Carb adjustment

[mellis18]

Now that I'm living about 4,000 feet higher than before (moved to Utah from California Central Coast) I know I'm going to have to adjust the carbs for the lack of oxygen at this altitude. They were perfectly adjusted before the move and I don't want to screw anything up when I make the adjustment for here. From you carb experts out there what would be the best approach to accomplish this??

[GeoffM]

Hi Robert,
Do you do your own adjustments? If so, You may want to take a conservative approach. I know that it would probably run rich so I would try it out and see if I could notice a lack of performance, sooty exhaust etc. If so, I would do the adjustment. If not I would run it for a while and check the plugs for fouling. If they are black, I would do the adjustment. If not, I would leave it. Perhaps they might have been slightly lean at sea level and now there still ok...slightly rich. Who knows.

If you have a shop doing it, I would go and get the carbs adjusted if it exhibited rich running symptoms.

On the other hand, I love tinkering with the SU’s so I would probably end up doing the nozzle adjustments required right from the get-go.
Dang....I typed this without knowing if you have solexes or SU’s.

[Gregs672000]

Solex, much easier; SU, I wouldn't have a clue! I do agree with the advice above. Might want to start clean with a new set of plugs, you can always install the older ones when the new ones wear out if they're still good.

[nismou20]

Does it drive better? Feel peppier? Or lacking? Depending, you can lean out the bottom knobs a tad on each. I like to keep mine a bit on the richer side just for safety. If the idle burbles more than it used to it may be a bit richer at your altitude.

[Linda]

Try using a Colortune if you can get one, takes some of the guess work out. Plus I always prefer the " magic number" method as a starting point for tuning.
Linda

[mellis18]

Try using a Colortune if you can get one, takes some of the guess work out. Plus I always prefer the " magic number" method as a starting point for tuning.
Linda

Linda - I do have a colortune but its pack up with the rest of my garage "junk". Won't be able to get to that until we move into the new house in about 60 days.

What do you mean by the "magic number method"???

[mellis18]

Oh yea - they're SUs

[Linda]

The "magic number" method is described in one of the Tech Wiki articles on SU carb tuning. In essence it instructs you to take off the carb dome one at a time, then with a digital caliper which has an extending measuring ruler, measure how far down the nozzle is from the carb body. The " magic number" is .087 deep. The key is that each carb is set exactly alike, at .087, which makes for a very good balance starting point. But what is good to understand is that perhaps you might adjust it a bit ultimately, perhaps to .088 etc. I tried to do the "3 turns out" method or whatever the number, but was surprised to see how off each carb was compared to the other. Just try the "turns out" method then measure each nozzle depth...highly unlikely they are even. Evenness counts. So I followed the "magic number" method and the idle was better than it ever had been, in my opinion.
Like I said, I just followed the Tech Wiki instructions! http://www.311s.org/pmwiki-311/pmwiki.p ... ion.SuTech
A Harbor Freight digital caliper works well enough too.

Linda

[DCooke]

Bam! Just adjusted the carbs per Linda’s suggestion along with a unisyn flow meter & a few small adjustments to idle and its runs great now! Carbs seem balanced, less smoke out the tailpipe and the idle is smother than It’s ever been.

[Linda]

Here is the link:
http://www.311s.org/pmwiki-311/pmwiki.p ... ion.SuTech
Nice they are working better.
Caliper shows .87 should be .087"
Linda

[GeoffM]

The calipers actually show .034" which may be too lean, as the starting point should be ~ .087" and adjusted richer or leaner from there.

[DCooke]

Crap, I need better bifocals!
...and apparently I assumed this measurement was metric.
Regardless, even with my mis-measurement, the carbs seem to be better balanced. I’ll dive back in today & re-adjust to the correct depth.
It’s a pretty easy adjustment, the biggest pain was getting the air cleaner assembly inner bolts on & off.

[Linda]

I don't take the air cleaner inner housing off at all. I can reach under there. Might try it. It is still going to be a small slight turn on the adjustment knob
Linda

[DCooke]

Yeah, I tried to get to the adjustment on the rear carb without removing the air cleaner. My hands are too big, I can barely touch the bottom of the carb with my fingertips...might need to recruit a toddler.

[Linda]

If I were closer I'd come by to help. Chicago pizza, yum.
Toddler would work for a cookie