Thermoquad issues...

[Hemi Rebel]

No it's not. Millions of 318s came with Thermoquads. 800 CFM Thermoquads. That's why they are such good carburetors. You can run them on anything from a 273 to a 440 with only minor tuning and no parts changes whatsoever. Same reasoning why Chrysler used them in just that manner. Besides, what he is encountering is a lean condition. What you describe would mean the carburetor is rich, which it does not seem to be.

Yeah, check the cam specs on a 318 4bbl vs 2bbl engine. He has a 2bbl engine with a 2bbl engine cam. Let me explain how a carburetor works. Its performance depends directly on whats happening underneath of it. How much vacuum is against it and the amount of air the engine moves all comes through the carb. Putting a bigger carb on an engine does not make it run rich, just the opposite. Air passing through the venturi is what pulls fuel into the airstream. The smaller the venturi, the faster the air moves at a given speed this will draw more fuel. Open the venturi up and at the same speed the air will not move as fast thus drawing in less fuel. Which is lean. The engine isnt built to handle that much carb.

 

[RustyRatRod]

Yeah. Ok. But that's not what's wrong with his engine.

Yeah, check the cam specs on a 318 4bbl vs 2bbl engine. He has a 2bbl engine with a 2bbl engine cam. Let me explain how a carburetor works. Its performance depends directly on whats happening underneath of it. How much vacuum is against it and the amount of air the engine moves all comes through the carb. Putting a bigger carb on an engine does not make it run rich, just the opposite. Air passing through the venturi is what pulls fuel into the airstream. The smaller the venturi, the faster the air moves at a given speed this will draw more fuel. Open the venturi up and at the same speed the air will not move as fast thus drawing in less fuel. Which is lean. The engine isnt built to handle that much carb.

 

[coloradodave]

Yeah, check the cam specs on a 318 4bbl vs 2bbl engine. He has a 2bbl engine with a 2bbl engine cam. Let me explain how a carburetor works. Its performance depends directly on whats happening underneath of it. How much vacuum is against it and the amount of air the engine moves all comes through the carb. Putting a bigger carb on an engine does not make it run rich, just the opposite. Air passing through the venturi is what pulls fuel into the airstream. The smaller the venturi, the faster the air moves at a given speed this will draw more fuel. Open the venturi up and at the same speed the air will not move as fast thus drawing in less fuel. Which is lean. The engine isnt built to handle that much carb.

I don't mean to be a jerk, but this is just not right. Please show us where this information came from. I'd be interested to see the theory in print. Thank you.

 

[Someotherguy]

I believe what he is saying is the heads/cam were matched to the fuel system by chrysler...I do not believe this is the case, the LEAN BURN fuel system put on this engine was designed to do one thing, and one thing only, PASS EMISSIONS....I believe the stock heads/cam have a bit more potential, not stock 4 bbl 318 power, but definitely more than the junk azz fuel system they put on it back in the 80's offered...

the thermoquad primary venturi's are not much bigger then the bbd 2 barrels...i think about 2/8th of an inch bigger, that # isn't going to make that much difference, in fact i think it will wake up the off the line potential of the engine once i fix the damn pump shot lol....then you have the secondaries, which only give as much as the engine can take....this obviously will not be an issue...

 

[Hemi Rebel]

I don't mean to be a jerk, but this is just not right. Please show us where this information came from. I'd be interested to see the theory in print. Thank you.

this is from TUNING TO WIN, A PERFORMANCE TUNING GUIDE by Don Gould. so call him an argue
In it he is referring to specifically to a demon carb, but the theory applies to all carbs.
This may not be the exact issue at the moment just cracking the throttle, but it will be an issue when he trys to mash the throttle when the light turns green, not matter how much fuel its dumping. Right now it could be fuel delivery issue(pump or filter clogged).

"You would be surprised at the people who call me for bigger carburetors or larger
venturi's for their RS carbs because the engine is lean and they are already
running alcohol jets, long time engine builders, experienced racers and Dyno
Tech's alike just can't seem to fathom that a 1095 Race Demon on a hot 350
runs lean. This is a constant battle, sometimes I win and sometimes there's just
no convincing them that their wrong. Carburetors are not panty hose: one size
does not fit all. So how do you choose the correct Demon for your combination?
The common belief is if the carburetor is too large for the engine, the result will
be a rich A/F mixture.
In actuality, the opposite is true. When the carburetor throttle plates and venturi​

dimensions are too large, the signal produced in the booster is diminished or

simply the air velocity is diluted as air speed is reduced. When this occurs, the
amount of fuel being pulled is lessened,​

LEANING the mixture. When trying to
tune a carburetor that is too big for the application, the use of huge main jets will
be required to try and fuel the engine and they still won't pull enough fuel to​

achieve the correct A/F ratio.

