Carter carbs leaking into intake manifold

[fmahannah]

Have issues with dual carter 3705s on wedge intake running pig rich. Cam is 509. Following everyones tips here I bumped up initial timing to get vacuum up, changed metering springs, etc etc. Still pig rich at idle and even part throttle.

So today I decided to pull tops and check float levels for the tenth time, but before I did I cranked the motor enough so it should have filled the bowls since I wanted to see what level they had when full.

When I pulled the tops the fuel level had already dropped to where there was just enough fuel to cover the secondary jets? So out of curiosity I manually filled both bowls to where I figured they would be when full and watched the fuel level. In less than ten minutes it was back down to just over the secondary jets. Both sides. This was with main fuel line to card disconnected.

I pulled the bottom and removed all fuel from it and blew it dry with a compressor. I set it on the garage floor with the edges on blocks and the primaries closed. Then I put enough fuel in each bowl to fill about half way and waited. Within a minute it looked like fuel was dripping onto the primary throttle blades from near the mix needles. It did not seem to be coming from the venturis. Within two minutes gas appeared to be running from everywhere under the carb?

Perhaps without the carb sitting on it's base gasket on the intake this is normal? I would not think so since even with a gasket this gas would and is ending up in the intake manifold.

Or could it be that the metering rods are not in place (but with engine shut off they would not be down and closing the jet passage).

I think these carbs might have major issues internally and need replaced, but if anyone has any ideas on what would cause almost all the fuel in the bowls to run out the bottom of the base plate with the carb out of the car please let me know what to look for. Until I figure out why fuel just runs through the carb when sitting I don't think any amount of tweaking will stp my rich running condition. I can post pics of anything you might want to see.

I'd hate to give up the carters and put eddys on it but don't want to wait for a full rebuild of the carters (if they can be) to be able to get to some shows

Thanks
Forrest

 

[steve340]

Either use Woodruff Carbs to have a look or replace them with new unmolested Edelbrocks.
You have been doing stuff/posting but it sounds like you have not made the progress you want.

 

[AR67GTX]

I think it siphons out immediately through the metering system. I had a similar problem on my Hemi carbs when the needles were not closing and fuel was running out the small vent holes in the top lid and all over the intake. I tried to remove the top lid as fast as I could to see what the fuel level was and it was always down to about 5/8 to 3/4” deep (normal) no matter how fast I whipped the lid off. It was somewhat a mystery to me also.

 

[toolmanmike]

Have issues with dual carter 3705s on wedge intake running pig rich. Cam is 509. Following everyones tips here I bumped up initial timing to get vacuum up, changed metering springs, etc etc. Still pig rich at idle and even part throttle.

So today I decided to pull tops and check float levels for the tenth time, but before I did I cranked the motor enough so it should have filled the bowls since I wanted to see what level they had when full.

When I pulled the tops the fuel level had already dropped to where there was just enough fuel to cover the secondary jets? So out of curiosity I manually filled both bowls to where I figured they would be when full and watched the fuel level. In less than ten minutes it was back down to just over the secondary jets. Both sides. This was with main fuel line to card disconnected.

I pulled the bottom and removed all fuel from it and blew it dry with a compressor. I set it on the garage floor with the edges on blocks and the primaries closed. Then I put enough fuel in each bowl to fill about half way and waited. Within a minute it looked like fuel was dripping onto the primary throttle blades from near the mix needles. It did not seem to be coming from the venturis. Within two minutes gas appeared to be running from everywhere under the carb?

Perhaps without the carb sitting on it's base gasket on the intake this is normal? I would not think so since even with a gasket this gas would and is ending up in the intake manifold.

Or could it be that the metering rods are not in place (but with engine shut off they would not be down and closing the jet passage).

I think these carbs might have major issues internally and need replaced, but if anyone has any ideas on what would cause almost all the fuel in the bowls to run out the bottom of the base plate with the carb out of the car please let me know what to look for. Until I figure out why fuel just runs through the carb when sitting I don't think any amount of tweaking will stp my rich running condition. I can post pics of anything you might want to see.

I'd hate to give up the carters and put eddys on it but don't want to wait for a full rebuild of the carters (if they can be) to be able to get to some shows

Thanks
Forrest

Check the fuel pressure. 5# or more is too much.

 

[steve340]

OP states he has the carbs off and sitting on the garage floor.
The way he described his test - the float bowl should hold the fuel level he topped up to - not drain out.
This is bound to be the over rich problem in my opinion.
Fix this and you may well nail the problem.

Sometimes carbs have drilled passages the manufacturers seal with lead balls - have these been removed or are leaking???
The carbs should hold fuel.

 

[toolmanmike]

OP states he has the carbs off and sitting on the garage floor.
The way he described his test - the float bowl should hold the fuel level he topped up to - not drain out.
This is bound to be the over rich problem in my opinion.
Fix this and you may well nail the problem.

