3269 3461 AFB Carter Carburetor

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

Clem;

I believe I and Tim have most of them and between us over the past several weeks on this subject we have probably both re-read them cover to cover trying to find reference to these little holes of some sort. I haven't found any, even for different models. When anyone tells you that one model carb is the same as another except for some slight jetting change, don't believe them. I'm sure you know what I mean.

It sure would be helpful if someone with a 62 with a 3269 would post.

Stu Fox

how about the restorers who specialize in AFBs,any one try them ???

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

question are these holes drilled or are they cast into the carb body ???

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

I will have some pictures of these holes in a few days because I am going to take my 3461 apart. When it goes back together these holes will be blocked with RTV so I will know for sure if my idle issue is resolved.

If the holes are needed for something other than air source then my secondary shaft bores are wore out. I find that hard to believe because the primary bores were not really that bad.

If John Heinsons has a digital camera I would appreciate it if he could post a photo of these holes in question. Clem, I believe they are drilled and not cast into the body. If I get a chance tomorrow I will call a Carter carburetor restorer and try to get more info.

Thanks everyone for staying with me on this issue, I appreciate the help.

[John H.]

Re: 3269 3461 AFB Carter Carburetor

Tim , they are drilled from what I can see. Another challenge, posting a picture. Will see how to do it in the next few days. - John

[Stuart F.]

Re: 3269 3461 AFB Carter Carburetor

Tim;

Just a thought; does your 3461S have a "Hot Air Compensator" and, if so, have you checked to see if it is working properly??

Sent a message to Cecil Loter on the subject who was very helpful/knowledgeable about AFB's for us back in October 2008. Don't know if he is still active, but we'll see.

Stu Fox

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

I wanted to post a follow up on this idle problem I am experencing with my 1963 300hp engine. After removing the 3461 top lid I used duct tape to block these holes we are talking about and the car runs exactly the same, still idles approx 7-800 RPM with the primary throttle blades closed and idle screw backed off completely.

The only other thing I can think of is something wrong inside the engine causing a vacuum leak in the intake somewhere. I did the test Clem suggested with the PCV and the engine draws a vacuum. I am very frustrated with this issue, the car runs fine and it' smooth.

Check out these pics, they show the holes in question and I thought for sure I found the air leak. I am completely stumped...but I think at this time I need to assemble the 3721 I have and try it to see if the engine acts the same..

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

I wanted to post a follow up on this idle problem I am experencing with my 1963 300hp engine. After removing the 3461 top lid I used duct tape to block these holes we are talking about and the car runs exactly the same, still idles approx 7-800 RPM with the primary throttle blades closed and idle screw backed off completely.

The only other thing I can think of is something wrong inside the engine causing a vacuum leak in the intake somewhere. I did the test Clem suggested with the PCV and the engine draws a vacuum. I am very frustrated with this issue, the car runs fine and it' smooth.

Check out these pics, they show the holes in question and I thought for sure I found the air leak. I am completely stumped...but I think at this time I need to assemble the 3721 I have and try it to see if the engine acts the same..

looks like another theory shot to hell.

[Stuart F.]

Re: 3269 3461 AFB Carter Carburetor

Tim;

Good to hear an update from you, but sorry you still have the problem.

Did you see my last post on this thread? I referred to the "Hot Idle Valve" (I may have called it a Hot Air Valve). I questioned whether your 3461S had it or not. Your picture shows the area where it would be, but I can't tell if you removed it to get your secondary air valve out. My 3721SB has one and I thought the 3461S had it too.

Also, I mentioned that I enlisted Cecil Loter to check his stock of AFB's this weekend. He said he has a 3269 and some 3461's. He provided us with a AFB service manual back in 2008 and seems to know them well.

Stu Fox

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

Stu,

This carburetor has the hot idle compensator and I have the channel blocked with a aluminum plug, if you look close in the picture it's visible. I also installed the compensator and gasket so it looks stock. This part does not show in the pictures because it's removed to get to the secondary air valve and below.

Once again, this engine is a stock 300hp with the GM 929 camshaft. At this point it's probably better to try a different carburetor to determine where to look next. The only other part that's been there since the beginning is the spacer between the intake and carburetor base, I wonder if that could be cracked. I have a hard time believing there is a vacuum leak in the engine..

[Cecil L.]

Re: 3269 3461 AFB Carter Carburetor

Tim;

Good to hear an update from you, but sorry you still have the problem.

Did you see my last post on this thread? I referred to the "Hot Idle Valve" (I may have called it a Hot Air Valve). I questioned whether your 3461S had it or not. Your picture shows the area where it would be, but I can't tell if you removed it to get your secondary air valve out. My 3721SB has one and I thought the 3461S had it too.

Also, I mentioned that I enlisted Cecil Loter to check his stock of AFB's this weekend. He said he has a 3269 and some 3461's. He provided us with a AFB service manual back in 2008 and seems to know them well.

