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Thread: xs650 Carb Sync

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    Default xs650 Carb Sync

    I have an XS without the the sync holes in the manifolds. Whats the best way to get an accurate Sync?

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    Hook up a tachometer. Pull a plug. Set the running carb to 600rpm. Then switch the plugs and do the same to the other side. In theory you just synced the carbs to 1200 rpms with balanced carbs.

    Just google. Xs650 dead cylinder sync for more info

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    What year carbs are they?

    Certain BS38 carbs require you to buy vacuum fittings in order to do a carb sync. You'll see a flathead plug on each side of the carb body that comes out, and you thread in the diagnostic nipple so you can hook up a manometer. You can make a manometer using ATF, a meter stick, and some clear tubing. Motion pro sells the diagnostic nipples, or you can make your own out of a grease zerk.

    Backwithabang's suggestion is not the ideal way to do it. If you have a CDI bike and attempt to use dead cylinder method without grounding the plug wire you'll fry the CDI. And if your cam chain, valves, and timing are off you won't be at a good baseline to do a carb sync. I have found that dead cylinder works best for mix setting in the idle circuit. Have you rebuilt the carbs yet?

    Make sure to set cam chain, adjust valves, and set timing before messing with the carbs. A good way to get a bench sync is to take a piece of paper and get each butterfly adjusted so that when you close the butterfly on the paper it just barely drags when you pull it out.

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    my method works great for a Pre cdi bike.

    I was on my phone and didn't feel like typing.

    But yes listen to the more extensive advice given. Cam chain and valve adjustments are easy as all hell. You can find YouTube links or a downloadable manual very easy with simple searches.

    Other problems you may encounter are leaking valves, cracked manifolds, exhaust leaks, shit timing. It all affects the overall bike and if you want it to ride well you need to learn about it all and throw a lot of tools.

    The carbs could be shitted up too, bad cables, we are talking about bikes older than most of us that have been sitting in a garage or backyard.

    Once you nail the carbs and idle you will encounter charging problems, and most likely the dreadful disappearance of neutral while riding.

    Change your oil, clean your filter and now you are leaking, maybe it's a right side gasket.. Fix it. Nail it all together and re fill it with oil only to realize you forgot to wind the kicker spring correctly and now you have to start all over.

    Finally your bikes running well and boom, you are spurting oil out of your left side case. Whoops the pushrod gasket let go. After three failed attempts and 25 bucks in the hole you finally get one in but shit.. You lost one of those ball bearings in your pushrod. Another week. Another package from mikes xs.

    Welcome to the world of the xs650. We have been waiting to share our frustration

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    That just made me laugh out loud. yeah i'm new to the XS world but not to the wonders of vintage machinery. Thanks for all the advice, ultimately, I am trying to minimize as much of the vibration this old thing creates as possible. I realize its the nature of the beast but im hoping through timing and a carb sync i can take care of some of it. Right now this bike vibrates your teeth out of your face. the seat cushion is so thin on the Omar's fender that you ass bones are basically sitting on the frame. That sends all that buzz right to your brain.

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    You need to rephase the beast. Check out Hugh's hand built blog or search this forum.

    With those pistons bouncing up and down at the same time you just have a rolling jackhammer. Shit leave it running in your garage to get a tool and it will wander away

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    yeah i've looked into that pretty seriously, I have another 1975 rolling XS that i would eventually love to chop, and if i do, that is going to be my priority. I'd like to do a big bore re-phase. almost doesnt seem worth the money though. I guess its the price you pay to have a one of a kind.

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    I hear the 750 seems noticeable with the rephase. I didn't do either to mine. Just made it quicker from stop sign to stop sign. If I'm going to dump a lot of cash into a build it's probably going to be British or American

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    Thats pretty much they way i look at i too. i think when i finally finish my street tracker i'll sell it and purchase something american.

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