Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: bob69 on February 21, 2022, 10:56:21 AM
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I'm having problems with the divorced choke on my SBC. I recently installed headers on the engine. The choke takes about 10 - 15 minutes to come off. Before the change the choke took no more than 3 minutes (winter time) to come off. I figured removing the heat riser is why.
I'm hoping someone has solved this problem without having to change to a later model q-jet. I would like to keep the original 7029202 DH, E9 date code carb.
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I also think it may be the lack of crossover heat if nothing else changed.
Here,s an easy way to verify it. With the engine cold, slide a square block
of wood into one exhaust pipe. Use a pair of vice grips clamped onto
the edge of the exhaust to keep the block from blowing out. Start it up and
see if your back to the 3 minute warm up. Some people have also shoved a
potatoe in one pipe to test.
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I've never seen that dramatic of a change and we frequently removed the heat riser or locked them open and not much change doing that either.
I'm not a big fan of headers on anything street driven unless it's a "weekend warrior" or "max effort" set-up. Like most other "high performance" items you purchase gains are not nearly what we are led to believe and they never tell you about all the negatives associated with the "upgrade".
Even the best made headers will blow out gaskets, burn up your plug wires and cook the starter on long runs unless steps are taken to prevent all that.
Matter of fact all the SBC powered vehicles that I purchased that already had headers were converted back to manifolds for the reasons above........
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I appreciate the input. I'd rather fix the choke problem than go back to the stock exhaust. After all, the headers are on and the money's been spent. I could use a later model q-jet and convert to an electric choke, but want to keep the original date coded carb.
I was checking other forums and read several write ups on after market electric chokes to replace divorced chokes. Does anyone have experience with these?
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I've never tried on e of these setups, but I don't see why they wouldn't work.
https://quadrajetparts.com/electronic-choke-conversion-chevrolet-1965-4bbl-carbu-p-2638.html
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Just FWIW I had a stock Q jet and intake on my '69 396 with the stock divorced choke and headers. The choke worked fine. The heat riser passage in the intake was open.
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How tight is the choke set with the engine cold? Maybe it could be adjusted a bit lighter?
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I suspect other issues. Even with the addition or headers and removing the heat riser valve in the exhaust manifold the intake should get so hot in less than two minutes your hand would literally melt to it if you touched the pad where the divorced choke sits.
Still using the stock intake?
Stock thickness gasket under the carburetor?
Intake gaskets open at the crossover?
If stock intake when was the last time the carbon was cleaned from the crossover?
The electric choke "conversions" that attach to a divorced choke carb are "flimsy" and complicated and I wouldn't recommend that route.
The electric divorced choke replacements are OK, but I still use and prefer the stock divorced choke coils. Might be time for a replacement if the intake is heating up quickly after start-up.......
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For those reading this I'll tell my first header story. It dates clear back to the early 1980's but worth the read. I purchased a 1979 K-5 Blazer with about 60,000 hard miles on it. It had the 400 small block engine, TH350 and 12 bolt locking diff. I absolutely LOVED that vehicles and decided right after the purchase to do a couple of "upgrades".
I purchased a set of full length headers for it, which required removing the exhaust manifolds, spark plug heat shields no longer fit, etc. I was certain it was going to make it a BEAST as header manufacturers advertised. I saw NOTHING for power improvement anyplace but it did sound bad-ass with the full dual exhaust and turbo mufflers that I added. I loved it to much I tossed the cast iron manifolds and all related hardware removed into the scrap heap, which turned out to be a BAD move on my part.
About a week into the header install I developed a loud "tick" at start up from one cylinder. It wasn't that noticeable at first but every morning on a cold start it got louder and louder then didn't go away and turned into a blah, blah, blah, blah even after it was warmed up. What I thought initially was a rocker arm tick was an exhaust gasket blown at one of the flanges. I replaced the gasket on that side, good to go. Then about a week later same damn thing from the other side so fixed that deal. Then a collector gasket blew out, one side then the other. Repairs were made, "improved" materials used, good to go once again.
