Carburetor adjustments and synchronizing

[markb]

Wasn't sure if I should post this here or under the fuel section.  Anyone have a good procedure for adjusting and syncing carbs (assuming that everything internally is correct and clean)?  I've always been able to muddle through it but always felt there had to be a better way.  There's a lot of info out there (maybe too much) but a lot of it doesn't pertain to our older style carbs (like bench syncing).  Maybe part of my confusion is in the terminology.  One question I have is the throttle stop screw what some people refer to the idle screw?  Anyway, does anyone have any good tips?
Mark 

[1941wld]

Hi Mark,
I've been working on a set of carbs for my K0 which are the same as the SC. The best way to adj the carbs is with the engine running. I have a mercury manometer and you can still buy them. To me, it is a must have. The first thing I do after I clean and inspect all the parts. I replace any parts out of spec, like 110 main jets. I start with 120 main jets because the bike is stock. I install the carbs on the bike with the air clean installed. You must have the air cleaner installed because it changes the adjustment with out it installed.
Put a fan on the motor to keep it cool while tuning it.
Crank the bike up and make sure it will run. I use an auxiliary gas tank so I can get to the top of the carbs. Attach the manometer, crank the bike up. Bring the idea up to 2500 or 3000 and hold it steady. Adj the cables on the top of the carbs till the 4 four mercury levels are the same. Remember the higher the rpms on each cylinder the lower the vacuum pull. After you get the cables pulling the slide in the carbs equal bring the bike to ideal. Adj the ideal screws on each carb to pull the same vaccum on all 4 keeping in mind you want the tack around 900 to 1000 rpms.
Before you adj the carbs be sure the valves are set and the timing in dead on.
My K0 is not running right, I've cleaned the carbs 3 times. I've changed jets and it's still running rich. I've ordered new slide needles and seats and I'm waiting for them to come in. I'm hoping this will fix it. The #40 jet is the ideal jet, it works from 0 to 1500 rpm. The needle and seat is 1500 to 4500/5500 depending where the clip is in the needle, the main is 4500/5500 to wide open. These are the numbers the I find work on my bike. Other people may differ on these numbers, this is just what I've found to be on my bikes.

[Steve Swan]

First, i adjust each individual cable, the goal for all slides to pull open at the same time.  Another way of saying this, i turn each cable adjuster until the ferrule of each cable housing will lift the same distance before starting to pull the cable taut, which in turn pulls the slide up in venturi.

Second, I adust throttle screws by feel.  i can feel the head of the screw strike the throttle slide, then i turn the screw one full turn.  Has always been a reliable way to have the slides all the same height in the venturi, even when the carbs are already installed.  (With carbs not installed, easy to visualize the slide begin to move when the screw is felt to touch the slide.)

Third, i set the pilot air screw per factory setting.

I use mercury "sticks" to adjust vacuum (w/ airbox installed) per procedure outlined in the workshop manual.  (I have found careful "static" setup of the carbs brings them in near perfect "snych" before using the "sticks.")

Finally, i go by feel and sound for doing fine adjustment settings of pilot air screw.

All that being said, i don't use mercury sticks any more, but still go through the first 3 steps above.

After i have the above adjustments made, i take the bike up to my friend who has an exhaust gas analyzer and he can adjust settings closer than the best tuner ever could.

I friend of mine bought a portable exh.gas analyzer a couple yrs back and was really happy with the results he obtained.  For final tuning (after cable height and thr.screw adjustments are made) nothing is better than the exh.gas analyzer.

[kmb69]

I've been working on a set of carbs for my K0 which are the same as the SC. The best way to adj the carbs is with the engine running. I have a mercury manometer and you can still buy them. To me, it is a must have. The first thing I do after I clean and inspect all the parts. I replace any parts out of spec, like 110 main jets. I start with 120 main jets because the bike is stock. I install the carbs on the bike with the air clean installed. You must have the air cleaner installed because it changes the adjustment with out it installed.

Which brand of mercury manometer are you using? Where can you still get them?

Keith

[markb]

Second, I adusting throttle screws by feel.  i can feel the head of the screw strike the throttle slide, then i turn the screw one full turn.  Has always been a reliable way to have the slides all the same height in the venturi, even when the carbs are already installed.  (With carbs not installed, easy to visualize the slide begin to move when the screw is felt to touch the slide.)

I like this tip.  Is this what some people call the idle screw?

Good feedback.  I use the Morgan Carbtune and it seems to work OK.  Anyone else use it?

[Steve Swan]

I have an old Motion Pro unit.  As i understand it, the mercury units quit being sold a few years back.  Have heard Motion Pro sells non-mercury units.

[Steve Swan]

Yes, idle screw same as throttle slide adj.screw.  

