Carb gasket replacement

**Jim T.** · July 17, 2007, 10:12 AM

Re: Carb gasket replacement

Kevin my 68 327/350 originally had a QJet from the factory. My intake is like yours with a trench. This trench is is a passage way for exhaust directed by the interference of the heat riser valve up from one side to the other. A lot of Corvette owners on this board recommend that the trench is plugged so the hot exhaust does not transfer. I am going to do this to my 68 when I remove the carb here soon, just don't need all that heat 24/7. Also, my 68's QJet was replaced with a Holley 6210 spreadbore and I used the stainles steel gasket that is reusable when removing the carb with a new gasket like the one you mentioned having a hole/cut slot in it except mine is of spread bore design. The stainless steel gasket is placed between the carb base and on top of the composite gasket. Check the archives for how to plug your exhaust passageway.

**Gerard F.** · July 17, 2007, 01:19 PM

Re: Carb gasket replacement

Kevin,

I think you have the right carb for your 66/350HP although it is replacement dated. From the 4 digit date code it is either 1979 or 1989. A 69 carb would have the 3 digit date code (year-month-week). They changed the dated coding to the 4 digit around the 72 model year.

I think what you are describing as the trench in the intake manifold is the "hot slot" on the cast iron manifold for a 66-67 300HP 327. I thought the 350HP had an aluminum manifold and not sure it had a "hot slot". (I think someone will chime in and correct me if I'm wrong)

But on the cast iron intake with a "hot slot" you would use a base gasket with a dogbone shaped cutout on it which goes over the hot slot. A baffle plate goes over the gasket between the gasket and the base of the carburetor.

The idea for the hot slot was for faster cold weather startups. But it tends to cook your carburetor at other times, and will give you trouble in the long run.

It is advisable to plug the holes in the hot slot. If you have the right size freeze plugs, it takes about 10 minutes if the carb is off the car. Some guys even tap a threaded plug in the two holes although I wouldn't do that with the intake on the car.

Take a look in the archives with a search under "hot slot" if you want to plug the holes. There are some pictures there and lots of comments on the issue.

If you have an intake with other than the 4 holes and hot slot, use a gasket that matches the intake holes without gasket material hanging over the intake holes. I'd still use the baffle for heat dissipation.

Jerry Fuccillo
#42179

**John H.** · July 17, 2007, 01:29 PM

Re: Carb gasket replacement

There's no "hot-slot" on the 350hp aluminum intake manifold; just takes the standard gasket (with no slot) between the carb base and the intake.

**J M.** · July 17, 2007, 03:05 PM

Re: Carb gasket replacement

I think what he is describing is the slot that is present on the baseplate when you separate the carb body from the carb baseplate. I just rebuilt my 3367 and know what he means. I think there are 2 gaskets in the kit and you need to use the one that has the same bore diameter as the baseplate. If you lay it on top of the baseplate, you will see how it fits.

**KEVIN BROOKS** · July 17, 2007, 08:31 PM

Re: Carb gasket replacement

Yes, folks. I am referring to the baseplate. The plate where the throttle plates articulate and links to the accelerator, etc.

There are two long (~1.5 inches) wavy-like trenches which actually runs from the front barrel's throttle opening to the back barrel's throttle opening. This is one long snake-like trench, ~1/16" deep and as wide, on each side. My question has nothing to due with the intake manifold. I already have a gasket for that which goes between the baseplate and I.M. My question, is does the long trenches have to be covered by a gasket? The old (throttle body) gasket I removed barely covered it on one side, if at all. Also, there is a half moon shaped opening (primary side and on left, bird's eye view)in the base plate. If I set the main unit (that which contains the multiple venturi's) on top there is no complimentary half moon shaped hole that mates against it. So does there need to be an opening in the throttle body gasket that exactly matches it, or can only a small circular hole suffice?

**Clem Z.** · July 17, 2007, 11:05 PM

Re: Carb gasket replacement

that slot connects the pri idle transfer slot to the secondary idle transfer slot to provide fuel when the secondary starts to open. yes that slot should be sealed with a gasket.

**Clem Z.** · July 17, 2007, 11:23 PM

correction it is not the idle transfer slot but

the idle feed hole that it connects BUT it should be sealed so there is no leak to the outside

**Gerard F.** · July 18, 2007, 12:05 AM

Re: Carb gasket replacement

Oh, you are talking about the carb body to base plate gasket and the tracks in the top of the baseplate, like the one in the picture, on each side

This is a 3810 base plate which I think is similar to the 3367. It uses the same original 4743 metering block as a 3367 (although you might have a 4508 on a replacement)

On my 3810, the gasket covers the tracks but has a circular hole at each end which corresponds to a hole in the body. The track connects to a hole in each barrel and I think it is the idle feed, if I'm not mistaken. (Guys, chime in if I am wrong).

