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This was next on my 600-mile service and involves some preparation. The procedure is outlined on our sister site yamahastarbolt.com (do a forum search there) and the youtube video:

There's too much scattered information in the starbolt forum threads so I summarize the essentials here.

My procedure used a home-built U-tube manometer fabricated from 18' of 3/16" ID PVC tubing with oil filled to 2' each side of the U. This measures the relative pressure between front and rear TB's that you equalize to balance.

The motor should be warmed up and I used an external fan during extended idling while fiddling with the recessed adjuster screws. The screws are hard to reach with the air filter ass'y in place but this is necessary for proper readings. The fiddly part is removal of the filter and case to access the vacuum ports to attach the tubing then button it all up again.

The rear port needs a T splitter to connect both the 3/16" manometer hose and manifold pressure sensor hose during measurement. The front port, normally sealed with a bung, is smaller diameter so the tubing needs to be stepped down to 1/8" to avoid a vacuum leak

The adjustment is VERY sensitive with less than an 1/8 turn on the adjuster screw(s) necessary. I marked the starting points for reference. The port with higher vacuum gives the higher level reading and this is the one I lowered by turning the adjuster screw out (counter clockwise).

The oil level didn't bounce around too much at idle being damped by the long tubing. The factory adjustment was out by 5 cm oil difference and adjusted to less than 1 cm difference. The level bounces around when blipping the throttle so a perfect balance is not realistic.

The air filter uses three sealing rings the service manual says to replace but mine were fine and reused. If they get old and stiff a coat of vaseline helps rejuvenate them. The pics show the manometer and tubing connections for reference.
 

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Great write up!
That inexpensive gauge you made is all one needs, really.
No mercury to be cautious around and if some fluid goes in the intake, no harm to the engine, either.

The first time I did a synchronization myself, I was so happy to get it dead on (to my eyes, anyway).
Right as I was about to shut the bike off {1989 Honda Transalp V-twin}, the needle on my TwinMax balancer started going crazy.
Then the bike went to running weird. What the heck?
One of the clear vinyl tubes had softened with engine heat and wilted down onto an exhaust pipe - melting it in two before catching fire!
It was a tiny flame, so I got that out , laughed and shut the bike off.
Whew! Crisis avoided.
 

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Being OCD I used 2-stroke oil, just in case of a dreaded suck back into the intake. Most use red ATF.
:laugh: I understand!
I had a mechanic who used to dribble ATF or Marvel Mystery Oil into an old V-8's open carburetor until the engine bogged, clear it out with some revs and do it again before pouring enough that the engine stalled. It was a smoky, nasty procedure he swore made a good top end cleaner. After letting it sit for a while, he'd change the plugs and run the engine until the exhaust cleared up.

PS: I omitted the procedure during my 600 mile service, but you got my curiosity going. So, I went out last night and checked the belt tension on #00035 and it was fine. =)
 

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This is the first time I've heard of a mechanic purposefully bogging and then stalling an engine, probably the first time I've hard of someone manually dripping oil into a carburetor. does it really work?
 

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This is the first time I've heard of a mechanic purposefully bogging and then stalling an engine, probably the first time I've hard of someone manually dripping oil into a carburetor. does it really work?
Years ago, I had a 1974 Olds Cutlass with a 350 V8 & the standard Rochester Quardajet 4bbl carb. I went to the dealership and got a can of top end cleaner GM used to sell. It came in a regular metal "oil can" type container and the instructions were pretty much as described above. Dribble a little in the carb at a time, rev it to keep it from dying, repeat until you had used most of it. Then you slowly poured the remainder in until the engine bogged and quit. Let it sit a while, run it again until the smoke cleared up & then change the oil. It appeared to be a solvent of some sort.

Seafoam users will take some and disconnect a common vacuum line and let it suck up the liquid with similar results.
I don't really see any of this as necessary unless the engine's got a ton of miles.
 

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Years ago, I had a 1974 Olds Cutlass with a 350 V8 & the standard Rochester Quardajet 4bbl carb. I went to the dealership and got a can of top end cleaner GM used to sell. It came in a regular metal "oil can" type container and the instructions were pretty much as described above. Dribble a little in the carb at a time, rev it to keep it from dying, repeat until you had used most of it. Then you slowly poured the remainder in until the engine bogged and quit. Let it sit a while, run it again until the smoke cleared up & then change the oil. It appeared to be a solvent of some sort.

Seafoam users will take some and disconnect a common vacuum line and let it suck up the liquid with similar results.
I don't really see any of this as necessary unless the engine's got a ton of miles.
Yup, you`re completely right, i`ve seen a number of videos on youtube that show exactly under what conditions it works well and where it`s just useless.

Best thing to do for someone with an engine old enough to have that carbon built up is to get a scope down a cylinder.
 

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Seafoam is one of those things you have to use very wisely. If you don't understand it or how to use it, stay far away from it. Another thing is that it's designed to clean out build ups and a lot of times, build ups on older engine is what kind of holds everything together like glue. Get rid of that and welcome to problem-ville, population, you. Lol.
 
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