I don't have time right now but he doesn't seem to have a clue. Of course the bowls will be almost empty when you pull the tops off. The floats are gone and damn near fill the float bowls. I didn't read much more.

 

[fmahannah]

Check the fuel pressure. 5# or more is too much.

Just installed pressure regulator at 5lbs because mechanical pump was putting out 6.5

 

[fmahannah]

OP states he has the carbs off and sitting on the garage floor.
The way he described his test - the float bowl should hold the fuel level he topped up to - not drain out.
This is bound to be the over rich problem in my opinion.
Fix this and you may well nail the problem.

Sometimes carbs have drilled passages the manufacturers seal with lead balls - have these been removed or are leaking???
The carbs should hold fuel.

Exactly. With carbs out if I fill the bowls they empty through the bottom of the carb within 10 minutes.

 

[steve340]

A carb can "siphon" so check for any blocked air bleeds also.
But I am not sure if this is your problem - and not sure if this could happen in the test the way you described it.
I am not sure were the air bleeds on a Carter are located.

The float bowls are essentially reservoirs. They should not drain themselves out to empty.

 

[fmahannah]

I don't have time right now but he doesn't seem to have a clue. Of course the bowls will be almost empty when you pull the tops off. The floats are gone and damn near fill the float bowls. I didn't read much more.

OK but does that explain why with the carbs on the car if I add any fuel to the bowls beyond the level I found after removing the tops it leaks fairly quickly and ends up in the intake manifold? In other words anything added that goes above the level of the primary jet leaks back down and into the intake? Is that normal?

 

[AR67GTX]

Once I got my needle and seat issues fixed that were flooding my front carb, it’s been running fine. But my bowls didn’t leak down to just over the jets.

 

[RJRENTON]

Have issues with dual carter 3705s on wedge intake running pig rich. Cam is 509. Following everyones tips here I bumped up initial timing to get vacuum up, changed metering springs, etc etc. Still pig rich at idle and even part throttle.

So today I decided to pull tops and check float levels for the tenth time, but before I did I cranked the motor enough so it should have filled the bowls since I wanted to see what level they had when full.

When I pulled the tops the fuel level had already dropped to where there was just enough fuel to cover the secondary jets? So out of curiosity I manually filled both bowls to where I figured they would be when full and watched the fuel level. In less than ten minutes it was back down to just over the secondary jets. Both sides. This was with main fuel line to card disconnected.

I pulled the bottom and removed all fuel from it and blew it dry with a compressor. I set it on the garage floor with the edges on blocks and the primaries closed. Then I put enough fuel in each bowl to fill about half way and waited. Within a minute it looked like fuel was dripping onto the primary throttle blades from near the mix needles. It did not seem to be coming from the venturis. Within two minutes gas appeared to be running from everywhere under the carb?

Perhaps without the carb sitting on it's base gasket on the intake this is normal? I would not think so since even with a gasket this gas would and is ending up in the intake manifold.

Or could it be that the metering rods are not in place (but with engine shut off they would not be down and closing the jet passage).

I think these carbs might have major issues internally and need replaced, but if anyone has any ideas on what would cause almost all the fuel in the bowls to run out the bottom of the base plate with the carb out of the car please let me know what to look for. Until I figure out why fuel just runs through the carb when sitting I don't think any amount of tweaking will stp my rich running condition. I can post pics of anything you might want to see.

I'd hate to give up the carters and put eddys on it but don't want to wait for a full rebuild of the carters (if they can be) to be able to get to some shows

Thanks
Forrest

IMO...
Carter AFB and AVS carbs specifically, have several drilled passage ways (and plugged) from under the primary and secondary jet wells to their end points (primary and secondary booster venturi wells) as well as the accelerator pump transfer passages to the accelerator pump discharge well. It is highly likely that one or more of these factory drilled and sealed passages are leaking. Perhaps you could dye the fuel and perform the leak test to see which is the offending passageway.....OR.... perhaps the body casting has a crack or possibly a porous casting. The passage plugs that were installed by Carter are best removed by a professional restorer to not damage the casting during their removal. Epoxy sealant could be used to seal the in place plugs/seals. This was a common fix to the earlier model of GM/Rochester Quadrajet carbs....at the underside of the secondary metering orifice passageways......the float bowl would be empty within half an hour.... just my opinion of course...
BOB RENTON

 

[fmahannah]

IMO...
Carter AFB and AVS carbs specifically, have several drilled passage ways (and plugged) from under the primary and secondary jet wells to their end points (primary and secondary booster venturi wells) as well as the accelerator pump transfer passages to the accelerator pump discharge well. It is highly likely that one or more of these factory drilled and sealed passages are leaking. Perhaps you could dye the fuel and perform the leak test to see which is the offending passageway.....OR.... perhaps the body casting has a crack or possibly a porous casting. The passage plugs that were installed by Carter are best removed by a professional restorer to not damage the casting during their removal. Epoxy sealant could be used to seal the in place plugs/seals. This was a common fix to the earlier model of GM/Rochester Quadrajet carbs....at the underside of the secondary metering orifice passageways......the float bowl would be empty within half an hour.... just my opinion of course...
BOB RENTON

Yes I agree that something is wrong with the carbs internally that is beyond me messing with, that the PO and dealer failed to mention. Depending on turnaround time I will likely have them rebuilt by Harms Auto or similar, and in the meantime replace them with the Edelbrocks from Mancini that are set up for the wedge intake manifold. Once the Carters are done then they will go back on, just because Unless of course someone here has a set they want to part with?

