Triumphrat

keanhi

Hi Punters.

Being a novice with mechanics has proven challenging, a slow process..but worth the effort.

Bought in a Carbtune kit from the UK and started (attempted) to balance the Keihin FCR's. Now...they were off quite a bit and I did manage to get them a a lot closer....around 28cmHg. (if that's good or bad..? have not idea)

However, I think it was more blind luck than expertise

Now the balancing is done via the top and has the Adjusting Throttle Valve screw & the Throttle Valve Synchronization Lock Nut.

Would have thought that you undo the lock nut...move the valve screw around and get it sync'd....then tighten the lock nut...no brainer.....not.

Loosened up the lock nut and things started happening....ok..hmmm...plan A out the window...lets make up a quick plan B.

So, thought that possibly ya adjust the valve screw (up/down whatever) and when you tighten the lock nut it would be governed by the height of the pre-adjusted valve screw....hmmm, nope. As a test I adjusted the valve screw way up and the lock nut would screw way down...so, that theory went outta da window mate.

I played around with the valve screw and the lock nut for a while...and after I got the valve screw in a lower position found that once ya tighten the lock nut the thing started to balance out...so played around with the valve screw, then tightening the lock nut...nope...a little more out on the valve and tighten the lock nut again....after a number of attempts...bingo...well, close enough until the weekend.

So, after...I lay spent on the concrete floor..smokin a cigarette...and thinkin, what the heck happened. I still have no clear idea on how that adjustment works as the tightening of the lock nut seems to do more that the valve screw....something ain't right.

Anywayz, I had my purge and feel better..........hey, if anyone has any clue about sync'in these carbs...your input would be muchly appreciated.

Time for another ciggy <cough, cough>

HiVel

Guess I better check mine.

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Anything worth doing is worth doing to excess!

2005 T100 Bonneville 865cc "Creamsicle"
2007 Tiger "Old Blue"

Scot03Bonnie

You actually do this with the carbs off the motor. Sounds like you found the slide linkage adjustment under the cap on top of each carb, it's an eccentric with a locking screw. The synch is really just using the adjuster and positioning each slide an equal distance gap between the bottom of the carb bore and the bottom of the slide using about a 1/16" drill bit as a go/no-go gauge. This will take a few tries until you get the feel of it, but you'll be rewarded with a sweet-running nice idling engine.

Read this, http://www.factorypro.com/tech/carbkei.html

it will give you a great run down on tuning these carbs.

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Scott- ATL

keanhi

Hi, thanks for that mate...found that and reviewed it prior to starting the adjustments....but ya can get to the top of the carbies while they are on..just unbolt and raise the tank a little for easy access and pop off the tops.

Shall fiddle around on the weekend, I'll have more time to take it slow and get a better understanding of the carbs...once this is done I'll take it back to the dyno.

One thing he mentions on that doc..is that the nut is used for the adjustments and the screw is for locking it into postion
Quote: "The nut is used for adjustments, the screw is to lock the adjusting nut in position. Loosen the lock screw of the slide you are trying to adjust"..........so that makes sense. In a diagram exploded diagram I had it said the nut is the lock and the screw is the adjustment.......now just found another exploded diagram on the web that describes the screw as a 'Stop Screw'....very strange that I have two exploded diagrams that are different....maybe due to translation from Japanese or something.

Now I just need to find out what cmHg range they should be in, or if that even matters.

Scot03Bonnie

Yeah I do it that way when adjusting needle clip position. Pretty easy. I just found it easier to get a true mechanical synch using the drill bit method from the engine side of the carb due to less distance to the bottom of the slide from that side, thus better feel, and so they have to be off to do it that way. And yes, the screw is a lock screw, the nut is the adjustment. It's back-asswards from the way you would expect. The amount of vacuum you see on the manometer isn't so critical really; that would have more to do with your idle rpm than anything else. I did the drill bit thing first, to get them as exactly alike as was possible, than installed them and began tuning. If your slides are exactly alike when you start, then your final adjustments will be very slight, and probably more mixture-related.

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Scott- ATL

keanhi

Hey Scot03Bonnie ,

I'll be pulling em out when I receive the intake manifolds from newbonneville...so I will try this method when the are out of
the bike...sounds good.

Thanks for your feedback mate...much appreciated.

Scot03Bonnie

Keanhi-
I wish you the best in your tuning, and glad I could help.
Oh yeah they work nicely with those manifolds, even better if you can clean up the transition surfaces inside where they match up to the intake ports. The FCR39's are good carbs but they have their own "personality" if you will.......they are very sensitive to variations in atmosphere, so your jetting needs to embody an accurate compromise for the conditions you ride in (elevation and temperature, mainly). I love the throttle response and throttle feel they give, makes the bike a lot of fun!

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Scott- ATL