Carb replacement

[alhnelson]

Just finishing up with our new 440 engine install and still having flooding problems with the ThermoQuad carb when warm. I have already rebuilt it once. I'm considering going to one of the Edelbrock carbs as many ACOC members have done. I know that some folks have used the 1905 which is intended to directly replace the TQ, but is very pricey. My question for those who have used the lower priced 1400 series are:

1)has anyone used the specific model 1400 (600cfm) which has the EGR hookup and is considered emissions legal? If so how has it worked for you, and what adapting needed to be done?

2)Has the 600 cfm been adequate?

3)The same questions for anyone that used other models in the Edelbrock 1400 series. Also, what changes did you have to make regarding vacumn and other connections (EGR,charcoal canister, etc)?

We have emissions requirements here.

Thanks lots, Al

[junebob]

Al in Colorado.
 Thermoquid carburators.I do not entend to cast any aspersions on any ones ability to properly rebuild a thermoquid carb.    Having said that, Based on past common knowledge. This is not a job to be done with:rolleyes: run of the mill re-kitting carb experience.I'll grant you there have been instances where individuals have home rekitted their Thermoquids and had them come out O.K., But I frankly doubt they are 100%Unless that individual has had extensive experience with this carb.The total rebuilding, including shaft replacement,proper jetting etc.[ Because in to many instances to many of these carbs have been tweeked by people who weren't really capable of changing the air filter properly}    Properly rebuilt and adjusted ,which includes properly adlusting the linkages when reinstalling in the rig,.Is an exacting job.These Carbs [arguebly] are the best possable units for these 440 powered motor homes. Anything else,[ excluding race car technical experience]    is a substitutestandard. And more expensive than the thermoquad TOTAL rebuild. Good  Clippering-Bob Chaney.

[Charlie]

Al,
I replaced my Thermoquad with the Chrysler set up Carter AFB from Summit Racing and it works great.  The price was around $240 and the only thing I had to transfer was the kick down linkage.  But, it isn't smog legal here in CA so I will have to put the Thermoquad back on to smog it, small price to pay for much better performance the rest of the time.  You will find a lot of die hard Thermoquad fans in the club.  I am not one of them.  I have installed the Carter AFB on small blocks and big blocks and it has always been an excellent performer.  Good Luck

[junebob]

Replacement carbs.
Charlie- You apparently are one of those that fit the caviot that I mentioned. You are using racing equipment and experience.    Bob Chaney.

[KEYSJUNK]

Al in Colorado:
I hace owned a 21 AC for going on 8 yrs. now. 440 eng., which had the original
thermoquad. It amazes me that after all the problems the members have had with this carb. there are still people that swear by them. From warped float bowels to sinking floats.  I've replaced the floats to the brass one and also replaced the bowl. Its always fun to be on vacation sitting in traffic and the carb. decides to dump it's load in the engine. STALLED AGAIN!  Two years ago I installed a 600cfm Holley purchased from a rebuilder in Miami. With the help of an adapter from the speed shop (base plate). I have now enjoyed two years of driving without distress. The mileage has improved some. This is probably from saving the dumped fuel wasted from the repeated flooding. Engine performs great. I haul a 10ft trailer also.  If you have the cash go the new manifold route. My conversion cost around $150.00.  If your fuel line still goes down thru the right exhaust manifold bakery, I would route it up the front of the right front side of the engine.

[Charlie]

I am in total agreement with member #41, the first experience I ever had with a Thermoquad was on a 360 Ram Charger and the plastic housing cracked, dumped fuel and caught on fire.  I never would want that to happen with my Clipper and it was actually leaking when I bought my Clipper.  I also tow a 20 ft. ski boat with mine and have never experienced any problem since replacing the Thermoquad.  Take a look at what Dodge installed and used on the Hemi racing motor, the Carter AFB.  All of this is just personal opinion mainly from experience.  One thing I didn't mention was that if you install a square bore carb such as the Carter AFB onto a spread bore manifold you will need an adapter plate that is available from almost any where including Summit Racing or PAW.