I appreciate the advice I get here, I really do. This is only my second Mopar but I have owned seven AMC Javelins from 71-74 and still own one that I have all the mechanicals done on and just need to get the body back together for the paint shop.

 

[Geoff 2]

As others have stated, with carb top off & fuel in the bowls but below the booster shelf [ what the booster sits on ], there should be no leakage ANYWHERE. Look for a crack, porosity, leaking plg.

 

[Dragon Slayer]

Do both bowls drain down or just one? If the jets remove easily for you (use largest screwdriver that fits slot) take the primary one out. Place some puddy or gum over the hole. Or use a brass plug 5/16"-24. Now fill that one bowl. If it still leaks down swap the plug. Still leak down cracked or holed base. Do the other side.

If it only leaks down when one jet is open, you know the source area. Under neath is a plug runs from under bowl at secondary to where venturi pickup is. Same on the primary. Only the primary plug would leak into the manifold. The secondary is on the outside. But the channel could be cracked. Other is the accelerator pump but that is on the outside of the carb not internal into intake.

A filled fuel bowl below the venturi base can't syphon up on its own. It could continue to run, after shutoff, but that is not your issue since your testing off th car.
The primary plus is visibal in the small slot near the the small triangle. The secondary channel is on the outside of carb but close to manifold inlet and the channel runs into the large channel around the secondary bores.

 

[fmahannah]

Do both bowls drain down or just one? If the jets remove easily for you (use largest screwdriver that fits slot) take the primary one out. Place some puddy or gum over the hole. Or use a brass plug 5/16"-24. Now fill that one bowl. If it still leaks down swap the plug. Still leak down cracked or holed base. Do the other side.

If it only leaks down when one jet is open, you know the source area. Under neath is a plug runs from under bowl at secondary to where venturi pickup is. Same on the primary. Only the primary plug would leak into the manifold. The secondary is on the outside. But the channel could be cracked. Other is the accelerator pump but that is on the outside of the carb not internal into intake.

A filled fuel bowl below the venturi base can't syphon up on its own. It could continue to run, after shutoff, but that is not your issue since your testing off th car.
The primary plus is visibal in the small slot near the the small triangle. The secondary channel is on the outside of carb but close to manifold inlet and the channel runs into the large channel around the secondary bores.

View attachment 1264667

Thanks! I was hoping someone could show me plug locations to check. Turnaround for a rebuild is 6-8 months and I don't want to wait that long to take this car to some shows. I will take a look this afternoon and let you know what I find. It only leaks down until just over top of the primary jets. But on both sides I think. Will test. Thanks again!

 

[HALIFAXHOPS]

IMO...
Carter AFB and AVS carbs specifically, have several drilled passage ways (and plugged) from under the primary and secondary jet wells to their end points (primary and secondary booster venturi wells) as well as the accelerator pump transfer passages to the accelerator pump discharge well. It is highly likely that one or more of these factory drilled and sealed passages are leaking. Perhaps you could dye the fuel and perform the leak test to see which is the offending passageway.....OR.... perhaps the body casting has a crack or possibly a porous casting. The passage plugs that were installed by Carter are best removed by a professional restorer to not damage the casting during their removal. Epoxy sealant could be used to seal the in place plugs/seals. This was a common fix to the earlier model of GM/Rochester Quadrajet carbs....at the underside of the secondary metering orifice passageways......the float bowl would be empty within half an hour.... just my opinion of course...
BOB RENTON

I have always put JB weld over those plugs after I got burned by them once.

 

[fmahannah]

Here is what the base of my carbs looks like. Can anyone point out where the plug for the primary should be? Thanks

 

[RJRENTON]

Here is what the base of my carbs looks like. Can anyone point out where the plug for the primary should be? Thanks

View attachment 1264677

The primary well plugs are located in the void space immediately adjacent to the secondary throttle plate bores at a upward diagonal direction. Sorry, I do not have a pdf editor that i can draw a arrow in your pix. Likewise, the secondary jetwell drillings are EXTERNAL on the sides of the carb shown in your example.
BOB RENTON

 

[HALIFAXHOPS]

Same here Bob looks like these but just the tops can be seen.