New engine with black sooty exhaust.

[Lyndon302]

67S. 2.0L. Dc30 cams. Wiseco hi comp pistons 81mm. Done 1000 kms run in
Doing my first service
Oil is perfect. No metal on plugs and oil screen.
155 psi on all cyls hot
Valve clearances still in spec.
Cams and rockers look perfect.
Nil leaks
Runs and idles well.
55 idles
125 mains
F26
32 mm chokes
180 air
I have rebuilt the carbs and have no idle authority at all. I get a good balance at about 5 or 6 on the snail.floats are good checked while running.
Have ordered
32 chokes
170 air
135 mains
F3 emulsions.
My exhaust is black and sooty. Even get this on my rear quarter if I wipe my hand on it. ( minor )
I run 95 and 98 fuel.
Is this normal. Fuel or oil.I know no idle control is not and still.working on that.
Advice please.
Lyndon

[Trackrash]

Webers on 911s will be a little sooty, from my experience.

If you install an air fuel meter, you will have a better idea on your carb setup.

[VFR750]

Carbs are sooty. An afr gage will confirm this.

Your plugs look pretty good.

I don’t t understand the comment on idle authority?

[Lyndon302]

I can screw the mixtures in and out. Nil affect on the engine.
I replaced the butterflies. I will revisit them I think. Might even put my old ones back in.
Lyndon

[Mark Henry]

Get a O2 wide band meter, weld an O2 bung into one of the heat exchangers just before the muffler flange.

What is your timing?did you have the dizzy re-curved?
Condition of carb? You cleaned them and installed new fuel filters right? Shafts were tight? The idle screws O-rings in good condition? Did you sync your carbs? Check float bowl level? Linkage?
A lot of parts have be in perfect sync.

Carbs you want a bit of soot in the tailpipe. You want an even tan (or grey, depends on gas) evenly on the center electrode ceramic and they should all look about the same.
-the first plug pick looks about right, maybe a hair rich.
-the 2nd plug pick looks about right, maybe a hair lean.
-The 3rd plug pick looks lean.
But pictures can be deceiving.

For 40IDA carbs you want to run about 12.8:1 air fuel ratio (AFR) @27-28 degrees BTDC at 3500 rpm.

With a meter you'll immediately see if you're lean/rich without guess work. Once done you can keep or remove the meter. If you want to check both sides you have weld in a 2nd bung, but really you only need one meter, just swap it out.
I'd try 30mm venturies especially if it's a mostly street engine.
Don't push the AFR beyond 12.8:1 or or the timing more than 28*, this Weber advice is what Paul Abbott told me.

I have a 3.0 twinplug with RSR pistons, 40 webers, 34mm vents and 120/104 web cam. I followed everything in the Performance Oriented tech pages and my 914/6 engine runs flawlessly. I might buy 46mm PMO's one day, it would help my top end, but right now I'm happy with what I have.
I didn't buy jets I reamed my own jets bigger with a $45 jet reamer set from cip1. I had two meters on it, I've taken one off and I might remove the other one as well.

[Mark Henry]

Originally Posted by Lyndon302

I can screw the mixtures in and out. Nil affect on the engine.
I replaced the butterflies. I will revisit them I think. Might even put my old ones back in.
Lyndon

Look for carbon tracing on the butterflys, if you see this your shafts or something is leaking air.
Replace the little o-rings under the mixture screws. I have a personal supply of these o-rings

[Trackrash]

You may want to try 60 idle jets and go up a size on the main as well. Most find 55s a little lean.

As mentioned, an AF meter will end all doubt about your setup. Not that expensive in the big scheme of things. I wish I had installed mine years ago.

[Lyndon302]

O2 sensor ? I take it its just for set up. Thus one unit to to swap side to side. E.g. hand held not dash mounted.
Any preferred type and fitting points. My carbs have been completely done. But clearly with no idle mixture something is a miss.
Will remove then and look again.
Lyndon

[VFR750]

I think you were running pretty clean for Weber or Zeniths. These old 3-bbl carbs are not designed for cruising.

Why are you both increasing fuel jets and decreasing the air jets? This will make it run richer.

Jumping from 55 to 60 will make the idle adjustments even worse.