The generic kits come with multiple gaskets. Look for the one which fits the barrel holes the best, and has corresponding holes in the top of the baseplate and the bottom of the body. There may be extra holes in the gasket which go no place in either the body or the baseplate. If there is no hole in the bottom of the body then the hole in gasket or base plate doesn't do anything. I think

Hope this helps,

Jerry Fuccillo
#42179

Attached Files

throttleplateafter3zs.jpg (50.4 KB, 24 views)

**Kevin Brooks** · July 18, 2007, 10:30 AM

Re: Carb gasket replacement

Yes, yes.

I did find a gasket which covers the long wavy trench, although the gasket does have a hole at each end where the gas would flow in/out. My old (removed) gasket allowed for a tiny leak. What effect would this have?

I spoke to an older, experienced wrench turner about the halfmoon shaped opening on the baseplate posted in my earlier thread. He mentioned that I may need to create a bigger/better shaped opening using an exacto knife. What's your/anyone's take on that?

(I jokingly said to my wife that I'd just as soon create my gasket if I had the material. She matter-of-factly replied "that's what my father used to do." Has anyone done that with any success? Are there better replacement gasket suppliers?)r

**Clem Z.** · July 18, 2007, 12:38 PM

Re: Carb gasket replacement

for holley carbs i would use genuine holley kits because some aftermarket ones do not have quality parts

**Gerard F.** · July 18, 2007, 12:46 PM

Re: Carb gasket replacement

Kevin,

If the old gasket didn't cover the trench, then you would have probably had a fuel leak out the side and it would have idled poorly. If the old gasket covered the hole at the end of the trench or only had a small leak it probably wouldn't idle at all or very poorly.

On the half moon shape hole in the baseplate, this connects to the choke vaccum port. My gasket has a slotted hole at this location, but I don't think the hole connects to anything in the body. I don't have my 3810 apart right now to check.

You should check the body base of yours at the location to see if it has a corresponding hole which is open. Blow some compressed air through it to check.
In fact you should probably blow compressed air through all the holes in the body base to see that they are all clear and where they go, especially the eight vents in the air horn in the attached picture:

I actually had to drill two of these out to a correct drill gage on this modified 3810.

I think I'd cut a hole in the gasket slightly larger than the half moon hole in the base plate, simply to prevent gasket material from being sucked into the intake. Just make sure you have a corresponding hole in the gasket to the baseplate holes, and I don't think you could go wrong.

These gaskets and baseplate castings are intended to be used with different applications, and like I said earlier, they have excess holes. It is really the holes and channels in the body matched to the metering block and plate that control the operation. You can get a better understanding of how things work by just blowing air through the holes.

I'm no expert at this, but I just like to tinker.

Jerry Fuccillo
#42179

**Gerard F.** · July 18, 2007, 01:04 PM

Here's the body bottom on mine

I think that that recessed boss left of the lower left barrel is where the half moon shaped hole in the baseplate mates to.

The surface on this one was machined flat along with the metering body and metering plate surfaces. If you have it apart, that's the best time to do this, at least check the surfaces with a straight edge.

Jerry Fuccillo

Attached Files

machinedsurfbasesm7mb.jpg (203.1 KB, 22 views)

**KEVIN BROOKS** · July 18, 2007, 08:38 PM

Re: Carb gasket replacement

Great responses everyone!
I never said my car idled w/o problems or didn't leak.
Actually, the reason I removed my carb was because I had noticed a discoloration on the sides of the carb all the way down to, and including, the top of the intake manifold. Last summer (at the most recent) I had cleaned the sides of the carb and top with Carb cleaner, but the discoloration/grime/varnish always returned. Also, my car never like cold starts. It would take repeated accelerator pedal pumps to get her started. Once running I needed to have the idle set at a higher rpm, e.g.750-850, in order to keep her from stalling in traffic. I figured enough was enough and thought the best way to get it tuned and running properly was a thorough cleaning - not to mention it would look better. I am apprehensive about removing the air/fuel mixture screws or needle/seat screws. Can I remove these carefully and return to exact location (number of turns, etc.) w/o much worry about idling and driving?
Great pictures everyone! I'm envious...how did you get the base plate so clean and shiny looking?

**Gerard F.** · July 18, 2007, 11:25 PM

Re: Carb gasket replacement

Kevin,

The base plate is aluminum so you need to clean it like an aluminum pot or pan.
Eagle mag cleaner works, simple green, brillo pad, nylon wheel on a drill, and lots of elbow grease. When you are finished give it a shot of WD-40 or Tri-Flow to protect it from moisture corrosion.

Don't be afraid to remove the mixture screws, replace the little rubber gasket with the ones in the kit, blow out and clean all the little channels in the metering block and body. The mixture is set with the car running and hot, see your service manual. Usual setting is about one turn out or one half a turn out from a lean roll position.

If you really want to get an education on Holley carbs of your vintage, as I did, just go to the Archives at the top of the page and search under "Holley 3810" or "Holley 3367", all terms. You will seen a lot of interesting posts on this forum from NCRS members a lot more experienced than I.

Jerry Fuccillo
#42179

Carb gasket replacement

Carb gasket replacement

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