.....continued
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Then we decided to take a long road trip to NC from Virginia where I was stationed at that time. It was early summer and really heating up outside. Steady cruising down the highway there was a LOT of heat coming from the floorboards, so much so that the ice cold A/C all the way up wasn't enough and my wife was picking her feet up and putting them on the seat and bitching at me most of the trip.
Then we pulled off for our first fuel stop. Topped off the tank, jumped quickly back in, turned the key and NOTHING......WTF? The starter was ceased up. I beat on it some with a hammer and made a half dozen trips to the bathroom sink at the convenience store to fetch water to throw on it. FINALLY it cooled down, groaned just a tad but started the engine.....cool....back on the road.
So we're back on the highway rolling along nicely and the engine develops a "miss". Not too bad at first then it got steady enough I pulled over to take a look. I opened the hood only to find a plug wire that was somewhat close to one of the tubes on the drivers side had spark jumping over to a header tube. I messed with the routing some and back on the road but ended up buying a new set of wires at the first opportunity and replacing it with some serious manipulating to gain as much clearance to that header tube as possible.
We finished the trip and stayed with friends on the Outer Banks of NC. Got up bright and early the next morning and loaded up for a day of beach fun and surf fishing. Cranked up the Blazer and the annoying "tick" had returned as I'd blown another flange gasket. Talk about a kick in the nuts, but I loaded up the wife and kids and off to the beach we went.
I'll shorted up the long story but over the next month or so I'd warped ALL the flanges torqueing the piss out of the bolts and replacing flange and collector gaskets a few more times. I'd also wrapped a ton of insulating heat shield material around ALL the wires where they ran near the tubes and made a heat shield for the starter, it worked OK but looked like chit when you picked the hood up.
When it was all said and done I ended up amputating the headers and putting a set of center dump factory manifolds on that vehicle and buying a new set of OEM spark plug heat shields and long wires to run under the manifolds and come up from underneath like the factory did with that set-up.
I went on to put about a zillion hard miles on the Blazer as it was my dialer driver and family vehicle for vacationing and such. NEVER had the first issue with anything else related to cooking starters, plug wires or blowing out exhaust manifold gaskets, etc. I'll add here that there wasn't the slightest bit of power difference, exhaust sound, fuel economy or anything else between the manifolds and the headers.
I repeated that EXACT same deal with two additional GM vehicles I bought years later that showed up with headers on SBC engines in them. Part of the "upgrades" to them were REMOVING the headers and going back to manifolds and factory spark plug heat shields.
....continued
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Before folks using headers "successfully" get their panties all wadded up understand that I fully realize that there have been tremendous advances in header flange gasket/collector materials, coatings, wraps, much better heat resistant spark plug wires and mini-starters that aren't a big heat-sink are commonplace in the hobby. I use ALL of those those items here on "max-effort" vehicles, weekend warriors, and strong running street/strip vehicles. I also realize that there are also MAJOR differences between brands of headers, which include much thicker flanges that resist warping with greatly improved clamping force on the gaskets, and construction to make bolt access easier and greater clearance for plug wires/boots, etc.....plus many are available already "coated" (highly recommended).
However, for mild set-ups, daily drivers and anything that will see a LOT of street use, especially long highway cruising headers are not on the list of "upgrades" here........FWIW.......
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77cruiser, thanks for the web site link. I checked out the electric choke and its just what I was looking for. The electric choke bolts on in the same location as the divorced choke and hooks up to the q-jets stock choke linkage. It will allow me to keep the q-jet unmodified.
It does looks a little fragile and wonder how well it will hold up. Has anyone had experience with this electric choke?
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Cliff, I'm working on a 1969 Chevelle vert I bought in 2008. It had a 307, power glide, performer intake, headers and a holley with an electric choke. It ran very good. No issues with cold starts. Its a summertime "drive through the coastal mountains on weekends" driver. The glide started acting up and was swapped out for a 700r4.
