Divorced choke and headers

[bob69]

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.   

[quadrajam]

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.

[Cliff Ruggles]

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........

[bob69]

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?

[77cruiser]

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

[von]

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.

[77cruiser]

How tight is the choke set with the engine cold? Maybe it could be adjusted a bit lighter?

[Cliff Ruggles]

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.......

[Cliff Ruggles]

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

[Cliff Ruggles]

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

[Cliff Ruggles]

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.......

[bob69]

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?

[bob69]

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.

[Cliff Ruggles]

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......

[old cars]

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."