i found an nos themroquad and decided to give one a try. it is a late 70s carb. id have to get the number off it. the engine is a low compression 400. honed, new rings small cam, performer intake and headers. it had an awful hesitation and sometimes pop when you would crack the throttle so i drilled the squirter out to .031. it looked like it was about .024. it didnt seem to change much. the acc pump has the 2 holes i moved it to the end that didnt really seem to change much either. i took it for a ride and if you hit it while under a good load it would pop and just run awful. there was also a bad stumble when shifting into each gear. i adjusted the rod hieght and that seemed to make it better but when you rev it up it still isnt as clean as it should be.
thermoquad help
- Thread starter jamesdart
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mischiefdart
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The secondary air valve spring adjustment is where I would start.
demon sizzler
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More than likely the jetting is too small for the 400. What #'s are stamped on the driver rear corner of the base and what #'s are cast into the top of the carb?
The fact that the carb is backfiring and the only adjustment that made a noticeable difference directly affected the jetting leans towards too lean a jet for the engine.
This info will make clear a lot of the problems as many T.Q.'s later than '74 need re-jetting and other mods on a non smogger application, David.
The fact that the carb is backfiring and the only adjustment that made a noticeable difference directly affected the jetting leans towards too lean a jet for the engine.
This info will make clear a lot of the problems as many T.Q.'s later than '74 need re-jetting and other mods on a non smogger application, David.
i had the vac guage on it when initially setting things up and it seemd to have decent vaccum, i think it was around 15. i thought it seemed like a lean condition too. it is a 9150 carb, what type of number am i looking for on top, i saw a few different ones. thanks.
demon sizzler
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The top #'s are towards the back more on the passenger side. Example is
6-2363.
Also if you look down into the choke tower to the front you will see two # 2 pencil lead size holes(see pic). Cover each hole with a small piece of tape and go drive the car. This will make all circuits richer and may save you from re-jetting.
6-2363.
Also if you look down into the choke tower to the front you will see two # 2 pencil lead size holes(see pic). Cover each hole with a small piece of tape and go drive the car. This will make all circuits richer and may save you from re-jetting.
demon sizzler
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That should be the correct top. If you see that the carb runs ok sealing the two holes in the choke tower, you can put a dab of epoxy over each, David.
demon sizzler
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You're welcome and glad to help, David.
dustoff440
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9150 is 440 truck 1978. I was working at a Mopar dealership at that time and if I remember 440's in trucks did not have the lean burn. That carb should work on a mild build as it is unless some one had changed out the jets and rods.
right it doesnt look like a lean burn carb, it has the electric bowl vent which is no big deal i have it hooked up. i i tried the tape trick and that made it run like crap. the list on here says it should have 99 jets and 2110 rods, but the jets look like 00 to me it does have the 2110 rods. i really dont think anyone had there hands in this carb before i got it. it was in a mopar bag and didnt look like it was ever bolted on. all plating was nice when i got it. spotless clean.
so the tape made it pop while cruising under load, no matter what i did with the metering rods. it idled like crap, it made the flat spot worse. i tightened up the air door some more, it seems to be running decent, but if you whack the trottle from an idle really fast you will get a pop through the carb. my next drill was 034 i didnt really want to drill the squirter that big, but decided wtf. it didnt seem to change much. the position of the accelrator pump linkage doesnt seem to make a big difference. i did find 2 burnt plug boots, i replaced them and they were burnt again after a cruise and i came back to inspect a few things. even with the fiberglass boots on them. i know that isnt helping.
dustoff440
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At this point I would tell you to start going the basics,a new set of decent plug wires, make sure you don't have a few plug wires crossed, look at all you ignition pieces carefully, do a compression test, check for things like a broken valve spring, bent pushrod etc.
its a fresh ring job, good adjustable iron rockers, new ball and cup pushrods, barely used springs from another build with very little use before a cam change, small summit cam, brand new msd super conductor wires, im going to throw a new set of plugs in and see what i have for wires to replace those 2 again. it idles great when the wires are good, listen to the exhaust and it sounds really good. when you get past that stumble it runs really well, smooth and when you have the rpm past that flat spot and whack the throttle, it will scream.
DocFiberglass
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I would say TIE OFF the secondaries for a test to see if the problem is on the primary side. Going up 006 on the acc-pump is a good step... a later 70's carb is normally lean.
It DOES sound like you need to adjust the secondary air-door. I have a tool for that.
thats a cool tool. i did think of locking out the secondaries, but right now the big problem is right off idle there is this awful flat spot, if you open the throttle above that it has great resonse. if you hold it there it wants to stall. if you hit it from an idle you get that hesitation and sometimes a pop. if you open it sort of slow, it will rev up fine. if you hit it second time before it returns to idle it will rev fine. im not even getting into the secondaries. if its idling in the driveway it has horrible throttle response. i see on demonsizzlers site he doesnt recomend going over 034 on the squirter. im not trying to come off and shoot your guys ideas down dont get the wrong idea, i want all the ideas i can get.
demon sizzler
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You said the carb looks clean but did you take it apart to 'confirm' the condition of the O rings, accelerator pump/check valve for the pump well(cover)and what 2ndary jets the carb has?
Also be sure the choke pull-off is not leaking and the front vent stack should be open at the top and not capped. The primary jets are ok, although a size or two large but you have a lean condition for some reason. The choke pull-off vacuum hose needs to be attached to the base port on the passenger side rear port.
What style of carb to intake gasket did you use? If it is a Quadra Jet style, it will cause problems on your 850 cfm T.Q.
Also be sure the choke pull-off is not leaking and the front vent stack should be open at the top and not capped. The primary jets are ok, although a size or two large but you have a lean condition for some reason. The choke pull-off vacuum hose needs to be attached to the base port on the passenger side rear port.
What style of carb to intake gasket did you use? If it is a Quadra Jet style, it will cause problems on your 850 cfm T.Q.
adjust the secnedary air door stiffer give it 3 degrees more timeing if it still backfires check the pickup coil in the distributer
:director:check the pickup coil in the dist
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