Carter carbs leaking into intake manifold

[fmahannah]

Honestly, I forgot that I actually did already drill the first holes in the primaries to get the idle off the transfer slot, but then discovered all the excess fuel issues and got sidetracked. Had to do this on my other Polara with a single carb as well to get decent idle with a 509 that did not burn my eyes LOL.

 

[4406bbl]

I see, the holes in primaries are not much of a problem until someone goes past 2 x.125 in total size, or 4 holes x.080 on a 440, once you hit that you go up .003-.005 at a time with bits you have measured with a micrometer not just the next size up in the drill bit set. This assumes you have the initial timing at 18, maybe more and steady not bouncing just to get it running clean. If you can get it there with the blades closed, and mixture screws responding then maybe even more timing. Shoot for a 1/2 turn off of the blades touching the bores. This gives you a little adjustment to add more timing if the engine wants it. It takes forever to get it right sometimes, don't give up.

 

[Dragon Slayer]

I don't know about an epoxy lasting, my experience with thermoquad wells was eventually everything failed but maybe for that it would work, or some newer glue tech.
If I was going after that I would find a tapered reamer that was close and long enough, or have one made or make one, grind the seat in the bore out with a ball burr, tig the hole up and leave it a little proud as you do not need every last cfm race car deal. I would then take a brass screw the same thread as the mixture screw, center drill it to make a guide to drill the initial hole, then do the same and make a guide for a reamer. The issue with reamers is they tend to be too long and fat so you have to cut it off and weld a new shaft to it so it will fit thru the threads and not damage them, hard to get it straight. An old mixture screw with a groove cut with the thinnest demel cutting disc and the threads machined off would work for a reamer, and may be smarter. I would buy 3-4 junk parts afbs to get good at the welding and drilling first. That should leave you with 1/8" of usable seat taper and should work, I have seen worse damage work.
I would make sure the idle feeds are not drilled, throttle plates are closed, air bleeds are not drilled, and it is not drawing fuel out of the transition slots, and there are no other fuel leaks before I went after that as I don't think those seats are the biggest problem, but have been wrong before. On tuning this I would give it a lot of initial timing, find a way to add idle air below both carbs, to be sure the blades are shut, a set of carb spacers with a hole drilled where both sets of primaries are with a small ball valve works to be sure the throttle blades are shut, for tuning.
At that point you may find those damaged seats are not that big of a deal. I would also play with restricting the idle fuel with a piece of wire until the idle cleaned up before doing anything with the idle seats.

They use epoxy on heads around guides, so not sure why epoxy would not work. Brass will not be as stable when drilling the new bore. So what is wrong with the steel allen head set screw? You need a method to put it in and out and center drilling it is easier than flat brass for the home mechanic with a drill press.

There is no tapered seat. It is a .0635 bore. The bore is deep not shallow. The needle is .080+" with a taper point. So ultimately it will seat into the bore. No need to go in with a ball burr and run the risk of cracking into the transition slot. If you do not like the idea of epoxy you could press fit (with glue) a brass fitting. I believe I have seen some AMC Carters that used this factory. Also on discharge ports on the secondary.
Welding up would be nice but not the easiest spot to work on.

 

[Geoff 2]

I said this earlier in the thread & got criticised for it, but your idle screws may seal well enough without doing any repair work or modifications to the carb.
Remove the springs from the screws & then screw in the screws & see how they bottom out. There does not need to be a perfect seal on the taper because there needs to be a gap for air & fuel to pass. Make sure it is the taper on the screw that bottoms out, not the end of the thread hitting a shoulder inside the carb; if this is the case, grind off the two leading threads & try again until it seals. If the springs coil bind, cut of a coil or try another spring.
It is worth trying.

 

[Geoff 2]

If you need to close holes in the blades, use soft solder & a plumbers soldering iron, about 80-100watt rating. Do NOT use any type of flame soldering iron. You can get alum solder if the blades are alum. I have done this maaaaany times.

 

[Dragon Slayer]

Carter Primary blades are aluminum for AFB, some secondaries are brass, but they transitioned to aluminum secondary in the mid to late 60's. His needle screw like most AFBs has a very long shaft and he is not hitting the threaded section. I am sure he is coil binding. They punched the shaft through. So the .063 idle mixture bore is now .080 and larger with the chipped out area in his picture.

So it operates more like the primary metering rod now than a mixture screw. If he is rich to start even with good idle ports (with these carbs and his cam) than he really will be rich now at idle. With no fine control, just super course once he opens it past the shaft and runs down the blunt taper. Basically he can cut the taper off that protrudes into the throttle bore and tune the idle mixture with blade holes. Each side being different since each idle bore is chipped different. How would you like to tune that motor?

So actually my first recommendation of getting a non afb mixture screw that has a larger diameter stem, but still 10-32 with a longer taper is the way to go. May be a holley, rochester, heck can be a lawn mower it it works. Ebay search and some of the carb sites have examples.

 

[Geoff 2]

Whatever. He should still try it without trying to repair the body.

