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Problems after carburetor replacement

Hi everyone,

Well it's been forever since I've posted! I'm finally working on the mustang again after a few years away from it and have run into a problem that I can't seem to fix. I'm hoping you can help. Here's the background.

This is a 66 coupe, 289 with warmed up cam, stock heads, tri-y headers, Edelbrock intake and Edelbrock 1405 carb. The car had been sitting for 2 years, only being started 5-6 times during that time period.

To get things rolling again I dropped in a fresh battery and rebuilt the old 1405 carburetor. Something went bad during the carb rebuild and after pulling my hair out I decided to replace it with another 1405.

I got the new one installed and dialed in pretty nicely. The car was driving at least as good as it used to, if not better. SO EXCITED. That lasted for a few trips, but then I noticed it struggling at low rpm after getting off the freeway during my last outing. It would run ok under part throttle to wide open throttle, but when easing on the gas from a stop or going very slowly it would sputter and lurch forward, clearly on the edge of the combustion envelope. I managed to get it home and by the time I did the problem seemed to clear up. The next day I tried taking it out again. It was fine until I took a brief 2-exit course down the freeway. Once again, after getting off the freeway it was struggling to keep an idle. That time I barely got it back.

Today I went out to try again and couldn't even get it to keep an idle. I started with simple things:
  • Try different step-up springs
  • Check float levels
  • Check the jets for junk (it did sit for awhile)
  • Check idle screws (nothing had changed)
  • Making sure the ignition wiring is tightly pugged in
Nothing improved the problem, and I wonder if maybe this isn't carburetor related since it ran fine for awhile. Something else? Fouled plugs? Some kind of ignition issue? I don't know!

Any thoughts/advice would be much appreciated!
 
vacuum leak is where I would start given the new carb should really limit the chances of it being anything with it. Make sure you didn't over torque it when installing and crack the base plate.
 
Thanks for the advice! I gave the vacuum and PCV connections a brief once-over, but this time I'll look closer.

It has also been suggested that since I was only keeping 1-2 gallons of fuel in it over the course of the last two years, the fuel system may have clogged with junk/varnish and plugged some of my shiny new carburetor passages with it. There may be some truth to this because taking the top off my carb, anything that's not wet with gas is sticky like half-dried wood varnish. That's probably not good.
 
Do you not have at least a simple fuel line filter in place? You can start there by replacing it and cutting open the old one to see what it was trapping. How old is the gas you are using? I guess i made the presumption you drained the tank and such.
 
yeah, old gas and rust is common problem when stored with just a little gas in the tank. Condensation and Ethanol are very bad combination. Modern fuel typically is 10 - 15% Ethanol. Ethanol attracts moisture. The moisture causes rust and Ethanol also attacks the metal tank and lines. Modern cars use a lot of plastic tanks and stainless lines to prevent this from happening.
I have an old 72 Chevy truck that sat for a long time in a field. I took the tank out (it had 5 gallons in it), and flushed it. I even took it to a shop to seal it. However, I still get some crud when it gets down to just a couple gallons. I run a Mr Gasket glass filter (see picture below) that I can take apart and clean. I also try to never let it get below a 1/4 tank. If the carb sucks any of that crud in there it usually means I have to take it apart and clean it with carb cleaner and air pressure. I have a Holley so I just pull the front float bowl off. But it does create similar characteristics, such as rough idle and hesitation. Once I clean it out, it runs good again. The glass filter allows me to see the crud and I can take it apart and clean it with carb cleaner. The old Chevy uses a lot of oil so I check the oil when I put gas in it. I always look at the filter too. Most of the time I can catch it before it gets in the carb. I really need a new tank but since it's in the cab I'd rather convert it to under the bed but just haven't had time to mess with it. Anyway, you may have some crud in your tank also.
720-9747.jpg
 
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Horseplay, I do at least have a fuel filter installed before the carb. It's actually the exact one that tarafied1 posted an image of. I will check that before anything else. I didn't see anything in the mesh with it on the car, but a closer inspection could change that. Hopefully I don't have to drop the tank but if I do it's my own dumb fault. Thanks for the advice guys. I'll let you know how it works out!
 
I would disconnect the tank and take a plastic jar , fill it up with a mixture off fresh gas and carb cleaner. And let it run for some time and then hit a back road with the jar hanging outside the car.
IMHO
 
Angelo, my fastback with same carb did that as well. I never fixed it but did figure out what was going on.

The engine driven fuel pump plumbed in a dead end way like yours and mine cause the pressure to build up to a point where it can not use the fuel as fast as it is delivered. This causes an increase in fuel pressure and the increase in fuel pressure causes heat in the fuel which starts to boil, kind of like a pressure cooker. Thus causing vapor lock.

The solution is to run a return line. Do a you tube search and there are several videos showing how to fit a return line.

Cost is minimal and it solves a few issues. You will see a small increase in fuel economy as well.

My Camaro has the same issue and the PO felt an electric fuel pump was the answer. He didn't install it but gave me the parts. I intend on running a return line on both the Captain America car and the Camaro.

