Author Topic: Need some carb help -- WITH VIDEO  (Read 3473 times)

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Offline flybox1

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Re: Need some carb help -- WITH VIDEO
« Reply #25 on: August 17, 2015, 06:56:07 AM »
cart before the horse, man.
how will you use a vacuum sync if you cant get your bike to idle?  ::)
even with a bad bench sync, your bike will idle.   
a vacuum sync device will not help your bike to idle well if your air fuel mixture is not close to being correct.
if you bike wont idle right now, your air fuel mixture is still off.  (pilot jets and mixture screws)

needle clip position can change and your bike will still idle. 

maybe this visual will help wrap your brain around it.
« Last Edit: August 17, 2015, 06:58:22 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mineā€¦"

Offline mrfish2

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Re: Need some carb help -- WITH VIDEO
« Reply #26 on: September 24, 2015, 09:34:39 PM »
It's high time I updated this thread. So it turns out that my issues with tuning the bike ended up being bugerred emulsion tubes (I'll get some pics up of them later). Along the way somewhere someone had hammered the tubes out and destroyed the inside.diameter, thus allowing different amounts of air/fuel to flow between the carbs.

Well after sourcing a used set of emulsion tubes from a guy on ebay me and a mechanic friend were able to get the bike dialed in pretty close. I ended up putting the stock air box back on to eliminate the K&N filter as a tuning variable and the way the bike is running right now I doubt I ever put the K&N filter back on.

The setting we ended up settling with are:
38 pilot jets
115 main (will do a plug chop later to confirm it's not too rich, but for now runs great)
Needle clips in 3rd position
Screws at 1.5 turns out

The bike takes off from idle without any hesitation now, and runs strong and smooth all the way to redline in all gears. The revs don't hang up anymore either. Needless to say I'm extremely please that for the first time since owning this bike I can finally rack up some worry-free miles.
1976 CB550K            1979 XS1100
1980 CB650C - Sold

It's a little motor and likes having the tits revved off it.

Offline harisuluv

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Re: Need some carb help -- WITH VIDEO
« Reply #27 on: September 24, 2015, 09:52:17 PM »
That's good, there are a lot of people trying to bypass the emulsion tube issue and instead try and correct the main jet and slow jet to significantly outside of spec.  It is a band aid that helps but not a real fix like you are experiencing.

This is also why I have turned away some jobs that are disassembled already, it's not a plus, it's a negative, if done incorrectly, the emulsion tubes (which are in fact a jet!) are easily mushroomed and damaged.  A set that has never been into before is always better/preferred than rebuilding an already "rebuilt" set.