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1970 240 - what is normal?

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1970 240 - what is normal?

Post #1 by rratselad » Sun May 17, 2020 3:46 pm

Hi there-

I have a 1970 240 that is in a E100 and everything is OE. I have a couple questions about what is normal and I'm hoping someone here can help.

  1. ~7 or so years ago (<1500 miles), I put a Autolite rebuilt Carter YF on. It started leaking very small amounts of fuel from the throttle plate onto the manifold. Basically, the leak was enough to stain the intake manifold, directly below the shaft. Here are some pictures of the carb in the area of the leak (replacing the carb again, now). Is this leak normal for this type of carb?
  2. When I replaced the carb 7 years ago, I noticed some rock-hard carbon at the base of the inside of intake manifold. This is where the exhaust system pre-heats the fuel/air mix in an OE configuration. I had the inside of the manifold blasted ~200 miles ago and see the carbon coming back now that I'm doing the carb swap. Is this normal or am I running too rich?

Last edited by rratselad on Sun May 17, 2020 4:01 pm, edited 1 time in total.

Blairsville Ed
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Re: 1970 240 - what is normal?

Post #2 by Blairsville Ed » Sun May 17, 2020 3:59 pm

Is it heat soak?
I have a 1968 240, F100. After I drove the vehicle a while and it was fully warmed up, then you shut it off, after 5 minutes the heat would rise up from the exhaust manifold and heat the carb bowl until the gas would percolate out of the Main Venturi.

I solved this issue by installing a 2000 rpm computer cooling fan to blow on the fuel bowl after the engine was shut off. I used a 104 degree snap disc switch to control the fan.

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Re: 1970 240 - what is normal?

Post #3 by rratselad » Mon May 18, 2020 6:56 am

It could be heat soak. Thanks for the suggestion. I’ll have to look into that a little bit more.

I’m also wondering, could the carbon buildup be oil from the PCV? Are these engines known for intake carbon buildup?

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Re: 1970 240 - what is normal?

Post #4 by THE FRENCHTOWN FLYER » Mon May 18, 2020 8:35 am

rratselad wrote:Are these engines known for intake carbon buildup?

I have disassembled several carbed engines where there was extremely high buildup of hard carbon in the intake ports and on the intake valves. I attribute this to several conditions -

Unequal fuel distribution of 1V carb through a log intake
Valve guide wear and breakdown of the valve stem oil seals
Faulty or mis adjusted choke mechanism
Lack of oil control by the ring pack

I didn't look inside the intakes because they were discarded parts I did not plan to reuse, but I suspect there would have been some carbon there too.

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Re: 1970 240 - what is normal?

Post #5 by rratselad » Tue May 19, 2020 8:58 pm

Thanks, Frenchtown flyer! The engine is newly rebuilt, so I have to assume it's the choke, unequal distribution of the 1v or possibly heat soak as suggested by Blairsville Ed.

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Re: 1970 240 - what is normal?

Post #6 by Lazy JW » Sat May 23, 2020 8:19 am

I have been inside several stock Big Six Fords and they have all had lots of carbon buildup in the intake passageways. I attribute it to a combination of the various things mentioned above, plus the relatively long overlap period of the stock camshaft which contributes to a significant amount of reversion.

Reversion pumping spent end gases/fresh air-fuel back and forth inside the intake manifold is bound to leave some deposits; this will be worse when operating at low speeds and doing short runs. I like to run a hotter thermostat to help offset my typical short runs.

It's just the nature of the beast.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)

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