Thermoquad tuning

TyK

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Hiya folks. Doing a mileage build on a 360 and trying out a thermoquad. The book I got for Mikes Carburetor parts is a little vague on specifics of tuning and I’m confused about the throttle shafts. Does anyone know the amount the primaries are supposed to open before the secondaries engage? It seems like the secondaries come in super quick and no matter how much I bend the linkage it doesn’t seem the have great effect. Additionally the primaries don’t come 100% open. They stop at say 80 degrees unless I bend the linkage so far the it’s able to come all the way around and then it holds open some at idle. I’m a little confused lol. Any help would be appreciated.

Thanks!
 

Professor Fate

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Welcome to the site!
As far as the primaries not fully opening, does it do this when working the throttle by hand, or just with the throttle cable and linkage hooked up?
 

TyK

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Thanks for the welcome!

I’m all on the bench right now so by hand.
The secondaries open all the way to 90 degrees but as I said the primaries don’t go much beyond 70-80 (if I were to guess).

Oh and one factor I forgot to mention (but from what I can tell shouldn’t change anything) the idle mixture screw was seized and broken off in the base plate so I swapped it for another 800 cfm base plate that the rebuild kit I have in it also matched with. The stop for the primaries is a little different but it’s not reaching the stop so it doesn’t seem to be a factor.
 

Bewy

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Congrats on choosing a great carb. Sounds the 'L' shaped link that opens the secondaries has been bent. This link is to control the WOT position of the pri & sec shafts, NOT the opening point of the secs, which is fixed.

Remove one end of the link & check that the pri shaft WOT stop hits the body @ WOT. The sec WOT stop is a roll pin that hits the body @ WOT. Bend the link until both pri & sec hit WOT.

Can you post some pics?
 

rumblefish360

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In the below picture, the pen points to a tang. Is this tang bent at a 90* or less angle? This is probably your primary opening angle issue. Bend the tang until full primary opening angle is achieved.

FBAF0125-E7A5-4439-9DFD-B5DF2FEDEAC1.jpeg
 

Bewy

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My post #5. The 'L' shaped link is above the tip of the pen in the pic above. If it is too long, the secs get WOT but the prim will not get WOT. If too short, prim gets to WOT, but secs do not. Bend it to fix.

In the pic above, the 'tang' is part of the fast idle linkage. I remove that linkage & choke because I find they are unnecessary. I believe the tang stops the secs opening if the choke/fast idle is on.
 

TyK

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Sorry for the late reply! I was out where its stored just briefly for ol' Canadian turkey supper last weekend and I think I have it sorted. I bent back that stop and it now has full opening of the primaries. I am going to have to play with its relationship with the linkage that tunes the secondary opening as I had it bent really far trying to get more out of the primaries. (Sorry I didn't get any pictures I completely forgot).

My next question is this. How far open should the primaries be when the secondary's start to open, the book I have just says "the secondary's should open once the primaries have opened to the required spec" real helpful that (There is not spec at the back of the book). It's a small primaries carb fyi. Additionally is there any downside (other than not having secondary's until later) to delaying the secondary's opening later than the spec? I'm going for a mileage build and wouldn't mind a bit more room .

Thanks for all your help!!
 

rumblefish360

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Going off of memory, without being exact, the secondaries start to open when the primary throttle blades are somewhere in the 80% open range. This should be plenty of throttle on the primary side for high speed cruising and the ability for a good “Get up and go” response off the line. Even while on the Hwy., the primaries should be able to give enough power to go around slower traffic reasonably well.

No matter the throttle position, the tune on cruise is your target to have a good AF ratio for mileage. I don’t see a Benefit to delaying then secondaries. If you mess with the linkage to delay there opening, you might off set the balance there built with to get the secondary side open all the way when the pedal is fully pressed down for acceleration.

Very seldom do I meet a TQ with purposely bent linkages. The factory settings are excellent as is.

What specific model TQ do you have?
 

Bewy

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Refer back top post #5.
Trying to bend the pri-sec link to control percentage opening of the prim will result in either the pri or sec hitting WOT, & the other not, depending on if the link has been lengthened or shortened.
The only way that I can see to change this relationship & STILL have the P & S reach WOT is to drill the link arm. Much ado about nothing, will achieve nothing that can be felt or measured & you now have a butchered carb.
 
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