backfire through carbs

[Ramses]

I just got my 73 started after 1.5 yr in restore process. I have replace the ignition. Cleaned out the carbs and fuel lines. Did this b4 I took her apart. She starts up perfectly, but will backfire through the carberators through accelleration. Is this a timing issue or a fuel issue. Otherwise she seems to run fine.

[wfl_colorado]

Assuming the carbs are clean, floats are working and such, then you probably need to adjust them. Are you running the original flat tops or does your car have the roundtop SUs?

[1980_280zx?]

Sounds more like a timeing issue. If it's backfiring through the carbs your timing is most likely off a few degrees.

[Pir0San]

advance your timing a little bit, that's what the problem was with my backfiring.

[Kyle]

Dashpot oil; if it's too thin or too low, the dashpots rise too fast, killing air velocity, leaving a gulp of fuel in the intake, ka-BOOM.

Leastways, the backfire is the way I know I need to add oil. :-D

Too lean will make that happen as well, probably for a similar reason.

[Ramses]

The carberators are the round su type. I cleaned them out yesterday and tried to advance the timing and found the bolt that holds the distributor to the adjusting plate was missing. It was real easy to time, but it would not stay timed. I pulled the distributor and got the bolt out with several easy outs. Fixed the problem And now runs great.

My windshield and back window are being re-installed today, then I am at a stopping point. Seats then carpet and a major cleaning job. I have been working on her for about 6 months.

Thanks again

[bjhines]

Lean running will cause the carbys to hiccup... it is typical for most carbys... check float levels and check operation of the needle and seats...

Most commonly... a lean condition at startup will cause that... considering the original "choke" mechanism is set up wrong on most SUs...

You generally have to apply full choke to start and then gradually reduce choke until the engine is warm... or it will hiccup...

The key is to get everything functioning and moving freely and then fine tune the bent rod to give just a few hundred extra RPMs at idle full choke... and then gradually reduce RPM to normal as you return the choke lever to the warm running position...

The needle must drop enough at full choke to provide extra fuel... and the extra fuel and RPM increase must also be calibrated to work together as you decrease choke action...

The choke system will work properly assuming you have everything else on the carbys set up properly... things like improper float levels, improper needle seating, improperly bent actuator rods, etc, will cause problems starting on cold days...