I have this carb laying around, and thought about using it on my 37. The motor is a stock 1979 360, out of a motor home, with 57,000 miles. I believe the carb is a 700 double pumper, but I think it has the wrong bowls on it. I have never rebuilt a carb, would this be a good one to start on? Is the 700 to big for my motor? Should I leave the factory carter carb on it? I am not looking for more hp, just a good running motor. Will it wreck gas mileage a lot?
If you are not sure about the cfm, look at the air horn on the driver's side. A 700 should have 4778. (4779 is a 750, 4780-800, 4777-650, etc.) IMHO this is probably a mid level carb to rebuild. There are carbs which are easier and carbs which are more difficult. Probably the biggest chore with one of these is making sure you use the correct parts to rebuild it. Holley made production changes over the life of the double pumpers so you have to be 100% sure you are using the correct gaskets. I would recommend a Holley brand kit. Double pumpers are not known for their gas mileage. If you stay out of the secondaries you will do OK. Putting your foot down far enough to open the secondaries dumps a whole bunch of fuel from the second accelerator pump, particularly if it is a 50cc unit. You can tell if the pump housing is larger than the primary pump housing. The other thing you have to consider is that a vacuum secondary carb opens the secondaries based on throttle position AND the engine load. The double pumper is full manual secondaries so you can end up with too much air and not enough engine depending on the load. Let's be honest, they are carbs designed for WOT racing. For the street I would be more comfortable with a 600 cfm for your engine. At 6000 rpm and 100% volumetric efficiency (not going to happen on a stock street engine) you are pumping about 625 cfm through the engine. A 500 - 600 carb will feel more "crisp" and you will get better mileage.
Without knowing your combination and intent for the car I recommend sticking with the stock Carter if the vehicle in question is a driver. The carb pictured has cathedral bowls which may be correct for the model number (stamped on the choke horn of the carb). Double pumpers are great for their intended purpose but over kill on a tame combination where drivability and economy are primary concerns. Your vehicle will not make more horsepower with this carb unless the current carb is too small for your motor. Yes, it will wreck your gas mileage...a lot. A double pumper has twice the pump shot every time you tickle the throttle (a accel. pump and shooter for primary and secondary).
This is the kinda of info I am looking for. I plan on driving this every day, and am looking for somewhat decent gas mileage. Is the factory Carter hard to rebuild, and tune.
79 360 would probably have a thermoquad....what intake manifold do you have, are the secondary bores a lot bigger than the primary side, like this?
redsdad is correct. A 600 vacuum secondary carb would give you better all around driving pleasure . They are easy to find and rebuild . He is also right about the Holley kit .
As far as I know it is the stock intake and carb. I got a friends book on Rochester's, then realized it wasn't one of them. It came out of a 1979 motor home from what I was told. The block I.D. says 79 360. Here are some pics of the carb, tell me what you can I will look for more things as I learn.
There are 2 different carbs in question. 1 on the motor and the double pumper not bolted to anything. Is the Thermoquad nice to tune.
That double pumper is a piece of junk and pollutes our air. Better send it to me for proper disposal.
Isn't it the Thermoquad that has leakage problems where the throttle shafts go through the main body ?
I personally am not a big fan of these carbs thay have had some problems with cracks in the plastic float bowl. Thay are not easiest to rebuild but can be done. I know that chrysler used some Quadrajets on some cars and trucks but not sure of year make and modle. I would be looking for one of them but that is because I like the Quardrajet.
For me the Holley can be more user friendly to tune to your application by seat of the pants driving, changing jets, pumper ramps, etc. watching spark plug color. Thermoquads were problematic BUT you will have others say they are not. I still would just get a Holley 600 1850 and be done with it................................
What can I say. I am not a fan. The unit will flow far more air than the engine can BUT it does have the air valve over the secondaries which will only open to the point which supplies only the air the engine needs. A leaking main well (similar to a common Quadrajet woe) and complex linkage are probably going to be your biggest challenges. Take photos of all the linkage paying particular attention to down or up through the hole shots. It is designed for the engine so the jetting is correct as is (although smog not performance). I found a pretty good article here which you ought to read. Has some good tips. http://www.moparmusclemagazine.com/...04_rebuilding_a_carter_thermoquad_carburetor/
"It is designed for the engine so the jetting is correct as is (although smog not performance)." I believe the factory jetting would be for the motor home as a hole not just the engine. Apples and Oranges if he put it in a lighter vehicle with diff. gearing...............
