Since my last post I’ve resorted back to careful Tuning & Research over driving hard to make performance improvements to 308427.
The car has Capacitive Discharge Ignition and a Pertronix Ignitor. I had changed none of this - and therefore I had not ever really known if my CDI unit was working optimally or not. Switching it out with another I won at auction didn't instill more confidence either... One that came on the car has the nice loud hum, the car did pretty well, but I left it alone as a seemingly functional Black Box.
Last week a beautiful 7300 RPM limited, Refurbished 3 pin CDI box from Kurt Donohoe at Partsklassik arrived in the mail less than 3 days after ordering. In the mean time I reconsidered the status of my carb settings, and I read.
The Weber Carburatori Tuning Manual can be read more than once… go ahead, its ok. It’s great actually!!!! I had forgotten everything I had begun to grasp while going through the carbs & seeing them sorta well tuned back in April. The description of the way in which Weber’s are designed, the color circuit diagrams, the tuning instructions. This on top of Paul Abbot’s notes (& the Haynes Weber Manual & Braden’s Weber book), and I began to see how to proceed in tuning and/or troubleshooting the carbs better than I had yet.
When I went through the IDS Webers, I was careful to put the throttle plates back exactly where they were, but I did not bench check the position of the plates with respect to the progression ports. Friday I worked in the dark with a flashlight and a mirror to examine the condition and arrangement of each bore’s 3 ports with the throttle fully closed (idle adjustment screws all the way off the tab) on the car. They were consistent: light could be seen through the upper two ports clean and crisp, while the lowest port was just more than half darkened by the edge of the throttle plate in each case. Very cool.
Study helped me to realize the connection between the port chamber and the Idle Jets was just as important to check / clean as the ports or jets themselves, so I blew 20 psi from the open port chamber to the open idle jet holes.
So what I had now was a pretty well tuned engine with NEW & IMPROVED CDI unit & clean, carefully examined Webers (the rest of my tuning process is unchanged from that already documented here).
I left the Idle Adjustment Screws backed out all the way and started the car. It had to be helped with the pedal for a few minutes and began to hold idle at 500-600 RPM. It popped some, but kept running better as it sat there warming up & filling my shop with exhaust. Turned on a big fan & just let the engine idle… nothin’ but Idle Mixture Screw supply and whatever air leaks around my throttle shafts. Kept comparing vacuum numbers from throat to throat quickly to catch a given RPM and started playing with the Compensation Air Adjusting Screws to improve on Synchrometer readings as the engine warmed at idle, throttle plates down. It just kept getting better, gaining some RPM as I tuned each Idle Mixture Screw by sound, rechecked vacuum in the throats, listened to the engine intently for some time, then shut it down. I had no time to continue with testing for 4 more days… until TODAY!!!!
Today I started the car at about 1:30 pm, the warmest part of the day. I now realize completely just how much assisted warm up means to a beast with no Choke Valve, so I am patient and I sit there happily helping the engine in lieu of a hand throttle. Basically the car got going fine, I backed it out and drove gently to continue warming it up. The car coughed and hiccuped plenty, but it really did not stumble much. As with the tinkering at idle, the car ran better & better as it simply warmed up. With no further tuning I was AMAZED at how well the car ran. Idle progression was still nothing to write home about & pops could be heard now and again, but the car flew up the Rio Grande to I-40 on ramp like nobody’s business and just kept going, smooth and even (except for my poorly balanced wheels). I ran the car through town to Tijeras Canyon and turned around.
The car was good & hot (though the carbs were still cool
Essentially, while I may have had some crud in the carbs (maybe NOT), improved Ignition has made the Webers more tunable. There is slight air leakage around the shaft at the throttle linkage on each carb. Idle is slow to return to 900 from 1100 RPM most of the time while warm. We’ll see how it does in this state while it warms up next time, but I honestly feel that I have it as good as I’m going to get it, and I know why & how it got there.
If I can manage, I’m heading back to check on that asphalt work tomorrow…
Thanks Kurt Donohoe for developing the improved CDI!!!!
Will I be able to get this level of performance out of original points and coil some day???
Cheers and Thanks for Riding Along!!!!!
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and that the gauge works. Performance has been my only criteria for attention so far. Had the car out last night in mild cool conditions and it ran perfectly. I need to plan careful float setting with hot carburetors.
