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My modified ’54 3100 is propelled by ‘67 283.
The engine was rebuilt some time ago, including a non-stock cam. I have no further details about the rebuild. The carburetor is an Edelbrock 1405 (600 cfm) on an Edelbrock dual plane manifold.
The acceleration performance is very good. However, I have been dealing with a low end problem - the engine tends to falter and /or shut down at idle, only when warm.

I will skip an account of long trial and error; I believe I finally have a diagnosis. I recently took a heat reading at the base of the carburetor. I read 175 degrees f.
My fuel is 91 no ethanol. I have concluded, after much research, that the 91 fuel will start to bubble at approximately 135 degrees.

I am looking at a couple of heat shielding products for placement between carb and manifold. One is .5” and made of a wood composite. It has good reviews pertaining to dealing with the type of heat issue I am dealing with.
The other is .32” , made of a rubber-like material, and is said to be specific to heat issues.

Any input on this type of problem would be appreciated here , as well as commentary on the 2 products being considered.

My manifold does have an exhaust port. It is capped at the downstream , external point. I am hoping to avoid removing the manifold and capping the other end because I just re-installed the danged thing for the 3rd time after correcting a crankcase ventilation problem. Don’t want to go through that effort again if I don’t have to. The spacer placement is easy, and I think it is the right thing to try next.

In 1957, Mr. Duntov determined the "perfect" carburetor for the factory RACE version of the 283 was 380 CFM, and your truck requires 600 CFM ???

As far as thermal spacers are concerned, the two most common materials are fiber, and thermoplastic.

I am unfamiliar with the products you mention, but you might check max temperature ratings.

Jon

Holley, and possibly Edelbrock made an aluminum heat shield that fit between the carb and the intake manifold. It was a butt-ugly thing, but it deflected enough heat away from the carb to avoid hot idle problems. It would require an intake manifold change, but the best option for your hotrodded 283 might be a Quadrajet calibrated for a Chey 305 engine. Those carbs have tiny primary barrels for good throttle response, and a secondary air valve to control top speed CFM to only what the engine needs. I ran a single Qjet for a 455 Buick on a 460 cubic inch MOPAR 440 truck pull engine, and got 714 HP on a dyno, corrected for temp, atmospheric pressure, and humidity.
Jerry

Waveski, when you had the intake off and on several times, what was the configuration for the exhaust crossover ports in the intake gaskets? Many intake gasket kits include several steel inserts so you can tailor the amount of exhaust heat crossing under the carburetor from one head to the other. If those ports are wide open with no restrictor inserts, it will add a huge amount of heat to the manifold and carburetor.

Could look into adding a bypass style fuel pressure regulator. I know several folks who swear that is the best way to solve this kind of problem.

JW ,
I can understand that circulating the fuel would lower the temp in the carb bowl, but that’s a plumbing project I would prefer to avoid.

78buckshot,
I did not observe or evaluate the upstream end of that exhaust port when the manifold was off - simply because I didn’t know any better. Now I know.

HotRod,
I think I remember from past discussions that you are a proponent of the Q-Jet. That said, I don’t know how that carburetor would be less prone to heating than the Edelbrock I now have.

Carb King ,
The 1405 4bbl in question came with the truck. My experience in this area is limited; my research indicates that this carb is on the upper end of the cfm range for the 283 , but should be compatible. You certainly have more real time experience to fall back on.
Again- the performance is very good in all ways except shutting down when idling warm. (coolant temp stable at 180)
As to the products , I am posting a better image of one of them. It is specific to dealing with hot carburetors.

Waveski, I would use the 1/2" insulator, the wood composite will probably be a better insulator along with the thickness compared to the rubber/steel. You may have to make some slight modifications to linkage, studs/bolts, etc. but it should be minimal. As far as running a Q-Jet, I believe we covered that possibility when you acquired the Edelbrock intake, it is drilled and tapped for a square bore or a spread bore (Quadra-Jet). It was marketed as a direct replacement for the small block spread bore manifold. If and when you install the insulator, triple check that the gaskets and insulator are the same footprint as the carburetor, the bottom surface of the carb probably has some vacuum passages that must be sealed against leaking to the exterior of the mounting surface.