One more myth is that Holly DP's 'use more gas' than other carbs. It's made by people who don't understand what a carb is or what it does. The comment that it has two squirters means little....the second one never squirts UNLESS you are moving the pedal a lot - and if you doing that, then why are you expecting good gas mileage? I drive my cars all over and never, ever need the back two barrels - so if you are tipping them open it's your own fault. Vac secondary carbs are great if you are in no hurry to get anywhere. A Holly DP is great carb and can be tuned lean enough, if you wish, to burn holes in the tops of your pistons. How much gas your engines consumes is up to you, not the name on the carburetor.
I believe that I have a Quadrajet on a 400 Mopar laying around, so that might be a good one to look at then. My main 2 things reliability, and ease of tuning. I also understand the more I screw with what ever carb the easier it gets.
That is the route I would take. Check the throttle shaft for slop and look close across the front where the two bolts hold the carb down and see if it looks flat. Some people over tighten them and warp the carb kinda hard to fix that but the throttle shaft is an eay fix. You can mail it to me and I can install bushings.
Went and looked at my other carb, and it also is a Carter- Thermo quad. I know from the numbers that my holley is a 700 cfm, is it worth detuning to run on my motor. I am trying to do this on a budget, so I really don't want to buy a carb.
What about an intake manifold? the Holley you have won't work on the factory Thermoquad intake without an adapter, and that's a kind of flaky way to do things. It also looks like you have a long ways to go before this project actually needs a carb on it..maybe worry about the rest of the thing before you get too worried about it. Maybe something will turn up in the mean time, now that you have a little bit of an idea what it is you really need.
Yes it can be set up for your engine but you will have to run an adapter. Post the list number off the the carb then we can tell you what jets it would have come with so you have a starting point.
If the bolt pattern for the TQ and the Holley are different, you'll be looking for another intake manifold and there goes the budget. If the bolt pattern is good and the manifold doesn't have the big secondary openings, maybe look into trading/selling the double pumper for something that work out better for you.
Back in the late 70's I ran an 850 double pumper Holley on a virtually stock (other than some sort of solid lifter cam) 350 SBC in my 38 Chevy. No choke, didn't need one, I drove it year around in Iowa and had no problems. Foolishly I put a smaller Holley on it and sold the double pumper, gas mileage didn't seem to change (not that it was a problem back then) and I had lost bragging rights on a carburetor that I would run today if I had it.
The only car I have burnt to the ground had a thermoquad on it. BUT with that said It is a better carb for the road than that holley. And I love holley carbs......peace
It as always been my considered opinion, based on real-world experience AND the words of Holley techs, that the Holley carburettor, ESP. the double pumper design is a suitable drag race carburettor. Which means it has a decent idle circuit, and good flow during Wide Open Throttle. Which is great for the street, as all you really do is idle at a light before hitting the gas HARD to get to the next light. So mid-range tuning is for other folk and wimps. And the bragging rights!! Boy, Howdy!! "Hey, man, I gots me a double pumper!!" While the Rest of us, those who have learned through vast experience, happily motor past with our Rochesters, Carters, Edelbrocks, etc. You know, carburettors that can be tuned in the mid-range, in addition to decent idle and WOT circuits. As for CFM, well, as with just about anything, there IS an online calculator: http://www.csgnetwork.com/cfmcalc.html And it says for the average 360, max useable rpm of 4500 (being totally honest), you'd be GREAT with a 400 cfm. But, you'll have to compensate for 'something' by lying about it. But, lets be also honest with ourselves, what Real value does a great running engine have, as opposed to "having a double pumper, Man!!" And, as you leave the fuel station, the words "Thank you, my friend" will actually have meaning, as you have contributed more than most to his boat fund. Cosmo
I have a Holley 650 on my 350. Came off my stock car 20 years ago. Rebuilt it changed the jets. Runs like a champ. Not so good gas milage. O well.
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