Technical 56 mercury 312 issues

Hi all, just picked up a 56 mercury custom with the 312. Having some issues with rough idle and stuttering on acceleration. The car was sitting for about a year before I bought it. I changed the fuel filter and put fresh gas in the tank. I’ve sprayed carb cleaner directly into the carb. The car will stumble when first taking off, but once on the gas it will go no problem with plenty of power. It will also rev clean when in park. The carb accelerator pump is shooting two strong sprays into each barrel. It’s a Holley 4bbl.

I’m replacing the distributor cap, wires, and rotor this weekend. It has electronic ignition.

I’m leaning towards fuel so I ordered a brand new carb and fuel pump, which did have a bottom leak before I tightened all the screws. Yet it is getting good fuel to carb, so maybe electric or vacuum? I checked all vac lines I could see
Thanks in advance, this site seems great
Ryan

 

Does it still have the old Load-O-Matic distributor (dual diaphragm vacuum advance)? Does it have a "tea pot" Holley carb?

I would highly recommend doing a compression test before shooting it with the parts cannon. I would also disconnect and plug all vacuum lines to see is that helps the rough idle. An engine with one leaking exhaust valve will have a pretty rough idle, but kind of run okay at higher rpm.

 

I was also going ask if it was the teapot Holley. I fixed mine by putting a 57 intake and newer carburetor (and distributor) in it.

 

^^^^^^ Especially the loadomatic and teapot. They only work as a matched pair.

If it sat for a year, you really should open the carb up. Bound to have some varnish from evaporated fuel (worse if it was 10% ethanol). As said, the parts cannon gets expensive and doesn’t always hit the target. Worse with todays parts, you might be swapping in a bad one and now you’re chasing 2 problems instead of 1.

 

Thank you all for the replies. It is not the tea pot carb, it’s basically the old version of the new 4160 Holley 4bbl. I’m unsure of distributor and was wondering that myself, I do know it only has one vacuum line going to it. I’ll post a pic later.

It seems to get better sometimes, and then worse again. Sometimes it idles smooth, the next day it’s rough again. I ordered a new carb as a back up basically because I planned to try and clean this one, but I totally agree not to throw parts at the problem which I have a habit of doing.
I was told the car was only driven a couple thousand miles in the last 20 years mostly sitting in a garage.

I also realized this is more of a hot rod forum, my apologies if I’m in the wrong spot. Every time I search Y block info this site comes up with great advice.

 

The line in red is what I was going to ask about. Odds are, you are breaking old gunk loose in the tank. Open up the carb and take a look at the fresh filter you put on.

 

Will do, thank you. I might need to go through a couple of filters too I suppose. What about a sea foam gas treatment?

 

I would just run some good quality gas through it and keep watching the filter. Also, is it just a plastic inline filter? Or a better quality cannister filter?

 

On my Buick that had been sitting for years, I just kept changing filters every time it would start to act like it was starving for fuel at all. It was just what @Tman mentions as far as the problem.

 

And this thread reminded me that I better look in the tank of my GMC. Started pondering re-using the stock tank........

 

in-line plastic filter, and the one I took off when I first got the car was super CRUDDY

 

Can I do a cleaning of the carb while it’s still on the manifold? I don’t mean a rebuild, but a better cleaning than just spraying gumout into it. I’ve done a lot of small engine carbs but never one like this

 

I have just taken the carburetor off and cleaned it all out with carb cleaner before without taking anything really apart. Sounds like your carburetor is working ok for the most part. Maybe changing the ignition parts and watching your fuel filter will make it run better over time. My Buick seemed to keep getting better the more miles input on it. I think I ended up with about 3000 miles on it in around 6 months when that was all that was put on it the 30 years before as well.

 

I would run a couple of those cheapo filters and toss as they crud up then add a good forever filter that you can change the elements in.

I would still pull the carb, super easy. Probably has a dried out base gasket anyway!