[Mark Henry]

Originally Posted by Lyndon302

O2 sensor ? I take it its just for set up. Thus one unit to to swap side to side. E.g. hand held not dash mounted.
Any preferred type and fitting points. My carbs have been completely done. But clearly with no idle mixture something is a miss.
Will remove then and look again.
Lyndon

Yes with carbs you only need the O2 wide band meter as a temporary install. I have a 914, I took an old ashtray screwed a flat sheet of metal to it and Velcro the meter to it. If you want to leave the O2 sensor in it has to be powered. Install the bung into one of the heat exchangers just before the muffler flange anywhere in the upper half of the tube, 10 o'clock to 2 o'clock.

My engine is a 3.0, big port, Web 120/104 cams, mahle high CR pistons, twin plug, 40 webers, 34mm venturis, 155 main jets, F3 emulsion tubes, 180 air correction, 55 idle. My AFR is a pretty solid 12.7:1 at cruise and WOT.
I've been driving it all summer, everywhere I go is at least an hour round trip, I've taken several 4+ hour trips. Gas mileage isn't the best but if I manage to keep the foot off the loud pedal it's acceptable.
I didn't buy new main jets, I used my meter and a jet reamer set.

Originally Posted by VFR750

These old 3-bbl carbs are not designed for cruising.

Disagree.
Not sure what you mean, daily driving where gas mileage is important I agree, but I can cruise 3-4K rpm all day.

[Lyndon302]

Originally Posted by VFR750

I think you were running pretty clean for Weber or Zeniths. These old 3-bbl carbs are not designed for cruising.

Why are you both increasing fuel jets and decreasing the air jets? This will make it run richer.

Jumping from 55 to 60 will make the idle adjustments even worse.

I'm getting jetting for 67S as per STD and 32mm chokes. ( 55 idles)
Seeing that is engine and will compare.

[VFR750]

My comment is based on data. Cruising around town will be fairly rich to tolerate transitions. Very small throttle plate openings and the crude transition port design is very hard to be lean enough to avoid carbon and still handle a light tip
In.

Highway cruising Is different because the throttle is opened more and the butterflies are in a region of more ports being active. Thus tuning for good mileage and tip-In is easier.

If you pull the plug and look at the ports you will see 3 or 4 small holes and the edge of the butterfly valve.

Throttle movement opens more ports. But they are very discreet holes and spacing.

The AFR goes through rich to lean to rich to lean as the valve uncovers more holes.

It doesn’t mean they don’t work. It just means there are fundamental limitations and if you plod along with a high performance engine, with big carbs, fouling and carbon build up increases.

[Trackrash]

These AF gauges will save you $$$$ in the long run. You are shooting in the dark otherwise. Reading plugs only shows the average of your AFM overtime, unless you are WOT on the track.

[VFR750]

Originally Posted by Trackrash

These AF gauges will save you $$$$ in the long run. You are shooting in the dark otherwise. Reading plugs only shows the average of your AFM overtime, unless you are WOT on the track.

Nice set up

I agree 100% AFR is Almost essential

[Lyndon302]

Ive pulled the pistons. Some glazing ?
Is this oil or fuel as they are filthy and looked washed. Engine has done 1000 kms.
It was an unknown car and it took a bit to get the carbs right on start up. Have I washed the bores.Lyndon

[trond]

your cylinders look like they may be on the rough side of the correct Ra4-5, but instead resemble my EBS supplied ones that were useless and always burning oil. Have Ra measured before even thinking about re-assembly. If they are recoated Nicasil that is

[Trackrash]

I am thinking there may be more than one problem with your pistons and cylinders. Looks like oil burning on the piston tops. I see uneven wear on the cylinders.

You, or some expert, needs to carefully and accurately measure every aspect of your pistons and cylinders according to the specs in the factory manual to determine were the problems are. My guess is someone honed some out of spec cylinders, put in new rings on the old pistons and called it good. But only careful measuring will confirm or refute my guess.

[Lyndon302]

Brand new pistons and rings. 81mm. Will drop them back off Monday to the shop that bored and honed.
Lyndon

[Lyndon302]

Thoughts on reusing the rings if the bores check out good and come up with a home.
I rang wiseco and suggested new ones but I got the feeling he was taking a company view.
Lyndon

[Lyndon302]

On a closer inspection today.
Most of my barrels have score marks on the thrust sides top and bottom. about a 15 mm wide for the travel of the rings. Pistons are unmarked. I'm presuming its the rings
Upon assembly I had 19 thou on the top and 27 thou for 2nd for ring gaps.
I will get it all measured up on Monday. 3 to 4 thou is what wiseco recommends. I have no reason to believe the machine shop is to blame. I use a small well respected shop here in Adelaide. Using one bloke only in this shop to do 911 work of which they do quite a bit .
Lyndon