Zenith troubleshooting needed

[milwaukeesk]

I’m looking to tap into the brain trust of the zenith experts to help troubleshoot my situation. I’m certainly no expert here but learning many of the nuances of these carbs quickly. I’m set on wanting to make these work as I switched back from Webers as I value the originality in this case.

I purchased 2 fully rebuilt zenith carbs. They look beautiful... but clearly once clearly has some issues that I need to sort out. I installed as is initially after correcting what I understood needed to be done with bench settings which were way off. Carbs were rebuilt with the inferior Walker rebuild kits also for whatever that’s worth. Knowing it was the walker I went back and trimmed the gasket that can restrict float movement just in case. Additionally I noticed the replacement accelerator pumps that were installed were binding up so I pulled an original pair out of an old set of carbs I had and used those instead with with new rubber gaskets. This seemed to work well. The carbs have the replacement float valves installed (with the pin, not the bearing). I left those in as they seem fine but debated putting back in the original. Not sure if I should be checking anything else.

Issue: One carb seems to be operating as it should. My issue seems to be with the other carb. On that one, it seems to be dripping a lot of gas into the throttle body. Not out of the overflow tube, just the regular spot but it’s dripping rather fast. Also, when I attempt to adjust the air mixture screw no matter how much I adjust it seems to make no difference in how the car runs. I would think the obvious assumption is that I have a bad vacuum leak somewhere but I’m not finding it but maybe not looking in the right spots either. I should say that this is the carb that I have the vacuum hooked up for the brake booster as well as the distributor. One other thing I noticed is when idling if I reach underneath and activate the secondary mechanism, the carb that seems fine revs up smoothly. When I perform the same on the leaking carb it bogs down. I think that’s it on what it most recognizable as being off.

Any advice on if this sounds familiar and how to tackle trouble shooting would be greatly appreciated.

 

[Peter Coomaraswamy]

Greetings young man! You may also want to connect a vacuum tube between the carbs which tends to even out the vacuum between them; I forgot what the proper name is for that tube but it helped on mine. Can you easily swap carb position? I forget how all that plumbing works since I installed the megasquirt. Can you post a couple of clear pictures- maybe someone can see if the on/off switch is in the correct position

Besides the carbs I hope everything else is going well!

 

[Stevehose]

I would replace the Walker float needle valves with the old style, check that you have the correct washer mm between the float valve and the body. Are you referring to the idle mixture screw? Remove them both and compare, I believe they have o-rings? Check their condition. Then swap them to see if the problem moves to the other carb. A pic of the flooding would be helpful.

 

[milwaukeesk]

Greetings young man! You may also want to connect a vacuum tube between the carbs which tends to even out the vacuum between them; I forgot what the proper name is for that tube but it helped on mine. Can you easily swap carb position? I forget how all that plumbing works since I installed the megasquirt. Can you post a couple of clear pictures- maybe someone can see if the on/off switch is in the correct position

Besides the carbs I hope everything else is going well!

Hey Peter, Happy New Year!

Good call on connecting the two carbs. I did in fact do that but failed to mention. I was holding off on swapping back and forth the carbs but that was certainly my last resort if I couldn't troubleshoot here... somewhat of a pain but agree it would help zero in on the issue.

 

[milwaukeesk]

I wuld replace the Walker float needle valves with the old style, check that you have the correct washer mm between the float valve and the body. Are you referring to the idle mixture screw? Remove them both and compare, I believe they have o-rings? Check their condition. Then swap them to see if the problem moves to the other carb. A pic of the flooding would be helpful.

Hi Steve,
You confirmed at least what I was thinking... I'll go through and replace the float needles back to the original. It would seem that is not the source of this issue but it very well could be so I will do so and rule that out. I'll also confirm 2mm washers for both.