Using a long, sm.diameter screw driver held against head of idle screw, i can distinctly feel the slide strike the screw, when throttle is allowed to snap shut from full wide open.  

To make sure the screw is at the point just touching the slide, I turn out the screw until i cannot feel the slide strike, then turn the screw in incrementally until the strike is felt through the screw driver.

I can readily feel the screw touch the slide, if the small spring is removed from the screw.  Also, there is a "T" mark on each of the screw's shafts to denote the approximate depth the screw should turned in to for an approximately correct idle setting.

I always like to "zero out" the screw, so i know when it is just touching and then turn each screw in the same number of turns.  The heads of the screws, as we all know, are slotted so one can make adjustments 1/6th of a turn at a time.  This method gives me a more accurate setting than going by the "T" mark.

Also, DITTO what Conrad (wld41) said.  Assuming valve clearances are proper, valve guides and valve stem seals are in good condition, the 4 vacuum readings should easily adjust to the same values.   If valves are out of adjustment, or guides/seals bad, will get disparate and "wandering" vacuum readings.

Conrad, your comment, "My K0 is not running right, I've cleaned the carbs 3 times. I've changed jets and it's still running rich."  Years back, I encountered the very same problem on a K1 set of carbs, despite thoroughly cleaning the carbs and then checking patency of passageways SEVERAL times, continued to run rich, sooting plugs in barely 20 miles of operation.  Replaced EVERYTHING NEW, experimented with needle positions, jet sizes, never did get the condition sorted.  Wound up using another set of carbs which carburated perfectly.  Keep us posted when you find the cause of your rich condition.

[hondasan]

Pretty much as Steve says. Firstly on the bench before re-fitting....
 - set the slide height using either the throttle screws by feel, OR by measuring the slide cut away to body gap through the rear of the body (use a small diameter rod / drill or similar and adjust the throttle screw till the slide just "nips" the rod)
- set the airscrews to the manual setting of 1 turn out
- once carbs are fitted, adjust the individual cable adjusters to allow the same free play in each of the four cables

When running, I use mercury type manometers using the Shop manual procedure:-
- ie, balance at idle first using the throttle screws, then at 2500 / 3000 rpm using the cable adjusters. (You must of course set the idle balance first, because that changes the individual cable free play, which can then be corrected by final balance at 2500 / 3000 - If you balance at higher revs first, then the subsequent idle speed balance will again change the individual cable free play and un-sync at higher revs.

As to the airscrews, as Steve says, you really need an exhaust gas analyser for these.

Not such a chore once you are set to do it (especially if you have ever tried the same job with a CBX 1000 )


Cheers - Chris R.

[1941wld]

http://www.speedaddictcycles.com/product/08-0009/Race-Pro-Deluxe-Mercury-Carburetor-Tuner-Synchronizer.html

Here is the link for the mercury carb sink.
This is the best price because it's free shipping. The price is the same everywhere, but this one is free shipping.
This the one I use. Don't buy the Motion Pro, buy this one you'll be happier with this one. I have both.

[Steve Swan]

What is the difference between thi RacePro and the MotionPro?  The RacePro looks like my old MotionPro.

[1941wld]

The motion pro uses glycol
This one uses mercury.

[kmb69]

Thanks for the link, Conrad.

Back in 1970, a very good friend of mine worked in one of the local chemical plants. He was able to get custom glass tubes made to his specification. He built manometer sets for both of us. These sets were 4 u-shaped glass tubes approximately 36" tall (72" total length) and required several ounces of mercury for each tube. They were mounted on plywood with graduations drawn on the background for easy visual from distance. We used long surgical tubing as they were mounted on the wall with room in front of the bike for a squirrel cage fan to keep the engines cool. They required NO dampeners like the OEM Honda vacumn gages. These sets were the most stable reading "vacumn gages" I have ever used and resulted in ultra-synchronized carbs. Unfortunately, after 40 years, I have no idea what happened to them. Please don't tell the EPA. I don't think I suffered any brain damage but often victims are the last to know.

Along the lines of the exhaust analyzer, I recently watched a friend of mine tune a H1 Kawasaki using an infrared temperature gage measuring the temperature of the exhaust headers at each of 3 steps. He used Steve's method of adjusting the slides to an "equal fixed heighth" just off idle and adjusted the air mixture screws. He then backed off the idle stop screws and synchronized the throttle cables. Lastly, he balanced the carbs at idle. Maybe the smoothest H1 I ever rode. Still went ring, ding, ding though.

Keith

[1941wld]

Keith,
You are welcome.

[kp]

Conrad, They are peachy looking manometer set that's for sure and they were they way to go years back. I haven't seen a mercury set for years. Yum Yum KP

[1941wld]

KP,
My set works great. I am very happy with them. Mercury is the way to go.
Best Regards,