512BB status on engine tune from repair shop low compression %234 cyl

The repair shop thats tuning my 512BB has made some good progress on the car and the stumble is gone and it runs very well now.

This is what was basically wrong with the car:

The floats were off, my method of using a micrometer on the edge of the carb to the top of the float just doesn't work on these cars, I tried this many times to get them right going for a 14mm height which I thought I had them set correct but clearly not so, it takes a proper side mount float gauge to set them correctly.

The short linkages to the carbs were off, the tech changed the linkage as well from the screw in type plug to a different type, he said the type on my car would drive anyone crazy and you can never set them correct.

Of course all the mixtures were way off, I had the mixture screws way out compared to were they are now, alot of this due to above issues and my gas analyzer giving me wrong info.

I haven't driven the car yet but visitors in the shop such as Roland Linder the ex race driver was very impressed with the car and how it sounded and so were others, so its close to where it should be, as I said the tech stated the stumble is gone which was the major issue.

Here's the one serious problem the tech found, #4 cylinder has only 60 lbs compression, the car has been sitting for over 5 years and running poorly so the valves could have alot of carbon on them or other issues such as sticking rings, we put some high octane race gas in it and the shop owner will drive it again tomorrow and recheck no. 4 cylinder, if it has not come up any I plan on just driving it for a few hundered miles to see if it helps as well.

From what I understand having low compression in 1 cylinder will not cause a major problem other than loss of performance since I am running on 11 1/2 cyls and the plug is not fouling with oil.

If compression does not come up I can live with it for awhile till the next major is due in about 2 years then address it then if it needs a valve job or something more major.


In final thought I enjoyed working on this car and learning about it but it really does take specialized knowledge to figure out issues such as linkage problems and such and using incorrect tuning methods as how I set the floats, I should have taken the car in sooner as I would not have wasted so much time making little progress myself, in conclusion it does take abit of black magic and much experience to understand these big carb 12s and make them run properly as they should and more than likely this car has not run properly in a very long time even though it did have a major a few years ago which is probably one of the reasons it has such low miles on it as it has not run properly in 10+ years.


Any opinions?

Just got back from a test drive at the shop, totally different car from before concerning performance, burns rubber easily in 1st and second from hitting the throttle hard and sounds incredible, the shop owner can't believe how well it runs and idles considering the low compression in that cylinder, the car is blowing out a bit of black soot on the drivers side exhaust which is from the #4 bank when hard on the throttle, maybe it has a bunch of carbon causing my problem.

Should have it by this weekend as he has some final tuning to do and needs to change the fuel filter. I'll then take it for a good run.

Jeff, Sounds like the saga continues, but is finally becoming resolved!
Hopefully the low compression is just due to a stuck ring, that could with some good running, work itself loose.
And I guess it shows just how much there is to Weber carbs and their proper and correct setting and adjusting.
I've followed all your posts closely, and agreed, as well as being impressed with your methodology, in sorting your engine problems.
Then a Weber knowledgeable guy comes on-scene, and can still point out problems! Yikes, shades of needing to be more than mortal man!
But it sounds that in the end, your car is going to be a real screamer, as well as gorgeous!
Keep the updates coming, and when you get it running great, come on over and tune-up mine!

I would pass on the high octane gas, it's just harder to burn.
Do a leakdown on #4 to isolate the problem.

Yeah, thought I was doing a decent job then its humbling to see a guy that knows what he's doing properly diagnose whats wrong. I never would have guessed the linkages were part of the problem as the throttle butterflys seemed in synch but the linkages caused the idle speed screws needing to be turned in fairly far compared to where they are now just touching which probably had the car idleing partially through the progession circuit in a few cylinders instead of the idle circuit causing tuning and balance problems.I know this as some of the idle mixture screws would have little effect before.Makes me wonder how long this car has been so poorly set up with these linkages.

These 12s are so smooth its hard to tell if they are not running exact so it takes someone with real skill to fix them,but you sure can tell when
you hit the throttle in its performance.The car makes such great power and idles so well it hard to believe it has such low compression in the cylinder.

Got the car back today,first time I drove it as the mechanic was driving it with me the other day and it runs very well with great power, it was at least 100' here and the engine was cool concerning oil and water,when not running well the car would get warm concerning coolant so its much improved, car still has very minor hesitation off idle so I am a little disappointed especially since this cost me $1500 for just basic carb tuning and linkage adjustments but the car performs very well otherwise. I can live with the hesitation as it only happens when easing on the throttle but I don't think their should be any.

The car has just started having a bit of wobble in the front end which the wrench checked it out and stated the wheel bearings are out of adjustment as you can feel the tire move.My next project.