Zenith Help

[HB Chris]

Chamonix is running rough. I checked green wire at coil, 11.45v and 8.0 after the ballast, with jumper from battery 12.4V and close to 9v after ballast. Don’t think this is a problem, coil checked out OK at 3K ohms primary and 9K secondary and it is new (black with 1.1 ohm ballast) as are points which I checked, condenser, cap, rotor, wires and plugs.

Runs like crap when cold, much smoother warm but something isn’t right. When cold chokes close and open progressively but it doesn’t have a fast idle, I have to hold it until it warms up. I have rotated the choke housing to a richer position. I pulled Zenith top case off on Sunday, cleaned idle air jet and upper jets on main and secondary. Maybe I need to pull again as in bottom of the 2nd stack are the other main and secondary jets, mixing/emulsion tubes run between the two. Will talk to Don’s expert tomorrow, another frustration on the road to completion.

 

[Arde]

DQ had mastered the Zeniths I believe. His input may be useful also.

 

[Stevehose]

Have you confirmed that the secondary bbls aren’t leaking air? Will the fast idle linkage adjustments not adjust/hold? If rebuilt, have you retightened the 4 bolts that hold the bodies together from below and then the bolts to the manifold? If you cover the small vent hole on top does the idle speed change - this would indicate either rich or lean depending on if it goes up or down.

 

[stphers]

hi Chris, did you adj the fast idle screws? They are a real pain in the ass to get to. There is a small opening at the bottom of the choke housing to wards the eng side, if you slowly rotate the accelerator, the head of the screw will appear and with a thin blade screwdriver, you can adjust it If you aren't at at least 1300-1400 rom cold, then the extra richness in the carb will bog the engine down. You may want to take the choke housing off an d check the fast idle set up ( and you can see that special adj screw ) just the three small screws, better.

Another failure area ( even with brand new ones , which are garbage ) is the o ring in the secondary base gasket, the thick one, does not seal properly and you don't get a good vacuum signal from there. I like to use the originals with a little sanding and new o rings

I like Zeniths and if they are set up right , work quite well and give decent power and fuel consumption Too bad I missed you in May, would have had fun setting them up with you.

Thanks, Rick

 

[bavbob]

I was wondering about that little box on the side of the carb, basically a cold start valve. You can pull it and try a hair dryer to see if it functions.

 

[HB Chris]

hi Chris, did you adj the fast idle screws? They are a real pain in the ass to get to. There is a small opening at the bottom of the choke housing to wards the eng side, if you slowly rotate the accelerator, the head of the screw will appear and with a thin blade screwdriver, you can adjust it If you aren't at at least 1300-1400 rom cold, then the extra richness in the carb will bog the engine down. You may want to take the choke housing off an d check the fast idle set up ( and you can see that special adj screw ) just the three small screws, better.

Another failure area ( even with brand new ones , which are garbage ) is the o ring in the secondary base gasket, the thick one, does not seal properly and you don't get a good vacuum signal from there. I like to use the originals with a little sanding and new o rings

I like Zeniths and if they are set up right , work quite well and give decent power and fuel consumption Too bad I missed you in May, would have had fun setting them up with you.

Thanks, Rick

Rick, I have been thinking this is the issue, I have been studying the Blue Book on this (fast idle screws in choke housing), Cain suggested the same thing.

Rob, I have power to the water chokes and enrichment device on side of carb, they are grounded by the temp sensor under front manifold which opens at a preset temp to disable. I may disconnect the sensor and see what happens too

Steve, I will try to find that hole and cover it. Carbs were not rebuilt, just accelerator pumps. Car ran fine after five speed swap coming back from Rey’s 30 miles on freeway in November. Maybe we have too much on the idle richness screw to compensate for a clogged idle air jet. I understand these carbs much better now after removing the top stack and plan to remove next stack to get to underside orifices. How do I test secondary barrels for leaking?

Thanks everyone.

 

[Stevehose]

How do I test secondary barrels for leaking?

insert the synchronmeter into the secondary bbl as best it can fit (or make an adapter of some sort) and take a reading. Fit it the same way to the other carb's bbl to get a consistent, comparable reading. It should barely pull any air - the butterfly is supposed to have a very small opening to keep it from binding shut but that's all. Let us know what your readings are. I block the fan turbulence with a piece of cardboard for doing carb readings.

 

[HB Chris]

Thanks Steve, we the meter on a cool whip cup right now!

 

[Stevehose]

Thanks Steve, we the meter on a cool whip cup right now!

