Rear carb not working?

[Xargon321]

well i got back to tuning my z and i get the front somewhat tuned and go to the rear car, when i press the lifting pin to check the mixture it dont do anything!! i even pushed up the piston with my finger and it didnt do anything. its is moving smoothy and it does suck air, need help please

[Xargon321]

forgot to add that i am getting fuel to the rear carb and itll will run so im getting spark but i dont know why raising the piston in the carb has no effect what so ever.

[beandip]

when you raise the piston of the rear carb and the engine still runs smoothly it is because the front carb is way toooo RICH.

[Xargon321]

then what whould it be? the needle and seat are new the float.. floats and the mixture nut was turned all the way in... in tuning the front carb when i push the piston it wants to stall the engine, this indicated a lean condition right?

[beandip]

When you lift the piston of one carb you are disabling it and testing the other carb to see if it is set too lean or too rich. If it is to rich then the engine will continue to run rather smoothly if it dies then the carb is to lean. adjust accordingly and then repetet the test on the other carb. If the carberator is adjusted properly the engine should continue to run but stumble when the other piston is raised. Usually a starting place is the adjusters turned counter clock wise about 21/4 turns from the stop. Hope this helps .

[Xargon321]

Lifting the piston disables the carb? woudnt that let more fuel in?

they are both set at two turns down, floats are at 15mm, the only thing is that the rear carb needle and seat seems firmer then the front the rear float dosent go down as far as the front one, will check the spring to see if its the right one.

[beandip]

Yes it disables the carb when you lift the piston . And no it dosent increse the fuel flow. Disables means just that it dosent work when the piston is lifted. So to repeat when you lift the piston on t he rear carb, you are then running on the front one only and if the engine dies then the front carb is set too lean. If the engine keeps running rather smoothly then the front carb is too rich . When you lift the piston of one carb the engine should stumble and still keep running !

[Victor Laury]

Originally posted by Xargon321

the only thing is that the rear carb needle and seat seems firmer then the front the rear float dosent go down as far as the front one, will check the spring to see if its the right one.

Whoa! that no small problem. That would account for MANY troubles while trying to set your carbs. This must be corrected first.

What most likely happening is the needle and nozzle are out of alignment. Remove the dome and wipe the interior clean as well as the outer ring of the piston. Don't want any dirt hanging things up. remove the piston carfully and inspect the sides of the needle, near the top (thickest part) for scraping marks. Inspect the nozzle orifice for wear.

The Absolute-correct way to align the nozzle and needle is with an alignment tool. But these tools are not common and you really can't do it with the carbs installed. (Well maybe but it would be a pain).

On the ZTherapy tape, Scott demonstrates a short-cut alignment by slightly bending the choke actuator (flat bar that attaches to the bottom of the nozzle) I was sceptical, Then a roadster owner stopped by for a tune up. Her front carb piston was not returning with the desired "Thunk". I didn't want to dissassmble her car too much, so I tried the "Scott Brunning Choke Tweak Manuver" and it worked.

With the alignment tool, you remove the piston, and nozzle. Insert the tool in place of the piston. Loosen the nozzle guide nut (The top nut on the guide tube which holds it in place on the trottle body). Reinstall the dome over the tool and tighten it down. Then you retighten the guide nut. Take off the dome, replace the nozzle, replace the piston and reinstall the dome.

[beandip]

Victor , I bow to the master. :classic:

[Xargon321]

i was talking float needle and seat, but thanks for the info, it turns out that the rear carb got way out of sync :stupid: now i have it where itll stumble and keep running.

[beandip]

BINGO !