Technical Straight 6 Dual In and Ex - One side leaner ?

About a year ago I noticed that the left exhaust pipe suddenly looks like it's burning leaner than the right one... see photos



At cold start in cold temps both pipes have the same amount of water droplets coming out.
Both carbs are synced perfectly across the rpm range and the spark plugs measure and look all the same.
Idle mix on both carbs is ideal and smooth.

I can't feel any difference, as the engine sounds and behaves the same as for the past 70K miles and 12 years when both pipes looked like the black one, until last year.

Just wondering what could cause that ?

 

Curious if you have an equalizer pipe between the two or are the two completely separate? I'd pull the plugs and compare them one pipe set against the other to see whats going on in the cylinders. Are you running chokes on both carbs or just one? If one choke is it on the pipe that is darker?

 

You might be out of sync. When I did my two Carters on a 235, I used a vacuum gauge to get the air fuel correct on them. Then I used my ear to listen that they sounded the same in pitch to get them in sync. I found that my front carb would affect the left exhaust and if my air fuel was wrong I would get a put put and not a smooth idle. The same with the rear carb as it affected the other pipe. Setting up my carbs were my biggest fear. I had been told I would be adjusting them all the time. I found it was relatively easy and I haven't had to touch them for years.

 

What exhaust manifold are you using.. It makes a difference

 

It looks like he's using Fentons and the rear has the stovebox for heat.

 

No equalizer pipe.
I will check all the spark plugs again
Only one choke and yes it's on the darker pipe side.
However it is rarely so cold, that I have to use it.

 

I recently checked the sync, but will do so again over the weekend.
I agree - I rarely had to re-adjust the carb sync on both truck and coupe.
I use a motorcycle synchronizer with a scale, giving very accurate readings.

 

Maybe one cylinder is starting to burn oil.

 

Check your plugs. It should be evident there.

If it is not, you may have not driven it enough since the change, to register on the plugs.

 

Don't know why I missed it. They shouldn't cause a problem but I've seen it when the welded stokers mess up plugs and running..