Running rich on cylinder 3 & 4 and perfect on 1 & 2

[jz56oval]

Hey all

I'm running a stock 36hp in my 56 bug. I went to check my spark plugs and the 3&4 plugs were black and the 1&2 are tan in color.

My exhaust tips were cleaned out and after 100 miles the right side was tan and the left was dark grey to black in color, same as the spark plugs.

Black is telling me that it's rich and tan is good. It's us a single 28pci.

I figured someone could chime in kn what they think might be an issue here or things to check.

Car runs good. Just has a bit of jumping around at idle. I notice it when I put the timing light to the crank pulley mark. It never stays in one spot.

Thanks in advance for any info or help.

[Multi69s]

Just a guess, but you might be running rich overall, but have an air leak on 1&2.
_________________
69 road Bug 2110
73 Squareback - 2L, T4, Automatic W/ AC
Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle
Gone but not forgotten 72 Baja Bug 2010
My builds
T4 into Squareback http://www.thesamba.com/vw/forum/viewtopic.php?t=458944&highlight=
Auto Trans Rebuild http://www.thesamba.com/vw/forum/viewtopic.php?t=516066&highlight=
AC in Squareback https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=

[jz56oval]

Thanks. That seems to make sense. There is only one carb so it all comes from one area.

Guess I'll be spraying the 1 and 2 area for leaks.

[modok]

Maybe vac leak, maybe heads don't match.

[oprn]

Could it be a worn distributor if the timing is bouncing around?

Just a thought.

[jz56oval]

I'll check for any vac leaks soon. Both of thr heads were rebuilt recently and looks to be the same.

[jz56oval]

Using starter fluid I checked for vac air leaks today and found one one at the throttle shaft. I could find any around where the manifold mou ts to the heads or exhaust attachments.

The starter fluid made the car bog down instead of increase the rpms when sprayes on the throttle shaft on carb.

Is it possible that a single carb can make the 3 and 4 cylinders rich and the 1 amd 2 side leaner? My thought would that it would be the same on both side unless there was a air leak on the one side.


Thanks

[KTPhil]

Heat riser burnt through into the manifold on one side?

[jz56oval]

[KTPhil]

Sometimes the damp and corrosive exhaust opens a hole connecting the heat riser and the intake runners, inside the weld or encasement where you can't see it. But the engine will see it as a vacuum leak, of course. There was a thread showing this happening a while ago.

[jz56oval]

[Howard 111]

My guess is it's an ignition problem. Could even be as simple as the ignition wires. The plugs get dark from not firing well on those cylinders. What distributor are you running?
_________________
1973 Karmann Ghia
Turbocharged, Fuel Injected
http://www.thesamba.com/vw/forum/viewtopic.php?t=531270

[jz56oval]

[Howard 111]

I would get a new distributor cap as well. With a new cap and the wires, that's everything replaced that could give you trouble. The Pertronix is fine. It wouldn't do what you are experiencing.
_________________
1973 Karmann Ghia
Turbocharged, Fuel Injected
http://www.thesamba.com/vw/forum/viewtopic.php?t=531270

[jz56oval]

Just an udate on findings.

I changed my carb to another one I had on hand that was in cleaner condition. The timing stays steady now and not bounce around like before. I still need to drive it a bit to see if the lean and rich issue is still present.

At least one thing is hopefully fixed.

Next, Gonna check compression on each cylinder

[Multi69s]

Thanks for updating
_________________
69 road Bug 2110
73 Squareback - 2L, T4, Automatic W/ AC
Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle
Gone but not forgotten 72 Baja Bug 2010
My builds
T4 into Squareback http://www.thesamba.com/vw/forum/viewtopic.php?t=458944&highlight=
Auto Trans Rebuild http://www.thesamba.com/vw/forum/viewtopic.php?t=516066&highlight=
AC in Squareback https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=

[jz56oval]

So after drivimg her for 45 minutes the idle seems to stay steady with the new carb and different jetting. Timing doesn't jump around like it use to and stays steady. Need to drive a bit more to see if my jetting is close.

Jetting now is

135 main
180 Air correction
23.5 mm venturi (down from the 24.5mm)

I did do a compression test on all cylinders

#1 - 100
#2 - 95
#3 - 106
#4 - 106

Are these numbers way off. Mayne this is why there is a leaner burn on 1 and 2 side and richer burn kn 3 and 4 side?

What do you guys think.