The 307 was just not up to the task of driving up and down the mountains. It was constantly down shifting on every climb. Vey annoying. I wanted an engine that could cruise at 1500 rpm (about 35 mph) without having to down shift on the climbs.
I settled on a 400 sbc, builted to be a low speed torque engine. It has stock 441 heads, mild cam, perfomer RPM, headers and a 7029207 q-jet. The crossover is functional and has the thicker carb gasket. The rpm intake uses the 1970 style divorced choke.
The choke did stay on longer than normal but as a summertime driver it was not an issue. That 400 sbc did exactly what I wanted. Low speed cruising without having to down shift on climbs. More time enjoying the drive with the top down and little time working the gas pedal to maintain speed.
Winter driving was a whole different situation. Every couple months the car was driven to circulate the fluids and dry out any accumulated moisture. The choke would stay on waaaay too long.
For example, I picked up the car from storage, drove 5 mile on the freeway, drove back to my house on surface streets, pulled in the driveway and the choke was still on! I can't explain it, but that's what happens during the winter.
I ended up changing the q-jet with a hot air choke model converted to electric. Problem solved! The engine starts and runs beautifully when cold. Choke goes off in about two minutes and runs great.
The engine really does not need the crossover to run well (not in calif) when cold. Just needs choke control for initial start up.
To the member with the 396 comment, I also have a 1969 Nova with a 396, headers and q-jet. If you know the car this is a very big engine in a small engine bay. Everything is very close and tight. The divorced choke is not a problem. Air flow around the engine is limited and the choke/engine heats up relatively quickly.
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I should note here that divorced chokes are fully adjustable and IF you use a thicker than stock gasket the rod becomes too short and it will stay on a LOT longer.
The time from open to close is set by changing the length of the rod running up to the carb (there is some range of adjustment bending the stock rod one way or the other). I'd certainly play with that before spending any money to "convert" to a divorced electric choke or a different carburetor.
I'd also add that unless you were the last one to install the intake I'd make damn sure "restrictors" weren't installed to keep some heat out of the intake.
The 400 SBC is an excellent engine, too bad they didn't make them in greater quantities, you rarely see any of them for sale these days......
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where did I get lost here.
"I would like to keep the original 7029202 DH,"
"I'm working on a 1969 Chevelle"
"I ended up changing the q-jet with a hot air choke model converted to electric."
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Cliff. Never could understand why someone would install headers on one of those smog low performance vehicles back in the day. I would cringe when someone drove one of those into my shop back in the day, needing spark plugs changed.
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ALWAYS start with the basics.
If your choke stays on too long verify that the pad under it is heating up quickly.
You have control of the delay (time from closed to open) by modifying the length of the rod. Any changes made to the distance between the divorced choke pad and carburetor effect the "time" it takes for the choke to fully open.
Carboned up crossovers in the heads or manifold slow things down.
Any sort of "aftermarket" intake will NOT have the same distance pad to carb and in many cases require a longer rod just like using a thicker carb to intake gasket would. Aluminum vs cast iron changes things as well.
Over the years folks who installed intakes and intake gaskets had a BAD habit of using restrictors to keep some heat out of the intake, BAD idea but it was done.
I've worked on hundreds of these engines dating clear back to the mid-1970's and not in one single instance has removing the heat riser, disabling it, or going to headers made such a dramatic change in the release time of the divorced choke that I couldn't correct the added opening timing without much more than bending the stock link or making a longer one from a piece of aluminum (easier to bend that steel) TIG rod.
I will say for anyone reading this that IF I installed any "high performance" part on a mild set-up and it started a chain reaction in me having to buy more parts to correct issues it caused I would AMPUTATE that part or parts and go back to the stock pieces.
I build a LOT of carburetors for Pure Stock and FAST Class cars that use stock iron manifolds and a couple run into the high 9's over 130mph with bias ply rear tires! I've owned and raced cars with headers and they absolutely SUCK BALLS on a small block Chevy application for the reasons I mentioned earlier.
