I recently purchased a 69 340 , the guy pulled it because it didn't produce enough vacuum to run his power brakes , he said he bought it from a dedicated mopar builder who built it to race and it had standard bore, pistons and a purple cam , he could not get it o run right but he said he is not mechanically inclined as he does body work , he believed it was getting too much fuel because it has a holly 750 carb , I haven't done much with this type of motor since the mid 70's and was wondering if the pistons should be marked with their compression ratio on them somewhere , I would be inclined to agree that a stock 340 is getting too much fuel with a 750 , I don't know if it should be getting enough vacuum to run the brakes , any thoughts would be appreciated.

 

You just need to know more about the engine build....

 

grumpy -

Aside from a vacuum leak or other defect, the first thing I'd think of is too much cam.
So yeah, like Bob said, need more info on the motor.

Archer

 

Thats why the question , there is no more info on the motor , the guy I bought it from said the man that built it had 3 of them and couldn't remember what he put in it

 

grumpy -

Without taking the motor completely apart, there are a few things you could do.

1. Check for vacuum leaks with engine running and a spray bottle of water.
If you spray a certain area and the RPM changes, you found a leak.

2. Compression test.
Probably not an issue, but you'll need a compression gauge.

3. Cam specs.
Lift: Pull a valve cover and measure how far a push rod moves, lowest to highest position.
You'll have to do that for an intake and exhaust valve.

You might be able to see the duration by measuring when the push rod starts "lifting" and how far you have to rotate the crank to get it back to zero. Just remember there's a 2:1 ratio there.
Ditto for intake and exhaust.

Or, get it to a mechanic or machine shop who can do it for you.

Archer

 

My sons a mechanic but but not too much inside the engines on cars like this , I bought it with valve covers missing , no oil pan the intake just sitting on top and he said he took the heads off but they are bolted back on , what I was trying to figure out was if it might have a hotter cam and thus the reason for less vacuum , the 68 it's going in had power brakes from the factory but somewhere along the line they were removed so vacuum is not an issue for me , the motor only has about 500 miles on it according to him and I was just trying to figure out it I should take it all apart to check

 

grumpy -

If you don't want to do the cam quesstimate like I described, put the motor together and see what the vacuum is.
If it's too low for the breaks, add a vacuum source into the mix.
There are several types on the market.

Archer

 

Well Glad we got that settled..... If you cant get anymore info that you already have... Then we just mess with what you have a see wea it leads us?
I dont think a 750 Carburetor is too much for a hopped up 340.. Sounds to me like it may have a large Purple Cam in it.... I agree on doing a compression test and see what that tells us...
Will hope its not more than 150 PSI just in Cranking?
Guessing it has X-heads or J-Heads on it indicated by the letter casted into the Cylinder head near one of the spark plug holes?
I also agree on checking for any vacuum leaks...
If you have it running at the moment... I would put about 16* for timing to start with... Check and see if it has any vacuum? maybe 10" of vacuum? at curb idle @ 750RPM if it will idle down that low?
Also May need a little looser Torque Converter to help it idle down.. like 2200-2800 RPM Stall

Lets see how we look Grumpy B... Cheers

 

Thanks for the answers but currently working on building a garage so I can start working on it , I was going to build a garage and then find a car but it was one of those popped up now with too good of a price to pass up so here we are.

 

Cant help much with the garage / shop. But when you get started on the engine. We are here to help... Cheers