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Re: Thermoquad secondary tuning?
[Re: ragtop]
#1100948
10/26/11 08:21 PM
10/26/11 08:21 PM
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Joined: Mar 2005
Posts: 862
Iowa State fan
kilroy
super stock
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super stock
Joined: Mar 2005
Posts: 862
Iowa State fan
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Since this was not touched on again Ill take another shot. The timing is about initiation of air\flow into the ventures' which starts the fuel flowing out of the boosters. My theory is by making it tighter (or slower acting with restrictors like Doc F) you are allowing the engine speed to come up more before the air door flops open creating the lean spot or possible over rich spot (??). Where as if you set it up like the factor with .1 to .3 of clearance the door is allowing air to begin flowing which pulls the door open immediately (kinda like a door in the house that is shut wont let air through, but if the door is cracked open a little and another door opens somewhere else in the house the pressure drop and air flow through the house either slams/flings open the door)
1973 Charger, former SE, former auto
I'm not trying to be difficult, it comes naturally....
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Re: Thermoquad secondary tuning?
[Re: kilroy]
#1100949
02/27/12 09:28 PM
02/27/12 09:28 PM
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Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
Dave Watt
master
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master
Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
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The factory setting is to adjust the secondary air door up until it just touches the stop. Then rotate 1.5 turns more on the spring.
Are you guys suggesting not even having the door against the stop in the first place?
I've tried every setting on the secondary door, the metering rods, and drilled out some squirters to .026", .028" and .031". Nothing will cure the bog at the hit of the throttle.
Two different distributors too.
Jetting is good at wide open throttle through a 1/4 mile pass.
Last edited by Dave Watt; 02/27/12 09:30 PM.
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Re: Thermoquad secondary tuning?
[Re: a12rag]
#1100954
02/28/12 09:37 PM
02/28/12 09:37 PM
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Joined: Mar 2005
Posts: 862
Iowa State fan
kilroy
super stock
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super stock
Joined: Mar 2005
Posts: 862
Iowa State fan
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Im NOT talking about WINDING the secondary spring door, Im talking about bending the choke pull-off to the air door as shown in this figure.
After establishing about 1.5 -2 turns on the spring tension then bend this rod for this clearance. I think you'll find this is the cure; and only then play with spring tension and door stop to tune the fuel curve and the actuation of the air door.
Ive tried to 0.040 clearance like it says, but on my big cam I have to run it tight against the stop as was suggested by tuners to me.
If you need the complete instructions Ill email my complete pdf of the manual.
Last edited by kilroy; 03/25/12 10:44 AM.
1973 Charger, former SE, former auto
I'm not trying to be difficult, it comes naturally....
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Re: Thermoquad secondary tuning?
[Re: kilroy]
#1100956
02/28/12 10:16 PM
02/28/12 10:16 PM
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Joined: Sep 2004
Posts: 2,091
oberlin, Ohio
Rapid340
top fuel
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top fuel
Joined: Sep 2004
Posts: 2,091
oberlin, Ohio
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Three things I would be experimenting with on the carb in addition to the initial opening gap and accel pump size size (once you have ignition timing close and you determine the linkage is working right). 1) Richen secondary jetting and set open airdoor angle to stock or a little tigher than stock. If you have blocked manifold heat and are running pump gas you will need to step up secondary jetting as well as primary. I would consider going straight to a .149 sec jet to start with. A wide band A/F meter is really useful here. 2) Choke pull-off orifice size (fill it in with jbweld and drill out in steps, starting with a much smaller than stock size) It may be easier to install a different orifice restriction in the vac hose going to the pulloff. I have seen some manual trans pulloffs with an orifice so small you can barely see it. 3) Air door tension (this is not as critcal as one and two, start with 2 turns and change in steps of .25. I dont think you need to go less than 1.5 turns or more than 2.5) If you get stuck PM me and maybe we can talk by phone. 
1971 Factory Appearing Duster 340 11.000 @ 122 mph
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Re: Thermoquad secondary tuning?
[Re: Rapid340]
#1100958
02/29/12 07:30 PM
02/29/12 07:30 PM
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Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
Dave Watt
master
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master
Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
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Quote:
2) Choke pull-off orifice size (fill it in with jbweld and drill out in steps, starting with a much smaller than stock size) It may be easier to install a different orifice restriction in the vac hose going to the pulloff. I have seen some manual trans pulloffs with an orifice so small you can barely see it.
Tried the pull-off air door setting at .040", didn't help.
The current pull-off orifice size is .025". My parts carbs have .028", .031" and .033". I'll have to look at the '72 340 manual carb also. I can easily make restrictors out of nylon rod that are the same outside diameter at the pull-off.
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Re: Thermoquad secondary tuning?
[Re: Dave Watt]
#1100959
02/29/12 09:16 PM
02/29/12 09:16 PM
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Joined: Mar 2005
Posts: 862
Iowa State fan
kilroy
super stock
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super stock
Joined: Mar 2005
Posts: 862
Iowa State fan
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I had to run mine tight against the housing stop, not at .040 as suggested; even at 0.040 I had a bog. I know some are run as loose as .100.
Let me ask you what your carbs 4 digit id #?
Last edited by kilroy; 02/29/12 09:19 PM.
1973 Charger, former SE, former auto
I'm not trying to be difficult, it comes naturally....
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Re: Thermoquad secondary tuning?
[Re: kilroy]
#1100960
02/29/12 10:37 PM
02/29/12 10:37 PM
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Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
Dave Watt
master
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master
Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
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Mine is a 6319s, correct for a '73 340 Auto.
Installed a restrictor in the choke pull-off that I drilled to .0135", too small to pull vacuum. Went up to .016". No more bog. The tires spin instantly at the hit of the throttle.
