ZCar Forum banner
Status
Not open for further replies.
1 - 6 of 6 Posts

·
Registered
Joined
·
645 Posts
Discussion Starter · #1 ·
i'm currently double parked out back of my apartment and i'm trying to adjust my carbs with limited success.

they are 72 SU carbs

here's what i'm doing:
0. completely back off balance screw
1. tighten mixture nuts until they seat, then back off 1 turn
2. tighten the throttle screws (or whatever they're called - the ones right next to the damper housing), then back them off about 3 turns each
3. start car, adjust throttle screws equally until rpms drop to about 700 and engine runs evenly
4. using an air flow meter, get a reading on the front carb

i have a question here: where should that little ball get to? i find no matter how i adjust the air flow meter, the highest i can get it to float is the first level unless i adjust the throttle screws (which adjusts my revs of course)

5. get a reading on the back carb and adjust the throttle screw until i get the same reading as on the front carb
6. tighten the mixture screws equally until i get the smoothest, fastest idle
7. adjust the throttle screws equally until i get back down to 700 rpms
8. repeat 5,6,7 until air flow readings are accurate
9. tighten up balance screw until visually it looks like both carbs are opening up equally

my results: driving easy, the carbs are boggy and jerky, but if i floor it they respond nicely.

oh yeah, valves, timing, points, coil and everything else ignition wise is good.
any help would be appreciated

hoping i don't get towed,
James.
 

·
Registered
Joined
·
625 Posts
TRY THIS

WITH AIR FILTER REMOVED LIFT UP ON THE FRONT CARB PISTON AND SEE WHAT HAPPENS.THIS WILL CAUSE THE ENGINE TO RUN ON ONLY THE BACK THREE CYLINDERS.IF ENGINE DIES THEN THE REAR CARB IS TOO LEAN.TURN YOUR FUEL MIXTURE NUT ON BOTTOM OF REAR CARB CLOCKWISE A HALF TURN AT A TIME UNTIL ENGINE RUNS SMOOTHLY ON ONLY THREE CYLINDERS WITH FRONT CARB PISTON LIFTED . REVERSE PROCEDURE AND TRY OTHER CARB.THIS SHOULD CURE YOUR PROBLEM IF THE AIRFLOW SCREWS ARE PROPERLY ADJUSTED. LATER,NORM
 

·
Premium Member
Joined
·
40,971 Posts
Stick or auto? if it doesn't get any better, you can always set the idle speed up a bit following the procedure you outlined. They tend to have a small bog with the stock dist when you try to pull from 700/750 rpm's. I've always set mine at 850-900 with lots of initial advance on the ignition (12deg). Not factory, but I like the way it runs like that.
You may also want to try switching fuel brands to see if that helps. A few years bac the difference between brands was dramatic, but now they're all formulated like shi* to atomize under High Pressure for FI cars. The real difference comes only when I buy racing gas, now. It's still formulated for carburetted cars. Good Luck, at least it's moveable! :)
 

·
Premium Member
Joined
·
40,971 Posts
yes, try norm's suggestion first

It's a REAL fine-touch adjustment for the mixture if your airflows are balanced right. I do it without thinking, after that, I set the car up as stated in my other post.
 

·
Registered
Joined
·
645 Posts
Discussion Starter · #5 ·
GOT IT!!!

thanks guys, i actually went back downstairs before i received your responses and played around with the carbs something like Norm suggested, and i've also set my idle to about 850-900...you're right tony, i think it runs a little nicer (less boggy) out of the hole like that

thanks again guys...now i can spend my $50 on beer, instead of parking fines (like i pay them anyway!)
 

·
Registered
Joined
·
107,695 Posts
RE: GOT IT!!!

You shouldn't have to set the idle above factory specs to cure the hesitation at low RPM. My Z used to have that problem, but I finally cured it through untold hours of tweaking the carbs. (Actually, about 5 hours). Replacing the jets and needles with those intended for the 1971 SU also helped. (Those are the 'N27' needles). You can have a nice slow idle and immediate response at the same time; you just need lots of patience. :)

You asked something a few posts back about how high the little indicator should go on the air flow meter.

It actually doesn't matter where the indicator winds up. It's just supposed to be the same for both carbs. If you'd rather see it closer to the middle of the tube, just turn the smooth round thing on the meter that faces the air inlet. (That thing *is* on threads :). That'll tighten down the air passageway and make it read higher. (On *both* carbs). You should actually just adjust that for maximum readability. i.e., right in the middle of the guage.

Have fun and don't stop tuning it until you're 100% satisfied. You can do a lot with some fiddling.

-rr
.
 
1 - 6 of 6 Posts
Status
Not open for further replies.
Top