Hope this helps and awesome to hear from you. Great that you are getting your car out!

It seems that this new gas blend is full of many surprises!

Give Katie hugs from us.

Mel
 
Hey thanks. I had never considered a return line. The thing that's bothering me is why now...why after a few rides did it start to struggle. Wouldn't it have happened sooner? Maybe not because the fuel tank had to drain again for the sediment and junk to get caught in there. Or like you said, maybe the vapor lock is taking hold. HMMM!

Well at least I DO know it's good to be back and working on the car. FINALLY.
 
To answer your question, why now?

I don't know. I drove the fastback as a daily driver for a couple months and never an issue. The suddenly the issue. I knew the tank wasn't full of crap. The filter was clean.

I think it must be something they are mixing in the gas that makes it boil under pressure. I would bet money if we had a special blend of gas using the same formula as in the 60s there would be no issue at all.

I had a friend that had a similar issue in a F250 2wd truck with a 460 in it. He put an electric fuel pump in line and when it gave him problems he flipped the switch and no more problem.

That is just a band-aid fix though. A return line with a regulator in line keep the pressure constant and removes the entire problem.

There could also be junk in the tank so, make sure to check that out as well.

The return line should T off after the filter to a small regulator and back to the tank. I think you could T off the line between the fuel pump and tank somewhere.

Be sure to use metal line under the car. Safety you know.

Mel

Sent from my XT1030 using Tapatalk
 
Liquids under pressure result in their boiling temperatures being raised. Consider coolant as an example...
 
I think you might be misdiagnosing the fuel pressure situation, Mel. It's far more likely that without a pressure regulator your fuel line pressure is overpowering the float seat and you have a "flooding" situation that can cause an engine to stumble, etc. Check the oil for the smell of gas is a quick way to see if you have something like this going on. This is one reason EVERY set-up should include a pressure reg and gauge. Carbs should only see up to about 6 psi of fuel pressure. Almost all aftermarket "speed shop" type fuel pumps deliver that much and more.

Also, a diaphragm type mechanical pump can't "build" pressure. The way it is designed limits it to what is marked to deliver.
 
I run E15 pump gas in my 67 and 72 both with no return line. I run 93 octane in the 67 due to the high compression but only 87 in the 72. I have never encountered a problem with too much pressure or boiling gas causing a vapor lock. The 67 I drive in extreme heat and in traffic as well. The 72 is a daily driver for my son until we get his car done. I do know when I shut the 67 off the engine temp spikes and I can get some boiling effect in the way of flooding. It still starts but you can smell it 10 or 15 minutes after you shut it off. Both my carbs are Holley's though so maybe the Edelbrock float/needle & seat is different? On a Holley the float is the only thing holding back the pressure. If the pump pressure is too strong it would force the float down and flood all over the place. I have a fuel pressure gauge on my 67 and it runs about 6-8 psi. I'd be interested to see what kind of pressure you are getting that would need a return line. Is it a high pressure or aftermarket racing fuel pump? I'm just running standard parts store pumps my vehicles.
 
I have had similar experience to Craig until the last year or so.

Then I watched one of the many car shows on a Sunday AM and they were talking about the return line. It made sense to me.

So, I did some searching on the net which we all know is just the most accurate place to get info, and found many people talking about it and doing it.

I read the before symptoms and the after results.

The symptoms all seem to be pretty much as described here.

There were other fixes like wrapping you fuel line from the pump to the carb in a heat tape like what is used on headers.

Some put a regulator before the filter and some switched to the stock hard fuel line and wrapped it.

Some used a return line and all who used the return line reported that the issue went away and they got 1 mpg more.

So, who am I to argue with anyone here or there. I am just a tinkerer.

I don't think it is a bad idea anyway, even if it doesn't fix the problem.

The Captain will be getting a Holley carb I have sitting here when I get to that point. Then I'll sell the edelbrock.

Mel

Sent from my XT1030 using Tapatalk
 
not arguing Mel, I am always open to ideas too. I am not familiar with Edelbrock carbs. I have a lot of experience with Holleys. They can boil the gas out for sure, I just never seen it from fuel pressure, always was related to heat. I don't think it's bad idea as long as the return line doesn't starve the carb. A regulator is not a bad idea either to control the pressure.
I hope the OP gets it sorted and it works for you too. be sure to share the results!
 
Didn't take it as an argument. Just good healthy debate.

This is how we all learn new stuff.

All the return lines I saw had some sort of regulations g device to keep from starving the carb.

I so miss my double pumper carbs. Haven't had one on many years.

I also like mechanical secondaries and mechanical advance.

Just old school I guess.

Mel

Sent from my XT1030 using Tapatalk
 
Without reading what you came across Mel I can't judge the validity of what you read. I can tell you that I can't think of a single factory carbed set-up with a mechanical pump I have ever seen with a return line. Only with the advent of fuel injection and the need for high pressure fuel feed systems did they come into being, as far as I know. Based on what you wrote to have read, I'm betting that the pressure regulator was added along with a return line (useless) as part of their attempts to find a solution without understanding the problem.
 
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