correct fuel filter for 65 AFB 300 Hp

[John C.]

I'm not quite clear on what type fuel filter is correct for a 300 hp 65. While looking for a 3721 carb, I've noticed that some appear to have had ( or do have ) the older style glass bowl filter, but then I'll see one that is set up for the canister filter. I checked Long Island and per their items for sale data, even a 64 had the canister, but there are AFB's for sale with date codes of C5 ( march 65 I assume ) that have the straight tube still in place that is for the glass bowl filter. So what's the deal. At what point did GM switch from the glass to the canister ?
Thanks in advance Guys !
JC

[Don H.]

Re: correct fuel filter for 65 AFB 300 Hp

John, Both the 64 & 65 300 hp used the gloss black metal AC GF-90 (white silk screen writing). It is in a silver (cad or zinc) metal bracket attached to the second from the front intake bolt (actually a bolt with a stud) on the right side. Many vendors sell the fuel line kits with a filter. Good luck, Don H.

[Stuart F.]

Re: correct fuel filter for 65 AFB 300 Hp

Rebuilt 3721's might just as likely have the wrong top plate on them with the straight tube inlet that you refer to. Beware! I've seen a number of them with the wrong clusters and other incorrect parts from a parts bin slapped together to appear complete. Even 63 3461s carbs are the ones, due to their being a unique one year only model, are often outfitted with incorrect parts. There too, the top plate inlet fittings come in several varieties as to what inlet fitting and gasket is used. The correct later ones (including the 3721s), use a slightly larger gasket with a matching sealing surface.

Stu Fox

[Frank D.]

Re: correct fuel filter for 65 AFB 300 Hp

Donald and Stu are both correct vis a vis the filter and 3721S carbs, respectively.

The shadier rebuilders have shoddy quality and bogus parts in many cases. You also have to be careful you don't have "hot slot" damage on the underside from improper installation (e.g. gaskets) -- see picture. HOWEVER, if you can find a good one they are excellent running carbs.

[John C.]

Re: correct fuel filter for 65 AFB 300 Hp

Great responses guys. I can see how things could get changed through the years as carbs are worked on by whomever. Just so I'll know, and hopefully not make a mistake and buy something that won't work, is there any reason why a 3721 that currently has the wrong fuel filter ( glass bowl ) can't be converted to the correct black canister filter ? It appears to me the only thing that has to be changed is the fitting right at the inlet and I assume the air horn is the same ( if it hasn't been changed by Joe-Bob at some point ). I've attached a pic of an example I'm referring to. I'm not actually considering this particular carb, but there are several out there for sale that have the wrong fuel filter inlet that might be a candidate for a restoration.
JC

[Frank D.]

Re: correct fuel filter for 65 AFB 300 Hp

All you need is the angled fuel inlet adapter. Here is a 3721SB on my '63 Corvette.
By the way - if you have a manual transmission IIRC you'll want the 3721SB; that "SB" designation is important...

[John C.]

Re: correct fuel filter for 65 AFB 300 Hp

Thank you Frank ! I've done some research, and the only difference I can find between the "s", the "SA" and the "SB" is basically the jetting, and it looked like the later cars had the SB. Is this correct ? And I assume since you mentioned it, my car should have the "SB". I also noticed it's acceptable for my car ( 118494 , late April ) to have been outfitted at GM with a carb dated as early as A5 through as late as a D5 ???
JC

[John C.]

Re: correct fuel filter for 65 AFB 300 Hp

According to what you fellas have told me, this is what I should have on the car, with the exception of having a somewhat late date code.
eBay item number:281416702214
Looks like I may be looking for a while to find the right one !
JC

[Joe R.]

Re: correct fuel filter for 65 AFB 300 Hp

JC,

Nice looking carb on e-bay however I think the idle screws are wrong and something looks not quite right with the choke. The originals are flat where the fitting attaches.
Also, I thought by 65 most of the GF90 filters were silver with red lettering or at least some were.

JR

[Frank D.]

Re: correct fuel filter for 65 AFB 300 Hp

Thank you Frank ! I've done some research, and the only difference I can find between the "s", the "SA" and the "SB" is basically the jetting, and it looked like the later cars had the SB. Is this correct ? And I assume since you mentioned it, my car should have the "SB". I also noticed it's acceptable for my car ( 118494 , late April ) to have been outfitted at GM with a carb dated as early as A5 through as late as a D5 ???
JC

I'm not familiar with all the "S" suffix nuances; I've been told that if you use a carb set up for a manual vs automatic transmission you could have a "sag" on take off/acceleration due to internal differences if you have a powerglide. Others may know more.

The carb you cite on eBay looks serviceable but it is priced at double what I would pay...

[Duke W.]

Re: correct fuel filter for 65 AFB 300 Hp

For Powerglide the sequence goes 3720S, 3720SA, 3720SB. For each revision level the jets/rods might be slightly different from the equivalent 3721... revisions, and I think the ...20 version may have something different on the throttle lever to accomodate the PG kickdown rod, but I'm not sure.

The SB versions were available through GM parts and the aftermarket well into the seventies and were replacements for all versions back to '62, and since they were set up for the 300 HP versions they were calibrated a little leaner than the '62/'63 versions that were also used on the 340 HP engines.

Duke

[John C.]

Re: correct fuel filter for 65 AFB 300 Hp

For Powerglide the sequence goes 3720S, 3720SA, 3720SB. For each revision level the jets/rods might be slightly different from the equivalent 3721... revisions, and I think the ...20 version may have something different on the throttle lever to accomodate the PG kickdown rod, but I'm not sure.

The SB versions were available through GM parts and the aftermarket well into the seventies and were replacements for all versions back to '62, and since they were set up for the 300 HP versions they were calibrated a little leaner than the '62/'63 versions that were also used on the 340 HP engines.

Duke

Thanks everyone for all the valuable information. I'll keep the radar searching for 3721 SB.
JC