4300D carb and fuel filter

[RC92234]

'73 351C-4V. After sitting awhile, roughly 6-8 weeks, I had the whole air filter out of the car while starting and noticed a new fuel leak from the top of the fuel filter where it screws into the carb. After a long period of non-op, it was a surprise that it was leaking. I tried wrench tightening it with no success (in a quarter turn it felt snug, but still leaked), so I removed the old filter and tried putting in the new filter I bought long ago for "just in case...".

It was as if the new filter was the wrong one it was so loose in the fitting. I pulled it and compared to the old filter -- identical in size, so I tried to put the old back in with the gasket from the new filter. It wouldn't secure enough to tighten, so I then tried the new filter with new gasket. If I held it just right (really straight all the way in) and then screwed it tight by hand then secured it by wrench, it stayed. But it was only take a quarter turn or so after hand-tightening. This time it did not leak.

But I don't understand what is happening. I can put the filter almost all the way in the fitting before it reaches to the threads. And then I only hand tighten enough to secure it in place to put a wrench on it. Then it's only a quarter turn -- I'm afraid to go farther (but it doesn't leak). With hand tightening followed by wrench tightening, it's not even one full turn of the fuel filter. Is that normal? Any thoughts on how/why it came loose?

 

[midlife]

Sounds like the beginning threads of the receiver are stripped.

 

[rvrtrash]

Sounds like the beginning threads of the receiver are stripped.

I second that opinion.

 

[RC92234]

Sounds like the beginning threads of the receiver are stripped.

That's what I think, too. It's the carb -- what can be done short of carb replacement? (eek)

 

[mrgmhale]

I hate it when threads in a carb component begin to strip (or are stripped). I have not seen it too often, but in the cases where I did see it the fix was always the same, except for once (below) - replace the carburetor. If you have stopped the fuel leak for now, count your lucky stars and leave it alone until the time comes for a rebuild - which will likely mean replacement due to the thread damage already done. It you are lucky you may have caught enough threading to prevent a fuel leak the next rebuild. Then again, you may get lucky twice. It may be worth a try to rebuild once again down the road, but be prepared mentally for a replacement.

Very recently I rebuilt a carb on our 73 Mustang Convertible, for its 302 2v 2100 carb. The reason for the rebuild was because it had a slight hesitation on light acceleration. The accelerator pump was working well, the distributor vacuum advance diaphragm was getting vacuum off idle and beyond, and the diaphragm was not leaking or ruptured. I figured a low float level. In short, I was correct, but I also found evidence of the carb having been rebuilt once before (Power Valve was double gasketed, Center air cleaner retaining bolt in upper air horn was loose, front passenger retaining nut for the carb base was not tightened properly), The fuel filter had also been run down as far as it could go into the carb's main body. I found this unusual for an engine with only a little over 21,000 miles on it (barn stored for over 40 years). I figured it was rebuilt due to excess varnish or leaking Power Valve after years of sitting in a barn, unused.

In any event, I hated the idea of having to replace the carb just because someone had run the fuel filter into the carb main housing too deeply. In my case I approached the problem from a way differently than ever in the past. The part of the carb around the fuel filter inlet was machined fairly smoothly and is very flat. I ended up getting an o-ring designed to stop oil leaks at a work oil drain plug, as opposed to using a plastic, solid, and fairly hard oil plug gasket. The idea was to put the o-ring around the 1/4" pipe threading of the fuel filter, then run the filter down as far as I could until just after the carb body and front face of the fuel filter both hit the o-ring. There was no need to intentionally go any deeper than a nominal o-ring contact, as long as the filter did not feel loose or wobbly in the carb inlet, I had already used teflon tape on the threads, but I also kept in mind teflon tape is meant to lubricate the threads, not stop a fuel leak - although it does work fairly well to stop liquid leaks at times.

Well, the o-ring did the trick. I have be able to pull that off a few more times with this 2100 carburetor. I do not recall off hand if the 4300 carburetor fuel inlet is 1/4" pipe threaded also, or if it is a larger inlet with a gasket as opposed to a 1/4" pipe threaded inlet. It has been many years since I have rebuilt or even worked on a 4300 series carb. But, from your description of your fuel inlet it does not sound like your inlet is a 1/4" pipe threaded design. So, my approach in using an o-ring to help seal the fuel leak may not work for you. But, it may help for someone else, hence why I even mention it in a reply. So, this info is offered for what it may be worth someone, somewhere, sometime. I made a YouTube video showing how the 2100 was rebuilt, which is a 3 hour long event with adjustments, etc. Here is the YouTube link for the full rebuild and adjustment, which includes the fuel leak o-ring repair:




if you only want to see the o-ring fix, I built a shorter excerpt (12 minutes) on YouTube at the following link:




It is worth mentioning that I found a 2nd fuel leak, a very slight leak, due to one of the new fuel filter hose clamps I had used, which was caused by badly shaped end of the clamp strapping under the adjusting screw saddle. In short, a part of the clamp's strap was bent downward, into the area where it would be pressed into the rubber hose's exterior diameter in a way that distorted the fuel line at a critical contact point. The resultant distortion of the inner diameter of the rubber fuel line where the offending fuel line clamp was located was just enough to allow a little fuel leak to occur (the video has a few shots that more clearly shows what I mean in this description). I simply used a different clamp, without the strap's end being shaped like the first clamp's strap, and 2nd fuel leak was also corrected.

Ultimately, between the use of the o-ring, and the replacement fuel line clamp, did the trick. So far there is no more fuel leak at the fuel filter or its rubber fuel line. For anyone who may have run into a similar problem(s), I am hopeful my remedies described above, and shown in the YouTube video covering these issues, finds this information of value. I know that for me the corrections helped me put off replacing the otherwise perfectly good carburetor. I also attached a few photos of the relevant areas covered in the YouTube Video links above.

