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Old 01-05-2013, 07:53 AM
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Thank you for that info

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Old 01-12-2013, 05:49 PM
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Originally Posted by cdminter59 View Post
I forgot about your vacuum lines. If I remember correctly, the Q-jet has a threaded fitting on the backside of the carburetor. This is where the vacuum line from the brake booster goes. The brake booster should have its own vacuum port, do not tee anything else to it. There should be a 3/8 port on the front of the carburetor for the PCV valve. You should have a vacuum port fitting that screws into the manifold behind the carburetor for your vacuum to modulator valve on the transmission. There will be other vacuum ports on the front for the distributor vacuum advance. Just remember the ports that have vacuum at idle are manifold vacuum and the ports that don't are ported vacuum. I have a picture from a website that might help you. Look at post #7. Good luck. PALEEZE help me hook up my QuadraJET and vaccuum stuff. - THE H.A.M.B.
Ok man, got the truck running and idling ok..... Now we have another issue that's kinda stopping us. I tuned the carb I set the timming good it will run and stay running fine but now when I put it in gear it dies out.... I can keep it running in gear with the idle turnt up or foot on gas and keeping it running! As soon as I let off it kills. I have a correction it is a comp thumper cam NOT a mother thumper. We were told we shouldn't have to have a stall with this cam. Are there any tricks am I missing something? There are no vacuum lines to the trans nor cables atached to the motor/carb from the 350 turbo trans. Thanks for any input!
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Old 01-12-2013, 07:26 PM
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Quote:
Originally Posted by Ltsulli1 View Post
Ok man, got the truck running and idling ok..... Now we have another issue that's kinda stopping us. I tuned the carb I set the timming good it will run and stay running fine but now when I put it in gear it dies out.... I can keep it running in gear with the idle turnt up or foot on gas and keeping it running! As soon as I let off it kills. I have a correction it is a comp thumper cam NOT a mother thumper. We were told we shouldn't have to have a stall with this cam. Are there any tricks am I missing something? There are no vacuum lines to the trans nor cables atached to the motor/carb from the 350 turbo trans. Thanks for any input!
The key to making the thumpr cam behave is more initial timing. I'd start w/about 22 degrees BTDC and work up or down as needed from there.

Vortec heads only need 32 degrees total timing, not counting vacuum advance. More on setting up the timing correctly is linked to below. Until you get the timing sorted out, you're going to have a hard time w/idle quality, nozzle drip, off idle response, etc.

Use a vacuum advance limited to 10 degrees, use ported vacuum for it.

If you find you're still having a problem getting a balance between idle quality and initial advance (advance isn't helping enough), you may need to add idle bypass air.

Not all Q-jets have a threaded rear port for a power brake booster. Use a manifold port if yours doesn't. The front large vacuum port is for the PCV valve.

Carb vacuum port ID

Advance curve

You most likely do need more stall, but sort the timing out first, then see what you need if anything.

Last edited by cobalt327; 01-12-2013 at 07:33 PM.
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Old 01-13-2013, 07:03 AM
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Originally Posted by cobalt327 View Post
The key to making the thumpr cam behave is more initial timing. I'd start w/about 22 degrees BTDC and work up or down as needed from there.

Vortec heads only need 32 degrees total timing, not counting vacuum advance. More on setting up the timing correctly is linked to below. Until you get the timing sorted out, you're going to have a hard time w/idle quality, nozzle drip, off idle response, etc.

Use a vacuum advance limited to 10 degrees, use ported vacuum for it.

If you find you're still having a problem getting a balance between idle quality and initial advance (advance isn't helping enough), you may need to add idle bypass air.

Not all Q-jets have a threaded rear port for a power brake booster. Use a manifold port if yours doesn't. The front large vacuum port is for the PCV valve.

Carb vacuum port ID

Advance curve

You most likely do need more stall, but sort the timing out first, then see what you need if anything.
This truck is strictly an off road truck it will probably never come out of 1st and or 2nd gear... Fuel milagr doesn't bother me... So can I completely get rid of or plug off vacuum advance? Will this help the truck from dying going into gear? I'm sorry I'm kinda virgin to the tuning part of things. Thanks again
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Old 01-13-2013, 08:26 AM
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Quote:
Originally Posted by Ltsulli1 View Post
This truck is strictly an off road truck it will probably never come out of 1st and or 2nd gear... Fuel milagr doesn't bother me... So can I completely get rid of or plug off vacuum advance? Will this help the truck from dying going into gear? I'm sorry I'm kinda virgin to the tuning part of things. Thanks again
You need more initial timing first. I edited my original post to include the vacuum advance. Having it might make the engine run a little better during the times you are under light throttle. If these times are rare, you can run w/o it.

If you are using a vacuum advance connected to manifold (full time) vacuum, this can cause the engine to stall if you don't have enough initial timing. When it goes into gear, the vacuum drops off. This can cause the vacuum advance to drop off as well, and you lose the timing it was supplying.

That's why I said to add initial timing- as much as the engine needs- then to use ported vacuum for the vacuum advance.
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Old 01-13-2013, 09:55 PM
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Quote:
Originally Posted by Ltsulli1 View Post
There are no vacuum lines to the trans nor cables atached to the motor/carb from the 350 turbo trans. Thanks for any input!
If this is the case you must not have a turbo. I have saw alot of rubber vacuum lines at the modulator dry rot and cause a bad leak. I would check the tee or port coming out of the intake behind the carb. Should be a rubber line running from it to a small diameter metal line that runs right down between the firewall and right side head, probably close to your trans dip stick tube, and runs to your modulator valve. Also, you should have your passing gear cable coming up on the left side running to your carb. Now some people that are in a hurry dont even bother with the passing gear cable so it may be tied up out of the way. I assume you are not running a reverse valve body so the cable should be hooked up.
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Old 01-14-2013, 03:13 AM
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350 small block vortec problems, stalls out

Look at the transmission pan on your car. A 350 turbo has a square pan with the right rear corner cut off. The turbo 400 has a odd looking oil pan with two or three dimples on the bottom of the pan. check yours to see which one it matches. Do you have the part# for your camshaft?
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Old 01-14-2013, 06:49 AM
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It's very possible the modulator just isn't hooked up. There's not many GM automatic transmissions w/o a modulator (overdrives like TH700R4/2004R). I would run a vacuum line to the modualtor after it's been checked for being bad/leaking vacuum. The detent (kickdown) cable can be left disconnected if you want to shift manually. If the whole cable's missing you'll definitely want to plug the hole in the case where it enters to keep dirt and water out.

Anyway, here's info on ID'ing your transmission.
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