Yes - was referring to idle mixture screw. When I adjust on the faulty carb it makes no difference in how it runs. Yes it has a washer, I actually pulled it out and popped on a new washer thinking maybe that was the issue but it didn't make a difference. I didn't swap with the other carb, but that's a great ideal. I will try that out later tonight and report back.

As for a pick of the flooding, I'll grab one tonight. but pulling from one of DQ's pics. the arrow is where the fuel is dripping out at a rather fast rate (not the curved overflow tube as I understand it to be).

 

[Stevehose]

Do you have a Synchronmeter to gauge airflow? If the airflow is too high at idle it can pull fuel up and dribble out. It could also render the mixture screw innefective. Also if you decide to swap the carb position, tighten the 4 screws on the underside, new gaskets can compress and need retightening.

As for a pick of the flooding, I'll grab one tonight. but pulling from one of DQ's pics. the arrow is where the fuel is dripping out at a rather fast rate (not the curved overflow tube as I understand it to be).

 

[milwaukeesk]

I typically like to close they loop on these sorts of threads when others spent time helping out. A big thanks to @Stevehose who provided some great guidance behind the scenes.

The sort take away here is that unless a "zenith" expert built your carbs you should not assume they knew what they were doing. I started with a pair that looked beautiful and seemed to be as fresh as the day they came off the assemble room floor. Upon finally taking the time to dig in deep, understand what might have been going wrong and fix them I found multiple things that were generating my issues. Those things ranging from, butterflies not moving freely, missing gaskets, or improper gaskets causing issues with blocking air passages or butterfly movement and vacuum leaks, binding accelerator pumps, air jets partially blocked, different and incorrect float valve spacers, secondary setting off, etc, etc.

It didn't take long to get a good idea of the issues and the fixes were all very intuitive. A carb dissection walk through that @deQuincey had posted awhile back was the perfect amount of guidance. The car is running mostly as it should now short of some final balancing that I'll get to in the next day or two and playing around with the choke starting high idle settings.

Lesson learned if you are having carb issues:

• The Walker kits are likely the cause of some of your issues.
• If you didn't have a zenith expert rebuild your carbs then it's likely you will have an issue or two to work out and it's worth going through them.
• Stating the obvious. It's a lot easier pulling the carbs apart on the bench than trying to do it while installed. If you suspect issues don't install and hope for the best. Go through them first.
• While carbs may appear overwhelming if not familiar, once you embrace understanding the nuances of the zeniths it's actually quite intuitive and enjoyable to make them right again.

 

[deQuincey]

I typically like to close they loop on these sorts of threads when others spent time helping out. A big thanks to @Stevehose who provided some great guidance behind the scenes.

The sort take away here is that unless a "zenith" expert built your carbs you should not assume they knew what they were doing. I started with a pair that looked beautiful and seemed to be as fresh as the day they came off the assemble room floor. Upon finally taking the time to dig in deep, understand what might have been going wrong and fix them I found multiple things that were generating my issues. Those things ranging from, butterflies not moving freely, missing gaskets, or improper gaskets causing issues with blocking air passages or butterfly movement and vacuum leaks, binding accelerator pumps, air jets partially blocked, different and incorrect float valve spacers, secondary setting off, etc, etc.

It didn't take long to get a good idea of the issues and the fixes were all very intuitive. A carb dissection walk through the @deQuincey had posted a while back was the perfect amount of guidance. The car is running mostly as it should now short of some final balancing that I'll get to in the next day or two and playing around with the close start high idle settings.

Lesson learned if you are having carb issues:

• The Walker kits are likely the cause of some of your issues.
• If you didn't have a zenith expert rebuild your carbs then it's likely you will have an issue or two to work out and it's worth going through them.
• Stating the obvious. It's a lot easier pulling the carbs apart on the bench than trying to do it while installed. If you suspect issues don't install and hope for the best. Go through them first.
• While carbs may appear overwhelming if not familiar, once you embrace understanding the nuances of the zeniths it's actually quite intuitive and enjoyable to make them right again.

well said, well done !