Yeah, thats good for synching once the secondaries are confirmed to be behaving

 

[bavbob]

deQ idea I used and it helped. When all is said and done with issue solved, run a vacuum hose from the base of one carb to the other to smooth them out.

 

[KHB]

The vacuum created once the engine starts should cause the chokes to open slightly. So if it still runs rough even though you've increased the RPM, it could be an issue with the small diagram in the triangle shaped housing.

 

[HB Chris]

The vacuum created once the engine starts should cause the chokes to open slightly. So if it still runs rough even though you've increased the RPM, it could be an issue with the small diagram in the triangle shaped housing.

Thank you Kevin!

 

[HB Chris]

deQ idea I used and it helped. When all is said and done with issue solved, run a vacuum hose from the base of one carb to the other to smooth them out.

I did this on Malaga back when it still had carbs and I could not tell any difference. Steve was a proponent of this as well as I recall.

 

[HB Chris]

Paul Cain says it could be float needles, a well known issue which he struggled with in his 74 that sold last year.

 

[Luis A.]

coil checked out OK at 3K ohms primary and 9K secondary and it is new (black with 1.1 ohm ballast)

I assume you meant 3 ohms, not 3K ohms…?

 

[Stevehose]

I did this on Malaga back when it still had carbs and I could not tell any difference. Steve was a proponent of this as well as I recall.

Yes it helped a little, based on experiments with a balance pipe system on my triples, I believe the smoothness comes from added slight richness with the pipe allowing residual mixture to be sucked in from the other manifold(s). I never confirmed it on Zeniths but did on the triples.

 

[deQuincey]

hi Chris, did you adj the fast idle screws? They are a real pain in the ass to get to. There is a small opening at the bottom of the choke housing to wards the eng side, if you slowly rotate the accelerator, the head of the screw will appear and with a thin blade screwdriver, you can adjust it If you aren't at at least 1300-1400 rom cold, then the extra richness in the carb will bog the engine down. You may want to take the choke housing off an d check the fast idle set up ( and you can see that special adj screw ) just the three small screws, better.

Another failure area ( even with brand new ones , which are garbage ) is the o ring in the secondary base gasket, the thick one, does not seal properly and you don't get a good vacuum signal from there. I like to use the originals with a little sanding and new o rings

I like Zeniths and if they are set up right , work quite well and give decent power and fuel consumption Too bad I missed you in May, would have had fun setting them up with you.

Thanks, Rick

you are very right Rick,
fast iddle screws are something to do right, and very difficult to access
bad thing if you can not count on a solid ground
first thing is to redo them completely so you know where you are as Steve mentioned too, leaks can be a pain to discover and solve
do not forget to set the basic settings as they will be the starting point to a synchro
there are too many things to fix or put right, once the basics are ok you will only fiddle with known parameters

 

[HB Chris]

I assume you meant 3 ohms, not 3K ohms…?

Yes!

 

[HB Chris]

Rick, I spent three hours removing front carb pieces, cleaned all jets and replaced float valve, cleaned carb components, dialed in the fast idle parts I which I finally figured out means top cover had to be back on to close choke completely, adjust the butterfly valve (?) to 1.5mm to the lever inside choke housing, turned in the fast idle screw one turn as it is so hard to tell where it is resting (I did this by opening throttle so screw was horizontal). I also made sure housing is rotated to the notch for initial setting. Tomorrow I will do the rear carb.

 

[stphers]

From what I can remember, one full turn on the fast idle screw is about 300 rpm One way to really check is to remove the choke housing away from he carb, won't lose any coolant. Than open throttle all the way, close choke flap to a 3/16 drill bit, let the throttle go and see where the fast idle screw is sitting on what should be the highest step on the fast idle cam inside the choke housing Good idea that some one had about checking the choke release diaphragm, it is needed so when the choke flap is closed, when eng is cold, this vacuum diaphragm just cracks open the choke flap so there is at least some air able to get into the carb. Good to do the frt carb first and learn about it cause the rear ones a bitch! Each carb should be set at about 1400-1600 rpm individually, once together should start at about 1400 and slowly come down to idle

Biggest issue with these carbs is vacuum and correct gaskets and most important, flat surfaces. The more everyone tightens all the different section screws, the more the plates get distorted and vacuum doesn't always goes where it is suppose to

Usually sec don't leak a lot, the secondary stop set set screw can only be accessed when the carb is off the car and is usually pretty frigging hard to turn

Once you get the carb fast idle set up, you can hook up the linkage and make the adj mostly on the rear carb.

Thanks, Rick