Stu Fox

Stu,
Sorry to take so long to respond, but I have been up to my eyeballs in an airplane project taking up most of my time.
I thought I had a 3269 and a 3461, but what I have is a 3460S and a 3461S, both dated J2. If i have a 3269 I haven't located it. I started to take the 3461 apart, but ran into a problem with some stubborn screws, so I have it soaking for a few days...the last thing I need is a broken off screw.
I went through my AFB Manual which covers the first Chevrolet Carbs. for 58-61 348 engines and could find no reference to the holes depicted. Just off the top of my un-trained head, from a layman's perspective, I'm thinking the holes could have the simple purpose of providing a means to lube the secondary shaft to prevent sticking or some such thing. Just a WAG, but there seems to be no obvious functional purpose for them and I doubt they would be the source of a significant vacuum leak.
Just out of curiousity, I may start taking the tops off of some of the other AFB's I have to see if there are other models with the same holes. My collection includes:

3012 for 60-61 solid lifter 320-340hp 348
3261 for 62-64 425 hp 409 (front)
3245 for late 62 380hp 409
3460
3461
3660 for marine application, (appears identical to
3270 for 61 409)
3783 for 64-65 400hp 409
3720
3721

Since the main body casting numbers of 1552 are the same for 3460/61 and 3720/21, it might be interesting to find out if the finished part number changed for the main body between the two applications.

PS
Figure 8-7 on page 108 of Colvin's CBN 60-64 shows the factory drawings for the 3362 primary carb for the 409 application. In the lower right it shows the cut-away view of the secondary side with what appears to be a passage through the bottom of the counterweight well to the throttle shaft. It's hard to tell for sure due to the reduced size of the drawing and my old eyes. Oddly enough, the drawing on the previous page and figure for the 3361 secondary carb doesn't show the same passage.

[Duke W.]

Re: 3269 3461 AFB Carter Carburetor

Two things come to mind. Even though you have what is a "correct" PCV valve, maybe it is not calibrated correctly - like some of these repro nVACs that aren't even close.

Find someone with a '63 and try his valve or buy an inexpensive OE replacement. When you remove the hose and plug the PCV it should loose 50-100 revs. If more, it may be flowing more than spec at idle

You say the throttle blades fit properly, but I'm not convinced. See my previous post about how to center them, and also make sure the secondaries are properly adjusted to fully close. See page 6M-7/Fig. 16 of the '63 shop manual.

Duke

[Stuart F.]

Re: 3269 3461 AFB Carter Carburetor

Tim;

Looks like some good ideas to chew on for you from Duke. Cecil is, as he says, checking his stock for any clues as well.

When you say you are using the standard insulator for your L-75 (the 3/8" phenolic block), I assume you are using the SS plate as well which goes with it. That certainly is something to inspect. I use the insulator on my L-76, but sandwich it between two standard base gaskets used with my aluminum manifold. It is one of the best "positive" seals I have found for an AFB. I have tried other sandwiches made up of SS plates and gaskets and they all were prone to vacuum leaks. I have found the AFB base likes a proper sealing gasket under it.

At least I think we can rule out those holes to the secondary shaft that puzzled us for this long.

Stu Fox

[Duke W.]

Re: 3269 3461 AFB Carter Carburetor

Good suggestion on the hot idle compensator. It's a bimetallic strip that opens up at high temperature to admit additional air to relieve an overrich condition due to fuel percolation in the bowls.

It should be closed at room temperature. I'm not sure at what temperature it begins to open, but if it's missing or open all the time it would cause an air leak that would cause the engine to idle higher and require the mixture screws to be turned out beyond the 1.5-1.75 turns that usually provide the best idle.

It's definitely something to check.

Way back when I thought there was something wrong with mine, since my 340 HP engilne tended to load up, loose idle speed, and even stall, but that turned out to be the 201 15 VAC that didn't meet the 2" rule, which would not be an issue with the 300 HP engine.

Duke

[Clem Z.]

Re: 3269 3461 AFB Carter Carburetor

Tim;

Looks like some good ideas to chew on for you from Duke. Cecil is, as he says, checking his stock for any clues as well.

When you say you are using the standard insulator for your L-75 (the 3/8" phenolic block), I assume you are using the SS plate as well which goes with it. That certainly is something to inspect. I use the insulator on my L-76, but sandwich it between two standard base gaskets used with my aluminum manifold. It is one of the best "positive" seals I have found for an AFB. I have tried other sandwiches made up of SS plates and gaskets and they all were prone to vacuum leaks. I have found the AFB base likes a proper sealing gasket under it.

At least I think we can rule out those holes to the secondary shaft that puzzled us for this long.

Stu Fox

i always installed a gasket between the carb and the stainless plate to make sure there were no leaks.

[Timothy B.]

Re: 3269 3461 AFB Carter Carburetor

Thanks everyone for the help, tomorrow I will remove the stainless plate and try another gasket in place of the stainless to see if this helps. I have the hot slot blocked so I don't need the stainless, it's there to look like original.

The hot idle compensator is blocked but still installed. I will check the throttle plate alignment but I want to try this gasket first. If I put my hand over the PCV valve the engine slows more like 2-300RPM. This is a AC 590C valve out of a 1969 dated box.

After I run the car again, I will let everyone know how I make out.