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Vac reading

adamforsythe

adamforsythe

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I hooked a vac gauge up to my carb and I am reading 5 at idel and 15-25 while reving.
What should I be reading????? School me on vaccum.
Thanks
Adam
 
you must have hooked it up to the wrong port becasue you should have a higher reading at idle, hook it up to a port that uses vaccum after the throttle plates not before
 
I'll hook it up to the intake this weekend. It's way to cold to do it now. What kind of stuff will the gauge tell you? I know it will tell you if you have a leak ( How ).
Thanks
Adam


1979jimmy350 said:
you must have hooked it up to the wrong port becasue you should have a higher reading at idle, hook it up to a port that uses vaccum after the throttle plates not before
Click to expand...
 
Thanks for the info guys. I think I am smarter when it coes to reading a Vacuum Gauge. :p:
Thanks
Adam
 
I just hooked my intake up to the gauge and I am reading 20 at Idel and if I gun it it drops down to 5, If I rev up slowly it stayes in the 20-25 range. The gauge does not sway between numbers at idel or if I hold the Rpms off from idel.
Thanks
Adam
 
How would i go about adjusting my carb with it????????
Thanks
Adam

trailblazr81 said:
Ive learned the ways of the vacuum gauge and always use 'em to tune carbs. :waytogo:
Click to expand...
 
Hook up vacuum gauge to a port on carb with constant vacuum. Turn in idle screw to lean it out. Do maybe 1/4 turn at a time. Do this till you get max vacuum. But remember every time your RPM's increase, lower them back down to original idle RPM. You want both idle screws (or 4 depending on carb type) to be about the same. So adjust one then the other, keep going back n forth. 1/4 turn left screw, 1/4 turn right screw... And of course different engines with different cams will have different vacuum readings. If she stumbles fatten 'er up 1/4 turn.
 
adamforsythe said:
I just hooked my intake up to the gauge and I am reading 20 at Idel and if I gun it it drops down to 5, If I rev up slowly it stayes in the 20-25 range. The gauge does not sway between numbers at idel or if I hold the Rpms off from idel.
Thanks
Adam
Click to expand...

You are at 20 at idle, yet after tuning my 388 with cam I never got above 16.
 
1985_K5_Silverado said:
That will help with the "how to tune a carb with a vac gauge" thing.
Click to expand...

its a good article.... i guess it pays to save that stuff... my tech folder has gotten quite large.... :haha:
 
Hello,
Sweet thanks for the info.
Thanks
Adam

trailblazr81 said:
Hook up vacuum gauge to a port on carb with constant vacuum. Turn in idle screw to lean it out. Do maybe 1/4 turn at a time. Do this till you get max vacuum. But remember every time your RPM's increase, lower them back down to original idle RPM. You want both idle screws (or 4 depending on carb type) to be about the same. So adjust one then the other, keep going back n forth. 1/4 turn left screw, 1/4 turn right screw... And of course different engines with different cams will have different vacuum readings. If she stumbles fatten 'er up 1/4 turn.
Click to expand...
 
Trust me i am saving EVERY link.

ryoken said:
its a good article.... i guess it pays to save that stuff... my tech folder has gotten quite large.... :haha:
Click to expand...
 
Cam selection has a HUGE impact on idle vacuum. Altitude also affects it. Here at 7,000 feet I only get about 13 inches at idle with my 383. :eek1: My stock TBI 350 reads closer to 17 inches.
 
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