Ford Muscle Cars Tech Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
22 Posts
Discussion Starter · #1 ·
Hey Guys! New to the forum but I've been poking around and I like what I see. Ford guy all the way and I'm working on '69 Mark III (I KNOW IT'S NOT A MUSCLE CAR but I have a '66 Cyclone too if that counts for anything).

Anyways, when I got the car, it had the original Autolite Carb on it, and needless to say, when I found out it wasn't worth re-building, I opted for an aftermarket and went with an Edelbrock. First mistake. Most of you may have good luck with them, but I did not. I'll fast forward to last week. After dealing with 3 years of hard hot-starts and choke issues up the wa-zoo, I went with a Holley 4150, 650CFM, 0-80783C.

Slapped it on, fired it up. Had to adjust the idle mixture screws to keep it running, but right out of the box, it ran pretty damn good. I drove it home, and quite honestly, it's the best the car ever ran. I didn't even dial in the idle mixture screws with a vacuum gauge or do much of anything else to tune it. I will say it had a bit of a rough idle, but totally driveable.

Now, the fun begins. The next day I went to fire it up and as it was already hot when I installed the carb, I didn't have the opportunity to set the choke. No big deal. I fooled around with it and got it to run at high idle when cold. Done.

Now, I'm going to start working on timing. I let it warm up to op. temp. and check timing. Of course it's off a little bit. I disconnect the vacuum advance (with it running, and also air filter is off as I was observing choke operation). BOOM! Huge fireball and back fire right out of the air horn. I should say that with the Edelbrock, I had the vacuum advance hooked up to manifold vacuum not timed. So maybe what happened was it retarted so far upon removing the vacuum line, that's what caused the backfire? Anyways, I reconnected it, fired it back up and timed it with the line connected, just a little advanced above spec, which is 10 BTDC. Test drive, pinging on load, and on and on. I fooled around with it to where it doesn't seem to ping and also to where it starts easy when hot and cold.

Here's the thing, and I didn't notice this after the initial install so I'm assuming it wasn't there and is now, resulting from the backfire. RAW FUEL SMELL and exhaust fumes that tear me up. This thing is running incredibly rich at IDLE. When I am driving, I get an intermittent raw fuel smell in the cabin. It comes and goes. I have searched everywhere and can't find a leak anywhere. Also, when I shut the car off and go to restart it in a 5-15 minute timeframe (haven't checked it after 15 minutes yet), it starts like it's flooded. I have to put the pedal to the floor and once it fires, I let it up the feather it for a second to keep it running then it's good.

When I accelerate, it has awesome (seems to me almost to quick) pickup and cruises beautifully, but I never had THIS problem with the Edelbrock. Also, the idle is very rough and when the choke comes up, it barely runs until it really gets warm.

I know Holley equips their new carbs with a power valve protection, but could a huge backfire just destroy a PV anyways?

I'm out of ideas on how to fix this. I just want the raw fuel smell and terrible exhaust fumes to go away. I'm not an expert on carbs and such, but I have a basic understanding. So I turn to you all pro's in hopes of getting some good advice! Thanks, and sorry for such a long post.

Here are some specs:

-460 cid
-Mild RV/Towing Cam
-Vacuum was around 15" at Idle and dropped to about 10" idling in drive with foot on brake
-Distributor is stock (actually a Cardone Re-build)
 

·
Registered
Joined
·
104 Posts
I agree, sounds like a PV. I've never blown one on a newer Holley, but it sounds like you did!

If you can turn all the idle richening screws all the way in (lightly seated) while idling and it still runs, then it should be the PV.

You should also check that the floats are set to the right level though.
 

·
Registered
Joined
·
22 Posts
Discussion Starter · #4 ·
I'm going to try and change the PV. While I've got it apart, I should make sure I use the right one. I know typical rule of thumb is 1/2 at idle in drive with foot on brake so 10" at idle I should use a 4.5" PV. This essentially just means less fuel for longer duration when compared to the stock PV, right? (fuel from power circuit comes in later with a 4.5" PV). Would that be beneficial for me?

Also, would jetting the carb down help with a rich idle, or no?

Have checked float level twice, so far, so good. I should also say I have a rubber fuel line from fuel pump to carb. Would that cause an issue?

Thanks
 

·
Registered
Joined
·
104 Posts
I don't know the text book "right way" to choose a power valve. You want it to come in when passing on the highway, or climbing a steep hill. I'd keep it a few inches below vacuum level at a cruise.

The power valve doesn't change the fuel flow, only affects at what vacuum level it will open. All Holley valves should flow the same volume of fuel when opened.

Changing the jets won't affect your idle richness. Rubber fuel lines aren't a problem. The idle richness is affected by the screws on the side of the metering block(s).

Did you test for the PV failure? Turn all idle adjusters in to lightly seated while engine runs. If the engine dies, the PV is OK. If it runs, then its getting fuel from somewhere it shouldn't, and the PV is the most likely candidate.
 
1 - 5 of 5 Posts
Top