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Carb Adjustment question

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JPSmit

JPSmit

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Oh, she's grumpy tonight.

Pulled the plugs - sooty black. ah says I, she's running rich - might even explain the hesitation. clean them up, re-check gap (.025) reinstall and turn the adjustment nut (HS4) anti-clockwise to lean it out. took her around the block, slight hill and she starts backfiring like crazy. came back it, turned 2 flats clockwise - no change, did this 3 times before I gave up for the night. BTW backfire is in the carb not the exhaust.

So to confirm the, adjustment is anti-clockwise for leaner, clockwise for richer - yes?
 
not timing - timing was set a week ago and has not been touched since. However I was messing with the carb - now I just want to confirm that I am adjusting it in the correct direction.
 
Turn the nut "into" the carb body to lean it out.

When you are looking down on the carb (bird's-eye-view) you are turning it counter-clockwise to lean it out.

From the bottom of the carb (looking up at the jet nut), you be turning it clockwise to lean it out.
 
thanks Nial

BTW - I had a book on carbs that talked about the plunger under the carb used to test mixture. As I recall, if you push it and the revs go up and then drop to normal, mixture is correct. but I don't remember what happens for rich & lean
 
It's a lift pin, raises the piston, can do with a screwdrive through the throat too. Lift a tiny bit, revs should go up slightly then settle back down if mix is good, if it raises and stays there, it's too rich and should be leaned out, if it falls off, it's lean and should be richened up a bit.
Not that I've ever done it mind you, I just happened to be reading up on it last night.
SUmixture.jpg
 
exactly what I meant - thanks, I love these boards!
 
It's easy for me to remember which way to turn by thinking about the jet moving as I turn the adjustor. Screwing up into the carb body raises the jet up higher relative to the needle resting position to reduce fuel. Screwing out of the carb body lowers the jet down away from the needle letting more fuel through. I also remember reading in the manual that certain conditions can exist where the lift pin method can give incorrect indications of fuel mix. I think it has to do with the carbs being way out of synch (one way too rich?) but thought i would mention it here. I spent the better part of a day reading the methods and trying them until I had a very smooth idle with a smooth steady exhaust note. Using the method of adjusting both jets so they are just even with the bridge then counting the turns to make sure they are the same throughout the tuning range gave me good results last time I did this.

Cheers,
 
John Peter you were turning the nut the wrong way sir. Looking up at the bottom of the carb clockwise is lean ani-clockwise is rich.
 
jlaird said:
John Peter you were turning the nut the wrong way sir. Looking up at the bottom of the carb clockwise is lean ani-clockwise is rich.
Click to expand...

No, was doing it right - anti-clockwise from top - just need to readjust enough.

thanks all for this thread - I get thing turned around in my head sometimes.

so,

for correct micture

1. use lift pin
2. listen for smooth running

any other mixture test tips?
 
JP

What is the needle number you have?

I could be wrong for your set-up

Mark
 
abarth69 said:
JP

What is the needle number you have?

I could be wrong for your set-up

Mark
Click to expand...

not sure - will get mixture sorted first, then needles (which mystify me completely)
 
and JP remember that adjusting the jet a couple "flats" can make a big difference, my plugs were "grey" opened the jets 3 flats & now the plugs are on the edge of being more black than brown... this weekend I will probably lean it out a flat & then do the piston lift to see if I'm in the ball park...
 
And that is exactly my problem - :wall:

BTW, how long for plugs to colour? IE how long should I drive before I pull them to check them?
 
For many racers, the classic way to "read" carb mixture is to do a "plug chop".

Warm up the engine.
Install new (correct heat range) plugs while you are near a major high speed road (or race track).
Accelerate gently onto high speed road and drive at a steady high speed (75 mph+) for at least 5 minutes or more.
Press in clutch, shut off ignition and coast to a halt. (do not turn key into "steering lock" position!)
Remove plugs and look deep into the center, ceramic insulator. It should be tan (not white or dark).

If things are not right, throw away plugs, rejet and do over.

May require 20 or more "trials" to get right.
I've done this.
It can be time-consuming and frustrating.

It is generally considered to be true that you cannot accurately "read" plugs this way if the engine has been idling or running at slow speed for even a minute or so.

The new air/fuel ration devices (like the " ~Innovate~ " seem like a better way of doing this to me.
 
JPSmit said:
And that is exactly my problem - :wall:

BTW, how long for plugs to colour? IE how long should I drive before I pull them to check them?
Click to expand...

Where I drive my Midget there is only one road in/out so the last 10 minutes of the ride to my garage is always the same, so I drive at 50 mph (country road 80kph), then less than a minute at 30 mph (50 kph sideroad), then just enough idle time to get into garage, because this is a constant (I always know the last 10/15 minutes of driving was the same conditions before I made a carb adjustment)then I can see the difference on my plugs when I do make an adjustment... if that makes any sense...
 
aeronca65t said:
By the by, there's a needle data sheet and needle selection program ~HERE~
Click to expand...

Nial, realizing I'm rapidly getting out of my depth here, could you explain in very simple words why I would change my needle and what the various numbers mean. I presume that somehow the diameter of the needle affects fuel flow at different rpm (carb openings) but after that my brain starts to shut down.

Help
 
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