Thermoquad tuning

thethee

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I'm looking for some help with tuning the thermoquad that's on the 440 in my '75 imp.

It's a remanufactured unit from Autoline, model 9054S.
Primary jets are 98 I think
Metering rods are 2109
Secondary jets are 137
Mixture screws are at 4 turns from seated
Stock distributor, don't know initial timing cause I don't have a light. Set the timing with vacuum gauge, runs smooth at 16-16.5 inHg. If I advance it further vacuum stays the same but idle gets rough.

Now here's where I'm struggling, when I'm trying to adjust mixture to highest vacuum I don't see any real response on the vacuum gauge, either half turn in or half turn out. Should I just lean it out further? I believe base adjustment would be 1.5-2 turns from seated.

Secondly, base adjustment of the step up piston for the metering rods I believe is 1.5-2 turns from bottoming out but this gives me a part throttle stumble. This only goes away when I set it way higher, like 6 turns. What does this mean? Low octane fuel, too small primaries, or something else?
 

saforwardlook

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I'm looking for some help with tuning the thermoquad that's on the 440 in my '75 imp.

It's a remanufactured unit from Autoline, model 9054S.
Primary jets are 98 I think
Metering rods are 2109
Secondary jets are 137
Mixture screws are at 4 turns from seated
Stock distributor, don't know initial timing cause I don't have a light. Set the timing with vacuum gauge, runs smooth at 16-16.5 inHg. If I advance it further vacuum stays the same but idle gets rough.

Now here's where I'm struggling, when I'm trying to adjust mixture to highest vacuum I don't see any real response on the vacuum gauge, either half turn in or half turn out. Should I just lean it out further? I believe base adjustment would be 1.5-2 turns from seated.

Secondly, base adjustment of the step up piston for the metering rods I believe is 1.5-2 turns from bottoming out but this gives me a part throttle stumble. This only goes away when I set it way higher, like 6 turns. What does this mean? Low octane fuel, too small primaries, or something else?

I would get a timing light and set the timing correctly - they are not very expensive - and set timing to 10BTC. I would also bypass the OSAC (orifice spark advance control - small black plastic box on the firewall) and route the vacuum line directly from the carb vacuum port stright to the distributor (this device was for emissions and delayed any spark advance for 25 seconds every time you let off the throttle - horrible for gas mileage and performance). This alone will help your tip-in stumble. I would set the mixture screws out more to around 4 turns out or go just beyond where you get maximum rpm when the timing is set correctly to 10BTC.

The adjustment to the step up piston is not very sensitive but after making the changes suggested above, I would set it to where the stumble on tip-ins goes away. Going from 2 turns from bottom to 6 is not a big deal so adjust it to where the tip in stumbles go away after the previous recommendations are achieved.

You should then be fine.
 

thethee

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I would get a timing light and set the timing correctly - they are not very expensive - and set timing to 10BTC. I would also bypass the OSAC (orifice spark advance control - small black plastic box on the firewall) and route the vacuum line directly from the carb vacuum port stright to the distributor (this device was for emissions and delayed any spark advance for 25 seconds every time you let off the throttle - horrible for gas mileage and performance). This alone will help your tip-in stumble. I would set the mixture screws out more to around 4 turns out or go just beyond where you get maximum rpm when the timing is set correctly to 10BTC.

The adjustment to the step up piston is not very sensitive but after making the changes suggested above, I would set it to where the stumble on tip-ins goes away. Going from 2 turns from bottom to 6 is not a big deal so adjust it to where the tip in stumbles go away after the previous recommendations are achieved.

You should then be fine.

Distributor is already hooked up directly to the carb, it doesn't have an OSAC. EGR and idle enrichment are also disconnected.

I thought about getting a timing light, that would take out the guesswork with the timing. Maybe a silly question, but a timing light is a timing light right? When I have timing set to 10 BTDC I'll look into mixture adjustment.

The metering rod adjustment I figured wouldn't be a huge deal so I'll just set it to where it doesn't stumble. As long as it doesn't hit the limit up top it should be good.
 

CBODY67

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There are a few different types of timing lights. The most useful is the one with the timing dial that lets you "dial back" when the light flashes so that you can determine things like centrifugal advance, vacuum advance, and of course, the initial timing. The price has decreased a bit over the years and would be worth saving up for, to me. Then, add a quality dwell-tach (as a seperate item) and you're set for years of fun and diagnostics.

Enjoy!
CBODY67
 

thethee

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I'm not sure what you mean by "dial back" but what I meant with my question is that for initial timing pretty much every timing light should work.
 

CBODY67

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By "dial back", if you have the engine running at (for example) 2000rpm, then you can point the timing light at the timing mark on the block and then dial back to 0 degrees total advance (using the knob) to see how much advance is in the motor at that rpm by how much you move the knob (on a scale in engine distributor advance degrees, which is twice the amount of distributor degrees). You can probably purchase some budget timing lights that don't have this function, but having one like this can be a help later on.

Enjoy!
CBODY67
 

USSMOPAR

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Until you have a timing light you are wasting our time.
Initial timing needs be 14-19 degrees BTDC not 10.
It will run like a pig at 10 BTDC
195 degree thermostat
 

CBODY67

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195 thermostat might have been the spec, but that was more for emissions purposes than power. 180 thermostat for best results.

