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Author: Subject: What can cause a sooty carb?

posted on 9/6/19 at 08:17 PM Reply With Quote
What can cause a sooty carb?

Good Evening,

Just wondered if anyone can help,

I've got a Tiger Super 6 fitted with a 2.0 Ford Pinto running twin weber 40 DCOE carbs.

The car starts fine and seems to run well, but sometimes makes a popping sound from the carb on cylinder 1 at idle (not quite as loud as a back fire, but like a little splutter.)

I took the carbs off today, to fit new gaskets on the carb to manifold and manifold to head. As I thought an air leak might be causing this sound.

The carb barrel which feeds cylinder 1, seems to be quite sooty (the other barrel seems fine.) I'm going to strip this down and clean it - but just wondered what could cause this?

I only started to notice this sound after replacing the cambelt (although it could of been there before), so not sure if it might be ignition timing causing this? Although I would of thought it would be apparent on all carbs?

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posted on 10/6/19 at 02:06 AM Reply With Quote
Exhaust pushing back into inlet.

So, maybe carbed up exhaust valve, worn cam or valve clearance not setup right.

Edit - Inlet valve may not be seating right for some reason.

[Edited on 10/6/19 by joneh]

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posted on 10/6/19 at 09:05 AM Reply With Quote
Have you checked the simple things like the spark plugs?

Worth having them out to take a look at them and see if they all look the same or if there's anything different/damaged with one.

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posted on 10/6/19 at 11:25 AM Reply With Quote
Hello Both

Thank you for the reply, I was hoping no one would suggest a problem with the valves haha. But If everything else doesn't sort the problem - I will pull the head off for inspection and rebuild it.

The cylinder that is the problem, the spark plug seems seized in. I replaced these only around 600 miles ago - but this was the hardest one to get out when I replaced them. So I'm going to clean the carbs up - change the leads and the dizzy CAP and see if this sorts the problem. Also check ignition timing and make sure the carbs are balanced and properly set up.

I found the spark plug was easier to remove once the penetrating oil had worked into the head and the engine was hot. So when it is back up and running I will check the spark plug as well.

Does anyone know what the ignition timing should be on a Pinto with twin 40's? I believe at the moment it is set a TDC which I presume is incorrect.

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rusty nuts

posted on 10/6/19 at 11:59 AM Reply With Quote
I would check and adjust the valve clearances with the engine cold before doing anything else. I would expect the ignition timing to be somewhere in the region of 6 to 10 degrees BTDC but would suspect that a rolling road session would sort out the optimum setting. Plugs seizing in a Pinto head was a common problem , probably better to use a torque wrench to tighten. ISTR there use to be a purpose made tool for the job?
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posted on 10/6/19 at 01:59 PM Reply With Quote
Running either too lean (most common) or excessively rich can slow down combustion enough that the mixture is still burning when the inlet valve opens, causing the pop back through the carb and the soot.

Check that all chokes are balanced, jets are clean and float levels correctly set and needle valves sealing.

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posted on 10/6/19 at 03:41 PM Reply With Quote
Thanks again for the replies.

It might be because it is running lean.

One of the reasons I stripped it all down was to change the gaskets on the inlet side of things as I suspected an air leak somewhere.

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