Carb Sync Procedure - 3rd Gen

The engineer should be taken out to a job site, and made to perform the repair or adjustment.
I could site MANY examples .

Thermostat UNDERNEATH the carbs. WOW. Stupid as it gets.
But they draw these things on computers and don't think.

 

New drinking game.... every time Donald gives his resume' in a thread everybody has to do a shot of tequila/rum/whiskey/vodka....

 

So I guess if I gave you the entire thing, I could kill you? LOL

 

Yeh ur gona burn the hell out of ur knuckles too!!! someone in japan is still laughing about that one. Wear some mechanix gloves and invest in a nice headlight for ur melon (you know like the gynocolgist wears when he's inspecting the poosy) Hands free chit RULES!!!! and seeing is nice too!!!

Far as dah tool goes, I gots me those old 1/4 carb socket tools (snap on) with the slot in the middle and used a knurled adapter to turn the hex adjuster on the bike. You wont see chit btw so its just by feel. I had to turn the bike off a few times and start again back when I did mine becuase I wasnt born with an Asbestos hand.

Payoff for the carb synch is fantastic off idle characterists as you just crack the throttle. Its worth it for your own bike but I would have to be paid well to do it on someone elses :smile:

What else???? Hmmmm>>??? How bout this, How do you tell a Triumph rider? Smell his finger...Harkens back to having to tickle them carbs. The good old dark days. :smile:

 

Results:

Well, it was much harder than I thought it would be - mostly due to the poor packaging of the adjustment screws and vacuum port tubes - but it was worth the effort. The bike is noticeably smoother at speed and sounds better at idle, which is smoother too. I had the benefit of the official "Honda Carburetor Adjustment Tool" (part number 07908-KE70000 on servicehonda.com, $40) and I can't imagine how you guys do this job without it! It took three people coordinating together to read the gauges, operate the throttle, hold the flashlight, and get the screws adjusted. None of us had done this before. I probably didn't do the job as good as any of you could have, but I'm pleased with what I was able to accomplish for my first go around!


Current Condition by James.Rogers.III, on Flickr
I still need to get my side fairings re-installed, but I'll ride a couple of days and make sure there are no issues I'm unaware of first.


Tuning Buddy - thanks! by James.Rogers.III, on Flickr
Big thanks to Cameron for his help this weekend!


Vacuum Gauge Cluster by James.Rogers.III, on Flickr
This threw me off at first; at idle the needles oscillated as pictured. When the bike was throttled up the needles would start to behave. I synched the cylinders at 5000 rpm. The front two and the back two are linked, but they don't get to the same pressure as each other until then. I've probably not done it right, but it's still better than what it was!

 

The gauge cluster came with a pack of those but I wasn't sure what they were for. Bah...guess I know what I'm doing next weekend.:frusty::doh:

I've just figured out why the front and rear cylinders were offset: I used those T sections to tie the existing vacuum lines into the circuit. That seems really obvious in retrospect. Ah well, live and learn...

 

I just hooked my home made setup to the bike. I used about 5ft of 4mm ID fish tank hoses on a board as is everywhere online, couple of t pieces, elbows and some basic have too's. Got mine almost perfect but will double check in the morning before buttoning everything up.

For those diy for $15 - I drilled out M5 brass screws with 2mm bit and superglued a nut in the middle so i could turn it with a socket. Then screwed into vac port with a o-ring hand tight, and attached the hoses to the rear end and then up to the top of the board where the fish tank tubes are with the ATF fluid in. In my 1.7m board i filled tubes with atf till about half full - it works well.

* Use ATF fluid, it works perfect and the color is easy to read.
*. If you carbs are out (like mine were) one cyl will suck most of the fluid up, keep yr hand on the key to switch off on the first few runs in case its really out - in this case, turn motor off, adjust and restart and see if it got better or worse.
* If your non adjustable carb is drawing more vac, then u have to INCREASE the others to get it to drop
* Space the tubes on the board close - u wont need such a massive wide board and it will give accurate readings
* Make sure the plastic joints joints are pushed in all the way. One of mine was actually sucking up tiny bubbles from the bottom throwing me off. for 20 mins!
* Leaving elbows at the top will allow u to pop the lines off, switch them and push out if u get any air bubbles - just makes it easier than having single long lines
* Make sure the hoses dont kink even slightly - fish tank lines are soft
* When u cable tie the tubes to the board - make sure u dont crush them. Just firm enough to keep them straight
* My brass screws heated up and the fish tank hose started leaking - I wd use a thick wall rubber hose for about 3-5" from the heads and then into the weak fish tank hose
* Increasing the idle to about 1500 rpms rules out any jumpy idle symptoms and generally gives u a better chance off the idle.
* Once u start to get close - check at various revs and see whats happening.. I doubt a slight rise/fall wd be noticeable on accelaration.