Now a new problem has shown up. As the car gets rolling through first gear, the engine feels as though the carb is either way too rich or way too lean, kind of shuddering. Eventually it gets better after shifting into second. Spark plugs checked good.
I adjusted the amount of opening on the air door but didn't help the higher RPM situation. I'll hook up the Air/Fuel meter to see what's up. Might have to back the jetting off now just to see if it helps.
I'll have to work on it another day.
Last edited by Dave Watt; 03/01/12 10:22 PM.
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Re: Thermoquad secondary tuning?
[Re: Dave Watt]
#1100961
03/01/12 09:22 AM
03/01/12 09:22 AM
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Joined: Jan 2003
Posts: 3,704
MICHIGAN
DynoDave
master
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master
Joined: Jan 2003
Posts: 3,704
MICHIGAN
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Quote:
The current pull-off orifice size is .025". My parts carbs have .028", .031" and .033". I'll have to look at the '72 340 manual carb also. I can easily make restrictors out of nylon rod that are the same outside diameter at the pull-off.
How does one determine this orifice size? Photo?
Quote:
I installed a restrictor in the choke pull-off that's drilled to .013".
No more bog. The tires spin instantly at the hit of the throttle.
Now a new problem has shown up.
Did you make this restrictor? Picture?
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Re: Thermoquad secondary tuning?
[Re: ragtop]
#1100965
03/01/12 04:58 PM
03/01/12 04:58 PM
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Joined: Mar 2007
Posts: 9,336
South-Central (Sebring), FL
Commando1
master
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master
Joined: Mar 2007
Posts: 9,336
South-Central (Sebring), FL
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Quote:
...says that some bogs cannot be tuned away unless the air door is tight against stop. He was right.
I just installed a new TQ from Scott @ Harms on my bone stock '76 440 (GREAT job, Scott, BTW).
The engine never ran smoother except for a slight bog upon stepping on the accelerator. Because of this thread, I went to check on the secondary air door gap. It was dead on according to what you guys described.
Frustrated, I noticed something. The bowl vent lever arm.
Picture no. 1 shows the position as it was on the new carb.
Picture no. 2 shows it as it was on my old carb.
I repositioned the lever on the new carb to the same position as the old carb and the bog went totally away.
I'm no genius on this stuff and I have no idea what I did and why it worked but I had to throw this out there to you guys.
Pic #1 (lever position similar to the new TQ):
Pic #2 (lever position that is on old TQ):
 but it cured the problem.
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Re: Thermoquad secondary tuning?
[Re: Dave Watt]
#1100966
03/01/12 06:45 PM
03/01/12 06:45 PM
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Joined: Jan 2003
Posts: 3,704
MICHIGAN
DynoDave
master
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master
Joined: Jan 2003
Posts: 3,704
MICHIGAN
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Quote:
Quote:
How does one determine this orifice size? Photo?
I have a tiny drill bit set that is #60 (.039") through #80 (.0115"). Some hobby shops have them. Just keep inserting a drill in the orifice hole until you get to a drill big enough that it won't go in anymore. No photo, sorry. I'll try the next time I work on it.
Quote:
Did you make this restrictor? Picture?
I found a 3/16" diameter plastic rod, drilled a .013" hole in the middle, then inserted it in the vacuum line.
Awesome. Thanks Dave. I was thinking maybe it was stamped somewhere or something.
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Re: Thermoquad secondary tuning?
[Re: DynoDave]
#1100969
03/03/12 10:20 AM
03/03/12 10:20 AM
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Joined: Feb 2003
Posts: 607
NY
old340dog
mopar
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mopar
Joined: Feb 2003
Posts: 607
NY
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Thanks for the great information and tips. This will be a great aid to me and others.
old340dog
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Re: Thermoquad secondary tuning?
[Re: Dave Watt]
#1100976
10/28/13 04:27 PM
10/28/13 04:27 PM
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Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
Dave Watt
master
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master
Joined: Nov 2003
Posts: 5,048
Atlanta Indiana
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I wanted to bring this thread back up. There are a few things that might help guys out.
Some of the carbs I've bought were completely stuck. A propane torch and PB Blaster can help remove some really stubborn screws, idle mixture screws, and loosen the throttle shafts.
Heat the area around the stuck screw or shaft, then shoot the area with the Blaster. Apply more heat until the area is smoking again, you might see the Blaster bubbling up which is great, shoot it with more Blaster. It may take 5 or 6 tries but eventually you should be able to remove anything. Be patient, don't force the screw or it will just break off. The Blaster will flame up but nothing scary. Work in a well ventilated, open area away from things that can burn.
Finally worked with the choke pull-off adjustment enough at the track that the carb doesn't bog anymore. The car has run 13.90 @ 101MPH at our local track, and 14.12 @ 99MPH during the Pure Stock Muscle Car Drags.
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Re: Thermoquad secondary tuning?
[Re: Dave Watt]
#1100977
10/28/13 10:27 PM
10/28/13 10:27 PM
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Joined: Jan 2006
Posts: 419
NY
F1Scamp
mopar
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mopar
Joined: Jan 2006
Posts: 419
NY
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Good tips Dave. Sometimes it doesn't seem to matter how much you want them to come apart, they still don't want too.
I experienced the dredded bog for the first time with the Duster at MIR. One pump shot adjustment and the next pass it was blowing the tires off again.
Work In Progress- 71' Duster F.A.S.T.- 10.36@130 Smallblock Record Holder.
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I know that demonsizzler says that some bogs cannot be tuned away unless the air door is tight against stop. He was right. Aluminum headed 440 with 250* duration, I had it gapped at .040 according to the rebuild and had to readjust mine tight even after tightening the airdoor to get rid of slight secondary hesitation.. Would like more info also.
