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83 Capri fresh 5.0l only 12hg idle vacuum TFS stage 1 cam.

5021 Views 15 Replies 4 Participants Last post by  Jimbeamrye
Well I just got my newly rebuilt motor up and running. It is a 1983 roller block with .40 over pistons. I am using a newly rebuilt Edelbrock#1405 600cfm carb along with a new distributor. Plain Autolight plugs that are recommended for TF aluminum heads. All cylinders are firing as all 8 headers are all fire hot. Engine is approx 9 to 1 compression. The cylinder heads: Twisted Wedge 170, FAC 61cc chambers. Cam is a TFS Stage 1 because I wanted a decent idle and daily driver abilities. TF Stage 1 specs: Duration at 050 inch lift: 221 int./225 exh. lift .499/.510, Lobe Sep-112. Ignition timing with dist vac advance plugged is 10 deg btdc. Exhaust is all new, BBK headers dumping into dual 2.5" H pipe.
When I first cranked her up, I had much trouble keeping the motor running. Had the two mixture screws on the carb at 2 turns out, had to adjust both to 2.5 turns. Got the idle adjust screw in enough to keep the throttle slightly open which was what keeps it running when I let go now. I also installed an A/F meter and the reading is about 12 or 13 "green" once the motor warms up and at a steady 1200 rpms or higher. If the idle goes below 800rpms, the A/F meter starts dancing all over the lean board reading 14 "yellow" up to 18 "red". I put a vacuum gauge on the manifold and am now clearly concerned. The vacuum only holds at 11 to 12hg if the idle stays above 1100. Even up to 15hg at 2500. Let off the throttle from 2500 rpms it will burst up to 18-19hg. But if the idle goes below 800, like the A/F readings, the vacuum starts to go erratic, bouncing from 11 hgs down to 8. Any less, she stalls.
The stalling typically happens when the motor is not quite up to full temp. I have made ABSOLUTELY sure there are no vac leaks, I have unplugged the brakes, pcv ect just to test and results are the same. I made positively sure that the cam was lined up correctly, no dial though.
Carburetor has new gaskets and the intake gaskets are premium. I even sprayed carb cleaner on all typical "leak" areas that are prone to leaks, nothing. Another thing is the manual choke I installed, it has not helped one bit with the starting or erratic running of the motor at low rpms. If I start to pull the choke while it is idling at 1100, I see the A/F meter start to go rich, but engine speed does not change. If I keep closing the choke she will just start to sputter and die.
I set the valves(stud type) zero lash at 1/2 turn past after the push-rod feels first bit of resistance.(fyi this was done before engine was cranked up months ago).
I have read so many posts on what Vacuum should be, but it appears to be a stock motor should be a min of 18hg. My 12hg seems terribly low, and the idle quality is terrible below 1000. I just can't fathom that a TF stage 1 cam could make the motor "lope" that much. So much that it wants to sputter and die just putting it into reverse. Auto trans with stock tranny.
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Might want to try going over your rocker adjustment. Spinning the pushrod is the worst method to use.
Ok, that is the worst it. Thanks:(
hey there. I have a very similar combo, cam is pretty close to yours. I also only get a bout 12-14 in of vacuum at idle. I've been told a few times it is due to the cam.

But, if you're running rough or can't idle, probably should fix that. Try re adjusting rockers, and re torquing intake bolts?
I agree it could just be the cam, problem is that I have found others running this cam saying their hitting 16 to 18hg. Maybe their full of crap, wanting everyone to think they've got the perfect running combo or something? What do you think about this, when I was searching for cams and doing lots of investigation I found that the TF stage 1 was ground with 4 degrees of advance already built into it. Could this be the reason for low vac on this cam. I have an adjustable timing chain, able to set it 4 deg retard which would nullify the advance built into it. Could this help even out the idle and help with vacuum you think?worried.gif
Every method for installing rockers on a sbf, with roller hydraulic lifters I have seen has stated to tighten them till resistance is felt on the pushrod while you rotate it between 2 fingers. Including the instructions that came with my newly ordered comp uh if that's the WORST way, mind enlightening us to the better method? are referring to "89Coupe" for that answer, right? I thought my reply to his statement was dripping with "don't leave me hanging bro", but guess so.
No problem! Just want to help and learn as I go!
If you change the timing of the cam by advancing/retarding, you'll change the valve events and it may not have the PTV clearance you need.
When it comes to PTV issues, what event is the MOST likely to occur. The piston comes up and hits the intake valve, or the piston comes up and hits the exhaust valve?
it depends on the cam. with mine, I found that the closest clearance was as the piston was travelling up toward a closing intake valve. I think that is probably common event sequence.
I got it, an opening Intake valve you meant!
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