easy carb tuning Question

Do the mixture screws add more air to the fuel mix as they are backed out ? If I pull my plugs
and they are sooty shouldn't I add more air to the fuel mix ? To get two of my bikes to idle at
1.75 k I have to increase the rpms with the idle knob. Then, after riding a few miles, I stop at a light
and the idle speed is 4-5 k rpms. I pull over, turn the idle knob in reverse till it slows to 1.75 k again.
I live at 7,500' elevation. If I pull the air filter and the engine speeds up would that indicate an over-rich
problem ? I thoroughly cleaned both carbs. On the second one I installed new throttle shaft seals and
new mixture screw "0" rings+washers. But, they both behave the same. Mixture screw 2.5 turns out.
"82"650 rj seca, "82" 650 maxim j.

 

No. The mixture screw sits in a part of the carb known as the pilot circuit. What it does is feed the air/fuel mixture (it's already premixed at this point) into the carb throat just past the butterfly -- it's also referred to as the "idle" circuit.

If you want to get a look at the insides of these things, hit up the XJ4Ever site and discover that Your Carbs Are Naked.

That's a bit high -- idle should be just over 1000 rpm.

 

The mixture screw richens the mixture when turned out and leans it when turned in. As far as your sooty plugs, this is from Len(member name Chacal) at XJ4Ever, the resident parts guru:

Why are my plugs carbon-fouled (dry, sooty black deposits)?:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

 

Your carbs are NOT synched right or you have a vacuum leak (usually intake boots or gaskets)

 

If idle is high like you describe one of your carbs is putting more fuel in than the others ( it settles down by adjusting knob ). You will need either the 4 vacuum gauge set up( MY preference) or build yourself the 2 bottle synch manometer .

 

Did you bench synch each rack after you cleaned them?

Gary H.

 

I bench synched with a sliver of plastic card before I reinstalled the carbs. New throttle shaft seals and an immaculate
cleaning job. Today I pulled the plugs and examined them. #1-light soot cleaned up with a toothbrush, #2- soot just a
bit heavier, #3- very light soot,wet with gas, #4- same as #3. I cleaned them and replaced them and tested for spark.
All the plugs were getting a strong spark on the tester. I changed the air filter from a foam one to paper and started it, it idled
faster than before and I turned it down to 1.25 K from 2k. I remembered that when I disassembled the carbs before cleaning
the mixture screws were set at 1-1.5 turns from bottom. When I reset them I used the standard 2.5 turns out from bottom. Maybe I set them
too rich. Should I turn 1+2 in .25 turns and 3+4 .5 turns in to lean the mixture ? And, what comes first, adjusting the mixture or
synchronizing the carbs ? Yes, I set the valve shims first. I have the 2 bottle set-up.

 

How many turns the idle mixture screws get depends on the thread pitch of the screws. Fine gets 2.5 turns, coarse gets 1.5.
Does the Maxim have a YICS engine, or a non-YICS engine?
More importantly are the idle mix screws fine pitch, or coarse?

 

I'll have to pull one of them in the morning and see.Thanks

 

Correct me if I am wrong; if your valve clearances are out of spec - this to can create incomplete combustion

 

Correct.

 

Compression numbers may help understand the condition of the engine. Low compression on a couple of cylinders won't help matters much either.

 

Gary H.

 

The integrity of the engine is good seal on all cylinders. If there are compression issues there will be tuning and scyncing issues.

 

+1. Has compression been tested?

Gary H.

 

the compression tested 118, 122, 120, 119 lbs. I tried synchronizing the carbs, but the yics tool I purchased
on ebay ( an aluminun rod with strategically placed "0" rings ) didn't work, the "0" rings fell off. But not before I messed
up the bench synch. so, I turned in the mixture screws, 1+2 one quarter and 3+4 one half turn. I pulled the carbs, bench synched
them again with a strip of credit card and reinstalled them. this time the bike ran more smoothly. The idle held at about 1.25 k
and rose to 1.75 k at the first stop light after a 10 mile run but dropped to 1.25 k when I goosed the throttle. The next move will
be building a home made yics tool that will actually block off the ports. The first thing I did on that engine was to swap the valve
shims around to put them in spec.

 

You don't need the YICS blocking tool to do a running synch.

 

Hi Why do you not need the YICS Blocking tool to sync carb's while running? Thanks I know this is an old post

 

general consensus is it is not needed. without tool you are realworld tune as bike is not riden with tool in place. not using tool will get you where you need to be.
if you are racing you may want to use the tool for tha added 100th of a second.

if you chose the tool make sure bore is clean and the tiny holes into head are clear.

 

Plus one, don't bother with the tool. If you were racing you still wouldn't use it.
Most peeps on here use a colortune to set mixture screws. I do it by ear, but it's not easy, and not guaranteed.