Leaky Inlet Frustration

[Shiny]

What is typically wrong when a qjet inlet fitting leaks?  Mine is the short style, with external washer.  The carb appears to have been bead blasted, which makes the gasket sealing surface seem rough, and it has also been helicoiled, which makes me wonder if the gasket is getting compressed wrong.  How do I tell if the leak is coming from the inlet gasket or the flared fitting?  The line is new, from Ames, but when first installed, it leaked at both the pump and the inlet, so I suspect the line might be unusually hard or   I have to whack the wrench on the flare nut with a hammer to get it to seal, which is just wrong... should I start replacing parts or is there an easy way to diagnose?  I don't see anything obvious by looking, but being as I'm making mistakes, I keep creating reasons to pull the carb off... and I don't want to destroy it to stop the leak.

Thanks for any suggestions.

[Cliff Ruggles]

It is quite common when installing a new carburetor to have a leak at the inverted flare fitting.  It is best to remove the fitting from the carburetor and use two good fitting wrenches to "form" the double flared portion of the fuel line to the fuel inlet housing male inverted flare area.  It often helps to spray the parts with WD-40 or light oil to help them "form" to each other.

One you establish a good fit, tighten the fuel inlet housing to the carburetor, a new gasket it a good idea.  Once sufficiently tightened, hold it with a 1" wrench while seating/tightening the fuel line nut.

It is also possible that there is damage to the sealing surface where the gasket contacts the carburetor.

Also keep in mind that the installation of a heli-coil involves exact precision, and the gasket must have even contact all the way around.  When the carburetor is cut with the heli-coil tap, we also loose some of the sealing surface, and the fiber gasket may collapse as the fue filter housing is tightened up.  A coated metal gasket will often correct this situation.

In some cases, we have to "spot face" the gasket sealing surface, especially if the heli-coil installation is off some and the nut is not in full contact evenly across the entire surface, or if the surface has imperfections on it that the gasket can't effectively seal......Cliff

[Shiny]

Thank you for the help.

Your support is amazing and so welcome in today's world of "customer no service".

What you said makes sense and I'll try the "pre-assembly" off the carb.  I also appreciate you confirming my suspicions about the possibility of the helicoil affecting the gasket seal.  I think I'll put some magic marker or maybe just a piece of tape and clamp it tight enough to see a "witness mark".  If it looks misaligned, I can pursue the spot-face solution or find a more compliant gasket...  I suspect my problem is the flare fitting after reading your experience and suggestions.

By the way, reading the book, I think I remember a suggestion to have a check valve in the inlet filter.  Is this a good idea?  The kit I bought from you, which was correct for my carb, had the long filter, but since I wanted to use a pre-formed line, I am using a short inlet.... but I don't remember seeing a check valve on the filter you supplied either.  I have noticed (too many times !!), that the line is empty when I pull it off the carb, so I assume gas flows back to the pump...  what is the trade-off?  I don't need to worry about flow...  thanks again.

[Cliff Ruggles]

The check valve style filter is only required or recomended if you have a drain back problem or condition.  They are somewhat restrictive compared to an open filter, so not as good of a choice for a really powerful engine pushing a relatively fast car around.

Currently available pump fuel evaporates off quickly, and this seems to be more of a problem than anything else. 

It doesn't help either when the carburetors bottom plugs are leaking, which is the #1 problem we see with carburetors being empty after the vehicles sits for several days......Cliff

[Shiny]

Cliff,

Again, thanks for the great help.

I had checked my carb for leaking bowl plugs when I rebuilt it using your kit, but did not see anything... guess I missed it, because it drained down overnight and I had to crank a lot to refill the bowl.  I lifted it up and sure enough, it was dripping gas into a big puddle in the manifold.  The plugs had been covered with epoxy before, so I bit the bullet and sealed per your book using a marine epoxy.  I think it was actually one of the small plugs (primary) that was leaking.

The inlet fitting problem was exactly what you said - the helicoil machining had reduced the diameter of the sealing surface in the carb.  I had a fiber washer in it that was a little too big on the ID, so when it dropped down, it did not mate well...  I replaced with the metal gasket and leaned on it a little and now have no leak !!

Now for the good part - the car fired right up and the idle circuit seemed to be working well.  I was able to lean it out and then backed the screws out until it idled well.  It warmed up and ran for about a half hour, which is a big thing for me.  I shut it down, came back a few hours later, and it started right up again, so I think the plug seal worked.