If they brought a LOT of power to the table I'd put more effort into using them but for at least 95 percent of the applications that get them they are WAY more trouble than they are worth.....IMHO
Folks should note here that there are a LOT of parts sold for these engines that are advertised to "make more power". I saw earlier where a Performer RPM intake was used on a small block 400.
.....contineued
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A few years back I was on the dyno with a 440CID engine with aftermarket aluminum heads flowing 260cfm, custom ground HR cam, 10.6 to 1 compression, and a factory cast iron intake. We made 497hp and 540tq once we got it dialed in. The shop owner had an Edelbrock Performer RPM intake in the shop and asked me to install it to "see how much power the engine will really make". I did so, and the very next pull with NO OTHER CHANGES was 491hp/535tq!
Yes, we LOST power with the larger intake. So how many folks buy those intakes to put on 180hp 350's and think they are making MORE power anyplace?
It's not much different with headers. We've dyno'd a few engines swapping from manifolds to headers and even tested different headers against each other. Sometimes you'll see dramatic improvements, sometimes none at all, and other times you stand there scratching your head and backside wondering why you LOST power? With a really well made header compared to a poorly made one I've seen 30hp, but typically NOTHING below about 4500rpm's or so. So even if all your efforts result in a little more top end charge, you have to weigh out the negatives with using them and make sure that your goals for improvements were stronger top end charge and that your engine has enough cam and head flow to make power that high in the RPM range.
I'll close here with this. I'm on here to help folks solve problems and get a good end result with these things. When I provide lengthy responses it is often to educate everyone involved and certainly NOT to be critical of the OP or what they have done. I've been doing this well over 40 years and coming up on 20 years full time. At this point in my learning curve I certainly don't know everything, but for sure I know what works poorly or doesn't work at all.
You'll also notice that I often go "against the grain" when it comes to the selection and use of aftermarket "high performance" parts. This comes from DIRECT testing, not from the fancy advertising the company selling them tells me, or what I've read from Google research, other Forums, etc.....
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Hi Cliff. I assemble all my engines. At first to save money, then because I really enjoy it. The machine shop I've been going to since the late 1970s does excellent work and the owner understands that I like to do the assembly myself.
Over the years I've collected dozens of chevy chokes and choke rods. Not afraid to tinker with them to get the set up correct. I've taken them apart and changed the coils "clock" position and even put a 1969 coil into a 1970 housing. I'm pretty good at bending chock rods too.
Reading about your experience with headers, my first though was " been there, done that". I had the same experience in the 90s just not as bad as yours. The header eventually burned a hole in the a/c suitcase. I removed the headers and put the stock exhaust back on.
Fast forward to the chevelle. The old headers were very rusty and ugly. When I put the 400 sbc in the headers were also changed. The headers were ceramic coated to reduce heat, the flanges are thicker to prevent gasket blow outs, pipes are thicker and the routing cleared the plugs and wires with no problems. Have no problems with them.
Experience taught me to check the header bolts frequently. After installation, I'd check the bolts every week or sooner on a cold engine. Always found one or two, or more that were loose. I kept doing this until all of the bolts stay tight. Surprised at how look it took to get all of them to stay tight.
I don't understand why a header manufacturer would build a header that interfered with plugs and plug wires. Like they don't know were the plugs are? Are they designed for a sbc head with angled plugs and yet still market them for stock heads?
Before the internet, you needed to know a guy that would direct you to the correct part. Today, do a search on-line and you will find lots of feedback on user experiences with a particular part. Keeps the manufacturers and vendors honest.
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Got to LOVE feedback. It's helpful but you have to sort thru it as some of the folks bad mouthing a certain part need to get out of the hobby and never work on anything related to it again.
Kind of related but I was on Amazon recently and saw where someone gave my book a bad review and 1 or 2 stars, can't remember which. He commented this:
"lots of history, lots of GM charts, little in the way of fixing and or modifying the Quadrajet.
Sorry I spent the money!"
Let's see, there is one chapter on "History", not a single "GM" chart in the book, and for sure that IDIOT didn't even read the book and very quickly needs to go straight back to his day job!.......FWIW....