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The previous owner of my 1979 Yamaha XS750 Special had some shop work done to it less than a year ago and not that many miles ago. This included compression testing and carb syncing along with some scattered other things like battery and rectifier replacements and some new cabling and new brake related things.
After picking up the bike about a month or so ago, I have thoroughly cleaned the tank, replaced the carb boots, removed all ethanol from the equation and filled up and stocked up on ethanal free, refreshed the K&N air filters, opened up and gone through all electrical hardware/switches with De-Oxit, and generally tinkered.
With the fuel line and air line work i noticed a very significant difference in start up. It just fires up immediately without clutch.
Then, with new carb boots added, the whole bike smoothed out and stopped overheating. There were lots of hairline cracks in them.
But i still had rather low idle no matter what stage of warm up, and things were lumpy in those low rev's.
So, at that point my agenda was do keep going and start with the basics in the Clymer Manual... Compression testing, cam chain adjustment, valve adjustment, carb sync.
But then i discovered that there is a single idle adjustment knob/dial in between carb #1 and carb #2.
I was going to hold off on touching this, but curiosity got the best of me. So, marking down where things were, i took the plunge and adjusted it.
At first i got it backwards, and turning it a 1/4 turn to the left brought my idle down to near death. I only adjusted it while the engine was not running,
So, correcting the direction, i readjusted the dial back to where it was and then went past it around a 1/2 turn this time instead of just a 1/4 turn.
Oh wow, yes this made a difference! Without the bike being warmed up, i was now idling just below 1000 instead of like 500-600. The XS750 Special is supposed to have an idle between 950-1050. This is all according to the on board gauge, since i don't yet have an outboard tachometer in my arsenal.
I then road the bike at two different instances during the day. YES. This is what a motorcycle is supposed to do at a stop light! Not easily stall, and not be a carnival ride!
I had some concerns about how high the idle would be after it warmed up, so after 30 minutes of pleasure i parked it and let it idle how it wanted. After a few moments it settled around 1200 rpm. So i turned down the dial just a bit for next time.
So, knowing that the previous owner had the compression tested and carbs sync'd.... I am wondering... should i just leave it be?
And if i should leave the carb sync as it is for now... what happens if i adjust the cam chain? Does that throw off our carb sync, valve adjustment, or anything else relating to timing?
Do i need to do all the basics together?
It's running quite nicely but still has minor hiccups. Definitely minor. Like little puffs of air randomly almost like it needs to clear it's throat. At high RPM's it's gone. I've added some performance cleaner to a new tank of fuel, knowing that i should be expecting there to be residual gunk. I'm almost assuming that this is the reason for the minor hiccups. Any maybe that clears out the last noticeable performance issues. If so, I'd feel pretty comfortable just leaving the basics as they are.
I think.
I also might decide to dive in fully and dig down into a fresh tune up.
Any thoughts?
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