What fuel should I run in my 340?

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The more I drive my baby the more problems she's giving me!! I have a fuel leak now idk how???
Also I took her to 3 mechanics and they all said 3 Differnt things
One said timing
Another one said distributor
And the last said the carburetor
And my main mechanic can't see the car till Monday
I'm taking the carb to be rebuilt or changed tomorrow
 
Promark said:
The more I drive my baby the more problems she's giving me!! I have a fuel leak now idk how???
Also I took her to 3 mechanics and they all said 3 Differnt things
One said timing
Another one said distributor
And the last said the carburetor
And my main mechanic can't see the car till Monday
I'm taking the carb to be rebuilt or changed tomorrow
Click to expand...


Sounds like it's time to start getting your feet wet or you will end up hating this hobby.

The hate that comes from paying others to do simple work.

Rebuilding a carb is easy and requires little more than a screwdriver and a couple hours (less time actually). Go get a rebuild kit and follow the instructions.


Replacing a carb takes 10 minutes if I'm being slow and lazy.
 
Buy a timing light. This is one tool every old car owner should have. An inexpensive one is better than none at all, one with a dial is even better.
 
My 340 will run alright on 94octane but most of the time I run 70 /30 which is 94 / 115 octane. I have a lot of internal goodies and the higher the octane the better she runs.
 
1968FormulaS340 said:
Buy a timing light. This is one tool every old car owner should have. An inexpensive one is better than none at all, one with a dial is even better.
Click to expand...

I hear the dial lights are more likely to be off, not all timing light will work with MSD hvc either.

You should have a spare edelbrock 600 carb, they got for around $100 on ebay. Holley's are cool carbs and make lots of power but those carter/edelbrock seem to idle better.
 
gas octane ratings have changed since our beloved MoPars rolled-out of Detroit ( or L.A. , or St Louis or ... ) .

gas used to rated in the U.S. by MON : Motor Octane Number ; this is the higher number .
in Europe , gas went by RON : Research Octane Number ; this is the lower number .

"R+M/2" = Research octane number + Motor octane number , divided by 2.
So , let's say your typical '68 - '71 340 has its 10.5:1 comp ratio . This indicated the need for ~98 octane , with optimum performance from 105 octane ( "Premium" vs "Supreme" ) .
When "R+M/2" was introduced , 5 octane points were relinquished ; 98 became 93 , and 105 became 100 .
So , today's pump gas numbers , equating to their new vs old ratings , are :
87 = 92
89 = 94
91 = 96
93 = 98
94 = 99

I'm not sure whether or not racing gas still goes by the old MON rating ; does 115 actually equal 115 , or is it 110 ?
 
The old gas had lead, lots of it. Help the octane and the lead made the octane higher the longer it sat.

An old trick in the early 80's before leaded gas was pulled, was to fill up half with leaded 89 gas and half unleaded 91 gas. It would make the fuel around 93 octane what we have today but with some lead.
 
I know many are still talking about fuel requirements but if you go back through the thread you will see that the OP is having issues, likely not associated to fuel grade.
 
I run 91 in my 10.5 to 1 69 dated 340 w/ iron X heads. If i try to run anything less i get detonation (spark knock).
 
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