1970 Mk III hot engine, hard to start

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sasilverbullet

sasilverbullet

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Aug 22, 2004
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San Antonio, Texas
Yes, me again with another issue with my newly overhauled 460. I didn't realize that I needed to be an automotive engineer to get all this stuff to work! I don't know that I'd do this over if I knew about all the hassles.

Car starts and runs great except when hot and sits for 15 min or so. Starting it takes quite a few cranks and when it fires, it seems to be running on two cylinders. I have to baby the gas pedal and get the rpm up to about 2500 for about 5 secs, then it runs fine.

I used a laser temp gauge on the Edelbrock 2166 manifold, right below the carb is about 204, and the Edelbrock 1406 carb right above the phenolic spacer is about 185 degrees.

The engine shop says I need to trash the Edelbrock and put a Holley on there.

What do you guys think?
 
Heat soak can be a bear.

If the carb is on a spacer that should not be a problem, though. Could be that the level is set too high and you actually are over rich on start up due to fuel percolation.

That would be most likely.

Don't fall for the bad mouthing on the carb. I have run them and they are great street carbs, just trickier to set up...
 
Some sort of electric Fan could work.
Some British performance cars using American V8's had this problem back in the day.
Cutting louvers helped a little, but an electric fan (that could run if the ignition was off) was the real answer.
Regulate it either by a timer or a sensor attached to the inlet manifold.
 
Hot rods... been a looonnng time.... Looks like this manifold has the exhaust ports crossing over underneath for better warm up.... that was OK with iron intake manifolds, but was awful with aluminum. I'd block those ports.
 
Originally Posted By: Merkava_4
So how does this work? Is there a passageway from the exhaust manifold going to the intake manifold?


Manifold mates to a passage in the cylinder head. This is intended to heat the manifold so cold starts are easier and better vaporization of fuel. Usually there is a coolant one as well. The problem is an aluminum manifold is already a bit too good at conducting heat!
 
On the cylinder heads, there will be a port for an exhaust valve that goes both ways.... one towards the exhaust manifold, and the other towards the intake manifold.

There's this tube like crossover cast in the intake manifold to join the two ends. Useful in snow conditions.... but summer in Texas with an aluminum manifold.... not a good combination.
 
Originally Posted By: NHGUY
Carbon buildup.

On a freshly overhauled engine? Carbon buildup takes more than a few weeks.
 
Originally Posted By: SteveSRT8
Manifold mates to a passage in the cylinder head. This is intended to heat the manifold so cold starts are easier and better vaporization of fuel. Usually there is a coolant one as well. The problem is an aluminum manifold is already a bit too good at conducting heat!


That is a beautifully worded post..........well done..........makes perfect sense now.
thumbsup2.gif
 
Originally Posted By: sasilverbullet

What do you guys think?


So when it starts up and acts like it's running on two cylinders, how black is the exhaust? I'm betting it's pretty black.
 
Check to see if the fuel line is in contact with anything that gets hot., and get a little distance between them. I have seen more than one vehicle with similar problems.
 
What is your timing at the crank? Does the mechanical advance work ok? Do you have the distributor vacuum advance hooked to the port vacuum?
BIG engine + carb + heat soak + todays gasoline that is not made for old style carbs = hard hot crank start.
Today's fuel is made for pressurized F.I. systems, not carbs.
 
Originally Posted By: sasilverbullet
Yes, me again with another issue with my newly overhauled 460. I didn't realize that I needed to be an automotive engineer to get all this stuff to work! I don't know that I'd do this over if I knew about all the hassles.

Car starts and runs great except when hot and sits for 15 min or so. Starting it takes quite a few cranks and when it fires, it seems to be running on two cylinders. I have to baby the gas pedal and get the rpm up to about 2500 for about 5 secs, then it runs fine.

I used a laser temp gauge on the Edelbrock 2166 manifold, right below the carb is about 204, and the Edelbrock 1406 carb right above the phenolic spacer is about 185 degrees.

The engine shop says I need to trash the Edelbrock and put a Holley on there.

What do you guys think?



The 1406 is a 600cfm? That wouldn't feed a smog era 460 truck motor with 4 degrees of retarded valve timing, The '70 Lincoln 460 is pretty hot. The 1406 is calibrated to a mild 350 Chevy for economy.

Jegs has a Chevrolet Performance 4160 Holley 770cfm, Electric choke with quick change vacuum secondaries for $431.99....That is CHEAP for a 4160.

ALL Edelbrock AFB carbs are designed to run NO MORE than 5.5 psi of fuel pressure, I run them around 5psi, Adjust float level...Which is always to high, & Use an isolated gasket or a small phenolic spacer....Do all this & the hard hot start will go away.
 
You might need to check the total timing. Not just at idle. there are recurve kits that allow faster timing advance and less total timing. Hard starts when hot always make me think about hot from lean/ timing out of whack.
 
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