Thread: Zenith Carb, new. (any good?)

Hi Ash,

It is usually helpful to have a tacho but it can be done by ear. If you screw it in until it is just starting to die then back off about 1/2 to 1 turn it should run smoothly. If you have a tacho you back it off until the revs are at their highest then usually put it back in about 1/4 of a turn from there. Timing has a very critical effect on idle speed and the perfect mixture so it is really a matter of adjusting everything then checking and resetting the timing, then adjusting everything again, then checking and resetting timing ..........., until you get it perfect. also though John is right about the idle speed for early motors the later ones with pollution control recommend an idle speed of 800 rpm. If the pollution control has been removed or blocked, which is very common, then you can lower it down again. I still tend to only go to about 600. Later motors also have a different timing setting to the earlier ones. I found though that if I used the timing and idle speed settings according to the later motor specs that i could not get the carbie to work properly so I advanced the timing and then I could get the carbie set right. Basically, play with it, drive it. and get it to where you are happy with the set up (play around anywhere from 500 - 800 rpm and timing anywhere from 6 before to 6 after but probably as far towards the required after as you can). Test drive to make sure it is not knocking under load if you have it fairly far advanced.

Hope that helps .

TimJ.

and yes, turning the mixture screw in makes it leaner.

Thanks a lot Tim, great info.

Just on the timing. If I set 6 BTDC I feel it is very down on power, it gets even worse if you retard it any further than that.

The best running I have found is pretty far advanced, it must be like 12 degrees at least!
I set using a strobe.

I'm pretty sure this is doing bad things to the mixture but cant see any way around it.

Whats your take on this?

Originally Posted by ashhhhh

The best running I have found is pretty far advanced, it must be like 12 degrees at least!
I set using a strobe.

I assume you have disconnected the vacuum advance and blocked the pipe to the inlet manifold and are testing at about 600-800 rpm?

Yep, sure have.

Hi Ash,

Mine is a 78 and has a plate in the engine bay that specifies timing and idle speed as 6 deg ATDC and idle speed as 800 rpm. I am assuming that mine is an 8:1 compression engine but haven't been able to verify that completely. There are a number of timing marks and if you are looking from the front of the engine ATDC will be to the right and BTDC to the left. When you rev the engine it will advance and that means further before top dead centre. Aplogies if I sound like I am repeating things but it sounded like you had it the wrong way round from your post above. I have mine set pretty much on TDC as that seems to work. If I put it on the 6 after that it is supposed to be and the revs at 800 it will not even continue to idle, it just dies, but all the pollution control was taken off before I owned it. I think if you put it too far advanced then it will knock under heavy acceleration. Also make sure that your points are set properly before you set timing. Use a dwell gauge while running or feeler gauges while not.

TimJ.

Also I looked at the plate before and it said to set with the vacuum line connected but that differs from what I have always done. That is for full pollution control though.

Timj.

No thats fine, probably my description was just bad.
I also have the setup with a jagged set of timing pointers. As you say ATDC on the right and BTDC on the left when looking down on it from the front.

If I set to 6 BTDC (left most marker) its not good.
I have to go FURTHER left than that marker, maybe about 20mm further!
It doesn't run on, it doesn't detonate.
Im starting to think my timing chain is stretched or something??

It generally runs well expect that the mixture doesn't seem to adjust quite as I think it should. (exhaust is a bit "puffy")

Has anyone got an audio clip so I can hear what it SHOULD sound like?
I dont know anyone else who owns one locally so I have no comparison.