Carburetor Issue on Rebuilt Engine

[Steve Harrison]

Ron and Dick,...sounds like you are possibly invoking the old addage,..."most fuel problems are ignition related"
Hmmm......
: )

[Jan Balder]

Alan,

Have you reversed #3 and #4 plug wires ?

[Alan Winer]

Steve-I don't believe it's an ignition issue because, as i stated, the problem follows the carbs when they are switched.
Jan-First thing I did was check #3&4 wire orientation.
Ron-I'm confident all the orifices and passages are clear. Busy today, but tonight or tomorrow will install new float valve and check fuel pump pressure and will check float levels with the carb installed on the engine instead of my 7ft hanging gas tank. When I checked the float level after the carb was installed on the engine, it was different than it was on the bench.
This restoration, 59-T2, one of the last few made, has been going too smooth. I was wondering when the gremlins would appear.
I appreciate all your input.
Alan

[Albert Tiedemann]

Switched carburetor sides and the reverse happen...so carb related. The carbs are rebuild. The float valve does not "appear" to be sticking and the floats "look" good.
Alan

Switching carburetors on the Zenith 2NDIX is a bit more involved than just swapping complete assemblies. All major components are initially the same. Throttle bodies are assembled opposite hand and the housing placed over each is marked L or R to assure ease of identification of unmolested units or to thwart the Concours Police. The triangular opening in the throttle body must match the corresponding one in the housing. The tops do not care as they must follow the orientation of the housing regardless of which side it is mounted on. Thus to "switch" carburetors, the least amount of work required would be just to switch the entire assembly that is mounted above the throttle body.
[4 M6DIN 84 fasteners with lock washers proportioned for a socket head cap screw] The only problem that could be encountered with this type of switch is with the troublesome stripped thread at the spring mounting bracket. If the thread in the housing has been repaired with anything other than a M5 x 0.9 pitch, whatever fastener/method has been recruited must follow the original spring bracket threaded/re-threaded hole. More on this subject in a later post.

"appear"and "look"--qualitative measures at best and difficult to evaluate without test. There has been no mention other than new float valves will be tried. New--from the kit that is furnished today? Or new/tested original ones that are spring loaded and marked 1.25? Ah, the spring that balances the force[resultant] of the float rising and shuts off the valve. A lot of engineering testing here with all the fuels around the world and the newer blends now. Perhaps, that is why the real ones were/are ex$pen$ive. If I were rebuilding the carburetors, I would use Grosse-Jet["two balls do the trick"]. They are made somewhere in MA[well they used to be]. I know that Vic does not like them, but I have used them for at least 25-35 [getting old is a bitch]years without incident.

A lot of talk in this post about the float, but no mention of checking its weight. Should be on the order of 25 grams. I think that that value can be found in either the little spec book or the manual. I had a problem once with a leaking float and it was difficult to trace because it only showed up, regularly and especially on long trips to the ECHs as it occurred in about 2 hours of running. New floats--then only $58- solved the problem.

From the discussion to date, there is every indication of a fuel inlet control problem. So, Alan, I suggest new floats and use Grosse-Jets. There is nothing wrong with the standpipe for the fuel pressure if you have the headroom to use it and refill it without taking it down. Unless you have a very, very accurate pre$$ure gauge for measuring low pressures, the stand pipe will be more accurate. If you can measure and fill the standpipe to within 10 mm, the accuracy of the pressure would be <.05 % . Presuming you can buy a pressure gauge with full scale of 5 psi and accuracy of 0.1 %, mid-scale [ideal range of measurement of any bourdon tube pressure device] would be in the ballpark of the standpipe--but check the cost of such a gauge. Measuring the float level on the bench with the standpipe should not give a result on the test bed of a measured .25 inch difference. I have never tried to measure the float level in the car with P77 or with my clone aft-P77. It is just too tight. Maybe on the test bed there is more clearance. Olivier Auvray showed a Zenith Factory tool that might work, but I am sure this is the only one in existence outside the Zenith Factory.