As mentioned elsewhere, on the RC24 bikes, the front left carb (#2) is the base.



(front)
2 4
1 3

Adjust 4 (front right) to 2 (base) first, then 1 and finally 3.

Good luck! Havent taken a test drive yet - but have been waiting months to do this - glad its finally finished.

Oh - not sure if its applicable, but shouldnt tilting the fluid at an angle give even more accurate results as u are reducing the effects of gravity? so if u have them all level, lowering fluids to 45+ degrees might show some minor differences - not sure if that wd be noticeable - but thought id throw it out there

 

Good post above !!

It's also best practice to snap the throttle a couple times anytime a synch screw is moved to allow linkages and throttle butterflies to settle into the new position. You should never need to adjust any synch screw more than about 1/8 turn from a good eyeball synch starting point. The SEQUENCE in which synch screws are adjusted is critical ! First adjustment matches left-right carbs on both front and back; then long link adjustment matches rear carbs to front.

 

hey squirrelman - im just curious, yesterday i found it was quite tricky getting them to line up - i didnt follow much of a sequence since each tiny adjustment makes quite a difference. . i thought of pairing the cylinders by splitting the tubing (syncing in pairs) - but having them all in seems to make more sense since they all affect each other.

Ill be fine tuning later today and see how the bike runs - very excited that I finally got them very close - i thought the bike was 'close' but it was wildly off(!!)

 

Having issues with bench-top sync. Using #2 carb (with black screw) as a start I've been going in the following sequence: #2, #4 (straight across) #3, then #1 (first in line when sitting on top of bike looking down). I cannot get the #1 to the bypass hole even with the screw all the way down. I can push it just enough to get it there using my fingers, but it seems like it doesn't want to be there. When they say first bypass hole, do they mean from the bottom of the carb? There is more than one hole on the wall, in the pic, I've put an arrow to the top (bottom) hole, is this the one I should be using as a reference?

 

It has been a while since I have read this thread or visited this site.
I would like to say that the liquid filled type vacuum gauges are really not easy to use.
I have found that the gauge type vacuum sets are much much easier to use.
Once you use them you will never go back to all those tubes and fluid hassles again!

As far as using a drill bit or anything else to set the butterflies is not necessary.
A .007 thousandths difference wil affect how the engine idles.
Just make sure the butterflies all close when the throttle is off.
Thats it. No slack in the cable.
Make sure that as you start to open the throttle that ALL FOUR butterflies start to open at the same exact time.
You can feel this with your fingers when the engine is off and the air box is off.


That drill bit scheme was used on some of the early Honda CB 750's but not on all of them.
Certainly not on the 1977-78 models. But it was still not necessary.

BTW...What is that steel bar and huge phillips galvanized screws in that butterfly for?
I hope it does not get loose and get sucked into the intake! See photo Post#34

Please give the year of the bike instead of saying "first generation" etc.,.
With the year given a much more exact answer is possible.

 

Amen to that "generation" crap. To even think that Honda or anyone else in the bike or car making biz does not make changes even in mid year much less a run of three and even four years is a hard sell.

Any new stuff from your shop lately?

 

Yeh, what happened to the "magna-toid chopper?"

Number 3 phillips heads look strange. I have a set of Morgan Carb Tunes and swear by them now, no more mercury stix for me! Gawd, what a pita. Cheers

 

OK, I found the issue. The tab on the third carb was bent down just enough to not allow full adjustment. Pulled the the sync arm, pulled the adjustment screws, bent it back and viola...perfect. Still waiting for my float seats for installation.

 

Getting new float needles and seat(if the seat is needed)is a very smart move.
It is absolutely critical.

BTW If you get a chance remove those four pilot air screws/fuel screws with spring, washer, and o rings, and make sure the O ring is in good.
condition. Many times they are banged up. Makes a big difference.
The idle is controlled by idle jet and pilot air screw.
BTW It does not matter if you call it a fuel screw or pilot air screw.
They all are adjusted by closing them and then opening them a certain number of turns. Period.

 

Yes I just finished? a Rigid Chopper with a Yamaha Roadstar 1700cc V twin stuffed into it.
It took one year. I am making final adjustments.