Author Topic: Carb sync after valve adjust - I'm wondering why  (Read 467 times)

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Offline Bucky

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Carb sync after valve adjust - I'm wondering why
« on: October 25, 2017, 05:45:48 pm »
I don't doubt what I read here, that it's good to sync carbs after valve adjust, I'm just wondering why.

 I'm not questioning that it's a valid procedure, I'm just ignorant of the connection between the two.

Thanks.


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Offline Stasch

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #1 on: October 25, 2017, 06:19:53 pm »
Here's my understanding on the issue.  A cylinder is like an air pump.

By changing valve clearances, you change the air flow (however subtle) for each affected cylinder from what it was before. 

A carb sync re-adjusts the carb's to these changes, to help smooth out the engine and throttle response, particularly at lower throttle settings and at idle.
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Online GeorgeRYoung

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #2 on: October 25, 2017, 06:21:28 pm »
There was some adjustment required on my first carb synch. I think it wasn't done either by the factory or the first owner. Since then, I've checked it once and there was no adjustment required. This was after a few valve adjustments.

Another thing that I did once and never again is check and grease the swing arm bearings.

Some things just don't need repeated tweakings.

Online Steve in Sunny Fla

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #3 on: October 27, 2017, 12:29:42 am »
If the valves are seating after each valve adjustment, then theoretically there is no need for a sync. However as the bike ages and wears, of course there's the possibility of airflow differences strictly from the throttle shaft adjustments points wearing. Another point would be if the previous sync was done on a less than 100% engine, the sync may be off, too... you're relying on how good the mechanic before you was. Maybe that's a good idea; maybe not.  ;) Steve
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Offline MizzouMike

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #4 on: October 27, 2017, 12:10:15 pm »
I always just consider it a package deal.   I am doing maintenance anyway, so it is just on the checklist of things to do. 
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Offline RWulf

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #5 on: October 27, 2017, 01:31:01 pm »
It's much easier to do after doing the valves.
You allready have the tank off and nothing is in the way.

Online MAN OF BLUES

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #6 on: October 27, 2017, 09:24:15 pm »
Well, if you own a carb synch tool, and have just done the valves... its kind of a "no brainer" to forgo inspecting and adjusting if necessary, considering at that point its like a whopping 5 minute job....and then you KNOW if they are in synch or not....

 :-[ :-[ :-[
 :motonoises: :great:

And as SISF notes, past adjustments, and time, do tend to take on some deviations, all in all, I don't think I've ever seen a bike that didn't benefit from that inspection and tweek even by a small imperceptable amount, after doing a valve adjust..
I still see as I'm sure SISF sees, many carbs still have those airscrew adjustment caps in place, as they left the factory with...
I still do occasional carb rebuilds for folks, and am amazed how many have gone soo long, as "delivered"... once the adjustment on airscrews are changed, so will the resultant synch show need for a touch..

Its free, so in my opinion not doing a look is silly.  Might even give you another MPG benefit.. kinda like a clean airfilter, or new plugs..
« Last Edit: October 27, 2017, 09:53:14 pm by MAN OF BLUES »

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Offline Bucky

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #7 on: October 31, 2017, 11:44:57 pm »
I don't have a problem with testing the sync, (aside from not owning the tool) I was more wondering if there is a direct mechanical correlation to a change in valve travel that would cause a sync change. 

That reminds me - I gots to hunt down a 4 port manometer near me.


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Online MAN OF BLUES

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Re: Carb sync after valve adjust - I'm wondering why
« Reply #8 on: November 01, 2017, 08:18:09 pm »
I don't have a problem with testing the sync, (aside from not owning the tool) I was more wondering if there is a direct mechanical correlation to a change in valve travel that would cause a sync change. 

That reminds me - I gots to hunt down a 4 port manometer near me.

Ya don't need a 4 port manometer, you ar synching between 2 carbs, for each stage of the synch...

Buy a TwinMax, and be done with it..
No better synch tool on the market for a concours. Period.

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