Carter carbs leaking into intake manifold

[fmahannah]

Since I can't buy everyone here a drink I just got gold membership to show my support and appreciation for all the advice!

 

[Dragon Slayer]

The dodge/plymouth service manual should have it also in chapter 14 fuel. The carter manual says the 3705 float from top of float outer end to air horn gasket is:
15/64" if a solid needle. 13/64" with resilient seat needle. Interesting enough each carb has a different set level. The early 3447/3505; the 3705 and the 3861. Float drop for all is 23/32".

I think you can drive up here to VA and buy me a beer. We have car shows in VA

 

[fmahannah]

The dodge/plymouth service manual should have it also in chapter 14 fuel. The carter manual says the 3705 float from top of float outer end to air horn gasket is:
15/64" if a solid needle. 13/64" with resilient seat needle. Interesting enough each carb has a different set level. The early 3447/3505; the 3705 and the 3861. Float drop for all is 23/32".

I think you can drive up here to VA and buy me a beer. We have car shows in VA

I would if I wasn't getting 4 miles to the gallon! OK so I think I have it backwards. I am set for 3/8 which is 24/64 and factory says 13/64 so factory setting actually puts the float higher in the bowl.
Less than a quarter inch for float level for factory setting.... so my float level is not causing the flooding I don't think.

 

[Geoff 2]

[1] Regarding the slots in the venturi gaskets. Many Carter carbs have a slot in the venturi itself or in the mounting base of the carb. So whether the gasket has the slot or doesn't, the fuel can transfer. Check your carb carefully to see. Using a slotted gasket with a carb that has slots will work ok.
[2] The 3447 is totally different to the 3705. 3447 has the small air cleaner neck & small primaries. 3705 has the large 5" air horn & larger primaries.
[3] No way would I use Edel carbs. The above carbs have specific calibration for a cross ram, Edel do not.
[4] These carbs are extremely reliable & trouble free. It seems something simple is being missed.
[5] Jetting info etc is in the MP engine book. FL is 7/32" & float drop 3/4".

 

[fmahannah]

Thanks for the info on the slots. These are definitely 3705s. Where can I get the MP engine book?

 

[Dragon Slayer]

There are Service manuals on line or purchase paper copy from ebay. The carter books come up on ebay, but most end at 1960. You need to ensure the one you get covers into the year of the carb you are interested in.

Float level is calibration for fuel level for jetting. Fuel level should not get high enough to flood out. If you take the secondary venturi off and fill bowl separately you can see level rise in the well for the secondary pickup. If you keep it from spilling over, and the level continues to drop and wet secondary blades/bore I am afraid you have leak under the fuel bowl in that channel to the venturi, or possible shaft (which runs under it).

 

[RJRENTON]

[1] Regarding the slots in the venturi gaskets. Many Carter carbs have a slot in the venturi itself or in the mounting base of the carb. So whether the gasket has the slot or doesn't, the fuel can transfer. Check your carb carefully to see. Using a slotted gasket with a carb that has slots will work ok.
[2] The 3447 is totally different to the 3705. 3447 has the small air cleaner neck & small primaries. 3705 has the large 5" air horn & larger primaries.
[3] No way would I use Edel carbs. The above carbs have specific calibration for a cross ram, Edel do not.
[4] These carbs are extremely reliable & trouble free. It seems something simple is being missed.
[5] Jetting info etc is in the MP engine book. FL is 7/32" & float drop 3/4".

EXCELLENT INFORMATION AND EXPLANATION. Contrary to popular opinion, Edelbrock (aka "Eddy" or "Eddie") and their successors, are not the universal replacement for the origional Carter applications. I support the premise of specific calibration points for the intended application of a cross ram manifold as the Max Wedge requires. The only downside is the cost and availablity of origional Carter carbs.....but....if origional performance and appearance is required or wanted, then NOTHING beats the origional equipment. Just my opinion of course.
BOB RENTON

 

[Geoff 2]

Bob,
Like most cross ram intakes, whatever brand engine, they require staggered jetting to get some semblance of equal distribution to each cyl. A relic from the past, better options these days, would only use for nostalgia.

