Vacuum Leak - ugh.
Mentioned earlier in the thread that i'd swapped from a home-made looking aluminum intake adapter; to a steel 1/4" one from Trans-Dapt. Upon startup after installation, there was a dog-whistle high-pitched noise that i first thought was a belt; but the idle was also really high - ugh, vacuum leak?. Over the weekend, after having spoken to rang-a-stang on ifsja.org, i used an auto stethoscope to narrow down where the whistle was coming from - under the intake adapter; To narrow it down, took carb cleaner & sprayed around the throttle body & intake & found a leak along the passenger side.
After thinking thru the process, i decided to re-torque all the bolts; remembered having tightened the adapter bolts down clockwise in a square... not in an X pattern.
First attempt to fix: Backed out the adapter & the throttle body bolts (had used OEM hex head originals), and retorqued the adapter bolts to 15 ft.lbs. in 3 steps (snug, to 10, then to 15 ft.lbs. in an X pattern) & throttle body bolts to 13 ft.lbs. Took a test drive yesterday afternoon & 80-90% of the whistle was gone, but would come & go depending on throttle position & the idle was still somewhat high.
A couple of days ago, was reading & came across an article on gearhead-efi.com where someone with a similar setup had a vacuum leak & was asking for advice.
EagleMark mentioned in this thread:
tbi adapter advice that the Trans-Dapt TBI adapters are too thin at 1/4", and that the mounting bolts hit the intake flange upon tightening, causing a vacuum leak. Aha! Hadn't noticed that 2 (driver & passenger side) of the TBI mounting bolts line up with the intake flanges...
Went out day before yesterday morning in the dark, & pulled the TBI mounting bolts to measure the depth to obstruction and that's it! The OEM bolts are about 1 thread too long...
Swapped from the OEM bolts to the Trans-Dapt supplied studs being careful to stop tightening them once they bottomed out & torqued the nuts to 13 ft.lbs. in 3 steps; & am closer. Engine idle calmed even further down to near normal, but there's still a slight tell-tale whistle at idle, that goes away off-idle.
Have reached out to Hamilton Fuel Injection to acquire an aluminum adapter (1/2" thick); which should fix the vacuum leak.
On the way home yesterday, i stopped by the auto parts store & picked up a 90-degree power brake vacuum intake fitting to improve the routing of the brake booster vacuum line. Currently, there's a straight connection just behind the throttle body, which makes the 3/8" vacuum line have to make a slow 90 without kinking, before heading to the booster. This 90 will allow a straight shot & not interfere with the coming intake adapter, or the air cleaner. Will update once I have things in hand.
