Zenith Wont Idle

[DesignerV]

Hello Everyone. I’m a new guy here, but have been trying to read up quite a bit, as I recently purchased my first Land Rover Vehicle. It’s a 1970 and has the 2.25 petrol engine. Had Jeeps for years, but never one of these.

I’m having a lot of trouble getting it to idle without being choked. Off idle, at around 1500 or 2000 rpm it will run great with no choke. But as soon as I let off the throttle it winds down to a stop.

When it does idle, its somewhat lumpy, but with no rhythm.
So, I fiddle with the idle setting and the idle mixture to no avail.

It dies at any idle setting below about 1000 if no choke, and the mixture screw seems to have no effect.
Makes a loud sucking sound from the carb when it dies.

I just rebuild and “fixed” the zenith, per the direction here:
http://c0007716.cdn2.cloudfiles.rack...ns/RNC959I.pdf
Lapping both, replacing all gaskets, and plugging the port shown in the directions.
I also verified that the fuel pump is working, and I think it was recently replaced or rebuilt. I also replaced the fuel filter. Doesn’t appear to be a problem there.

I have sprayed water and wd-40 around the joints to look for vacuum leaks, none found.
I was able to get it to run a little more smoothly by slapping my hand across the inlet until it slowed and then removing.

It has a crane fireball ignition system, installed by the previous owner. When I mess with the adjustment knob on the distributor, I get no changes.

Only thing that I can think of at this point, is timing or ignition might be the issue.
Perhaps I will replace the spark plugs and wires, and the coil?

I’m not sure how to check the timing but I could probably read my green bible and find out.

Any help or suggestions would be appreciated, I really just want to get this thing going!

[Opabob]

Do you have a vacuum Booster for the brake? I eventually discovered that was leaking enough to cause idle problems. Just a thought.

[DesignerV]

You know, that occurred to me while I was having dinner, but wasn't sure if that could happen. Good input. Will try blocking that off next. Thanks!


Update: I tried removing the hose to the booster and plugging the port, but to no avail.
Took some videos and a picture the I'll post shortly.

[DesignerV]

Well, tonight I messed with it some more but go not progress. I did record a video of it running, to see if anyone might have suggestions there. In the video I was holding the choke plate open, but the high idle was active from the lever supporting the throttle plate. It tries to die at one point. It is running very lump in the video, but i think it's hard to tell past all the sucking noises from the carburetor. Any suggestions?




Also, would adjusting the thumbwheel on the distributor have an effect on the slow running if I have the Crane points conversion unit inside? The book says to initially set it at four lines showing on the vacuum tube side, but I can't see any marking there, so I set it in the middle-ish.


Lastly, just a picture with the lights on for fun.



Thanks Everyone!

Update: I also got my first "What year is that Jeep?" Tonight...

[SafeAirOne]

If you're positive there's no vacuum leak anywhere, and you can't get any satisfaction by adjusting the idle screw, then I might investigate a possible obstruction in the idle fuel circuit or it's vent system, as it'll take more vacuum to suck a sufficient amount of fuel into the venturi to get a good idle, meaning that you'll have to either choke it a bit to increase the vacuum or increase the airflow (bring the RPM up).

This is, of course, presuming your ignition system is working well.

Good gouge on the Zenith carb can be found here: http://www.carolinarovers.info/compo...l?download=134

[DesignerV]

Thanks Mark, enjoyed reading that!
Truthfully, I'm still not positive about there not being a vacuum leak. I am going to try a smoke test next. After that, I will probably dismantle the carb again for three things: checking the idle circuit like you mentioned, unblocking the port that I blocked since more reading tells me that it's part of the economy valve circuit, and checking the floats again. I noticed that the green book says 33 mm, and that's what's listed in this Document for rubber floats, whereas mine are black plastic, which I'm figuring is nylon and should be set to 31mm. Not sure if that will make a difference...will try it out tomorrow evening.

http://5037e1fccabb179f1658-62e5af32...arburetter.pdf

If not, then ignition work might commence...

Thanks again!

[Revtor]

Does your carb have an Anti-dies eling solenoid? If you've got one it may very well be bad,(or the wiring to it bad) thus closing off your idle circuit....
-steve

[DesignerV]

Hi Steve,
This one doesn't have the emissions additions on it, just a plain old early version. Good thought though. Thanks!

So, tonight I made a smoke device out of some tube, a cigar, and a water bottle. It worked really well at generating smoke, but for better or worse, the only place I could get smoke to come out of, and only then under reasonable pressure, was the part where the choke shaft enters the body. Also tried pushing it through the brake booster but couldn't see any coming out of there when I tried.



The smoke coming from the shaft.


So, after that was done I pulled the carb off again and opened it up.
I have the black plastic floats, and one of them has been filling up with gas. I had sealed it with some fuel-resistant sealer, but it has not worked, it was full again. I'll use JB Weld this time and hopefully it's better.
Otherwise, I unplugged the economy vent port, and blew out all the slow running tubes in the emulsion and top plates, in hopes that it might get better. Does the slow running jet have a little spring valve in it? I was wondering if the rebuild kit spring worked a little different than the old one, so I cleaned the old one out and put it back in.



I'll try to reassemble later this week, and provide an update then!

[Les Parker]

Another thought is to check the valve clearances, especially if it has not been done for some time.
That and the ignition timing, plus a new float in the carb. could get it running like a sewing machine again.

2p

[DesignerV]

Les, Thanks for the input!
I have no idea of the history of this engine, so it's probably not a bad idea to check that stuff.

I found this article, which I think discusses valve clearances, but I will need to cross-reference that with the Green Book to know what the heck I'm looking at. Is this the sort of adjustment that you meant?
http://www.lrfaq.org/Series/FAQ.S.tuning_2.25l.html

I actually don't know how to set the ignition timing... Might be time to learn!

Last night the JB Weld went on the leaky float. Splined it pretty thin, but will sand it a bit to reduce any possible weight increase.