68 Brougham: still shaky idle

[Thomas Klak]

Hi guys,
in the last time, the following parts were renewed/rebuilt, but the engine is still not running that good and shakes while idling.

completely rebuilt heads
new lifters
one piston replaced with original 68 10,5:1 piston
new rings
chain looked good, had already metal gears
cam looked good
new rod bearings
new Rochester carb 7029232
new ignition system: distributor, plugs, wires,points,condenser,cap
Vacuum system all hooked up, (thanks to Glen again!)

I tried to put in the distributor on 0 5 and 7,5 degrees.
5 seems to me the best solution.
Turning the idle/mixture screws has only little effect
What else can i do?
What is the right way to put in the distributor? Vacuum can all the way up to climate compressor or in the middle or near to manifold?
On 5 and 7,5 degrees the engine was running fair, when the distributor can was all the way up to the climate compressor.
Thanks again. Great forum!
Best
Thomas Klak

[wrefakis]

Problem is,read your 68 owners manual,operating engine with fuel octane rating below 97 can cause engine damage,and void warranty!

[Thomas Klak]

everytime 100 Octane fuel and lead additive is used

[35-709]

Get rid of the "lead additive".  Don't know if or why that would make a difference in the idle but you do not need it anyway.
 

[TJ Hopland]

Problem is,read your 68 owners manual,operating engine with fuel octane rating below 97 can cause engine damage,and void warranty!

97?


Does the vacuum advance run of manifold or ported vac?   Its it working?  Running off manifold usually helps the idle unless its already too far advanced for some reason.

The orientation of the dizzy does not really matter as long as you can get it timed to where you want it.

New carb? Like old stock? Some sort of rebuild? PArts store rebuild or builder with a good rep?  Same ? about the dizzy.  Parts store stuff tends to be more of a one size fits all and even at that the tolerances seem quite wide.

What happened to the piston and rod bearings?

Most of the time you should be able to kill the engine by going all the way in on the idle mixture screws.  With work being done on that motor did anyone look close to make sure the intake is seating/ sealing onto the heads?

[wrefakis]

there was a service letter out back around 71 to the dealers to inform service people at cadillac dealers not to promise a smooth idle,have owned over 100 of these with 10.5 472's all with low miles,and ever since around 73 never had one run even close to smooth, are you actually able to buy 100 octane fuel from the pump???  the 74 472 can be made to run perfect at idle,as can the 500 75& 76 engines,but good luck with your 68,and I just sold a 10k mile perfect 68 dvc,and have a perfect 10k mile 70 here,both have an idle rock!!! part of the charm!!!

[Stampie]

So you are saying that it's a pot luck dinner?  What makes one example better than the other?

Stampie

[Guidematic]

 Here's a little You Tube video of my 472 idling. It shows that they can idle very slooth.

 http://ca.youtube.com/watch?v=aYv_G-d1szo

 Mike

[wrefakis]

74 472 and 75 76 500 are tuned to run on low octane fuel

[Guidematic]

 Starting in '71 all GM engines were designed to run on unleaded. That's the reason for then compression drop.

 Mike

[homeonprunehill]

08-31-08@2018 HOU
Thomas, I'M not an expert or Rocket Scientist but, something you stated in your discription of the problem you are having, and another RS picked-up on was your statement,"turning the air/fuel mixture screws has no effect on the engine. It should have a lot of effect on how runs.
My suggestion would be to buy new air/fuel adjusting screws,or useing a drill and fine file(be careful not to get hurt) put a point on the old screws. HTH Good Luck,JIM

[Thomas Klak]

Hi again,
thanks for all the infos.
Some answers:
Yes, here in Germany, we are able to buy 100 Octane fuel at the gasstation.(1,65 Euro per litre ), that should be around 9 Bucks per gallon)
What wrefakis wrights is very very intersting. I only saw one 69 deVilleConvi idling very smooth.
Maybe an electronic ignition kit will help
When I bought the car from seattle, the compression on the fourth cylinder was not good,
we found,that two rings were broken and the piston was broken around the ringsection too. While
changing the one piston I decided to rering the other pistons and install new rod bearings.
Turning the mixture screws has little effect on shaking,while screws are out around 3 to 4 turns.
Vacuum can is working like it should,installed a new ported vacuum switch (delco with d c mt) to
connect it the original way.
Intake is sitting tight, old and new carb (both 7029232) worked/working like they should.
Thanks for your replies. Have a good day!

[Guidematic]

 I really did not have a lot of issues with the points as far as idle. There were issues when I bought the car, severe lack of power being the biggest one. Overhauling the carb fixed most of that (the emulsifier tubes had fallen off)

 But the HEI, and getting rid of the transmission controlled spark was the biggest boost in both power and idle quality.

 But, yesterday, after giving the car a good wax, I decided to service the distributor. It has not really been looked at since I put it in 13 years ago. It mysteriously stalled on me a couple of weeks ago, but then eventually restarted. In servicing it, I disturbed whatever made it die, and it would not restrt. After an afternoon of frustration, I finally figured it out. There was an intermittent connection in the battery positive wire in the small harness that goes to the module. A broken wire inside the insulation. That was a new one on me for these distributors.

 Mike

[wrefakis]

in my quest for a "smooth idle" in 1985 I took the heads off my 19k mile 70sdv did them to spec,all new gaskets,carb,etc,added HEI,which does reduce spark knock,put it all together,ran great!!! of course,still had an idle rock,a video of my engine will show a smooth runner as well,put it in gear,leave it 15 seconds,hold the wheel,idle rock,again,the reason they showed my the service publication at cadillac in 71 or 72,was that I drove them nuts trying to obtain a smooth idle,likethe 70 olds 350 that I drove around the same time,ditto,the 71 impala rentals ,all the winners at the GN 2008 in 69/70 are cars I owned,none idled smooth,good luck in your quest!!!

[Thomas Klak]

Is it possible, that a faulty voltage regulator can cause shaky idle?
My generator/regulator seems working ok.
No flickering headlights, power options work, gen light not glowing.
But yesterday i checked the new coil with "ignition on" with voltmeter:
only around 5,5 Volt
Any ideas?
Thanks!

[Guidematic]

 There is a resistor wire inside the harness to drop the voltage to the coil to prevent it from overheating. But during cranking, the coil gets a 12V boost to aid in starting. At this time the coil is fed off the "R" terminal on the starter solenoid.

 But, 5.5V is a bit low. It should be around 8-9V with a fully charged battery and the engine running. You can take a jumper wire and put it on the "+" terminal on the coil temporarily and see if it improves the idle. A poor quality spark certainly can affect idle quality.

 You can check for a faulty regulator by checking the volatge at the battery with the engine running, all accessories off. Voltage should be 13.8-14.2. Lower voltage can affect the operation of all electrical systems and put undues strain on some.

 Mike

[Thomas Klak]

Thanks Mike,
btw, great Brou!