 

[fmahannah]

Does anyone have photos of the correct venturi clusters for a Carter 3705 carb? Need to know what tubes and how many should be coming out of the top and bottom.
Yes I know its a strange question.

Thanks

 

[Geoff 2]

Jon Hardgrove can probably help you.
www.thecarburetorshop.com
He bought all the left over Carter stuff & has a huge amount of info & parts.

 

[Dragon Slayer]

They have part numbers engraved on the top. The secondaries are 151 and 152. The Primaries 755 and 756. No $50 consultation fee from the carb shop required

 

[fmahannah]

They have part numbers engraved on the top. The secondaries are 151 and 152. The Primaries 755 and 756. No $50 consultation fee from the carb shop required

Thanks, I will check the numbers.

 

[Dragon Slayer]

I take it they are different between the ones on the car, and the ones you got? If I remember right, the secondary will NOT have any tube on the bottom. Secondaries do not have tubes out the top. No access for it.

Primaries would have an idle tube for sure, and most likely a larger pickup tube on bottom. They do have an air bleed on the top going into the carb top. Caveat is I do not have this carb, but that is customary for primaries on all the AFB I have seen and that includes GM, Ford, Chrys, and Marine.

 

[fmahannah]

They have part numbers engraved on the top. The secondaries are 151 and 152. The Primaries 755 and 756. No $50 consultation fee from the carb shop required

OK I do have the correct clusters. Thanks for that The reason I had asked is that I watched a Carter AFB rebuild video (not 3705 specific) and the clusters on that carb were very different with both the primaries and the secondaries having two tubes on the bottoms. Turns out it was actually an edelbrock carb.

In the carbs on the car I have the jetting/rods set as Dvorak recommended:
750 CFM
Primary Jets .101”/.101” (.071”/.047”Rod)
Secondary Jets Throttle .089” Choke .077”
thick throttle blade angle-Primary 0/Secondary 5

Does anyone have a different recommendation to use on the carbs I am rebuilding? (the jets are all missing from these carbs I bought)

Also, the carbs on the car were tagged LEFT and RIGHT by someone who rebuilt them in the past. Shaped like factory tags but obviously not.
Did the factory somehow indicate left and right carbs on the max wedge cars using 3705s or if not tagged what were the differences to look for?

Thanks again!

 

[Geoff 2]

That jetting is different to the original factory jetting, but Dvorak's combo might be different to the factory set up [ headers, cam etc ]

 

[Dragon Slayer]

Interesting, he leaned it out from a Carter setting. You can look at a SVM for your car and chapter 14 specs should give the jetting and rods.
Carter shows:

16-76 Meter rods both sides (.0665" x .053")
120-161 (.104") Early 3705 Primary jets both sides
120-171 (.1065") Primary both sides
120-176 (.0635) Secondary Choke side
120-159 (.089) Secondary Throttle lever side

No right or left carb. But if someone had modified jetting specific to their car, they may have tagged them.

 

[fmahannah]

Interesting, he leaned it out from a Carter setting. You can look at a SVM for your car and chapter 14 specs should give the jetting and rods.
Carter shows:

16-76 Meter rods both sides (.0665" x .053")
120-161 (.104") Early 3705 Primary jets both sides
120-171 (.1065") Primary both sides
120-176 (.0635) Secondary Choke side
120-159 (.089) Secondary Throttle lever side

No right or left carb. But if someone had modified jetting specific to their car, they may have tagged them.

Interesting. One of the ones I bought still had the 120-171 primaries in it. Dvorak said he was going for best driveability with hs recommendations on jets and rods.

 

[Dragon Slayer]

For primaries he leaned the jet and rod .005" each. Significant area change I would think. Moving .002" in rod size was considered 1 step rich or lean.

 

[fmahannah]

Update. Out of three carbs I bought I managed to build two. On one of them the linkage is snapped off meaning somebody dropped it. Not sure if you can buy linkage, butterflies, etc separately?
On one of the carbs the secondary seems a bit sticky so will take that apart again and get it working correctly before I drive it much.

Anyhow the fuel leaking into the intake issue is now finally resolved, idle smoothed way out and acceleration is much crisper! Must be a crack or leak internally in both of the original carbs, not floats since I used the top halfs of the original carbs on the newly rebuilt carbs with float settings like I had them. Still a little rich at idle which I hope the new vac adv distributor will help with but other than that I finally have a running car thanks to all the advice I got here. Thanks!

 

[Dragon Slayer]

Glad to hear. What snapped off exactly picture would help. If your interested I would take a look at the bottom half of those 2 carbs to see if the leak fix is simple.

 

[fmahannah]

Glad to hear. What snapped off exactly picture would help. If your interested I would take a look at the bottom half of those 2 carbs to see if the leak fix is simple.

With the blown out idle ports probably not worth it. So far a couple big carb shops said they would not fix those. I think it is cracks somewhere because it was not the fill plugs leaking that I could see.

On the linkage it is the ends of the arms for the primary and secondary linkage that are busted off. Here are a couple pics. Two pics of broken ones and one pic of a good one