10 degrees BTDC will be a good starting point.
 

Big_John

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I'm not sure what you mean by "dial back" but what I meant with my question is that for initial timing pretty much every timing light should work.
You can do what you need to with a simple, run of the mill, timing light. That's all I had for years and it worked just fine.

That said, the "dial back" timing light is a great piece and I have one. In this case, for example, lets say you wanted 12 degrees advance timing. You would set the timing light at 12 degrees, start the engine and aim it at the timing marks and adjust it until the zero marks aligned. With a conventional light, you'd be looking for 12 degrees on the timing mark.

That's not a big deal, but where the dial back light shines (pun intended) is when you want to check advance. Let's say you should have 25 degrees at 3000 RPM. With my light, I would set it to 25 degrees and watching the handy built in tach, run the engine to 3000 RPM and aim at the timing mark. If all is good, I should see the zero marks align.

I have one of these: https://smile.amazon.com/gp/product/B000EVYGV4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
 
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This would be great, but a little out of my budget unfortunately.

If you have a single exhaust (?), you can make do with a single sensor AFR gauge. And you can get them within the European Union, so you avoid "single package" import duties. I bought an AEM 30-300 from finjector (cheapest one from a authorized dealer I could find). Installed it this weekend (might make a thread later) in my Imperial.
X-Series Wideband UEGO AFR Sensor Controller Gauge with X-Digital Technology. Includes:: X-Series Wideband Controller Gauge, Bosch LSU 4.9 Sensor, (AEM 30-0300) - Lambdameters, ECA etc. Air fuel ratio gauges - Finjector.com
I figured the price is less than 2 tanks of gas over here, so as soon as you have saved around that amount from a better tuned engine or by not driving around testing your latest adjustment; it has paid for it self.
 

thethee

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You can do what you need to with a simple, run of the mill, timing light. That's all I had for years and it worked just fine.

That said, the "dial back" timing light is a great piece and I have one. In this case, for example, lets say you wanted 12 degrees advance timing. You would set the timing light at 12 degrees, start the engine and aim it at the timing marks and adjust it until the zero marks aligned. With a conventional light, you'd be looking for 12 degrees on the timing mark.

That's not a big deal, but where the dial back light shines (pun intended) is when you want to check advance. Let's say you should have 25 degrees at 3000 RPM. With my light, I would set it to 25 degrees and watching the handy built in tach, run the engine to 3000 RPM and aim at the timing mark. If all is good, I should see the zero marks align.

I have one of these: https://smile.amazon.com/gp/product/B000EVYGV4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Digital dial-back timing light is on its way
 

thethee

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If you have a single exhaust (?), you can make do with a single sensor AFR gauge. And you can get them within the European Union, so you avoid "single package" import duties. I bought an AEM 30-300 from finjector (cheapest one from a authorized dealer I could find). Installed it this weekend (might make a thread later) in my Imperial.
X-Series Wideband UEGO AFR Sensor Controller Gauge with X-Digital Technology. Includes:: X-Series Wideband Controller Gauge, Bosch LSU 4.9 Sensor, (AEM 30-0300) - Lambdameters, ECA etc. Air fuel ratio gauges - Finjector.com
I figured the price is less than 2 tanks of gas over here, so as soon as you have saved around that amount from a better tuned engine or by not driving around testing your latest adjustment; it has paid for it self.

I have a true dual exhaust, but still, AFR sensor is probably interesting to look into
 

Robert Saigh

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Hey Steve remember one of the issues with my '75 Imperial? Just using a timing light made all the difference! 1400 miles later....not a problem! I'll still say Thank You for the help!
 

cbarge

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With today's corn fed gas stations I recommend bumping up the timing and richen the fuel mixture.
You may need to adjust the metering rods and accelerator pump to shoot extra gas upon acceleration to avoid a dead spot.
But as mentioned get a good timing light.
Dana from Woodruffs maybe he can chime in..
Also a good recurved distributor really helps. Big blocks like about 12 degrees initial with 34 36 degrees all in at 2500- 3000 Rpm.
You cant get that out of a factory distributor....
 

halifaxhops

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Totally agree with the curve, just make sure whatever one you decide on has a proper curve, if it is not listed pass on it, most are full in fast.
 

thethee

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Now that I have my timing light I will try to map my curve this weekend. I never did this before so might take a few tries. Will get back to you guys with the results.
 

Dana

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TQ idle mixture Screws get unresponsive when there is no more fuel to give. You are on the right track with your tree all the way up also another indication of a lean carburetor. Idle circuit and most likely primary circuit as well. Look down in the choke horn towards the front of the car. And see if there is 2 idle bypass holes running vertically. Mass rebuilders are known to mix and match parts, so they might be there or not. If they are try sealing them off with silicone or seal-all. It should bring your mixture screws back into play.
 

thethee

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TQ idle mixture Screws get unresponsive when there is no more fuel to give. You are on the right track with your tree all the way up also another indication of a lean carburetor. Idle circuit and most likely primary circuit as well. Look down in the choke horn towards the front of the car. And see if there is 2 idle bypass holes running vertically. Mass rebuilders are known to mix and match parts, so they might be there or not. If they are try sealing them off with silicone or seal-all. It should bring your mixture screws back into play.
This sounds like a good idea, will definitely try plugging these holes and see what it does. Thanks!
 
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