You are correct that the QuadraJet was thoroughly discussed earlier. I was curses to why that carb was brought up in the context of overheating.
(Side point : I am still toying with the idea of trying a Q-Jet at some future time, but I won’t introduce another variable into my current situation)

Thank you for the caution about close examination of the carb footprint details. In the course of my off- season work on my truck last winter I made several jobs more difficult than they needed to be due to ignorance. Lots of do-overs. Learning as I go.

Like Hot Rod Lincoln, I am a fan of the Q-Jet, but you are correct in the thought of the heat issue, swapping carbs probably won't correct anything if in fact heat soaking is the main problem. If I remember correctly, you have a friend that helped with setting up the manifold/carb combo you currently are running. Does he have time to check or recollection of the float setting specs in the Edelbrock? With the small engine and technically more carb than you need, the float could probably be set to a lower limit and help with fuel percolation, just a thought to help you retain the combination you already have. Edelbrock offers a decent tuning kit for their carbs, Carbking could probably recommend some fine tuning tricks. The Quadra-Jet was available in two CFM's, the 750 CFM was standard on smaller displacement engines up to the 400 cu.in. range, it fueled millions of GM engines for 20 years. The big block engines would normally have the 800 CFM Q-Jet, found at the end of the carburetor era on hundreds of thousands of GM trucks with the 454. The difference in CFM ratings were attributed to a slightly larger primary bore for the 800. Jets and needles are available for the Q-Jet for fine tuning. I had 5 GM pick-up trucks from 1967 - 1984, small blocks, big blocks, all had the Q-Jet and had VERY little trouble with them, my 1978 Vette is still running the original Q-jet, it can sit for months in the garage and I can fire it up and drive any time. I'm just giving you this info to help you get a picture of what can be done with your truck, and a little history of the Q-Jet.

Oh, I forgot to add in the post above, Chrysler used a Carter Thermoquad spread bore, it had the center section/float bowl made of plastic to help with heat issues on the big blocks.

I have a "New in Box" 1978 Q Jet in case you're interested. PM me. (I believe it was for a Trans Am but I don't remember off hand.)

Otto, when you have time, check the top of the carburetor for a black electric plug, that would make it an early computer assisted Q-Jet. Some vehicles had it, some not.

Hi 78,

I just took it out of its General Motors box and looked. The only electrical connection on the carb seems to be the choke. The box actually says Oldsmobile (hand written).

Tell me where to look for numbers and I'll further identify it or take pictures. Chrimmas stuff is starting so I might no be able to get the information pronto.

On the drivers side of the carb you will see a vertical small pad with stamped numbers, may begin with 70, roughly 8 digits. The small bores face the front of the engine, drivers side will have throttle lever and secondary linkage. Chevrolet used a side fuel inlet on the top right, Oldsmobile used a top front center fuel inlet.

Jon and I have a similar take on Edelbrock carbs- - - - -if you're a fisherman, use it for a trot line weight the next time you want to catch a bunch of catfish. Then buy a Qjet and stop worrying about carburetor issues.
Jerry

The imitation AFB you have is aluminum, and while the imitations are permanently banned from our shop; I have two GENUINE Carter AFB's on my non-Chevy shop truck. After shutdown of a hot engine, BOTH are bone dry within an hour (percolation, and evaporation). The imitations are worse. I use an electric fuel pump.

The Q-Jet does have an aluminum throttle body, but the rest of the castings are zinc (different rate of heat transfer) plus there is an insulating gasket between the throttle body and the rest of the carb.

The Q-Jet (opinion) is one of the two finest carburetors ever built for a single carb application on the street (the Carter TQ being the other).

As mentioned previously most Q-Jets are either 750 CFM or 800 CFM (there is also a scarce and expensive 850). But one has to understand these CFM numbers. All three have a variable 600 CFM on the secondary side; but the primary side of the 750 is 150, of the 800 is 200, and of the 850 is 250.

The primary side of the original RACE only 283 carburetor I mentioned earlier is about 200, the street version about 175.

Contrasting that, your imitation is approximately 250 on the primary side (much lower venturi air velocity).

When considering 4-barrel carbs, it is important to consider primary CFM / seconday CFM as well as total CFM.

