TR6 '74 TR6 backfiring / popping

[Slider748]

On deceleration, I get a lot of popping and it almost sounds like a backfire at times. My timing is adjusted correctly and the car recently failed an emission test due to excessive Co2 at idle. Any idea on what could be causing the problem?

Thanks.

Gene

 

[zottlander]

How do your plugs look? Are you running to rich? I was too rich and i had popping in the exhaust system.If you disconnect the O2 pump it will stop, but not solve the problem. Not to mention the damage from washing of the cly. walls with too much gas.

 

[TR4]

My guess would be running too rich as well. Try the Colortune kit if you can borrow one to see if the color of flame in the cylinder is proper.

 

[sammyb]

There are a bunch of things that could be happening...

Two that are most common are: 1) One of your deceleration bypass valves on your dual strombergs are "floating." Don't know if you have adjustable ones, but if you look at the carbs, on the right side of the carb body is a little thumb screw pointing out towards the front of the car(if it's adjustable.) You'll need to reset these per the shop manual.

The other likely problem is that your idle screws are not even, so as you decelerate, the carbs aren't in sinc at idle, causing a popping.

You could also have an exhaust leak, or if it is a car with a smog pump, the diverter valve or inline check valve could be bad...these will give one loud backfire as you let off the gas quickly.

 

[Slider748]

Thanks for the great information everyone. I read that a special tool is required to adjust the idle mixture. Do you know if it can be adjusted without this tool?

I'll check the bypass valve. I've never even heard of this. Also, I should probably invest in a carb sync tool. Any recommendations?

 

[sammyb]

Definitely look at getting a synch tool...it can be done without them, but requires a good ear.

It's probably not the idle mixture, more likely vastly different idle levels...you'll see a screw that pushes up on the throttle for each carb (on the left of each carb body.)