CArb Synchonizing

[fermin]

After building my own $2.69 manometer I attempted to synchronize the carbs over the weekend.  The problem is that one of the carbs always pulls in a lot more vacuum than the other and just cranking the engine sucks the oil to that side.  Its very fast not even allowing the engine to start.

The carbs are statically adjusted prior to the sync process with a 3/4 out idle mix and engine  speed of around 1100 rpm, 4 mm play at the cables, choke off and vacuum .  Carbs cleaned and diaphragms changed, valves adjusted, new plugs and engine warm.  The only thing I havent touched yet is the timing.  The idle mix screw has a rubbery fell when turning sort of making squeaky noises.  I did not replace the o rings when the carbs were cleaned because rings in the the kit that came with the bike appeared brittle and one broke while attempting to replace an existing one, thus I kept the old ones.

After the static mods the bike is harder to start and dies now and then while in neutral. It sounds better at 1200 rpm idle.

Also the generator warning light is on until the 1500 rpm mark.  Is this normal.

[nhmaf]

Normal for the GEN light to be on until 1500+ RPM.

I generally set my idle on my R65 for around 1100 RPM.  IT is possible that have got a dried out O ring or one that itsn't seating right with the mixture screw.

Tne cheapo DIY manometer is VERY sensitive.   What are you using in it, ATF?   You can desensitize if a bit if you can find some short length of plastic hose that has a tiny/small inside diameter and which will fit inside the hose that you've used to attach to the vacuum ports on the carbs.  Or alternatively, a double ended hose barb that you can splice into those vacuum lines that has a much smaller inside diameter.  Either of these will still allow the device to measure differences in pressure, but will slow down the response time of it so it won't react so fast to slight differences.

[ukzknos]

You have an engine speed of 1100 rpm but it sounds like you have the idle adjustment screw on one carb screwed further in than the other to achieve this.

Leave both mixture screws at 3/4 turn then back off both idle adjustment screws and adjust them again to achieve 1100 rpm but with the manometer balanced.

Once you've achieved this adjust the throttle cables so you still have balance when you rev the engine higher, i.e. 3000 rpm.

It's a knack but once you've mastered it you will be impressed with the results!

Steve

[fermin]

I am using gear oil. I think the small diameter of the tubing didnt help (1/8 in), and the oil would stickto the sides and take a while to be cleared. Now using a 5/16 or so on the reservoir end and 1/8 on the tubes reaching to the carbs.

I think I'll use only a less oil in the U tube (3 in or so) and dampen the line with a small hose barb.
Thanks

[Flash]

I'll agree that it sounds like the idle adjust screw isn't out far enough on the side that shows too much vacuum. That's why it runs better with you opening up the throttle a bit.

[Yikes]

I had trouble getting my home-made manometer to work right for me.  I tried Snowbum's alternate side shorting method, fabricating the plug extenders from the tops of old spark plugs and copper wire.  Find that method here:

http://bmwmotorcycletech.info/synchcarbs.htm

I found matching the way each cylinder sounds when the other is shorted to be pretty easy.  First at idle, then off idle.  It made a whale of a difference for me in smoothing out my power curve.  The other good thing about the shorting method is that you can carry the plug extenders easily in your tool box and stop and slap them on and do a tweak just about anywhere.   Not possible with the manometer.

[fermin]

Yikes Ive seen and read that article but cannot figure out the tool, one end threads into the plug top and the other grounds to the cylinder head fin??  I have a hard time visualizing that .  

[nhmaf]

If you've got the dosh, I'd recommend the Morgan CarbTune product (it looks like a set of vertical liquid gauges but is actually stainless steel slides encased in tough glass tubes - a rotameter, for those so inclined.
It works well, IMHO, and I use it on my airhead and on other multi-carb engines, including my Kawasaki Concours/GTR1000.

P.S. They also sell the colortune product on the same website, though I don't have one of them - most places I have plugs (except for the airhead) there is no good way to look at them anyway..

[Ed Miller]

"Yikes Ive seen and read that article but cannot figure out the tool, one end threads into the plug top and the other grounds to the cylinder head fin??  I have a hard time visualizing that ."

Our spark plug caps don't use that little cap that threads onto the spark plug.  But the end of some motorcycle spokes will thread into that, and leave enough thread to thread the other side onto the spark plug which is still installed in the bike.  Cutting a little notch in the top end of the spoke portion will allow your spark plug cap to engage that end of the spoke.  Set both spark plugs up that way.  The motor will run like this, the spokes are conducting the current to the spark plug.  Use a screw driver (insulated handle may be a good idea!); touch it to the cylinder firmly, then touch the upper part of the shaft to the spoke.  That will make the spark on that side cut out, as you are grounding the current.  The motor will run on the other side.  You switch back and forth until you can make the cylinders, running individually, sound the same.

[Yikes]

Fermin, here are the shorters I made from the spark plug tops and copper wire.  Pretty crude but work OK.
The silver ends of each shorter are the threaded metal top of a spark plug (the bit that the spark plug wire cap attaches to on a whole plug) and the metal screw on cap that comes with the plug, but has to be removed to use.  Just gently smash the porcelin of a douple of old plugs with a hammer and they come right off.
the wire I was using was a little small in diameter, so I flattened each end enough to get a good friction fit into the ends of the two cap pieces,  A bigger wire would be better and a properly sized bit of threaded rod, like a spoke, would be much better.
To use them, remove the spark plug cap from the plugs on the bike, scerw the rounded barrel cap end of the shorter onto the threaded top of the plug and push the spark plug cap onto the top of the shorter.  The shorter acts as a bare wire extension of the spark plug wire.  When installed, the bike runs normally.  When a screwdriver iis touched to the bare wire and any part of the cylinder head, the circuit is shorted and that cylinder stops firing.
To balance the carbs, just follow Snowbum's directions, and go back abd forth between the cylinders, shorting and listening and adjusting the throttle screws at idle until the right and left sound the same and fire at the same speed when one or the other is shorted, then repeat at off-idle using the cable adjusters to match the carb sounds the same way.  It really worked well for me and I have zero experience tuning carbs, much less synchronizing two carbs.  And my carbs were way, way out of synch after the rebuild.  I thought I must have botched something in the assembly, but it just needed adjustment.  Just follow Snowbum's cautions so you don't fry your ignition system or yourself in the process.
Good lock with it!

John McC