Zenith issues

AndyP

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Guys,

just checking before I rip it apart on a long weekend. At around 4k RPM needle flicker and engine stutter. This happens in all gears. Has new fuel pump. Am assuming my carbs are gunked up but don't understand why the car would run at all if the carbs need to be cleaned. Runs like a champ when it's cold - pulls nicely to the 4k RPM threshold, but am having problems getting it to start when car is warm. Every now and then a little engine sputter after ignition is off. Carbs? Will I damage anything if I continue to drive it? Thanks in advance for your insights.
 

velocewest

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Sounds more like an igntion system issue than carbs. Check condition of points and check dwell/gap. Check to see if the advance plate in the dizzy is binding. Make sure you don't have a bunch of play in the dizzy shaft, it could be moving under load and changing the dwell. If the points need replacement, might as well grab a Pertronix so you don't have to deal with them again.

Also could be coil. If the coil is dying, it might not be able to recover at higher RPM, and might be weaker when warm.

Could also be worn out plug wires.

Other than the secondary circuit, carb problems tend to manifest at or just off idle, not under load at higher RPMs.
 

CookeD

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V - He should not be having a dizzy advance problem that far up the tach, though if it's only sporadic...? It would start earlier and/or continue/get worse with revs. Seems like a spark delivery problem would also be earlier than 4K...

If you're also having hot-start problems, I'm going with initial diagnosis-- fuel/carbs. Sounds like the carbs are going rich via the secondary circuit, and the secondary circuit is also loading up with fuel once warm and causing a flooding issue at start-up.

Have you ruled a vacuum leak out? Vacuum leaks can cause all kinds of weird things.

Good luck.
 

Malc

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I can't be 100% certain but I suspect that Zeniths are similar to Deloroto's, Webers etc. I have set a lot of them up on other cars so here are the basics

Float chambers - no sticky valves, both set up correctly - often causes flooding if leaking and or not seating properly
linkages - no "slop" ie both open and close at the same rate.
Jets - no blockages.

Fuel pump, especially mechanical - bad diaphram, some have internal filter gauzes which get blocked

If you get really stuck I could find the correct bits of the official workshop manual - let me know
Cheers
Malc
 

velocewest

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I'm sticking to ignition issues. Zenith secondaries are vacuum, and their most common failure mode is not actuating at all because the diaphragm leaks and won't hold vacuum, or the throttle plate sticks.

The only symptom I would immediately attribute to the carbs is the dieseling. Could be an idle cutoff solenoid problem.

I'm leaning more to coil or plug wires, but I'd check the dizzy too.

I think we need a pool on this one! :)
 

AndyP

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Thank you!

Guys, thanks for all the feedback and ideas. If I had a "pool" you'd all be here having beers with me. I'll let you know when I build it. :D

I am going to trouble shoot this based on your recommendations. Plug wires are brand new and so are the plugs. Coil is an old blue Bosch - will start with that one, work my way to the dizzy, vacuum, check the carb secondaries, etc.


Thanks.
 

Tom M

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Andy
Start by checking the condition of the points. If they are pitted or the dwell is wrong you will have a problem with the higher revs and warm start.
If they are pitted, replace the condenser also. It needs to be matched to the coil to have good point life.
 

AndyP

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still (not) working on it

Guys - quick update on my issues. Have not been working on my baby but rather on my other two 3-month old babies. The wife made it clear in that female way we all love that the nursery takes precedence. :) I'll let you know when I go through the checklist you recommended, stay tuned.
 

AndyP

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I think it's fixed.

Guys - quick update on what's going on. Decided to get the Crane Cam and a new coil (red), put everything in and it seems to have fixed the issue. Did not find a vacuum leak. Car idles very smoothly around 1k, the speedo jitter at 4k is gone and I am actually able to push beyond 5k. Haven't taken it all out yet and still need to adjust timing a little - it's not running 100% smooth when coasting. But at least I know I don't have to rebuild the carbs yet. So thanks again for the advice. Oh yeah - I put the Crane control unit right next to the radiator on the top front bracket. Seemed to be the best spot, or am I asking for trouble?
 

velocewest

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How difficult and expensive is it to correctly and completely re-build Zenith's? Is there a "specialist" shop that does this?
I've rebuilt a couple sets, I'd rate them a 5 on a scale of 1-10 for difficulty of carbs I've rebuilt (a VW solex is a 1, the Mikuni on my '88 Montero was a 10). All the instructions are available in the tech links from this site. Complete rebuild kits (including the diaphragms from the secondary actuators) are about $40 each IIRC.
 
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