all original settings were used. I have also fitted air filters from Mikes XS. I am pretty sure everything is airtight.
Fuel flow seems to be okay although a fair bit of air collects at the top of the right hand fuel pipe. The carb link pipe is always full.
Has anyone got any ideas?

Many thanks

Tim
 
Tim
What you want is to get them in sync with each other. To do that, set one carb up the way you have been, except set the idle speed to about 600 rpm. Then do the same for the other. When you pull the wire off the sparkplug, make sure you ground it to the engine. Otherwise you will burn up that coil. You can use an old sparkplug to ground the cable.
With each carb set to 600, when you connect both plug's, the engine should be at about 1200 rpm.Fine tuning should bring them in even closer, just be sure to turn each idle screw the same amount. You want the butterflie's to be open the same amount . So that each cylinder draw's the same amount of fuel.:banghead: Once you get them close, you will start to get what your looking for. Just go slow, also, a fan in front of the engine while tuning will help keep the engine from overheating.:)
 
To do the "dead cylinder method" you must adjust the "idle mixture screw" (pilot screw) as well as the "idle speed screw". You should be able to adjust the engine speed down to around 300 or 400 rpm on 1 cylinder firing. If you can't do that, then you're not doing it right,or you have air leaks etc. You have to adjust both screws to achieve this. As you adjust the pilot screw, keep lowering the idle speed screw to get the rpm down.

The important thing to realize, is that the throttle butterfly must be almost completely shut, in order that the pilot screw can be adjusted. This is because the butterfly must be covering up the 3 by-pass holes in the carb throat. If the butterfly is open even slightly, the mixture coming through the 3 by-pass holes over-rides the pilot screw, and you are unable to adjust it.

If someone has had the butterflys removed from the carbs, they may not have re-installed them correctly. The butterflys need to be self-alined. This is done by leaving the butterfly screws loose, while allowing the shaft and butterfly to fully seat against the side of the carbs.............the screws are then tightened (use thread locker on the screws).

Don't worry about some air in the supply line to the carbs. I quite often have air bubbles in the clear filters above the carbs, and it makes no difference to the carbs operation.
 
Well, a little different, say maybe 1/4 turn, is OK, but they shouldn't be way off from one another. That could indicate other problems within the carb like passageways blocked or float level incorrect.
 
I think the pod filters I got r partially blocking the air ports. They didn't have ridges but they were only 2" and forcing them on made uneven ridges in them. I ordered some xs perf filters that r supposed to b here today. I'll c if that helps
 
I have new xs perf filters and replaced philips screws with allens to get carb clamps tight. set pilot screws and sync screw with tach and dead cylinder method. runs really good but some poping out left pipe. tried adjusting sync screw 1/8 turn both directions and left pilot screw 1/8 turn out and ran worse both times. then put adjustments back where they were and tried right pilot screw 1/8 turn in and it ran worse again. so I put everything to where it was when I adjusted with tach again. runs real strong and transition from idle to mid range is great so I guess i,ll leave it there. popping is minor and only when decelerating with throttle all the way closed.
 
Yeah a bit of popping is normal especially if you have the idle set on the low side. Wasn't many years after this they started adding "decel valves" to stop the popping. Typically a cylinder charge that was too lean to burn that gets lit off by the next successful fire.
 
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