Thermoquad adjustments..............
#225766
02/15/09 03:04 PM
02/15/09 03:04 PM
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Joined: Oct 2005
Posts: 708 Mechanic Falls, Maine
4BBodies
OP
mopar addict
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OP
mopar addict
Joined: Oct 2005
Posts: 708
Mechanic Falls, Maine
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..........I am getting my Plymouth closer everyday that I play with it, I have a question on the metering tree height. I had the tree at 1 turn, and it was lean off idle, (not smooth) I raised the tree and it is much smoother, but still slightly surges at off idle speeds. I can see the tree going up and down, like it is searching for the right spot. It is now at 1 1/2 turns, I have tried the timing in different spots, and it doesn't seem to change. How far out can I raise the tree? It is a '73 340 with a .48 purple cam, 2.02 intake valves, 10 to 1 pistons, stock electronic distributor, with the advance plugged. It doesn't run well un-plugged (before you ask.) The spark plugs look great. The carb is a '72 auto trans version. Idles good, is responsive........when you put it in gear, it doesn't stall.........the rpm's just seem to wander slightly at speed. Maybe it needs a load (as in driving) on it? I haven't been able to try that yet, the roads are still too crappy here. Please advise, give me more things to tinker with. I will get it, I am close. Thanks.
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Re: Thermoquad adjustments..............
[Re: 4BBodies]
#225767
02/15/09 03:42 PM
02/15/09 03:42 PM
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Joined: Apr 2005
Posts: 46 Detroit, USA.
MagnumGT
member
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member
Joined: Apr 2005
Posts: 46
Detroit, USA.
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OK! Sounds like you are close. You have almost the identical setup we had except it was a 6bbl. Take out the spring that returns the tree and let the tree rest down. With a cam, the low vacuum will cause it to be erratic. It should move with the throttle unless there is no lever inside. Without opening up the carb, look around for metering rods #'s 1996 or 1997. They are not stock, they are from the '80's tunning kit that Direct Connection sold. Most TQ's have .095 primary jets and if you use a nice tiny rod they should do alright. Take out the rods and notice the profile, if it has two definate steps down to fairly small, keep them. Late smoggers have almost no taper down, they are lean and the suck unless you jet up a couple sizes. I kept a log of all my builds from 1982 until now, so if you have a spare carb to work up, leave yours running for now. Glad to help with TQ's as you either love'em or you don't. Oh yea, 1-1/2 turns from all the way down is where to start, no lower or they will just sit there until about 1/3 throttle.
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Re: Thermoquad adjustments..............
[Re: 4BBodies]
#225769
02/15/09 04:34 PM
02/15/09 04:34 PM
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Joined: Jan 2003
Posts: 826 Stone Mt, GA.
DEMONSIZZLER
super gas
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super gas
Joined: Jan 2003
Posts: 826
Stone Mt, GA.
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Too much cam for the stock metering rod piston spring. You will need a much lighter spring(tension)for the carb. Less vacuum=less spring tension. If you have a simple ball point pen with spring loaded action, get the spring and 'stretch' it in the middle a bit and install it. This should stop the metering rod tree from bouncing, David.
ThermoQuads:stock, street/strip and race;
800/850 cfm's, 860/910 cfm's and 1,000 to 1,060 cfm's.
New parts for all OEM 1971-1984, Competition Series and SuperQuad carbs and custom fabricating.
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so you get the right carb the first time.
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Re: Thermoquad adjustments..............
[Re: 4BBodies]
#225774
02/16/09 09:39 PM
02/16/09 09:39 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Hook up a vacuum gauge (sears has them) and measure the manifold vacuum at idle. The TQ will need about 10 inches of Hg at a hot idle in gear to keep the metering rods seated.
Did you try advancing the initial timing to 14 to 16 degrees?
If you are running a single plane intk, then maybe shoot for 16 to 18 degrees initial.
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Re: Thermoquad adjustments..............
[Re: quickd100]
#225777
02/16/09 10:08 PM
02/16/09 10:08 PM
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Joined: Jan 2003
Posts: 14,610 Not2farfromNashville, TN
Rug_Trucker
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,610
Not2farfromNashville, TN
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Quote:
I fought with the metering rod tree spring trying different spring tensions all last summer. I finally took mine out entirely
How did you come up with that idea Dave?
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Re: Thermoquad adjustments..............
[Re: 440sat72]
#225779
02/17/09 08:36 AM
02/17/09 08:36 AM
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Joined: Oct 2005
Posts: 708 Mechanic Falls, Maine
4BBodies
OP
mopar addict
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OP
mopar addict
Joined: Oct 2005
Posts: 708
Mechanic Falls, Maine
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Well, from what I am learning, with a high lift cam (low vacuum) like mine, the tree acts differently. You could see my tree going up and down as it was surging, it was fighting the spring tension. Demonsizzler recommended a lighter spring, and it is steady now. Lower vacuum needs a lighter spring. I am going to put my vacuum gauge on it next, I finally found it. It was in one of my many parts boxes still full from moving! I am going to re-jet it next, it is still lean. My plugs still look great, a slight brownish color, the idle is as smooth as one would expect with this cam, (It sounds nasty) and there is no off idle bog when you punch it. It is right there. Getting the choke adjustement right was the worst part of this so far, and that seems fine. God, it ran like s__t when I first started it! Got it good enough to hold it at 2500 rpms to run the cam in, but it wasn't happy. Everything I do makes it a little better, in steps, thanks to this site, and helpful people like the folks above!
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Re: Thermoquad adjustments..............
[Re: 440sat72]
#225780
02/17/09 03:37 PM
02/17/09 03:37 PM
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Joined: Jan 2003
Posts: 1,762 Windsor, ON, Canada
Diplomat360
top fuel
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top fuel
Joined: Jan 2003
Posts: 1,762
Windsor, ON, Canada
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Quote:
what i would like to know is: what exactly does the spring do? and why does a lighter spring help stabilizing the tree?
The idea here is that this is a fuel mixture enrichment system. If the engine vacuum drops and is NOT enough to pull the step-up piston down into it's bore that allows the spring to push the piston up, thus moving the meetering rods OUT of the primary jets and richening up the mixture.
When running a large cam you will typically get a low engine vacuum reading...with a stock 'strength' spring it may force the piston up even though it does NOT need to be in the up position. As it forces it up, extra fuel is available, the engine picks it up and surges, the vacuum increases, the piston gets sucked into the bore, mixture leans out, then the vacuum drops again as engine RPMs drop and the whole cycle begins over...thus the surging, etc, etc.
What I never understood is the mechanical level which will force the tree up? Why not just rely on the vacuum...???
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