Zenith Diagnosis

[printjunky]

I'm putting the final touches on bringing my '73 SWB back to life. Sorted all the ignition issues, looks like. now it's on to fuel. Couple of gallons in the new tank; pump's working fine. But it appears I have a hurdle at the carb. My suspicions are increased by how it got rebuilt (It came uninstalled, and the car had been sitting for 8 years or more, so I figured it might need a freshening up) Bought the kit (there seems to be more than one level of kit - so for reference it was from Trevor at RF (Sorry, RN)). But the overall rebuild, including lapping the halves, took several weeks done sporadically between other projects. So I can't say for sure that I didn't do something incorrectly on the rebuild or miss (or lose!) a part.

When it was installed, and getting fuel (bowl was full), fuel was dripping out of the main circuit outlet (16 on the service bulletin diagram), but it dripped pretty unregulatedly, it appeared. And under no circumstances did I ever get any fuel jet spraying anywhere when the throttle link was moved. And that was the only thing that happened. some dripping from that horn. Now I have it back out of the vehicle, ready to diagnose or rebuild.

This is my first Zenith experience (previous Rovers had Webers) so I'm not even sure what I should be looking for to start this level of troubleshooting. I've read the service bulletin thoroughly, but I'd like some real-world examples of what to look for. I might just order another kit (unfortunately) because I'm worried I might have missed a part, or done something else wrong. But if I can narrow down what the problem might be, I might be able to avoid that or buy fewer parts. I suppose I could take remove all the jets and parts (it's broken open already) and try re-rebuilding it.

Thanks for any help.

[printjunky]

OK, let me try a shorter version. I do tend to ramble.

Any hints on what I'm looking for that might help determine if my zenith is working properly or not without the Rover running?

Car cranks, fires, but won't catch. I understand it might still be ignition, but is there any way to eliminate carb, since I think I have ign sorted?

[TriedStone]

Bought the kit (there seems to be more than one level of kit - so for reference it was from Trevor at RF (Sorry, RN)).

And under no circumstances did I ever get any fuel jet spraying anywhere when the throttle link was moved. And that was the only thing that happened. some dripping from that horn. Now I have it back out of the vehicle, ready to diagnose or rebuild.

I want to state upfront that I have not been into a Zenith but have had experience with many others (rochester, carter, aisin, solex, etc), so someone with more Zenith specific experience should chime in. With that in mind I'll proceed...

Sounds to me like the accelerator pump isn't working to start with. The carburetor should squirt fuel when the linkage is actuated. That's assuming the carb has fuel in it and the passages are not restricted.

How did you clean the carburetor? A spray can of cleaner or did you dip it in a gallon of cleaner such as Berrymans Chem Dip? If you didn't get a gallon of carburetor cleaner and soak it. It will remove old gas and varnish as well as mineral deposits. Did you make sure all the passage ways were clear and unobstructed by blowing them out with compressed air?

As for the kit. Not sure what brand Trevor sold you, but if its an All Makes I question its completeness (nothing against Trevor). If you are buying another get a genuine Zenith. RDS has them for 90 bucks.

While somewhat dangerous and not the best course of action simply pouring a little fuel down the carb to try and get it to start would rule out the ignition. Make sure you put the elbow back on top incase it backfires. Again not very safe.

There are so many variables in a carb this may be hard to diagnose online, pic's help...

If you do it correctly you can easily spend close to as much as a professionally rebuild one. But wheres the fun in that.

My$.02

[gudjeon]

My experience with Zeniths leads me to do the following: Remove the top cover along with the float assembly. Turn upside down and remove float, shaft and needle. Then use 7/16 wrench and remove seat and jet body/venturi screws (2). Systematically (one at a time) remove each jet and clean with a thin copper wire. Not catching engine on start suggests looking at the main jet and compensating jet. The jet that operates the accel pump well is a one way valve and this should be checked as well. If it sticks or leaks back, accel will be weak or non-existent. The accelerator pump jet is also a long skinny one which empties right into the throat. Make sure you use a screw driver that fits these well. Otherwise, you can snap of a portion of their head very easily.

To re and re the top potion of the carb can be done in situ. Flat screw driver, needle nose pliers for the accel link and carb/throttle interlink pins, 5/16 for choke cable, and pull off the throttle link and fuel hose. Tighten down the four main screws gradually and evenly. Over tightening these is usually what warps the cover. When assembling the top layer back on, make sure the o-ring holds the top float/jet body just proud by a tiny bit so that the o-ring is being compressed upon assembly.

I also set my float 1mm under what the specs call for (32mm I think). This keeps it from flooding and running rich on idle. If you pump is good, it will have no problem with this slight float "underset" at higher speeds.

Good luck

[printjunky]

Good call on the kit. I pinged Joe Curto. guy's got a stellar rep in the Brit carb game. Apparently he doctors his own kits and says he sometimes has downdraft 1bbl Zenith kits made up. If not, I'll go with the fully complete OEM kit from the hosts, can't find it at the moment, but I'm pretty sure I saw it there in the $90-range as well.

[Les Parker]

Hello there,

This is the link to our hosts (why go elsewhere?) Zenith carb overhaul kit.
Available from our stock.


http://www.roversnorth.com/store/p-2...s-iia-iii.aspx

[printjunky]

Les,
Thanks for the link. I have a new, never-run proline kit in it now (well in mid-disassembly).

Are there parts included in the genuine kit that do not come in the proline kit? Or are we just talking about a fit and quality difference. I ask, as this might help me diagnose if I'm missing something or imply that something included with the genuine kit should be replaced, but wasn't because I cheaped out on the proline.

[Les Parker]

I have found that the gaskets are a better fit on the Genuine kit.
This kit contains a few more jets, cotter pins and external parts.
From reading the posts, I would suggest taking the top of the carb. off again and dis-assembling the accel. pump.
This should slide easily in the bore of the body of the carb. and have only minor scoring in the bore and on the body of the accel. piston.

Hope this helps.

[printjunky]

Ok, here's what I've found so far (pics attached, not getting insert image to work using my work server - will figure it out):

On the side of the emulsion block, pump jet (the one with the little spout that goes into the throat) (#15 in the Zenith bulletin) has a plug on top of it, and when I removed that plug, it appears that the jet itself cannot be removed - no slot on top to turn it out. (I do have a replacement from the kit I got). So either this one's different, or the top of the jet is broken or stripped. Any advice on getting out? Should I try? It appears clear.

Also, the Accelerator Pump Piston (bulletin #12) looks like it's in good shape, but after disassembly, the ball that acts as the non-return inlet for the pump (bulletin #11) is looser than I remember it. Still captive, but it rattles around, which I guess makes sense considering how it works, but I don't remember it being loose in there at all, previously. It's seated well, and held in by the clip.

I tried blowing through the pump hole, while blocking the top (where the ball goes) and I expected to get air through the pump jet mentioned above, but got indeterminate results. Anyone know what I should expect there?

[printjunky]

And one other thing I noticed, the progression holes (Bulletin #24) are wide open. In the bulletin, it looks like the exterior hole is plugged with something, but I don't know what. Nothing I have in the rebuild kit or spares seems like it would fit there.

Everything else seems to be intact or to work - allows air to blow through where expected, etc.