Think of this like your shop vac, if you were to install a 6" diameter hose on it you
won't be able to pick up a dog hair, go back to the 1.25" hose and you can pick
up a silver dollar. Same with a carburetor the motor is just a vacuum cleaner that
sucks air and fuel instead of iron filings and washers off the floor. The motor or
air pump hasn't changed you've just changed the velocity by increasing the
orifice so it can't pick up the maximum amount of fuel flow through the booster
resulting in a lean condition.
The air speed through the booster needs to reach speeds in excess of 400MPH+
to maximize flow, if the venturi and boosters are too large for the displacement of
the engine to reach this air speed then the result will be a lack of fuel and it will​

lean the engine out."

 

[RustyRatRod]

How many engines have you torn down? I've torn down literally hundreds. When I was sixteen, I was the core buyer and teardown guy at the machine shop for the first year I worked there. I tore down many a 318 with '2 barrel heads" (as you call them) and a four barrel intake that was FACTORY installed. Chrysler did it to millions. The 360 big port four barrel intake slapped right on top of the small port 1.78/1.50 valve heads, STRAIGHT from the factory. I don't know where you've been, but that's a well documented fact that is known pretty much industry wide.

I'm not getting into this discussion that you think somehow the fact that his two barrel engine is "not enough....blah blah blah". Sorry you're just wrong on that. His problem is the acellerator pump is simply not working properly and the rest the carburetor is simply not tuned to the engine. That carbuertor could care less about which cam the engine has in it. It simply needs to be repaired and tuned to the engine it's on and it'll run great. Chrysler had no trouble with them in the 80s and since there's been no rift in the space time continuum, nothing has changed and they will work fine now. You sound like you may not be familiar with how a Thermoquad works, or you wouldn't be arguing the point.

800 or 850 CFM (whichever one it is) is the MAX that it can flow. Through tuning and adjustments, I can make either one flow a MAX of anywhere between 200 and 850 CFM. That's why Thermoquads work so well on a variety of engines. I can make that Thermoquad actually a SMALLER carburetor than the two barrel it replaced. The small primaries are its key. Trust me, it has absolutely ZERO to do with camshaft, or the "two barrel" heads as you call them.

 

[Hemi Rebel]

Who said heads? I said cam. There is a difference in cams for sure.I have been doing this for 20 years myself ok. And I learned this on my very first car that i got when I was 14. A 74 duster with a 318 that somebody pulled the 2 barrel and slapped a 4bbl on. Did the same thing as this engine. I put a 2 bbl back on it.
good luck

 

[RustyRatRod]

You kept saying "two barrel heads". That's what I was referring to. I'm not knocking you or your experience.....don't take what I said personally. I didn't mean it like that. All I am saying is his carburetor is the problem. It's not more complex than that. That's all.

 

[Hemi Rebel]

If I said heads, I appologize. I never meant to say that. I meant cam. And if you can tune that carb to work on that motor fine. It pretty much defeats the purpose of putting a 4 barrel on in my opinion, but to each his own.

 

[RustyRatRod]

If I said heads, I appologize. I never meant to say that. I meant cam. And if you can tune that carb to work on that motor fine. It pretty much defeats the purpose of putting a 4 barrel on in my opinion, but to each his own.

Hell, I mightta been seein things. lol I don't know...I think in a mild app, especially if including headers, slappin a four barrel on will make a noticable difference. Certainly not as much as adding other things like a cam...I agree. But the difference would be a gain I believe. At least he'd have the four barrel THERE for future mods.

 

[Someotherguy]

ok folks, besides all this 2bbl/4bbl/heads/cams/etc crap :grin:....I think i found my problem, i got the top of the carb off, and the pump plunger looks to be in new condition, along with the rest of the carb internals..I do think the float settings are totally off..They are both set at almost an inch and a 1/4 height...I'm getting between 27/32nds and 29/32nds for the stock settings in google search...

Can someone verify the settings...thanks

here's what i have...

 

[Someotherguy]

oh btw, the carb # is 9128s

 

[Meep-Meep]

Yeah, check the cam specs on a 318 4bbl vs 2bbl engine. He has a 2bbl engine with a 2bbl engine cam. Let me explain how a carburetor works. Its performance depends directly on whats happening underneath of it. How much vacuum is against it and the amount of air the engine moves all comes through the carb. Putting a bigger carb on an engine does not make it run rich, just the opposite. Air passing through the venturi is what pulls fuel into the airstream. The smaller the venturi, the faster the air moves at a given speed this will draw more fuel. Open the venturi up and at the same speed the air will not move as fast thus drawing in less fuel. Which is lean. The engine isnt built to handle that much carb.

This is absolutely correct. Many believe that the larger carb = richer mixture. Not necessarily true. The above description is great and I'd like to ad that it's the difference in pressure that causes the fuel to move into the air stream. The low pressure at the venturi is allowing the atmosphere pressure on top of the fuel in the bowl to push it into the air stream.