 

[fmahannah]

Well I think I am getting a little closer. Took carbs apart again and noticed on the venturi cluster gaskets that the new ones had small corners where the old ones were rounded, and I think it prevented the venturis from seating against the gasket correctly, so I trimmed them. BUT I noticed that on one carb the mixure screws at 1.5 turns stuck the pointed part quite a ways into the bore, and on the other carb the points were just entering into the bore. Figured the mixture screws were incorrect for one of the carbs, but when I remove and measure them they all measure 1.4 inches. Noticed on one carb the screws gently bottom out pretty quickly, where on the other they screw in a lot and completely compress the spring before stopping. Took a look and it seems that someone overtightened them in the past and it punched the hole where they normally seat out so that they don't stop at that small opening in the bore where I think they are supposed to bottom out?

How badly would this affect the way the car runs at idle? I think even if I tried to adjust by counting the turns in from starting on the good carb and matched that on the bad carb so they they are both pretty close to the same distance into the bore that it would still not be correct since the hole size for the tip has been enlarged? Am I screwed and need a new core?

I took some pics, one carb has one mix screw that when lightly bottomed fits the seat in the bore (circled in red), the other seems slightly broken and allows the screw to enter a little farther into the bore. The other carb is a mess. Both screws lightly bottomed ends up maxing out the springs and as you can see the screws end up bypassing the seat completely as they are both blown out. I would think these would just allow fuel to flow unregulated?

Thanks as always
Forrest

 

[RJRENTON]

Bob,
Like most cross ram intakes, whatever brand engine, they require staggered jetting to get some semblance of equal distribution to each cyl. A relic from the past, better options these days, would only use for nostalgia.

Thank you for your comment. I'm aware of the theory of how the system operates and what is required to achieve optimal air flow and fuel distribution. I'm a firm believer in the origional design and the carbs needed to make the system work as intended. The origional Carter 3705S were specific to the application, in terms of optimum air flow. Fuel flow and distribution were tailored and optimized. Are present day Edelbrock and their succsuccessors or wanta-be's are adaptations, based on air flow, off idle fuel transition, or both, and mounting configurations or linkage connections? I really don't know.....just some catalog cut sheets and magazine articles and internet presentations just do not provide the information I desire. To this end, if I could do a side by side comparison between old vs new .....to satisfy my curiosity. For my money, I prefer the old equipment...but this is just my preference. BTW....what are the "better options" you spesk of?.....hopefully not fuel injection.... Just my opinion of course....
BOB RENTON

 

[Dragon Slayer]

Yes that is a problem and will be rich at idle since you won't have the control to limit fuel. Venturi seating correctly can cause issues too so using correct gasket and installed correctly for each side. That still does not explain the leaking fuel into secondary. Far bigger issue.

 

[fmahannah]

Yes that is a problem and will be rich at idle since you won't have the control to limit fuel. Venturi seating correctly can cause issues too so using correct gasket and installed correctly for each side. That still does not explain the leaking fuel into secondary. Far bigger issue.

Leaking into secondary did not occur this attempt. So it was either float levels which I reset again or the gaskets I trimmed or a combination. But then it was still way rich no matter what at idle and when I took them off I looked closer at the mixture seats

Is there any fix for the mixture seats or do I have to find good cores?

 

[Geoff 2]

Bob,
I think the difference between a CR intake & modern tunnel ram or single 4bbl intake is that the modern intakes have the carb more centralised in relation to the runners & this gives better distribution.
The fact that an intake needs staggered jetting is an indication of uneven airflow & the greater the difference in jet sizing, the greater the airflow disparity.

 

[RJRENTON]

Well I think I am getting a little closer. Took carbs apart again and noticed on the venturi cluster gaskets that the new ones had small corners where the old ones were rounded, and I think it prevented the venturis from seating against the gasket correctly, so I trimmed them. BUT I noticed that on one carb the mixure screws at 1.5 turns stuck the pointed part quite a ways into the bore, and on the other carb the points were just entering into the bore. Figured the mixture screws were incorrect for one of the carbs, but when I remove and measure them they all measure 1.4 inches. Noticed on one carb the screws gently bottom out pretty quickly, where on the other they screw in a lot and completely compress the spring before stopping. Took a look and it seems that someone overtightened them in the past and it punched the hole where they normally seat out so that they don't stop at that small opening in the bore where I think they are supposed to bottom out?

How badly would this affect the way the car runs at idle? I think even if I tried to adjust by counting the turns in from starting on the good carb and matched that on the bad carb so they they are both pretty close to the same distance into the bore that it would still not be correct since the hole size for the tip has been enlarged? Am I screwed and need a new core?

I took some pics, one carb has one mix screw that when lightly bottomed fits the seat in the bore (circled in red), the other seems slightly broken and allows the screw to enter a little farther into the bore. The other carb is a mess. Both screws lightly bottomed ends up maxing out the springs and as you can see the screws end up bypassing the seat completely as they are both blown out. I would think these would just allow fuel to flow unregulated?