 

That’s my plan is to keep driving it as much as possible, sounds like you were in the same boat as me

 

That was my next question, if I pull the carb I definitely need a new gasket right?

 

Yes, very slight chance that it won’t tear. And, they are cheap for that gasket so no reason not to change it.

 

Will do, thank you

 

Neat car by the way. One of my best friends has that exact car other than color and it is lowered.

 

Thank you, I’m real excited about it, and so are my 3 girls!

 

Here is his.



And, very cool that your girls are excited as well. Making this hobby about family and friends is my favorite part. The cars are just a fun backdrop to what is really important.

 

Great car! And yes, I’ve had cars before my kids and this is way better, cruising as a family is twice as fun

 

That's funny as that is my experience with Holley carburetors. Every car I've had with a Holley carb experienced changing idle smoothness. On my 57 T-Bird many times it only takes a small tweak of the mixture screws to smooth it out again.

My take on Holley 4 bbl carbs is; if you want to put a whole lot of gas down a hole, as in racing, get a Holley. If you want to drive it on the street, get something else (unless you don't mind fooling with the mixture screws on a regular basis).

 

Check what the fuel pressure should be for your carb, maybe install a regulator/guage combo then is set to that.

 

I watched a video and a guy had a gauge and regulator setup and I thought about doing one

 

Two ways to tell if it is a Loadomatic distributors uses the same points as a 6 cylinder the points are straight. 57 up points are curved and if you grab the rotor and try to turn it CC wise the late distributor will turn about 15 degrees the early unit won't. 57 up pointshttps://www.ebay.com/itm/2029452489...1291&msclkid=61cae5c2addf1a0efb4781b50fc24e95

 

If you dont have a return line (into the tank), run a new tube back, at T it in to the line near the rear. I have that set up on one of my cars and works.

 

No points anymore, electronic now, but I’ll try the rotors spin idea

 

The loadmatic style was probably replaced when the Holley installed. It’s been well known since 1957. Is the electronic ignition a Pertronics? The number on it will tell you it it for the loadmatic.

Is there an adapter under the carb? If it’s a direct bolt on you have a 57 manifold. (good).

Stock fuel pumps have approximately 4 psi and no flow back or regulator needed. The Chinese replacements are not consistent. I’ve removed the line, started the and used a pressure/vacuum gauge from HarborFreight attached to the feed line. The engine will run for at least 30 seconds and-an easy way to check.

There are many here that can definitely help. y-blocksforever.com is another one

 

Hang on a sec. You bought an old car, that has been sitting a year.
When a car sits like that at that age it is easily and quite common for the tank to rust , they inside on the ceiling of the tank. All that rust dust fall into the fuel.
As others have suggested use the cheap see thru filters and start back at the tank to eliminate one source at a time. New carbs and cleaning don't fix that permanently.
Also if it is the tank, the problem doesn't usually go away. Either get a new tank or screw around for a couple of days and money trying to seal the one you have and when it doesn't work you buy a new one anyway. Been there done that. Also this issue goes right on down the line as in fuel lines, be ready to replace. Remember, sitting for a year.
After this is checked out okay, fuel need to be checked that it does indeed shoot fuel out the delivery side. I disagree that you don't need a fuel pressure gauge to monitor this.
Then on to carb. Clean up, check needles and seats. Very basic to run decent.
Then on to distributor and the vacuum pot. It needs to draw good vac.
I think if you do these things first instead of buying parts from the other end you'll be ahead.
There's nothing mysterious about the Y-block 312 engine. It does have some differences but you can work them out to run well. Just don't jump to conclusions. And don't listen to chevy guys about how it's SO different. Make sure you have a car and engine manual from Ford Mercury. Their still available and worth it. Dizzy runs counterclockwise so you need to learn the yblock firing order.
It should make you a real good runner. Cool car!, Have fun with it.
And let us know what you find out to add to the knowledge base.