That seems like a very reasonable ignition timing curve.
Thermoquad idling issues
- Thread starter toypar
- Start date
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toypar
Well-Known Member
After running the car today and noticing smoke or fuel vapor after shutting the car off, I couldn’t see where the fuel is coming from. I removed the carb and set it in the table for a few minutes. Picked it up and kept the carb level, looked at the bottom of the base plate and it was drenched with fuel. Dripping a few drips on the primary side of things. I wiped it up and set it down for an hour and checked again. Bone dry
toypar
Well-Known Member
At this point I think I am going to shelve this particular reman carb. My dad has collected lots of mopar parts over the years and he has never ran a Thermoquad. He has always been a Holley guy. I found a few Thermoquads he has stored for years. I found a 4972s that looks quite different from what I have. Also a 6139s, which looks like it has been remaned before. The shafts are bare metal with no teflon coating. Also a 6322s, which is the nicest. Looks untouched with teflon coating on the shafts. Also found a new thermoquad strip kit. The 6139s and 6322s both have a little play in the primary shafts. Not sure if it will matter much. Which of these thermoquads would suit my engine the best?
The one with the least amount of vacuum ports in the best shape and hopefully the large primaries.
toypar
Well-Known Member
Looks like that would be the 6322s. Looks to be off of a 73 440. Are brass floats the way to go? Or plastic?
The one I would use would be one with the large primaries and the vacuum nipple for ported vacuum sticking out of the plastic body in the front at an angle on the passenger's side. That way you'd have the option of trying both ported and manifold vacuum on the distributor.
Comments.
- Use the plastic floats, set FL to 29/32".
- 9-10" of idle vacuum & the fact that the engine wanted to die when you pinched off the PCV tells me what I suspected all along: the PCV pintle is not closing off at idle because of the low vacuum....resulting in a LARGE amount of air being supplied to the engine at idle......which is why the pri blades are nearly closed at idle.....
- A correctly working PCV supplies air at idle equivalent to a 7/64-1/8" orifice. Quite small. When the PCV does not close fully because of low vacuum, it supplies a HUGE amount of air.
- you can buy [ expensive ] adj PCVs. What I do is essentially put a washer or plug in the PCV hose that has a 1/8" hole in it. Fixed.
- I would try one of the other 6XXX TQs you have.
- Use the plastic floats, set FL to 29/32".
- 9-10" of idle vacuum & the fact that the engine wanted to die when you pinched off the PCV tells me what I suspected all along: the PCV pintle is not closing off at idle because of the low vacuum....resulting in a LARGE amount of air being supplied to the engine at idle......which is why the pri blades are nearly closed at idle.....
- A correctly working PCV supplies air at idle equivalent to a 7/64-1/8" orifice. Quite small. When the PCV does not close fully because of low vacuum, it supplies a HUGE amount of air.
- you can buy [ expensive ] adj PCVs. What I do is essentially put a washer or plug in the PCV hose that has a 1/8" hole in it. Fixed.
- I would try one of the other 6XXX TQs you have.
toypar
Well-Known Member
I may just order an adjustable PCV valve. If you put a 1/8 orfice in your PCV line, won’t that equate to oil leaks and crankcase pressure at cruise because you don’t have the high PCV flow anymore?
Nope. At cruise, you have high vacuum, so the PCV will be the same as at idle, nearly closed. You still have the breather to vent crankcase pressure. Lost count of how many engines I have used the above procedure on, zero problems.
Wow, the new TQ strip kit is a heck of a find! Ever price those rare babies on EBay? Hope you can get another TQ going. Great carb. Who knows what the reman guys did to the other one.
toypar
Well-Known Member
I looked the part number up on eBay, I was surprised! Merry Christmas to me I guess. I will update this thread once I get the rebuild kit and a proper PCv valve.
So you have a 4972 TQ for a 71 340 manual transmission. That is worth only $500-1,000. That is what I ran on my favorite 273, it would be the last I'd ever sell. The 6139 TQ is a 1972 340 automatic transmission carb, I've run this one also on a number of small blocks, one of the best. The 6322 is a 1973 440 Automatic transmission carb rated about 850 cfm, very nice carb and sounds like untouched, the best condition. What a great bunch of choices. I run brass floats, I guess because of rebuilding Quadra-Jets. They would always soak up fuel. Never had a problem with brass floats.
transman
Well-Known Member
For what this is worth, you might also want to check out >> www.harmsauto.com << . He's up in Spokane. A customer of mine, from my working days, sent one down to him to be gone through. He was more than pleased with it, and if you didn't know better, you would think he just purchased it new at his local Chrysler dealer. My customer by the way was a mechanic, but for some reason, he wasn't comfortable rebuilding thermoquads. Good Luck.
Be real careful if you buy new brass floats. There was a run of them that the brackets were soldered on upside down and they are not all out of the system yet. So pay close attention.
toypar
Well-Known Member
After looking the number up I noticed they were a one year only carb. Looks to be in very nice condition except it’s missing the linkage connecting the secondary air door and choke. Sounds like that’s going to be hard to find.
toypar
Well-Known Member
I will have to give him a call. That’s only a 2 hour drive from my place. It might be worth it for him to restore the rare 71 carb I have.
toypar
Well-Known Member
I will make sure to keep that in mind. Thank you
transman
Well-Known Member
From what I saw at my customers shop, and what he told me after he got it on the engine, I don't think you can go wrong. He said that all he had to do once it was on the engine was adjust the idle. It's not inexpensive for sure, but after almost 40 years in the automotive repair industry, I've come to believe you only get what you pay for. On a side note, and maybe who cares, Mark Worman of Graveyard Cars uses Harms exclusively. Best of luck.
toypar
Well-Known Member
I decided to pull my trouble carb apart again while waiting for my rebuild kits. I think I found the problem. A crack by the main well. I filled the bowls up with fuel and can’t get a leak. It must pull fuel through the crack with vacuum when the engine is running.
Anybody know where I could get a reasonably priced replacement body?
Anybody know where I could get a reasonably priced replacement body?
That's not jagged enough to be a crack.
toypar
Well-Known Member
It sure felt like a crack. I will clean it up with some scotch brite and see if the epoxy comes off.
Did you ever try adjusting the metering rod tree?
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