[Alan Winer]

Well, it appears I have solved the issue. It’s not that I had any great insight, I just chased my tail long enough to achieve something. And I can’t be too specific because I made a few changes at once which never helps pinpoint the cause or cure. But it all relates to a high float bowl level, and not excessively high. Even though I checked the float level on the bench multiple times, the left carb would not hold that level when installed and this was the cause of my confusion. With the help of Ron LaDow, great advise from Carb Rescue and those on the forum I made the following changes;
1-Installed an old original float valve. Two newer versions both seemed to fail (bad batch?, maybe)
2-Measured the float bowl level on the engine and not on the bench. This showed the level had changed from the bench reading after running the engine. I was able to install the P77 tool, it was tight.
3-Brought the bowl level down to 20mm using only aluminum washers not crushable fiber ones.
4-Tightened the float valve more than I usually do to prevent leaking.
5-Changed the plugs on 3&4.

I had resolved the problem before Ab’s posting, his diagnosis and as others suggested, was correct, “there is every indication of a fuel inlet control problem.”
I has switched the carbs just to test. I switched the entire carb including the throttle bodies. When switched the throttle linkage could not be connected so I just adjusted the idle screws to keep the rpms up.

I understand how a high float level will cause the cylinders not to fire, but It still intrigues me that a high float level could fill up the starter chamber. I never noticed gas pouring into the carb.
Alan

[Craig Richter]

Before we leave Alan's post subject, I would like to endorse Ab's suggestion about using Grosse-Jets. These double-ball inlet valves require very little float movement to function correctly. This may be the reason they have gotten a bad rap in the past, because some mechanics didn't know how to set-up. But once the float drop is correct, they will last the life of your car, and no matter how hard you flog it around the corners, no flooding!
Just my 2 cents...

[Albert Tiedemann]

Switched carburetor sides and the reverse happen...so carb related. The carbs are rebuild. The float valve does not "appear" to be sticking and the floats "look" good.
Alan

Switching carburetors on the Zenith 2NDIX is a bit more involved than just swapping complete assemblies. All major components are initially the same. Throttle bodies are assembled opposite hand and the housing placed over each is marked L or R to assure ease of identification of unmolested units or to thwart the Concours Police. The triangular opening in the throttle body must match the corresponding one in the housing. The tops do not care as they must follow the orientation of the housing regardless of which side it is mounted on. Thus to "switch" carburetors, the least amount of work required would be just to switch the entire assembly that is mounted above the throttle body.
[4 M6DIN 84 fasteners with lock washers proportioned for a socket head cap screw]

Just to tidy things up a bit--especially for the new folks or those that have not done this before- I am adding this addendum to the quote.

Switching all the elements above the throttle body requires that you disconnect and remove the throttle return spring and disconnect the accelerator pump rod at the lever in the cover. On the former, note the correct orientation of the spring. When reinstalling, the longer loop is attached to the throttle plate bracket [for a reason that will become obvious when the throttle is fully depressed]. On the latter, make another orientation observation. The pump rod is installed correctly if the right hand threaded rod is installed at the lever in the cover in the hole farthest from the pivot. The right hand threaded rod will have a thin lock nut and the left hand threaded rod will have a thick nut [if you have original issue or early replacements/reproductions], otherwise observe slope of thread{right hand threads slope left and visa versa}. After you remove the 4 screws mentioned in the quote you can now switch the normally installed "right" carburetor housing and the cover as a unit onto the normally "left" throttle plate, and reinstall the 4 screws and connect the accelerator pump as above. You will need to move the spring anchor bracket to the appropriate threaded hole location in the housing such that the return spring will form an angle of 45 degrees or so when the spring is installed--correctly as above. The normally "left" elements are switch in an analogous fashion. When you have done this properly, all linkages will line up and the engine can be run "like normal".

[Mervyn Hyde]

Thanks for the tip on the angle and orientation of the return spring Ab.

[Bruce Smith]

Nice instructions Ab. Here are pictures of L/R Zeniths:

http://sparkingplugs.com/5.html

Bruce
www.cfi-auto.com