Thanks as always
Forrest

View attachment 1266244 View attachment 1266245

IMO....
The pix's of the throttle bores seems as if someone damaged the idle mixture discharge ports, likely from forcing the mixture screw too tight against its tapered seat. Possibly, in the carb's history, someone used the wrong mixture needle (short thread length, long taper) and that person, while trying to deternine the initial setting, forced the needle in until it bottomed out but the tapered needle enlarged the seat and b4 the needle bottomed. Should you look for a new/used body casting? Depends on if you can obtain a satisfactory repeatable quality idle . Is your carb repairable? I have no experience in that regard, but, I believe the origional discharge port was tapered, using a tapered reamer to form it during manufacturing. Just talking out loud.
BOB RENTON

 

[fmahannah]

I am asking Brian at crossram connection if he can repair this type of damage. I can't get a quality idle at all, lightly seating the mixture screws has no effect, runs rich to the point of burning your eyes, and some of the fuel ends up laying in the intake (worse on the side where both seats are damaged) Floas are new and correctly set now, I even backed the fuel pressure down to 4.5. Transfer slot is not overexposed and idle circuit is getting too much fuel even when it should not get any. Secondary plates remain dry now when idling. As long as there is airflow, fuel is coming through the idle system, but it is not being metered by the mixture screws correctly.

Yes someone definitely went way too far tightening the screws or using incorrect ones, even though the correct ones are in them now. I am hoping these Carters can be repaired, can't seem to find any for sale that is for sure.

 

[RJRENTON]

Bob,
I think the difference between a CR intake & modern tunnel ram or single 4bbl intake is that the modern intakes have the carb more centralised in relation to the runners & this gives better distribution.
The fact that an intake needs staggered jetting is an indication of uneven airflow & the greater the difference in jet sizing, the greater the airflow disparity.

Yes.... I'm aware of the fundamental differences.....but the Max Wedge cross ram manifold (and later the Hemi cross ram manifold) was developed by tuning the intake runner length and plenum volume to provide a reverberation phenomenon that builds and reinforces a reflective pressure wave at a certain engine RPM range (~ 2800 rpm to 4200 rpm for example) creating a ram charge affect, similar to super charging, but static, allowing the engine to make more power. The Chrysler Corp design was unique.
BOB RENTON

 

[Dragon Slayer]

Let us know what Brian says. I would think they could be welded and redrilled. But a lot of work.

 

[Geoff 2]

Idle mixture screw holes. They could have been enlarged in a misguided attempt to increase idle fuel delivery. They may work OK as is, as long as they bottom out for the starting point. Screws may not be out as many turns, but ok as long as they regulate the idle mixture.

 

[Dragon Slayer]

Idle mixture screw holes. They could have been enlarged in a misguided attempt to increase idle fuel delivery. They may work OK as is, as long as they bottom out for the starting point. Screws may not be out as many turns, but ok as long as they regulate the idle mixture.

Did you actually look at the pictures, and read his comments? Those holes are pretty bad. Once you punch through and chip, you will be severally limited in your ability to get the idle mixture right and balanced. The idle mixture screw for your carb is the 30A-80 which is the same screw the hemi carbs used in 66-67. Also some other AFBs. The Hemi idle mixture port is a #52 drill bit .0635-" in measurement on several I calculated. This is the correct dimension for stock Idle mixture screw 10-32 x 1.430 (.080 dia x .645 L blunt tip, grooved head). So you could remove the idle screw, measure actual opening of the port.

There are 10-32 screws that have larger diameters needle shaft and it may be an alternative to use them as a stop gap. Off course you may have a sensitivity issue with a larger bore dia. I find it interesting the bleed down stopped. You stated you poured liquid into bowl and it drained down to jet level and liquid was in secondary bore. Primary issue complicates matters, but that would not be the source of secondary liquid on the bench.

I am not as familiar with Max Wed as the hemi carbs, but the 413 got the 3447 and 3505 carbs, the 426 got the 3705, 3861 I believe. Supposedly AT 3705, MT 3861. Seem like there are plenty more 3861 around. Jetting is the only significant difference. The Primary and secondary venturi are the same. So that could be an alternative for you.

 

[fmahannah]

I think 3447 were smaller carbs than the 3705s. Will have to look up the 3861s but mine is an AT. Right now I am willing to try anything I can actually buy and not wait weeks or months for. Thanks