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post #1 of 3 (permalink) Old 04-16-2019, 12:25 PM Thread Starter
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Startup and idle challenges

Folks,

First off, thanks for all the help that you've been providing to me so far. I really appreciate this community. I was hoping I could pick the collective brains of this forum yet again.

I pulled the 2.0 out of my '78 recently to replace seals and give it a general cleanup. Pulled the carbs, ultrasoniced them and replaced O-rings and gaskets throughout.

I put the engine back in last weekend and fired it up on Sunday. Starting with all idle-mixture screws 2.5 turns out I was able to adjust out to 3.0 turns for a smooth idle. Brought the RPMs to 1200 at idle and synced airflow across both carbs with an Empi airflow meter. It idled like a dream and moved through the revs responsively and without signs of over-fueling/choking. The car started up (warm) very quickly and smoothly throughout the next few hours.

Last night, after work, I went out to the shop to start it up and check fluids. Starting was an incredible struggle and idling was non-existent. 4 pumps of the gas and holding at ~1/8 throttle and I would crank and crank and crank until it finally caught and then coughed and bounced around. The engine refused to settle into a good idle and I can't for the life of me figure out why. Before the rebuild it always started well and kept running with light throttle play. Sunday afternoon it was running better than I've ever had it run.

Any input folks can offer would be greatly appreciated. This is my first Alfa and first time tuning dual Dellorto 40s.

Kindly,
Mark
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post #2 of 3 (permalink) Old 04-16-2019, 11:49 PM Thread Starter
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Who’s got two thumbs and may have ate paint as a child? This guy!

Got home tonight and took a look down each barrel of the front carb. Stroked the throttle and confirmed fuel squirt upstream of the butterflies.

Did the same for the rear. No fuel. Accelerator pump or check valve? Pulled the carb, tossed it on the bench and pulled the lower accelerator pump cover. Yep. Some idiot put the spring on the wrong side of the diaphragm. Swapped it to where it belongs, reinstalled the carb, turned the key to let the bowls fill, and cranked it for less than a second.

Fires up immediately. Idles smooth. Still some fine tuning to do, but what a relief! As per usual, the biggest problem with most cars was found between the steering wheel and the driver’s seat.

Last edited by MarklotS; 04-17-2019 at 12:07 AM.
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post #3 of 3 (permalink) Old 04-17-2019, 12:56 AM
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We've all done something similar ! I once rebuilt the carb on my wife's Mini, but the large spring that retards the diaphragm on the SU carb rolled off the bench during rebuild, and was omitted. She drove to work the next day, and called me once she arrived saying the car would not go faster than 15mph. I told her 'don't be ridiculous'. Then walked into the empty garage, and saw the spring lying in the middle of the floor.....

My twin Dell'Orto's have never been properly tuned..I am now tempted to follow your lead and give them a clean/rebuild/tune as a spring task.

Glad to hear you got it sorted. Nothing more frustrating than doing a job like this, getting great results, then finding the next day it runs worse than ever !!

Chris
1977 Spider 2000
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