 

[RC92234]

I hate it when threads in a carb component begin to strip (or are stripped). I have not seen it too often, but in the cases where I did see it the fix was always the same, except for once (below) - replace the carburetor. If you have stopped the fuel leak for now, count your lucky stars and leave it alone until the time comes for a rebuild - which will likely mean replacement due to the thread damage already done. It you are lucky you may have caught enough threading to prevent a fuel leak the next rebuild. Then again, you may get lucky twice. It may be worth a try to rebuild once again down the road, but be prepared mentally for a replacement.

Very recently I rebuilt a carb on our 73 Mustang Convertible, for its 302 2v 2100 carb. The reason for the rebuild was because it had a slight hesitation on light acceleration. The accelerator pump was working well, the distributor vacuum advance diaphragm was getting vacuum off idle and beyond, and the diaphragm was not leaking or ruptured. I figured a low float level. In short, I was correct, but I also found evidence of the carb having been rebuilt once before (Power Valve was double gasketed, Center air cleaner retaining bolt in upper air horn was loose, front passenger retaining nut for the carb base was not tightened properly), The fuel filter had also been run down as far as it could go into the carb's main body. I found this unusual for an engine with only a little over 21,000 miles on it (barn stored for over 40 years). I figured it was rebuilt due to excess varnish or leaking Power Valve after years of sitting in a barn, unused.

In any event, I hated the idea of having to replace the carb just because someone had run the fuel filter into the carb main housing too deeply. In my case I approached the problem from a way differently than ever in the past. The part of the carb around the fuel filter inlet was machined fairly smoothly and is very flat. I ended up getting an o-ring designed to stop oil leaks at a work oil drain plug, as opposed to using a plastic, solid, and fairly hard oil plug gasket. The idea was to put the o-ring around the 1/4" pipe threading of the fuel filter, then run the filter down as far as I could until just after the carb body and front face of the fuel filter both hit the o-ring. There was no need to intentionally go any deeper than a nominal o-ring contact, as long as the filter did not feel loose or wobbly in the carb inlet, I had already used teflon tape on the threads, but I also kept in mind teflon tape is meant to lubricate the threads, not stop a fuel leak - although it does work fairly well to stop liquid leaks at times.

Well, the o-ring did the trick. I have be able to pull that off a few more times with this 2100 carburetor. I do not recall off hand if the 4300 carburetor fuel inlet is 1/4" pipe threaded also, or if it is a larger inlet with a gasket as opposed to a 1/4" pipe threaded inlet. It has been many years since I have rebuilt or even worked on a 4300 series carb. But, from your description of your fuel inlet it does not sound like your inlet is a 1/4" pipe threaded design. So, my approach in using an o-ring to help seal the fuel leak may not work for you. But, it may help for someone else, hence why I even mention it in a reply. So, this info is offered for what it may be worth someone, somewhere, sometime. I made a YouTube video showing how the 2100 was rebuilt, which is a 3 hour long event with adjustments, etc. Here is the YouTube link for the full rebuild and adjustment, which includes the fuel leak o-ring repair:




if you only want to see the o-ring fix, I built a shorter excerpt (12 minutes) on YouTube at the following link:




It is worth mentioning that I found a 2nd fuel leak, a very slight leak, due to one of the new fuel filter hose clamps I had used, which was caused by badly shaped end of the clamp strapping under the adjusting screw saddle. In short, a part of the clamp's strap was bent downward, into the area where it would be pressed into the rubber hose's exterior diameter in a way that distorted the fuel line at a critical contact point. The resultant distortion of the inner diameter of the rubber fuel line where the offending fuel line clamp was located was just enough to allow a little fuel leak to occur (the video has a few shots that more clearly shows what I mean in this description). I simply used a different clamp, without the strap's end being shaped like the first clamp's strap, and 2nd fuel leak was also corrected.

Ultimately, between the use of the o-ring, and the replacement fuel line clamp, did the trick. So far there is no more fuel leak at the fuel filter or its rubber fuel line. For anyone who may have run into a similar problem(s), I am hopeful my remedies described above, and shown in the YouTube video covering these issues, finds this information of value. I know that for me the corrections helped me put off replacing the otherwise perfectly good carburetor. I also attached a few photos of the relevant areas covered in the YouTube Video links above.

I knew exactly what you were talking about because I had accidentally ordered the 1/4" a long time ago. Fuel filter for the 2100 on the left, for the 4300D on the right. Clearly a different beast but thanks for the writeup!

 

[mrgmhale]

I knew exactly what you were talking about because I had accidentally ordered the 1/4" a long time ago. Fuel filter for the 2100 on the left, for the 4300D on the right. Clearly a different beast but thanks for the writeup!

Yep, same thing only different! heh heh... I was pretty sure my memory was correct with me remembering the 4300 fuel filter inlet being much larger, but they can still strip out or get cross-threaded. I thought that although that was not the specific subject of the O.P. it would still be worth mentioning what I did to fix our 2100 fuel filter inlet fuel leak. I hope I never have to replace our 2100, as they are such reliable and enduring carburetors. Perfect for pure stock street use and cruising.

 

[c9zx]

This might work, I have never tried it so, I can't say. Chuck
http://tds.henkel.com/tds5/Studio/S...mat=MTR&subformat=NAT&language=EN&plant=WERCS

 

[RC92234]

A non-Mustang person recommends a Holley 650 replacement, which I think would necessitate a new intake, too.

In any case, opinions from the Mustang people?

 

[MikeGriese]

Would a helicoil work? I don't know how fluid tight they are.

 

[InjectedMach]

I have a 4300 from a 69 429 if u want to purchase it. Rebuilt it to temporarily move around a 302 car we got last month.