Finally got the motor put together and fired it up on the test stand, broke the cam in at 2000 RPMs without issue. Currently struggling to get this thing to idle correctly though due to very low vacuum below 1400-1500 RPMs. I did not have a cam card for this engine as I bought it from a gentleman who had put it together a decade prior and lost it (only thing he wrote down was .500 lift, .270 duration). Used Stage 1 valve springs which Cad Company recommended. I installed the cam dot to dot (camshaft at 6, crank at 12), new cloyes timing set. Rebuilt a qjet with kit and advice from Cliff Ruggles but still have the stock qjet that came with motor. The distributor had a recurve kit put in, red springs installed from what I can see. Cannot get vacuum above 5-8 inches at anything under 900 RPMs. Vacuum at 1200-1400 RPMs is 18-25. Very responsive to throttle and anything above 1300 RPMs. Nozzle drip noted on the qjet so dissembled the rebuilt qjet, test fuel inlet seat seal with vacuum, reindexed the throttle blades so they're as close to fully closed as possible, rechecked float level, still having nozzle drip but not suprising with the low vacuum. I also installed the old cadillac qjet and same thing, nozzle drip and very low vacuum at lower RPMs and unable to get close to a idle. So I removed the aluminum intake, it appeared like the previous gasket may have had a leak. Reinstalled a new gasket with high tac and RTV around all ports and pretty much along the entire gasket surface. Still the same situation. I installed the distributor at -10 BTDC for #1 and ran like trash until I advanced it considerably and would run great above 1300 RPMs. I have run out of options for things to check besides possibly installing the cam 4+ and see how it reacts? Or possibly could have something wrong with this distributor? Any advice would be greatly appreciated. Did check compression on all cylinders, all at 150#-180#. When I had the intake off and valve covers off I did not notice any damage or anything out of place.
Struggling with my 500 rebuild
- Thread starter tschmitt
- Start date
DaveM
Member
I have read your post 4 times and would hate to point you in the wrong direction. I keep thinking you have a vacuum leak. You tried two carbs and got the same thing. So we can put a carb problem on the back burner. When the valve job was done were they vacuum checked?
Thanks for the reply Dave, the three angle valve job was done prior to me buying it and I'm not sure if they were vacuum checked. I do agree I think there could be a vacuum leak somewhere or the valve timing is off.
DaveM
Member
Not to say I have done this before, But what if you take off all the rockers so all the valves are closed. Then take off the carb and make a plate to block off the top of the intake with a fitting so you can pressurize it . Now with the plugs out you can hear any leaks. Let,s say it is a vacuum leak or a bad carb making it not idle, you could try adding more gas down the carb to see if you could get to idle.
samIam
Member
Some things I'd do...temp the headers to see if each runner is about same temp, spray something around intake to see if idle goes up, turn the motor by hand with valve covers off to see if valves are closed when piston hits tdc(cam issue), revisit the weights in the distributer and/or vacuum test the vacuum advance. Just a couple things I'd be doing.
Installed new valley pan (third time) and went back with the stock intake and now have about 14-15 inches of vacuum at idle around 850-900 RPMs. Doesn't seem to like to idle below that RPM range but I'll keep tuning and see how it goes. The cam is quite lopey which is fine but may never have great vacuum at idle. Fine tuning the quadrajet now but so far everything is looking up. The cam came from Chet Herbert in 1994 and is just now getting broke in. Definitely not the smooth idle I know from my other 500 but I'm ok with that.
cadillac512
Well-Known Member
Hi tschmitt;
I have some experience with pretty serious cams in 472/500 Cads. First, it sure sounds like your first intake had a leak somewhere since the second one made a big difference. If the first one was an aftermarket unit, yes they have problems sometimes and may need to be milled to fit.
The idle manners can be helped with a few things. Checking the cam timing with a degree wheel when installing is very important. I had one cam that was ground 12 degrees retarded...yeah, 12 degrees. Advancing the cam 4-6 degrees from true split overlap will help.
More ignition timing at idle and limiting the centrifugal advance at full advance will help a bunch.
The Q-jet may need the idle feed restrictors opened up. Not fun or easy as they live down at the bottom of the idle feed tubes and need a longer than normal bit to reach. I'm sure Mr Ruggles has info on that!
Your cranking compression is pretty good-and may get higher if you advance the cam.
Sure would be nice to have that cam card...shame it's lost.
Oh, nozzle drip may be from having throttle plates farther open than normal to keep it idling. Addressing the other issues may let you back the idle screw out and remedy that problem.
The good news is the Cads really like more cam when the throttle is open...big smiles!
Terry
I have some experience with pretty serious cams in 472/500 Cads. First, it sure sounds like your first intake had a leak somewhere since the second one made a big difference. If the first one was an aftermarket unit, yes they have problems sometimes and may need to be milled to fit.
The idle manners can be helped with a few things. Checking the cam timing with a degree wheel when installing is very important. I had one cam that was ground 12 degrees retarded...yeah, 12 degrees. Advancing the cam 4-6 degrees from true split overlap will help.
More ignition timing at idle and limiting the centrifugal advance at full advance will help a bunch.
The Q-jet may need the idle feed restrictors opened up. Not fun or easy as they live down at the bottom of the idle feed tubes and need a longer than normal bit to reach. I'm sure Mr Ruggles has info on that!
Your cranking compression is pretty good-and may get higher if you advance the cam.
Sure would be nice to have that cam card...shame it's lost.
Oh, nozzle drip may be from having throttle plates farther open than normal to keep it idling. Addressing the other issues may let you back the idle screw out and remedy that problem.
The good news is the Cads really like more cam when the throttle is open...big smiles!
Terry
Thanks Terry, made some more adjustments with the idle bypass air, idle tubes, and down channel restrictions per Cliff's recommendation and it's getting better but still needs some more fine tuning I think. I can throw a Holley on it and it runs better at idle with less timing, about 11 degrees (rpm at 850, vacuum between 12-14), total timing of 33 all in by approximately 2800 RPMs. With the quadrajet I have to advance the timing to 15-16 and the thing will barely start but once it does it's much more responsive to throttle vs the Holley. I did buy the aftermarket Power master starter which should be here next week so that may help. I also was able to get the throttle blades on the qjet closed enough now to stop the nozzle drip so it's a improvement. Just seems like it's not getting enough fuel possibly. I can shutter the choke flap when idling and the RPMs increase by 300-400.
cadillac512
Well-Known Member
Sure sounds like it needs more idle fuel. May have to open up the feed restrictors more yet. Just a thought....if you're running vac advance you might connect to full manifold vac just for the heck of it. Bound to help the idle (if it's rich enough of course) and won't crank so hard as setting the initial higher. Sometimes I wonder why I modify things so much,lol! 
