The PO of my 544 with SU carbs adjusted the mixture just before I picked it up, only he was not sure which way to adjust it to lean it out a bit.

After a nice 70 mile drive on secondary roads, the plugs are dry and BLACK.

Which way do I turn the mixture screws on the bottom of the carbs to lean them out? I would like to reverse his change only if he was wrong.

Welcome to the PO did the work club. When I bought my 544 the carbs were way rich and way out of balance. The front carb opened a good 1000 RPM earlier than the back. JC Whitney sell a nice gauge to use to syncronize carbs. John had pretty good advice on mixture adjustment.

As long as we're here. I'm a little puzzled. I have had HS6's for years and love them. I just started messing with different needles and am amazed at the differences. I get 4.5 miles per gallon MORE with ZH than KN. The car feels like it's starving and probably is.
http://www.georger.com/su_needles.htm is a link to a chart I did with some popular profiles. Take a look and see the differences. ZH is the bottom and very lean for a B20. My engine is .030 over and compression is 9.8 and I use premium grade fuel. On ZH it felt like I had a trailer fully loaded. KN's are richer and better. I have W02's in ther now and the milage is down to 21.5 or so but it has plenty of grunt. Today I'm going to put in the RH which are richer in the lower range than KN but leaner than W02. These are all new needles so the test should be kinda valid and I'll be driving 300 miles per week on the highway. I do have a question for carb experts. I have fuel squirting out of the front bowl at idle and spilling to the ground. Tapping it doesn't seem to change much but accelerating uses the fuel and it stops. Sometimes it will hold an idle without leaking. I have changed out the whole top of the bowl and still it might leak. What is the pressure that SU's usually get from the mechanical fuel pump. I have an electrical NAPA pump that gives 4-6 lbs. Is this the right pressure? I have changed the needle and seat for the float but I must be missing something when it happens across my changes. Comments?

Christopher Virgilthevolvo V2

Ideal would be about 2.5 lbs fuel pressure. Just buy a fuel press regulator, set it to 2.5 and your float bowl leak problem should be cured. Try a set of KD's if you can find a pair. Happy needle swapping. Keep us posted with the results.

Jim

Sounds like too much pressure to me. Unless it is little bits of grit holding the valve open.
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I'm JohnMc, and I approved this message.

They aren't really screws, at least if we are talking about HS6's, which is what a PV would have come from the factory with. Rather a large nut that goes around the bottom end of the jet. (In the picture, at the bottom of the main carb body, about 1/4 inch above the red base of the jet - not all jets are red like that though!)

Screwing it 'in' (facing the outside of the carb, moving the outside edge of the nut forward) raises the jet, and pushes it farther onto the tapered needles, which leans the mixture. Screwing it 'out' lowers the jet, and richens the mixture. It's sort of confusing to talk about clockwise or counter clockwise, because you reach up underneath the carb to adjust it, but look down on it from above (unless you are really short!).

There is a whole sequence you use to arrive at the proper mixture, which involves using a little pin located surreptitiously under the edge of the dome to raise the piston slightly, and noting what the idle speed does when you do that. Google up an article or two, but here's the gist about how to read what happens when you use the pin to raise the piston:
RPM's rise and stay up, that carb is rich.
RPM's rise briefly, then drop, mix is about right.
RPM's fall, engine gets rougher - mix is lean.
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I'm JohnMc, and I approved this message.

Moving the jet down or the needle up makes it richer. Sounds like it is
already too rich so you want to adjust it to where the jet comes up just
a bit. Depends on which engine and carbs you have how you do this.

It amazes me that a guy who doesn't know which way is richer is adjusting
carbs for you....
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George Downs Bartlesville, Heart of the USA!

...and you don't really NEED a balancing tool to get the carbs matched up. They are nice to have, and should only cost about $25 (try a motorcycle shop).

I use a mechanic's stethoscope with only the earpieces and the rubber tubes connected. I take off the tip and the probe. I put one hose into each carb opening (throat) and listen to the balance of air noise. The sound will seem to move from one side of your head to the other until you get them right, and it's in the middle of your head. Follow that OK?

ALSO, while we're doing some tune-up stuff here, the PO probably used the wrong feeler gauge to set the valve lash, too. You need a wire-type feeler gauge, not the flat blade type. The rockers tend to wear a little across the top, and trying to measure the gap with a flat blade usually leaves them too far apart.

Insert the wire parallel to the rocker shaft, i.e. front-to-back, not across the motor from side-to-side.

Have fun!