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Carb adjustment/balancing frustration (long)

To: mgs@autox.team.net
Subject: Carb adjustment/balancing frustration (long)
From: William Killeffer <wkilleffer@comcast.net>
Date: Tue, 09 May 2006 22:12:16 -0400
Hi everyone,
I am trying to adjust the carbs on my 1974 MGB, with a 1972 engine and 
HS carbs. Just about the time I think I've got it right, it seems like 
I've done nothing right. The part that's really throwing me for a loop 
is the part where you're supposed to push up on the piston lifting pins 
to determine whether or not the mixture is correct for each carb. This 
will be my third try, it's getting late and I need to be able to drive 
the car in the morning.

The vacuum advance for the distributor has been connected the whole time.

I started out by disconnecting all interconnections and adjusting the 
throttle stop screws 11/2 turns in, raised the jet even with the bridge 
and backed it down 12 flats. I started the car and it got to NOT 
quickly. Then, I backed the idle speed down to just under 1000.

After that, I used a carb balancer to check the airflow into each carb. 
The rear always seemed to be higher than the front, so I'd tweak the 
idle screws to bring both carbs to the same place on the balancer.

Then, I started turning the jets flat by flat until I got the fastest 
running speed with an even fire and exhaust sound. This necessitated 
adjusting the idle speed and re-checking the airflow with the balancing 
tool. The airflow was never the same with either carb at that point.

At that point, the directions say to push up on the piston lifting pin 
first on the front carb and then on the second. If the speed rises, the 
carb is too rich, if the engine tries to stall, it's too lean, and if it 
briefly goes up and comes back down, it's just right.

What if I get none of the above? Well, sometimes it's obvious that it's 
trying to stall. But otherwise, I might get the slightest quick blip 
upwards, and then an attempt to stall. A few times have brought no 
change at all.

All the books seem to give a different amount as to how far up one 
should push the pin. Trying to push it up 1/32" and keep it steady is 
almost impossible. It's really difficult to push it anywhere but all the 
way up with any consistency.

Part of me just wants to stop before I get to that point and hope for 
the best. But that just doesn't seem right. I'm trying to use less gas 
while still having fun and retaining reliability. But it's no fun if 
unsuccessful attempts to adjust the carbs use 1/4 of a tank.

The carbs have been reshafted and rebushed in the last three years, and 
don't show any signs of leakage around the shafts.

There probably haven't been too many times that I've had the carbs 
adjusted all the way right, so I'm trying to do it this time. Any 
suggestions would be appreciated.

Thank you,

-- 
William T. Killeffer
1974 MGB




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