Jon

Carbking has only a single tuning tip for the imitation (see Jerry's post above about fishing!).

Jon

Otto - there are a number of possible formats of identification numbers STAMPED on a Q-Jet.

78 buckshop is correct about location (pump side, center casting vertical stamping about an inch from the rear of the carb).

If the carb were produced by Rochester these could be:

(1) 7 digit beginning with a 70nnnnn (most 1965~1975)
(2) 8 digit beginning with a 170nnnnn (1976 and newer)
(3) 5 digit beginning with a 2 (on some 1968 and 1969 carbs the leading 70 was omitted.

If the carburetor was produced by Carter, then the 3 above are possible plus:
(4) 5 characters ENDING with the letter S as in (Sam) nnnnS

There are a number of "number decoders" on the internet (and to my embarrassment, one of the first published was by me almost 30 years ago). Mine was published with a caviat, which I have not seen on others. The decoder is approximately 95 percent correct WHICH MEANS IT IS APPROXIMATELY 5 PERCENT WRONG. IGNORE THE DECODERS AND LOOK UP THE NUMBER!

Buckshot, like you, most enthusiasts refer to drivers side and passengers side, but since some folks drive on the wrong side of the road the carb companies referred to pump side and choke side.

Jon

Well Shoot! up here in the north woods we don't do a lot of catfish, it'll have to be modified for walleye, lake trout, perch, blue gill. We could use it for a depth sound weight for ice fishing though! You want to come up here in January and help out?

I worked on only one Edelbrock carb 25 - 30 years ago, guy bought a new one along with the big tuning kit, I just set it up to run on his truck for him, never had any follow-up. Thank you HRL and carbking for taking time to help Waveski.

Mr Skorzeny-
PM sent.

The only "positive" I got out of ice fishing in my year in northern Minnesota was there were no mosquitos or "no see ums".

Since we are recommending Q-Jets in this thread, I think we should also mention the Carter TQ, especially in a thread about heat issues. The TQ is short for thermoquad, or a 4 barrel with a thermoplastic body. My opinion on street 4-barrels: the Q-Jet is number 2, but the TQ is number 1.

To be fair, both the Q-Jet and the TQ have a fair number of detractors. Have heard "quadrajunk" and "quadrabog" hundreds of times, and a number of folks complain their TQ split its bowl (believe me, the bowl had help to split )

But in the "for what its worth" category, with 150,000 carbs to choose from, I have a TQ on my 350.

So far, the moderators have been kind with their tolerance of the Q-Jet (never used on a stovebolt), as well as other brands in this thread. I will not try their patience by saying more, however if one of the moderators would like an article extolling the virtues of the TQ, they only have to message.

Jon

Jon, since this is the Hi-Po forum, I'd say talking about just about any carburetor would be OK.
As far as an article on the TQ carburetor, that might help some here. There's no Tech Tip forum here in Hi-Po (yet), but I'm sure it wouldn't be vetoed if the content and interest is there. Just fire it off to editor@stovebolt.com and Peggy and John will eventually get to it. As you probably know, they're still getting settled in their new digs, so tech tip work has taken a back seat.

Thanks Kevin - starting new topic.

Jon

Course of action decided -

I needed to decide between
- Installing thermal spacer between existing Edelbrock carb and intake
or
- replacing Edelbrock carb with a QuadraJet
I needed to consider the amount of work involved, expense and the underlying fact that I am very satisfied with the performance of the existing carb - except for dying when hot/idling.
After getting set up in winter storage I spent some time under the hood. All linkages , vacuum lines and fuel line will easily handle a 1/2” lift , with the exception of the transmission kick down, I’d need to modify the bracket there.
I’m taking the spacer route. (1/2” , phenolic) I think that the odds of it curing my hot carb problem are very good , it’s an easy job , and I’ll be out only about $50. Re-routing linkages and vacuum lines did not sound like fun ; I carefully organized and replaced all of that last winter. The Q-Jet probably would have performed well, with it’s smaller primaries and zinc bowl casting , but “bird in hand” prevails.

Thanks to all for the valuable input. I have learned from it.
I’ll report back when appropriate.