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Old 07-16-2021, 06:10 PM   #1
threepointsmach
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Default 59A running rough

New to the flathead v8 world, with a 59a engine in my '33 truck. Navarro 3 twos'(Stromberg 97's, center carb blocked off), Edelbrock heads, Winfield cam, crab distributor, 3/8x3/8 b and stroke. Compression runs at 145-150 on all cylinders. I am having trouble getting rid of a random miss and high idle. Seems to be running rich on most cylinders, and puffs out a little blue smoke when it backfires. Engine sat for about a year. New plugs, wires, points, cap, and rotor. Can someone point me in the right direction?
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Old 07-16-2021, 07:44 PM   #2
corvette8n
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Default Re: 59A running rough

Try a vacuum gauge to see if you leak.
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Old 07-16-2021, 08:00 PM   #3
flatjack9
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Default Re: 59A running rough

When does it backfire?
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Old 07-16-2021, 10:00 PM   #4
drolston
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Default Re: 59A running rough

Sitting for a year is just not good. Crud happens. Could be a sinking float in a carb or debris in the needle valve, causing fuel level too high and partial flooding.

Run it for a bit then shut it down and start pulling tops off of your 97s. Any with fuel level much higher than half inch below the gasket surface would be a problem. If so, check floats for leaking and partially filling with gas. Fill the float bowl near the top with gas and then see if you can blow through the fuel inlet. Takes pretty good pressure to blow the needle valve or ball off of its seat when the float is up on it. If leaking even a little, blow carb cleaner through the needle valves and try again.

Good compression says not intake valves, but for an engine that sat that long, I would drizzle a pint of MMO through each carb while jazzing the throttle, just to be sure.
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Old 07-16-2021, 10:39 PM   #5
Tinker
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Default Re: 59A running rough

I concur. Might be stubborn valves not closing under load. Exhaust valves take the brunt of sitting and carbin' up. Leaded fuel (which is no more for good reason) was used to lube the top end on L head blocks. (Ya you don't need lead additive, mmo it) Worth a try and cheap. Engines don't like to sit around. Best when they are run. Back fires indicate a rich mix, ignition, or a valve not closing. Start simple and work your way out. Drizzle MMO down the carb till it smokes out and run the crap out of it. Repeat. If it still happens.... An engine like that doesn't always jive with a lot of idle time.


As mentioned a vacuum gauge is just an analog engine diagnosis tool. Will tell you a lot. Combustion engines are really just an air pump. Why super chargers are a thing. My 36 has a full time on board vacuum guage, so I can monitor engine under load. Best of luck!

Last edited by Tinker; 07-17-2021 at 01:50 AM.
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Old 07-17-2021, 10:22 AM   #6
Terry,OH
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Default Re: 59A running rough

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3X2 with center blocked off so your running 2X2. There are several things to think about.

Typically the 3x2 outer carbs are dumpers and have the idle circuit blocked. Plus other modifications can be done. The center carb does all the idleing. Have your other 2 carbs been modified?

Running a 2x2 and both carbs are in near stock configuration. Running rich could be due to the jet sizes. Have you synced the carbs so both are working the same. What jets are in the two carbs?
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Old 07-17-2021, 11:13 AM   #7
38 coupe
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Default Re: 59A running rough

Is the gas a year old? If so I'm surprised it runs at all.
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Old 07-17-2021, 12:24 PM   #8
drolston
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Default Re: 59A running rough

Quote:
Originally Posted by 38 coupe View Post
Is the gas a year old? If so I'm surprised it runs at all.
Year old modern gas is still better than the gas these cars originally ran on. It may lose some of its ethanol but the other additives are stable.
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