Vacuum Issues - Post Cam Swap

[OldsFan]

Hi Everyone,
Got a bit of a head scratcher going on here. I finally had some time and I just swapped the cam on my 1985 305.  It broke in fine, 2500-3K for 30 minutes and I changed the oil over to fresh zinc supplemented oil.  The cam is nothing wild: Summit 1102 cam (204 int./214 exh at .050, 0.421 int./0.444 exh.  lift, 112 LSA)

The problem I am seeing is that I am only getting about 15" of vacuum at idle.  2 weeks ago, I was getting 19" with the stock cam. The rpm does hunt a bit, but nothing crazy (30 rpm sweep, maybe). I drove it in my neighborhood and it seems quite peppy, but the vacuum numbers are bothering me.

Is there any way that this could be "normal" for this cam?  I don't think so - no overlap - but it is a bit longer duration than the stock cam, very close on lift numbers.  I'll put the details below, but if anyone has any suggestions as to what to look for, I'd appreciate it!  Thanks!

Here's what I have checked (and rechecked) so far:
* New base gasket for the quadrajet
* Blocked brake booster, trans modulator, EGR, PCV, etc.
* Timing set to 11* base, blocked vac advance
* Idle about 800 rpm in neutral
* Rockers are at 1/2 turn past zero lash. Double checked this today by pulling the valve covers and resetting them earlier today.

Here's the parts list:
* Summit 1102 cam (204 int./214 exh at .050, 0.421 int./0.444 exh.  lift, 112 LSA)
* fresh lifters
* new timing set
* new rear main seal
* new oil pump w/ driveshaft (Melling stock replacement, standard everything)
* new gaskets for all (intake, exhaust, etc., etc, etc.)
* assembly lube, high zinc break-in oil, oil filters, etc.

[bd]

That cam should produce ~18" Hg vacuum.  Use some aerosol carburetor cleaner and recheck for vacuum leaks.  Verify that the harmonic balancer hasn't slipped.  Did you verify the camshaft is properly timed with respect to the crankshaft (aka, degree the cam)?? 

[OldsFan]

Hey bd - thanks for the reply. I figured so.

I did degree the cam. I didn't have solid lifters available though, so I dealt with the bleed down of the hydraulics. I did set it up at "zero" in the timing set, though. If you look at the attachments, the timing set is in there, but I had rolled the engine into TDC compression on 1. It is hard to see in the image, but I marked the zero points with yellow in real life. I added the red arrows to help, but the image quality is a little limited.

The new oil pump seems to make more pressure than the old one even though it is a Melling M55 (standard V/P). Also, I am running straight SAE-30, high zinc at the moment. Could parasitic draw on the oil pump with thicker oil (at about 35 degrees outside temp) cause this level of change?

Ok, never used vimeo before, but there should be a video of the vac gauge and tach at this link:
https://vimeo.com/495086888

Thanks!

[VileZambonie]

Advance the ignition timing

[OldsFan]

I just hooked up the vac advance to manifold vac and it then shows about 30* BTDC or so. Obviously, that sped up the engine speed (over 1K) and it makes more vacuum, around 18".  But when I slowed the engine down via the idle screw, the vacuum drops back down to around 15".  Still hunts a bit (.5" vac swing), but nothing dramatic.

If I _had_ messed up the crank gear on my timing set (like installing it in the retarded position), it would cause more serious symptoms, right?  I know I installed it right (see pic) but I keep second guessing that...

[bd]

The timing set, as imaged, was correctly installed at zero.

[OldsFan]

I had the timing set on and off 3 times setting things up, but I am pretty sure that pic was the last one I took before putting the cover on. I just keep second guessing myself now because of the issues I am seeing.

So here's what I am thinking of trying:

• Borrow an intake smoke machine to look for some really hard-to-find leak
• Change over to thinner (normal, multi-viscosity 10w-30) oil, adding zinc separately
• Get an A/F gauge on it, but I think it is running a little lean at idle (covering air horn causes it to speed up a bit)
• If all else fails...  double check the timing set to make sure it is at zero

Could my new, stiff oil pump be generating that much extra load?  I remember the drill working pretty hard to prime it, but not insanely so...

Thanks!

[TexasRed]

Did you set the idle mixture again after the cam swap?

~30 degrees with 11 initial, so the can adding 20 degrees is about normal. I like to limit the advance on the can to 10 degrees, which off the top of my head is like .110" of movement. Shoot for 20 to 22" at idle with mechanical plus the vacuum can advance.

I doubt it's the oil. Once the oil is warm, 30 weight is 30 weight for the most part. There may be a difference inside the 30w, as in one may at the top or bottom of the viscosity specification. The oil pump may be tight but I doubt it's causing that much of a load, is your drill a battery powered unit that maybe the battery was a little low on? Now, if that "high zinc" oil is something like 60w, that may cause a little extra umph to power through, and it may require more power if the oil was cold as well.

