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I'll be curious to hear your feedback on how the part throttle cruise is when driving down the road. It may need more primary jet or, the metering rod tree may need adjusted to compensate for the additional air being brought in by the primary throttle plate holes you drilled.

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I played around with this problem in the past on a stroker motor with a bigger cam.

1) Drilling throttle plates may lead to booster fuel dribble.

2) Cracking open secondaries could be difficult for a number of reasons but mainly because they are so big and it would need to be done almost to perfection.

What I did was take a tee off of the PCV hose and used different orifice sizes, it seemed to work well but I did not mess with it very long. You would want to have this extra orifice take in filtered air. I tried many orifice sizes and dont remeber what I ended up with but it was not small, (I think around 3/16 inch) You would want to use a wideband A/F device to iron out your system.

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I couldnt figure out how to crack the secondaries as they seem to come to a rest on the base plate as a stop

I thought about drilling the secondaries to counter act the possible velocity on the booster causing dribble as you suggested but what worried me, along with cracking the secondaries, was the the timing of the air velocity/ fuel/ timed vacuum open created by air bleed in the plate.

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Hmm...good to know what sizing worked for you. I haven't gone quite that big...was a little worried.

I wish there was a way to run a channel into to secondaries base plate. Sort of a controlled air leak, say, adjustable with a air-bleed type jet. The other approach would be to crack the secondary throttle plates just a tiny wee amount to let some air in, but not initiate any of the secondary fuel system....easy to say, quite a bit more difficult to actually implement.

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Not trying to start any arguements but I open up the low speed jet about .003 and adjust the initial timing to cure that problem. I've run cams at 274 to [Email]292@.050[/Email] duration with thermoquads using these fixes. I DON'T drill the butterflys. Dave

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On that 605? or smaller motors? Just the bleed on top or the tube? Ive tried a some to a whole lot of intial and could not get what I was looking for so I settled on 19* intial. How about your transfer slot, were they in the square to normal range? Thanks for input.

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First theres a tang for the secondary stop you can bend to adjust the amount the secondaries stay open. Its in the rebuild book. Theres also a set screw on top of the tree you can adjust.. I like to do that instead of cutting the spring. Thats just butcher work when you cut the spring. I understand there might be a vacuume issue but unless your idle vac is below 10Hg.. I wouldn't cut it. Theres a couple air bleeds under the tin covers one can also drill out. Bunch of things you can do to have a crisp, bog free Thermobog. As a last resort I'd drill the throttle plates, but the above usually gets everything running peachy. Oh.. and TQ's LOVE lots of initial timing.

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Where are the air bleeds on a TQ?

Great thread!

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