Zenith carbs. Again...

Luis A.

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After living with my slight hesitation for over a year and a half, figuring it wasn't that bad, I am now driven to get the Zenith's running perfectly after a ride in Arde's gorgeous verona coupe equipped with webers. I just couldn't believe how silky smooth and seamless power delivery is. A veritable sewing machine; better than fuel injection. I gotta think I can get the Zeniths to behave that well. So back I go into the dark rabbit hole of Zenith tuning.

My symptom is a slight hesitation (very small at idle, a non-car person would not notice it) primarily noticeable around 25-45 MPH. It's not noticeable at highway speeds. It's like a light 'coughing'.

I've replaced coil (w/ correct resistor), plugs, wires and pulled out the Pertronix in favor of points, just in case. It might be a bit better with points but it may be placebo effect. Timing and dwell correctly set. Valves were adjusted before this whole ordeal started about two years ago and I've never seen valves cause this hesitation. They don't audibly click.

Over the last year and a half I have re-gasketed and sealed the carbs and carb bases, cleaned, adjusted primary, secondary, linkages; sync'd them and tried just about every suggestion by those in the know over the last 12-18 months. I have checked for the float hanging on the gasket in the past and recall the gasket wasn't anywhere close to touching the float. I Eliminated the dribble from the rear carb at idle. Jerry's secret idle air hole test has the car run roughly when covered, which seems the correct result, right? It definitely doesn't run better when I cover the hole.

Spraying copious amounts of starting fluid on every outside surface of the carbs and base elicits no response --I don't believe I have leaks.

Here's my question. I'm troubled by the inability to actually measure the float chamber level to determine if it's correct. I once messed with the one of the floats and bent the arm slightly to try and adjust it. Could an incorrect float level cause this slight hesitation? How can I determine what the correct bowl fuel level should be so I can remove each of them and measure what it actually is and go from there. The whole washer under the ball valve thing is predicated on perfect floats...

Or am I chasing zebras and the problem is elsewhere?

Any insights? Thanks guys!
 

Stevehose

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I was able to achieve Zenith nirvana so it can be done. I didn't see anything from you on the accel pumps, did you replace these and adjust the little spigots correctly?

Regarding Jerry's secret air hole cover trick, I believe you are shooting for little or no reaction, if idle rises you are running lean, if it falls you are running rich (or vice versa, I don't remember exactly) so an idle mixture tweak is in order, perhaps the man himself can verify.

Usually an acceleration hesitation is cause by a lean condition (fuel being slower to reach the engine than air when needed quickly) so if you slowly rev it up with the screw and you reach a point of rough running, try richening the mixture to see if that makes it go away. This is also why the car has the accel pumps to cure the lean condition when accelerating by blasting raw fuel down the throats.


After living with my slight hesitation for over a year and a half, figuring it wasn't that bad, I am now driven to get the Zenith's running perfectly after a ride in Arde's gorgeous verona coupe equipped with webers. I just couldn't believe how silky smooth and seamless power delivery is. A veritable sewing machine; better than fuel injection. I gotta think I can get the Zeniths to behave that well. So back I go into the dark rabbit hole of Zenith tuning.

My symptom is a slight hesitation (very small at idle, a non-car person would not notice it) primarily noticeable around 25-45 MPH. It's not noticeable at highway speeds. It's like a light 'coughing'.

I've replaced coil (w/ correct resistor), plugs, wires and pulled out the Pertronix in favor of points, just in case. It might be a bit better with points but it may be placebo effect. Timing and dwell correctly set. Valves were adjusted before this whole ordeal started about two years ago and I've never seen valves cause this hesitation. They don't audibly click.

Over the last year and a half I have re-gasketed and sealed the carbs and carb bases, cleaned, adjusted primary, secondary, linkages; sync'd them and tried just about every suggestion by those in the know over the last 12-18 months. I have checked for the float hanging on the gasket in the past and recall the gasket wasn't anywhere close to touching the float. I Eliminated the dribble from the rear carb at idle. Jerry's secret idle air hole test has the car run roughly when covered, which seems the correct result, right? It definitely doesn't run better when I cover the hole.

Spraying copious amounts of starting fluid on every outside surface of the carbs and base elicits no response --I don't believe I have leaks.

Here's my question. I'm troubled by the inability to actually measure the float chamber level to determine if it's correct. I once messed with the one of the floats and bent the arm slightly to try and adjust it. Could an incorrect float level cause this slight hesitation? How can I determine what the correct bowl fuel level should be so I can remove each of them and measure what it actually is and go from there. The whole washer under the ball valve thing is predicated on perfect floats...

Or am I chasing zebras and the problem is elsewhere?

Any insights? Thanks guys!
 

Luis A.

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Steve, The hesitation isn't when accelerating at all. There is no hesitation then, it launches strongly. The hesitation is constant and mild but there and visible when driving at moderate speeds. At highway speeds it might be there but I think it's masked so I don't perceive it.

Question on the air hole for the idle circuit; maybe for Jerry. Isn't that air hole there to provide air for the idle fuel and make up an emulsion of fuel/air therefore there will be some response when you cover it? Do you cover yours and nothing happens to the engine?
 

Stevehose

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Ok I think of hesistation as a function of when trying to accelerate. So it's at a constant speed that it's stuttering or missing? Sounds like a lean spot if it happens at steady speed. I have 3 Webers now so I can't test the air hole, sorry.

I would think if it only happens at 25-45 mph or at a relatively low rpm and not higher would exclude the float, unless it's masked at higher rpm's. Either way, if it is not ignition related, a lack of fuel could cause it to sputter, either from supply (float) or mixture (idle jet). I don't know how to measure the floats, perhaps others can help there.

Steve, The hesitation isn't when accelerating at all. There is no hesitation then, it launches strongly. The hesitation is constant and mild but there and visible when driving at moderate speeds. At highway speeds it might be there but I think it's masked so I don't perceive it.

Question on the air hole for the idle circuit; maybe for Jerry. Isn't that air hole there to provide air for the idle fuel and make up an emulsion of fuel/air therefore there will be some response when you cover it? Do you cover yours and nothing happens to the engine?
 

KHB

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Luis, To partly answer your air hole question, covering that hole should reduce idle speed significantly. If nothing happens, you have a vacuum leak somewhere. Mine ended up being the carb base to manifold gasket.
 

Luis A.

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Does this mean the E3 is done?
Define "done"... ;)

Stan, you know some cas as never 'done', and I have a feeling that Si will be one of those.

Bumpers went on last night and all chairs are in. Planning on taking out to a nearby cruise night event tonight.

I'd say it's 99% done but that 1% will take a long time and a lot of effort
 
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