A72CUTLAS

Okay, this helps, real world experience. I've also found after a little more research that multi-port injection is also available (I said from the beginning I was sorta new). And for only a few bucks more than the TBI systems I can get all the benefits while keeping my Cutty pure. Thanks cutlassefi and all who posted.

Killian_Mörder

It's easy to underestimate an oldschool tool. A vacuum guage to a mechanic is like a stethescope to a doctor who first uses one to find out if the wheezing is just asthma or tuberculosis, before sending the patient into an expensive to diagnose computer tomography tube. Using a simple instrument can often save plenty of time and unneccesary work: http://www.3geez.com/forum/carb-tech...does-mean.html

cutlassefi

Correct. And depending on the severity a vacuum leak typically has little to no effect once it's off idle. However leaky valves will effect running quality throughout. And if the leaky valves are due to worn guides etc then excessive oil consumption will occur as well. Again more symptoms and effects than just a vacuum leak caused by another source.

Seff

IIRC the adjustable part throttle does just that. It's hard to get to, but it exists.

garys 68

What's an "adjustable part throttle" on a Qjet?

garys 68

For the efi interested, here's a post I put on another forum where someone was suggesting an inexpensive alternative efi TB to an LS motor swap. It's worth every cent you paid to read it...if you can stay awake reading it.

"You could probably put together a GM TB efi for a couple hundred bucks. But you wont get anywhere near the performance or gas mileage of a modern engine. The engine, cam, heads, efi, spark, gearing, etc are all designed to work together.
The stock LS heads flow better than the older hi performance heads, that's how they make hp. Carb applications on LS motors can easily make more hp than efi because of this.
The cam design, intake, spark control, efi are designed to generate high cylinder pressures at low rpm. Even a 400hp LS cam uses 116 LSA. That combined with gearing (under 2:1 overall) gives you the 400 hp with 25+mpg. Sequential port injection was designed to give optimal fuel delivery at these low rpms.
More recently things like variable valve timing have been added to optimize both aspects. Increased gears in the trans allows for lower shifts to increase mileage. Active fuel management to shut down cylinders. Now direct fuel injection in the new LT1 allows higher compression to make more hp and torque throughout the rpm range, increasing both hp and mileage.
If you bolt on a $2k efi you'll probably get a little better mileage than a poorly tuned Holley or worn Qjet, but don't expect it to turn it into an LS motor."

Seff

Info for you.

http://www.crankshaftcoalition.com/w...APT.29_setting

garys 68

Oops, getting old, forgetting about carbs...actually never adjusted that in a Qjet, they were always really good in metering the primary circuit.
But I do agree optimizing the carb and spark is certainly much more cost effective.

janoah365

Brake issues because of vacuum?
I got a 455 EZ EFI im throwing in, I was warned about vacuum issues because of no more carb!

cjsdad

You're replying to a 9 year old thread, but changing from carb to throttle body EFI shouldn't effect your vacuum. Changing the cam would, but the fuel delivery system shouldn't.