Carb Issue?

[trb41]

Car idling at 1500RPM. When I take my foot off the gar pedal it keeps stalling. Found Vacuum leak and replaced vacuum hose to Fuel Trap. Now car idles at 850rpm and engine is missing and stalls out. Replaced Spark Plugs, Distributor Cap, and Rotor but still is missing and running rough. Adjusted throttle on each carb to get idle at 1000RPM but still runs very rough and is missing when engine is cold. After it warms to operating temp is smooths out a little but still has a slight miss. Listening at the tailpipe the engine sounds rough but I can drive it without it stalling. Had converted Dist to electronic ignition a few years ago. Can't find out what is causing this problem. Need some advise. Thanks.

[andyf]

It might be worth doing a compression check, it could be valves, mine had a slight misfire that I could not trace and it turned out to be a burnt valve.



1980 Persian Aqua DHC

[Hasbeen]

Yep & check your clearances too. Missing or backfiring is a symptom of closing inlet valve clearances.

When I was recommissioning my current 7, I managed to set fire to my sons arm with the combination of flooding carb, & a slightly riding inlet valve. It was running like a hairy goat too.

It was occasionally backfiring through the front carb, & sometimes flooding on it as well. It did both, just as he was lifting the piston of the SU to check the mixture.

It was probably only half a teaspoon of burning petrol it blew out, with some of it landing on his arm. I had to question his priorities, when he was more interested in extinguishing his arm than the car.

So trb41, check your valve clearances. Once an inlet gets down to about 5 thou, they tend to cause missing, lousy idle, & backfiring through the carb, even if they don't ignite your son.

Also check your tank & any inline fuel filters for water, then check the carbs float bowls. Many of ours are full of corrosion after years of ingesting water from the fuel. Someone had a post showing very messy float bowls recently, but I can't remember who. [Damn this old timers disease]. They were chasing lousy running too.

Hasbeen

[Workshop Help]

This is a topic we haven't visited in a while. For starters, and assuming you are truly blessed with a pair of Z-S carburetors, remove, one at a time, the bell top of the carburetor which is held down with four screws. Set it and the spring to one side. Gently remove the slide.

Examine the diaphragm for deterioration and the needle for crusty gasoline deposits. If the diaphragm is torn or mal-shaped, replace it. With 1000 grit sand paper, clean the needle. Do this on both carburetors and retest. If the O-ring for the needle holder has deteriorated, I have an article in The Workshop Manual for your perusal.

If this procedure does not work, we will next delve into the float bowl.

Please report back on your progress. We will get you thru these travails. Also, some photos of your adventure under the hood will be helpful and entertaining for the assembled masses hereabouts.

Mildred Hargis

[trb41]

diaphragms okay. Found TR7 carb man. Said problem is with the FASD. Going to rebuild both carbs and clean out FASD. Valve in FASD will only partially close.

[Workshop Help]

Ummm, you might want to hold off on the carburetor work just now. Please peruse the excellent article on the FASD in The Workshop Manual. Follow the steps outlined to free up it's action, then, if necessary, rebalance the carburetors.

Mildred Hargis