[Plante]

I replaced my Thermoquad with a 750cfm Edlebrock Carb & manifold.  My mechanic told me the Carter AFB and the Edlebrock are very similar carbs.  My rig runs very good; no hesitation, plenty of power, no backfires, and good mileage.  However, it will not pass DEQ the way it is adjusted.  When new plates are due my mechanic retards the timing and adjusts the carb to make it pass.

[alhnelson]

Thanks for the input so far on carbs. I have also been doing considerable research on this website as well as from many other sources. For what it's worth, I have found.

1)The thermoquad is a great carb for this engine, if it works OK. (if it aint' broke don't fix it). That said, the plastic body on an older TQ can and has led to many problems, especially flooding. The little O rings inside can also cause that problem but they are easy to replace. There is a strong feeling, especially amongst mechanics and others, that once the TQ develops problems, it may be best to replace it. A remanufactured TQ may be OK if you know it has a new body. One of the advantages of a good working TQ are the small primaries and large secondaries which should help fuel economy under normal driving.

2)Some folks have changed to the square bore earlier Carter AFB models which are also a good carb. These are basically the same design as the Edelbrock 1400 series which includes 600 and 750 cfm models. The specific 1400 at 600 cfm is also designed to work with EGR and is considered emissions compliant.

3)Some folks like the holleys which may be simpler but some say not as economical. I really haven't looked that much at them.

4) Another alternative is the original Rochester Quadrajet which was on GM big block engines from the mid 60s to mid  80s. It is very similar to the TQ in concept and general design with small primaries and large secondaries but does not have the phenolic plastic bowl to cause problems. It is also spread bore and a direct bolt up to the 440 manifold, but does require some reworking of linkage and vacuumn lines. While I haven't read of any Clipper owners switching to the original Quadrajet, several have bought the Edlebrock Q-jet 1905 carb which is the original Rochester Quadrajet design adapted to fit the TQ application(linkage, vacuumn, etc). It's probably the easiest way to get the Q-jet design applied to a Clipper if you don't mind the price. The other models of the Edelbrock 1900 series are the same Quadrajet design for GM applications of different years. The major differences between them are the types of choke applications and CFM ratings. From what I've read, most original Q-jets were 750 cfm and some were 795 or 800 cfm. There is some debate in the literature as to what cars the 800 was used on. Several articles have noted that it takes someone who knows this carb to get it working well, but once that's done, it will be a trouble free carb for many years.

Now to my application. I worked with my mechanic, who has extensive carb experience, to go through the flooding Thermoquad again. It still flooded, and he recommended not wasting any more time on a carb that probably had a warped body. He happens to be a lover of the original Quadrajet and suggested replacing it with that. I searched a Denver junkyard and found a 1979 Cadillac with a good looking Rochester Q-jet and pulled it off for $25, and took it back to my mechanic who rebuilt it. That year Cadillac was a good choice because it was late enough to be an emissions era carb but still had an electric choke. Most of the original Q-jets didn't start putting the electric choke on until early 80s at which time they also started putting on electronic carb control which was no good for my application. Turns out the carb itself IDs as being built in 1978 which made it the same year as my chassis so I could expect it would be in the same emissions control period. The carb seems to be working smoothly and not flooding but we are still tweaking the installation so I can't give a full report yet.

One other thing I've learned is that there are as many strong opinions about different carbs as there are carbs. As it said on one website, "the thermoquad is like a harley, you either love it or hate it". I guess you could also compare it with anchovies.

Thanks again for your input. I'll let you know how our application works out down the road.

Al in Colorado

[alhnelson]

Another quick question. Sounds like most of you who have switched to the Edelbrock carbs have gone with the 1400 series (e.g. carter AFB design). Of those, who has gone with the 600 cfm and who with the 750 and has the 600 cfm been adequate? Has anyone gone with the 1900 series, specifically the Edelbrock Q-jet replacement for the thermoquad? Thanks again.
Al