Author Topic: Another Rebuilt Thermoquad question  (Read 2283 times)

Offline e-tek

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Another Rebuilt Thermoquad question
« on: March 07, 2009 - 10:21:07 PM »
Hey guys-I'm hoping you aren't too sick of TQ questions to help me out. I rebuilt a TQ to put on a rebuilt 318 and was just trying to start it on my Engine Test stand. The motor fires and runs when I pour gas in (of course), but then dies. When I look down the carb primary and work the throttle lever I can see gas coming out the pump jets (mostly right side...I'll have to resoak and blow it out), but not as much as you'd think should come out and not enough to keep it running. Isn't there an idle circuit that should keep enough gas in the carb to run it?
As well, there's a wire that goes to the Bowl Vent - is it critical that that is powered? Is it a constant 12V? Isthat partof my problem?
Thanks for any help you can offer.




Offline femtnmax

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Re: Another Rebuilt Thermoquad question
« Reply #1 on: March 07, 2009 - 11:40:37 PM »
I'm concerned there is not equal amounts of fuel coming out both accelerator pump discharge nozzles when you work the throttle.   Suggests passages may not be cleaned properly.  Question is what else is not cleaned properly.
Idle circuit uses the two idle mixture screws located at front of throttle plate assy.
Gently turn the screws in clockwise until the gently bottom out, then back out about 2 full turns.  You will have to adjust them from there.  Could write a short book about just setting the idle mix, but you want the fastest idle speed by turning the mix screws while keeping the throttle shaft idle speed at a slow throttle nearly closed setting.
When I rebuild carbs, would be great if you can soak the metal parts in carb cleaning solution.   I don't have access to it anymore, so out comes cans of gumout.  I do not use any other brand.  I'm sure there are other good ones, but some other brands don't clean well enough so I stick to gumout.  Buy several big cans, I go thru a couple for one carb rebuild.
I spray off the outside of each part, spray down along the throttle shafts while working them back and forth.  I spray clean every square millimeter.  I mean it.  I spray every hole, if they are dead end holes you'll get a good shot of carb cleaner in your face so wear eye protection.  So I spray every hole, the spray will exit a passage way someplace else, so then go the the other end of the passege and spray back the other direction so each passage is sprayed two directions.  Do this several times each passageway.  Spray out thru each accel pump nozzle.  The same amount of spray should come out both nozzles.  I have found itty bitty pieces of gravel in some nozzles, had to use a cutting torch tip cleaner or tiny drill bit to remove the grit.

With everything clean I blow every passage out with compressed air.  Use more carb spray again if necessary and repeat blow with air again too.
There are idle air bleeds, emulsion tubes, etc that must be spotless.  You should be able to eat of this thing when your done.
If the problem is only idle mixture, then the engine should run steady with throttles open part way.  If it still won't run, then you have more problems.
I hope this is not a fresh rebuild as you need the engine to start and run steady for 15-20 minutes to properly break in a flat tappet cam.
Sorry to just touch the surface, there's lots of details to be stepped thru solving carb problems.
The TQ is a great street carb, and can be made a good race carb too.  I had one on my 340 duster for 140,000 miles.  Worked great even worn out.  I would put in the brass floats, throw away those foam ones.
Phil

Offline Bullitt-

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Re: Another Rebuilt Thermoquad question
« Reply #2 on: March 08, 2009 - 08:44:31 AM »
You don't need to supply power to the bowl vent, that's part of a pollution setup used on later models.... I've had a early 80s unit that worked fine...

Remove & clean the accelerator pump jet as well as the check valve under it.
Check the measurements of the accelerator pump travel & adjust (bend) linkage, or your floats may be set too low & not covering the accelerator pump completely. 

  Are you sure your fuel pump is working correctly & the fuel is fresh ?
Is your choke & choke pull-off adjusted & working correctly ?

......Another helpful hint.... After the engine goes through a heat cycle re-tighten the screws & 4-base bolts, they will be loose.
« Last Edit: March 08, 2009 - 08:51:17 AM by Bullitt- »
Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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Offline femtnmax

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Re: Another Rebuilt Thermoquad question
« Reply #3 on: March 08, 2009 - 01:44:16 PM »
Here's a couple of pics of float settings from "super tuning and modifying carter carburetors" by Dave Emanuel.    Has good basic info but no carb adjusting specs or part numbers for application.  There's some good web sites, I just don't have them handy.
« Last Edit: March 08, 2009 - 02:04:07 PM by femtnmax »
Phil

Offline e-tek

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Re: Another Rebuilt Thermoquad question
« Reply #4 on: March 08, 2009 - 08:38:47 PM »
Thanks guys - I took the carb off and went through it again. Blew out all passages and adjusted the floats.The foam floats where way high, had to bend them down a fair bit. Also went through all the other adjsutments, re-checked the choke links and vaccuum pull-offs. All good. Put it back on and cranked it over - same thing. Fires hard, but only for one round off the distributor... As well, got lotsof Fuel pressure - sprays out hard.
Tomorrow I'm going to go through the electrical again. There's just so many damn connections from the ECU and balllast, maybe something's amiss there...

Offline femtnmax

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Re: Another Rebuilt Thermoquad question
« Reply #5 on: March 08, 2009 - 11:06:25 PM »
If the fuel is ok, as you say the only other choice is electrical.  Unhook the coil wire from distributor, hold it close to ground, should see sparks cranking the engine over with the key.  Also should see sparks if turn key to ON, then jump across the starter solenoid with a screw driver and crank engine that way.  Ballast resistor problem??   Its been so long since I've messed with one I don't recall the test proceedure.
Phil

Offline Bullitt-

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Re: Another Rebuilt Thermoquad question
« Reply #6 on: March 09, 2009 - 07:36:44 AM »
Seem to remember a bad ignition switch that would start in crank mode but when released to run mode lost power..  if you have a dual ballast resistor the run side can be bad also.
« Last Edit: March 09, 2009 - 08:22:44 AM by Bullitt- »
Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
Screwed by Photobucket!