Thermoquad to lean ?

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lilredridinghoo

lilredridinghoo

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hi there, hopefully someone can help me with my TQ issue
but first some specs.

engine: 273cui 040 over, low comp pistons
cam: (similar to an 340 stock cam),
heads: 318 stock heads - ported, bowl blended
headers: Long tube

intake: orig. 340 mopar TQ intake from the 70ies
ignition: rev-n-nator box - 18 ° in idle (Distributor with an 18 degree stop plate - so max will be 36°)

trans: 904 with shiftkit
converter: stock
rear end: 3,91 sure grip (26 Inch tires)

carb: TQ 850 cfm

Problem: on low speed like City traffic, e.g. when leaving a Rotary and trying to accelerate i will get backfire sometimes.

when hitting the pedal right from an stop - i will have something like a bogging or a dead point and after a few milliseconds it will come back and roar and pulling like hell.

i tried to adjust the airdoor - which cures the symptoms a bit but i´m a bit worry to go to far and end up with messing up the spring) it´s now 1 and 3/4 turns from that point when the air door makes contact when giving tension to the spring

i also tried to adjust the idle mixture screws. max vaccuum is reached with 4 3/4 turns, but then it still has this backfire. the backfire is now gone with 5,5 turns.

the accelerator pump is set the way, that it will spit when the throttle lever starts to move (within the first 1 or 2 Millimeter)
but in my opinion it is only a minor squirt compared to what my former Holleys or Demons have made - would it be an option to open up the squirter nozzles a bit with a drill to achieve more squirt ?

maybe the carb is to lean in General ? to be honest i do not know what size the jets in the mainbody are

any hint will be appreciated (as i want to go to the track next Friday/Saturday)
thanks
 
Sounds like your on the right track.
The secondary air door can be adjusted tighter.
The screws turned out that many turns (4-3/4) is a lot. That in itself indicates it is lean. It should hover around two to three turns.
The accelerator pump may have a bad pump. Or it maybe miss adjusted. The arm lever has a spec that should be maintained no matter where the linkage sits on the three options holes. It'll take me a little while to find the spec.

You can use AFB rods cut down 3/4 of an inch shorter and rebent so they can be used and hung on the TQ tree. This can help enrichen the carb. You will have to know what you have in the carb now.
 
What I like to do is isolate the primaries from the secondaries and tune them one at a time.

It does sound like a lazy pump though.It needs to flow immediately when the throttle moves the tiniest wee bit. Not within 1 or 2 millimeters.
Dont forget about that little screw right in the center of the m-rod tree.Give it a full turn CW and retest
 
Make sure the pump rod is installed in the hole nearest the carburetor body in the pump rocker arm.
 
thanks for the first hints.

guess i will check the size of the jets today or tomorrow.
also checking and testing with the M-rod-tree

RustyRatRod - pump rod is installed correct
i do have some spare TQ which i can use to donate some parts like jets and m-rods, to modify and play with.


btw. the TQ is an rebuilt unit purchased from Rockauto.com
 
You can also adjust the step up piston, though don't get carried away with too much adjustment at once. Clockwise for rich, counter clockwise for lean. I would adjust no more than 1/2 a turn at a time, so as not to loose where the original adjustment was.
 
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