I would have never figured all this out without your book, emails, and forum responses, so kudos to you again.

I'm excited to see how the carb works when I get the car driveable.  I may be back for more help, but so far, it seems killer compared to the 2-bbl that was on it...

[Cliff Ruggles]

Good news!  I was hoping that you could get the fuel filter housing to seal up without having to "spot-face" the sealing surface.

Also good new on getting the bottom plugs sealed up and the carb working correctly......Cliff

[Shiny]

Well, I celebrated too soon.  After sealing the bottom plugs, the car started and idled well, so I moved on to attack power steering, which now seems to be working.  Today, my son and I went out to bleed brakes so we could drive the car and check out the carb.  I had to crank a lot, which made me nervous about the leak again, but it started fine after the carb got some gas.  After warming up the engine, I pulled my plug off the vacuum port at the rear base of the carb to put on the brake booster hose and liquid gas puddled out of the fitting.  I had my son push the pedal to the floor and hold it, and there seemed to be a lot of fuel vapor coming up from the manifold....

So I pulled the carb again, and sure enough, there is still a gas leak from somewhere.  The gasket was visibly soaked.  As I lifted the carb, there was a drip and the base seemed wet in general.  I tilted the carb a little toward the choke side, and gas pretty much poured out...

So now I am getting even more frustrated, but really, I guess it is more a case of being humiliated by something so seemingly simple.

I tipped the carb upside down to pour the gas out, then checked the inlet again with my vacuum pump.  It held vacuum fine, so I don't think the float is the root of this problem.  I must have another leak somewhere or I used the wrong gasket or something??  arrrrgggghhhh

Any suggestions as to what I should look for this time?  Some things that may be related:

1.  the plastic baffle has been cut off the bottom, presumably to allow more gas in the bowl ??

2.  I set the float height at 1/4"...is that too high for this carb (29240MD) ??  Is there a chance fuel is spilling over somewhere ??

3.  I got pretty aggressive removing the APT screw from the base.  I heli-coiled it and used your replacement screw... all seemed fine.  Is there a chance I could have drilled through something or left the APT spring too high and somehow created a fuel leak??? 

I guess I'll pull the top off and fill the bowl with gas or something else and see if I can see a reason.

Any suggestions on how to solve this (finally, really) would be greatly appreciated.

[Cliff Ruggles]

Did you pressure test the bottom plugs while the carburetor was apart?.....Cliff

[Shiny]

On my original attempt to diagnose the leak, I put a tapered air nozzle with about 50psi behind it into the 2ndary metering orifices where the rods go, but I could not totally seal the pressure, as there are many ways for the air to go... but with whatever pressure I developed inside the well, I did not see bubbles with soap, yet that is the location of my original leak (or at least where the gas was dripping).

So without ever confirming the leak, I went ahead and drilled/tapped/sealed with marine epoxy on all 4 wells.  I used set screws on the small ones and cut up a 7/16" bolt to fabricate plugs for the big ones.  I did NOT try checking with my air nozzle again, because I didn't detect a problem the first time.

I will pull the air horn and try again to verify my seal was effective, this time I'll try to make sure I get pressure built up on my new plugs.

Is there a better way to pressure-test these seals on the wells?

I am still suspicious I have another problem, so I will also fill up the bowl with solvent and look harder..

Is there another "common" path for leaking besides the seals?

I guess I will pay more attention to the gasket sealing surfaces too...

Thanks for eliminating the float height as a possibility.

[Shiny]

Pressure-tested plugs I had installed and no leaks.

Filled the bowl with gas, covered with saran wrap to slow evaporation, let sit for 30 minutes on a paper towel, and no leaks...bowl was still filled, towel had no spots, plugs looked dry.

So I am baffled, stuck, and just about out of ideas.

Seems like I must have a float problem, but the inlet valve seats fine with vacuum (new valve and float from your kit).  My pump is mechanical, so I don't expect the pressure to be high, but is it possible for a mechanical pump to have too much pressure?  what is the best way to measure?

Is there some other reason a float might stick?

I will try lowering the float a little too, but I just can't find a reason for the leak or overflow or whatever is behind this...

[Cliff Ruggles]

Vacuum or pressure test the fuel inlet seat assembly. Sometimes they will leak at the fuel inlet seat seal if there are imperfections at the gasket sealing surface.

Yes, mechanical pumps can make too much pressure, rare problem, but we've seen a few up near 8-9psi....Cliff