I'd hook up the PCV valve before setting the idle mixture.

[OldsFan]

Hey TexasRed - thanks for the response.

I haven't touched the idle mixture at all since the swap. I have the screws pretty far out (like 6 turns on the Qjet) and it was giving 19" of vac on the original cam. It has always bothered me a bit that the screws need to be so far out...

I have the advance can at maximum, so that is where the 20* degrees is coming from, I guess.

I wonder if I've got a vac leak somewhere even though the vac seems to stay pretty steady, just low. Unfortunately, I can't borrow an intake smoke machine for a couple of days to really search, but I do have all the accessories disconnected. Stopping the truck without the brake booster makes me really miss it.

Are there any vac leaks I might just not be thinking of? An internal leak in the carb? Intake manifold not sealing properly on the bottom of the ports, into the valley?

[VileZambonie]

Disconnect the vacuum advance and plug it. Set your timing to 36° BTDC at 3500 RPM. Put the vacuum advance on a full vacuum source at the carburetor instead of ported. Adjust your idle speed and mixture.

[OldsFan]

Ok, I'll give a clean reset a shot, just as you say.

That said, I think I have a vac leak going on somehow. I threw an air/fuel gauge on it today and saw that it was running lean at idle.

If I open the throttle to about 2000 RPM, I see the vacuum build up to around 20".  If I hold it there for a few seconds, the air fuel ratio goes back lean (16+).

Here's the video of all that; ignore the crappy quality of the video:
https://vimeo.com/495660816

I am thinking the pump shot initially pushes it towards rich (very beginning of the video) and then as vacuum builds, it gets leaner as it pulls in more unmetered air past the leak?

I may end up having to pull the intake manifold, I guess...  Any other ideas or thoughts?

[TexasRed]

It doesn't take much throttle to bring the engine to 2k rpm when there is no load. So you may still be on the idle circuit which hasn't been adjusted for the new cam.

You can check for vacuum leaks by spraying water on the intake from one of those squirt bottle things to see if the engine changes speed.

I would not pull the intake yet.

[OldsFan]

Hey TexasRed - thanks for that. I held off on pulling the manifold and I think I am glad I did.  I managed to borrow an evap smoker today. I pulled the Q-jet off and taped over the ports, then bolted a flat plate on to keep it sorta sealed. Connected the smoker to the vac tree behind the carb where the trans would normally get its vacuum signal and regulated it to 1.5 PSI.

After a few minutes, I didn't see any smoke (amazingly) and pulled the smoker off. Smoke POURED out of the vac line. I think the intake must've held the pressure.  I tried it a couple more times and even blew into the line and felt it build pressure.

Long story short - I don't think I have a vac leak unless it is in the carb base or something along those lines.  I am thinking of trying a different carb (another Q-jet I have around) and reset the timing as VileZambonie mentioned.

I am really starting to consider the idea that I must've retarded the valve timing by accident and (Murphy's Law) didn't take a final picture to confirm it.  Is there any way to confirm it without pulling the timing cover? Or should I just get ready to pull the whole front of the engine off again?

Thanks again and Happy New Year, everyone!

[TexasRed]

Why not just plan for doing the LS engine swap with 4L80E transmission? I joke.

The easiest thing to try next is to, set your timing as VileZambonie says. Use the vacuum gage to then reset the idle mixture to get the highest vacuum and then put all vacuum accessories back on the engine leaving the vacuum can hooked up to full vacuum at idle. There are better timing curves but this should get you really close.

This should take less than 30 min and most of that time will be letting the engine warm up.

[blazer74]

How does it run, happy with performance? Starts hot? If you are happy with performance that may be your answer.
You say Hunts a little at idle, before you pull the intake off gently spray brake cleaner around the gasket areas of the intake, vac fittings and carb base gasket looking for engine rpm change.
You mentioned lean at idle, tip your choke blade slightly towards closed. If the idle improves you are a bit lean.
Adjust your carb mixture. Turn each screw in one at a time until stumble then back out 1/2 to 1 turn.
Repeat and reset  idle speed each time. 6 turns out is not uncommon with an 85 quad assuming that’s what’s on there. Aftermarket carbs are a crap shoot but you said it was fine before the cam change . These later carbs have fine pitched threads on the mix screws which require more turns.
You shouldn’t have nozzle drip or it would appear rich at idle.
10 degrees initial is plenty. Vac advance is  what works best for your engine ported or manifold, I prefer manifold.
You posted your timing marks on the cam  earlier and was confirmed correct by another member.
Tearing down the front of the engine would be my my last resort.