What could it be

1fasEG

Black soot coming out of the exhaust what could be the problem?

kz6fittycent

Is the catalytic converter gutted or cut out? It's not totally uncommon for carb'd vehicles to put some soot out when starting up. After it's warmed up, it should be clear. If you're still seeing black soot coming out when the engine is hot, you've got a jetting problem with the carb, or you have something affecting the mixture. If you've got a Weber, you can buy a jet kit, but make sure that all the settings are correct before you do that, to include the lean-best idle setting on the carb. I'll let others chime in about other items to consider.

P.S. There's also the potential that it's oil related, but typically burning oil is unmistakable and usually white/bluish smoke.

MazdaMitch

It's running too rich. Need to adjust the carb, tune it better.

kz6fittycent

Easiest way to determine if you're rich, lean, or stoich, is to pull your plugs and use this chart to compare:

You can see the first set (top left) that show an oil fouled plug and then on down (bottom right) to what is way too hot or lean. Your plugs should be somewhere in the green section. You can always optimize your tune to get it "just right", but with carbs, altitude and weather can impact the tune to some extent. It's truly a YMMV situation.

MazdaMitch

Lets also not forget it is winter time and when you use the choke, if you let it stay on choke too long it will run rich and cause soot.

1fasEG

MazdaMitch how do you adjust in that situation?

kz6fittycent

MazdaMitch you know, @MazdaMitch this keeps coming up. Maybe this chart, along w/ your Weber baseline tuning video could be a sticky? I think I've shared this chart several times in other threads.

rev10eight

Thanks for the picture of the spark plugs. I have that in my phone now.

Axel-Breaker-Earl

1fasEG how do you adjust in that situation?

You change to a hotter or colder spark plug.......depending on which direction you need to go with it.

MazdaMitch

kz6fittycent I have already stickied what I feel like is the most important links.
All that are new here see it first thing.
That should do it.
If people would take the time to read.

Some forget this is a website first and a forum second.

https://mazdaminitruckin.com/forums/d/442-important-links-to-files-and-more

kz6fittycent

MazdaMitch I know - however, I was referring to the spark plug chart. It might be a good tool for those who want to get their tune "just right" and/or troubleshoot. Just a suggestion.

OGMB2K

I know on these "fancy" fuel injected cars the winter fuel blend affect only gas mileage, is there a significant change in performance on the winter blend fuels with our Weber's?

Would it best to just run the non ethanol fuel if available at your local fuel stations?

kz6fittycent

OGMB2K straight non-ethanol gas is very limited where I live. I typically just run Exxon since it's right next to my neighborhood. That said, my experience with other carb'd vehicles running straight gas is that they run much better.

MazdaMitch

OGMB2K I know on these "fancy" fuel injected cars the winter fuel blend affect only gas mileage, is there a significant change in performance on the winter blend fuels with our Weber's?

Would it best to just run the non ethanol fuel if available at your local fuel stations?

You press or pat the gas before cranking, this activates the choke. You crank it, and if you leave it on choke too long without patting the gas to let the butterflies open up, yes you will burn more gas as its a rich condition.

Its ALWAYS best to run non ethanol gas in everything. I have ran the numbers and you get better mpg no matter what vehicle it goes in. I run it in all my trucks. My Dodge charger, I run it in there and get extra mpg and it = saving $100 a year despite the extra fuel cost, and hopefully after Trump gets in office that will get even better.

This is from a Honda dirtbike I recently repaired for someone and they ran ETHANOL fuel in it.
This is the fuel pitcock.

Look at the corrosion.