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Old 07-29-2020, 03:55 PM   #1
drolston
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Default Function trumps Awesome

Planning to take the '41 across the country in the Spring, for which reliability becomes the priority.

I have been fooling with my Offy 3x2 with chrome Super 97's (1 primary with choke and idle circuits, 2 secondaries) for three years and it is just a very fussy setup, even with the most expensive progressive linkage. The engine is a 284 inch 59A/B with 425 Offy heads and a mild cam (Schneider 248F). Vacuum dithers between 12 and 13 at idle. Stock transmission.

Runs great on just the primary, and will go like hell when I floor it to open the secondaries, but after such bursts of RPM and power, it stumbles for a while. And I have never been able to cure the problem of having the engine die when coming to a stop. Tried all suggestions I have found, to no avail.

The '34 Pickup has a Holly 390 on an otherwise stock 53 Merc engine. It goes great and has been flawless in all driving and weather conditions.

What four barrel intake manifold would work best on the 59A/B block, with a generator mount and vacuum port for the crab/Pertronix distributor? I also hope to stay with stock throttle linkage. Is there a better choice than the Holly 390? Any particular version or tricks I should know?
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Old 07-29-2020, 04:01 PM   #2
Terry,OH
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Default Re: Function trumps Awesome

What engine and distributor?
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Old 07-30-2020, 11:25 AM   #3
drolston
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Default Re: Function trumps Awesome

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What engine and distributor?
284" 59A/B; crab with Pertronix.
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Old 07-30-2020, 11:33 AM   #4
Jack E/NJ
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Default Re: Function trumps Awesome

>>>Runs great on just the primary>>>


Seems like the answer. Block the secondaries for the trip. Or try straight linkage to see how it goes. Jack E/NJ
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Old 07-30-2020, 11:47 AM   #5
Ross F-1
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Default Re: Function trumps Awesome

It almost sounds like after a burst of speed, it's running out of gas. Stock fuel pump?

Does it die at stops regardless of whether you've had your foot in it?

I can understand wanting to go with Simple for the long trip. Crabs run on manifold vacuum, don't they? So no carb compatibility issues like on an 8BA/8CM.

PS -- Would be interested in hearing about your trip!
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Old 07-30-2020, 12:25 PM   #6
drolston
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Default Re: Function trumps Awesome

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Originally Posted by Ross F-1 View Post
It almost sounds like after a burst of speed, it's running out of gas. Stock fuel pump?

Does it die at stops regardless of whether you've had your foot in it?

I can understand wanting to go with Simple for the long trip. Crabs run on manifold vacuum, don't they? So no carb compatibility issues like on an 8BA/8CM.

PS -- Would be interested in hearing about your trip!
Stalling at stops seems to happen randomly, whether I have had my foot in it or not. Happens with idle jets set rich or lean. Floats are set a shade under 1/2 inch. Never fails to start right up.

I will post any interesting car stuff along the trip.
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Old 07-30-2020, 12:28 PM   #7
drolston
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Default Re: Function trumps Awesome

Quote:
Originally Posted by Jack E/NJ View Post
>>>Runs great on just the primary>>>


Seems like the answer. Block the secondaries for the trip. Or try straight linkage to see how it goes. Jack E/NJ
Good suggestion, and a lot cheaper than a whole new manifold and carb setup.
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Old 07-30-2020, 10:06 PM   #8
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Default Re: Function trumps Awesome

Vacuum seems low. Getting it to around 18-20 will help with the idle. But 3x2s might be the right vacuum. Big holes in the intake system.
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Old 07-30-2020, 10:50 PM   #9
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Default Re: Function trumps Awesome

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Originally Posted by drolston View Post
Stalling at stops seems to happen randomly, whether I have had my foot in it or not. Happens with idle jets set rich or lean. Floats are set a shade under 1/2 inch. Never fails to start right up.

I will post any interesting car stuff along the trip.

I really look forward to your travelogue. I always loved seeing ol Henry on his trips. We all need an armchair adventure, but I'm sorry I can't add to your 3x2 questions.
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Old 08-01-2020, 07:52 PM   #10
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Default Re: Function trumps Awesome

Update on the erratic idle.

Put my hand over the secondaries at idle and they were both breathing way too much air in. Turns out the secondaries were not going all the way closed with foot off the pedal. To avoid too much tension in the progressive linkage, I left the accelerator pump lever springs off of the secondaries, thinking that the shaft springs would do the job. Bad idea. The linkage between the secondaries was sticking about 1/16" from full closed. So I replaced the accelerator pump lever springs, and added another linkage return spring.

The idle mixture screws were way out to compensate for the volume of air leaking through the secondaries. They are now set at a more normal turn and a half out from closed. The idle is now smoother and repeatable. I gave it a good hard test run and it no longer runs rough after getting on it. Also did not die when coming to a stop. Having the throttle plate close reliably makes a big difference.

A bit surprised that the vacuum at idle did not change; dithers between 12 and 13. Could that be because of the cam with longer duration?

Next issue to work is missing or slight roughness at full throttle in second or high. Any suggestions?
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