I also know that 318's and 360's came with the TQ carb, not to mention countless SBC's and Q jets, and they worked well from the factory, even with single exhaust, so the actual problem may not be a mismatch of carb and engine. It should also be noted that these engines all came with divided plenum dual plane intakes, further contributing to their successful operation.

 

[Someotherguy]

fixed it :grin:

I set the floats at 29/32nds, and she eats good now

 

[RustyRatRod]

Awesome. I bet it's got a good pump shot now. lol

 

[Someotherguy]

hell yeah it does lol.:grin:...it still need to adjust the tree, i set it lean at initial start up...and i think i need to play with the timing a bit...

Anyone have a good time setting for this type of setup..?

 

[RustyRatRod]

I can get you in the correct factory static position and you can adjust from there.


With the engine OFF.

Get a small screwdriver that fits the slot good in the primary piston screw. I cannot remember which way to turn the screw here....BUT whichever way makes the metering rods go DOWN, that is where you start.

Here's what you do. Press the metering rod tree down until it seats FULLY, but don't press it hard. Keep it held there for this entire adjustment. Now, turn the screw whichever way to make the tree go DOWN. Continue turning the screw and pay close attention to the tree. When it STOPS going down, stop turning the screw.

Keep the metering rod tree depressed. Now, turn the screw the other way and watch the tree rise. Keep turning the screw until the tree stops. Now, turn the screw the other way SLOWLY. JUST as the tree starts to go down, STOP. This is your base adjustment.

From there, adjust the metering rod tree DOWN for lean and UP for rich.

 

[coloradodave]

this is from TUNING TO WIN, A PERFORMANCE TUNING GUIDE by Don Gould. so call him an argue
In it he is referring to specifically to a demon carb, but the theory applies to all carbs.
This may not be the exact issue at the moment just cracking the throttle, but it will be an issue when he trys to mash the throttle when the light turns green, not matter how much fuel its dumping. Right now it could be fuel delivery issue(pump or filter clogged).

"You would be surprised at the people who call me for bigger carburetors or larger
venturi's for their RS carbs because the engine is lean and they are already
running alcohol jets, long time engine builders, experienced racers and Dyno
Tech's alike just can't seem to fathom that a 1095 Race Demon on a hot 350
runs lean. This is a constant battle, sometimes I win and sometimes there's just
no convincing them that their wrong. Carburetors are not panty hose: one size
does not fit all. So how do you choose the correct Demon for your combination?
The common belief is if the carburetor is too large for the engine, the result will
be a rich A/F mixture.
In actuality, the opposite is true. When the carburetor throttle plates and venturi​

dimensions are too large, the signal produced in the booster is diminished or

simply the air velocity is diluted as air speed is reduced. When this occurs, the
amount of fuel being pulled is lessened,​

LEANING the mixture. When trying to
tune a carburetor that is too big for the application, the use of huge main jets will
be required to try and fuel the engine and they still won't pull enough fuel to​

achieve the correct A/F ratio.

Think of this like your shop vac, if you were to install a 6" diameter hose on it you
won't be able to pick up a dog hair, go back to the 1.25" hose and you can pick
up a silver dollar. Same with a carburetor the motor is just a vacuum cleaner that
sucks air and fuel instead of iron filings and washers off the floor. The motor or
air pump hasn't changed you've just changed the velocity by increasing the
orifice so it can't pick up the maximum amount of fuel flow through the booster
resulting in a lean condition.
The air speed through the booster needs to reach speeds in excess of 400MPH+
to maximize flow, if the venturi and boosters are too large for the displacement of
the engine to reach this air speed then the result will be a lack of fuel and it will​

lean the engine out."

Apples and oranges. Race carburetors with mechanical secondaries and large venturis don't begin to equate with a Thermoquad. I see that he solved the problem by adjusting the float level, so I assume we're done...........food for thought, at the least.

 

[Someotherguy]

I can get you in the correct factory static position and you can adjust from there.


With the engine OFF.

Get a small screwdriver that fits the slot good in the primary piston screw. I cannot remember which way to turn the screw here....BUT whichever way makes the metering rods go DOWN, that is where you start.

Here's what you do. Press the metering rod tree down until it seats FULLY, but don't press it hard. Keep it held there for this entire adjustment. Now, turn the screw whichever way to make the tree go DOWN. Continue turning the screw and pay close attention to the tree. When it STOPS going down, stop turning the screw.

Keep the metering rod tree depressed. Now, turn the screw the other way and watch the tree rise. Keep turning the screw until the tree stops. Now, turn the screw the other way SLOWLY. JUST as the tree starts to go down, STOP. This is your base adjustment.

From there, adjust the metering rod tree DOWN for lean and UP for rich.

thank you kind sir

I will do this today...

 

[Someotherguy]

got the tree set, she sounds even m0 bettah now :grin: