Zenith purgatory

[Neubie]

Ok, so I was having issues with my carbs after changing the points and plugs...!?! I have since pulled off the carbs, cleaned everything, blown out all passages, replaced float valves, (even though old ones seemed to be fine) replaced totally shot secondaries, replaced mixture screws (old ones had a shoulder or step filed into the first 1/8" or so instead of pointy all the way in) regasketed and reassembled. The car is still having the some serious issues. It will start up fine, run ok for about 4 or 5 seconds, and then die. Serious applications of throttle kinda keep it lugging along, sounding very unhealthy, but running, occasionally getting some revs out of it, but I can keep this up for only 20 or 30 seconds at best. Really, it sounds to my untrained ear like its getting too much fuel somehow, yet wont idle by itself.

I've read through all the posts about tuning zeniths, and the Jamie Kopp manual, have set the mixture screws at about 2 turns out, dashpot seems to be in the right place. Throttle linkages haven't changed since it was last running well. Idle speed adjust is set high at the moment, only because it was completely stalling out before I rebuilt the carbs if it wasn't cranked way up. Not sure if this would affect its present problems, but I cant get it to idle well enough to set it properly anyway....

Ive run out of ideas to diagnose the problem, and run out of time (Car has been parked on city street for at least 3 weeks, an eternity in downtown San Diego...) and the city is threatening to tow it..

I hesitate to think its the ignition side of it, the timing isnt really on, but it runs well enough to start. Not well enough to time it properly till i can get it to idle...points were set properly., Ive thought about changing the new set out and back to the old pitted corroded set, but that seems like grasping at straws.

I realize from my formers posts at trying to solve this issue that it is difficult over the internet, but I am hoping I at least eliminated some possibilities? Any words of wisdom?

[Blue 72 250]

I would get it towed before the city does it for a crazy amount of cash. If you are worried about the $, get a AAA membership and get it towed, you will save more in tow than the cost of membership. The carbs can take some time to get right and the city street is not a great place to do that.

[Neubie]

No, not a good place to work, talk about adding to frustration! I can play cat and mouse with them for a while...unfortunately I have nowhere to really tow it to, so fixing is the way forward.

Discovered a few things this am tinkering, front carb the fuel level in the bowl was quite low. Also, the float bowl vent valve is pushed all the way in on the front carb when the throttle is at rest, where as on the rear carb it is just touching. The rod connecting the gas pedal portion of the linkage to the carb has been modified by a PO at some point, and is at full extention. it needs to be longer to push the lever aft in order to release the float bowl vent valve at rest. Are these problems linked? I tried extending the idle stop screw but it doesn't go far ewnough to prevent the lever from pushing in the vent valve.

Head scratching continues....

Marc

[Benzcrusher]

Call 1-800-4ME-RCED

and they'll tow it for free to you local MB dealership...

[230/8]

MArc:

From your description I suspect your problem is with the carb adjustments...I would be guessing that some uninformed mechanic has tried to adjust them in the past and totally botched it. Zenith equipped cars are really quite reliable if they are worked on by knowledgable folks who have the proper tools. If the Zeniths are out of whack, they will mimic symptoms for other things, like timing, point dwell, bad wires, lean jets, bad fuel pump, etc.

Just get them tended to by an experienced MB man with Zenith knowledge and tools, and I bet all your troubles go away. This site has a wealth of information on dealing with these old carbs. USe it and get the tools if you want to do the work yourself. The vent bowl observation tells me the connecting linkage may be wrong. Disconnect it and check the vents. When the engine is off the linkage should just crack the vents open to prevent hot vapor flooding. When you connect the connecting link between the carbs the affect should be neutral on the carbs. That is why you adjust the carbs with it off, set idle speed, balance and mixture, etc with it off and then adjust its length and re-connect it so it does not alter those basic settings. Then you can do the dash pot adjustments for in-gear idle speed etc with all the linkage hooked up.

You must use the proper tools to balance Zeniths, listening to each carb with a piece of rubber hose is a waste of time regardless what others might try to tell you.

230/8

[Blue 72 250]

if you are working outside of your house on the car, to avoid having the car towed, try to keep a close eye on the tires for marked by the parking Nazi's. If they are still persistant, one of your neighbors is the snitch.

I may be beating a dead horse.... but, Backing up to the timing, are you positive that you have a clean and reliable spark? Timing light gives you a constant reading on the scale regardless of the poor running of the carbs? you will be chasing a phantom without it.

[Neubie]

Not beating a dead horse Blue, Im always open to overlooked options. Problem is at the moment, its not running well enough to even think about timing it. Even with someone else at the key, it wont run well enough or long enough to get anything useful out of a timing light. Ive tried rotating distributor both with it running and incrementally between starts, and the current position is the best I can come up with. I.E. it at least starts and attempts to run. Spark is strong.

Nice to know about free towing to dealerships, but methinks thats a bit like the free lunch they offer at strip clubs...cheep to get in, pricey to get out.

230-to some extent that uninformed mechanic is me, but also of note, the carbs were working while in my care, this isnt a case of getting a car that wasnt running properly to begin with. The only adjustments I've made to the carbs prior to their recent problems and subsequent rebuild were the idle speed adjust (coil and nut type on rear of carb) and the mixture screws. not the linkage, not the fast idle, nothing else. While I realize these have an effect on how the carbs run, there are also only so many combinations and its fairly easy to undo any damage here. that is the frustrating thing about this whole endeavour, I don't understand quite what went wrong or how...

"Just get them tended to by an experienced MB man with Zenith knowledge and tools, and I bet all your troubles go away. "

Yep, I agree. But again, It would have to be towed to a mech. between that and the cost of professional help would quickly exceed the value of the car. While I enjoy driving her, I've already passed the rational limit for energy and money dumped into it. Frustrating as it is, I know its something that can be done. After all, as I said earlier, it was running ok, and I didn't change all that much. Ive seen people ressurect much worse problems with the help from this board. I keep sifting through the posts, and keep trying what I can think of. I'll get it!

"The vent bowl observation tells me the connecting linkage may be wrong. Disconnect it and check the vents. When the engine is off the linkage should just crack the vents open to prevent hot vapor flooding. When you connect the connecting link between the carbs the affect should be neutral on the carbs."

In order to accomplish this setting I would need to make up a longer connecting rod between the fwd carb and the pivoting arm that eventually connects to the accelerator pedal. Both are at max adjust and it still needs about 3/4". IE to connect the socket on the connecting rod to the ball of the throttle actuator I need to pull the actuator forward which in turn pushes the vent up. This is the open position? I will try this, but if its a vent, I don't see how it affects the fuel level in the bowl.

Sorry for the long post, just trying to be as detailed as possible.

thanks all!

M

[230/8]

M:

You misunderstood my comment re: connecting link. I was refering to the link that connects the front carb to the rear carb. This link should be removed when balancing and otherwise adjusting the basic idle speed and mixture. Once those basic settings are done and the two carbs are in balance with the engine running smoothly, you can reconnect the link between the carbs to make the final settings for the dashpot. It is at this point when you reconnect the link that you must check its length to ensure it does not pull or push one of the carbs slightly open which would then alter your settings. It's just a matter adjustment...if it is very slightly off, (you always recheck balance after connecting the link) you can then rebalance out the small change with the link connected.

Oh, by the way, I am assuming you are making all these settings with a temporary connection between the cam cover and the manifold PCV inlet. If not, you will have a huge air leak to overcome and that will prevent proper settings on the carbs.

Hate to see you give up on the old dear. Have her towed to your place and invest a few more hours in trouble shooting; you can fix this problem.

One last thought for you: don't get too focused on ignition timing. Unless it totally out of time so that it cannot run, (off a tooth or two) you can be off a bit and be fine. There is a 3 degree tolerance in the specs and you can be much further off and it will still run pretty well...good enough to get you home.

230/8

[Neubie]

230/8-

No, won't give up on the girl. Not yet anyway. fortunately, although she is on the street, it is on the street in front of my apt. so I guess its not as bad as it could be

I think you're a bit ahead of me though with the linkage, Im having troubles getting it to run, much less tune the carbs and worry about the finer points.

This afternoon, I went out and cranked out the idle mixture screws and while it is running very rich, it at least got close enough to idleing that I could run around to the front and observe what was happening. There is a definite problem with too much fuel. There was a fuel leak around the gasket where the throttle body and the jet block meet. When I could get it to rev up, gas was literally spurting out the barrels of the carbs. and at lower RPMs, still getting droplets, not atomization out of the fwd carb. I am on the middle set of spacer washers for the float vents, and the distance is correct, just about 13/16". If I put the larger ones in, the float sits at such a strange angle, it just doesnt look right. Is there another way to control fuel level coming into the carbs other than the float valves?

I have a hose connected to the front of the fwd carb, just fwd and below where the fuel line comes in. I'm assuming this is the fuel return line, but there is no valve of any kind on it. not sure how this is supposed to work....

Re: the cam cover to manifold PCV connection. There is a old cracked hose that connects from the cam cover to the air filter when its in place, is this what you mean? The PO told me this was some kind of emissions control and didnt have any effect on the engine really. The car has been run with it disconnected pretty much the entire time I've owned it...Not sure where the PCV you're refering to is on the manifold. Could you elaborate?

[230/8]

Marc:

Forgive me, I cannot recall the specific year and model you are working on, so will make some assumptions...

There is no PCV valve. The rubber hose from the cam cover to the air filter leads crankcase vapors from the engine to the intake manifold. Remove the air filter and look at it carefully. The rubber hose connects to the AF top. Inside the AF housing there is a passage that directs the vapor through the housing and out the bottom. When you removed the air filter from the car, there should have been a small plastic pipe fitted against the bottom of the AF housing that fits to the housing with a rubber fitting. The plastic pipe connects into this rubber fitting and leads to the intake manifold down between the two carbs between the carbs and the cam cover. The engine vapors travel this route throught the AF without mingling with the inlet air. The engine vapors are sucked into the manifold below the carbs at that manifold inlet between the carbs.There is no PCV valve, per se, only positive ventilation of the crankcase vapors via the piping arrangement I just described. If you do not have this arrangement, and the inlet at the manifold is open to the air, you have a major air leak that all the adjustment in the world will not cure.

I hope you have some kind of manual, even a Chilton or Haynes will do, to show you the layout of your system. The factory CD ROM is only $20 and a great investment. If you discover the PCV system is not correct, if you are missing the small pipe work under the AF, you can open vent the cam cover and seal the manifold down at the inlet port to cure the vacuum leak until you get the proper pieces. As an alternative, you can take a piece of 3/8" fuel hose and clamp it to the manifold connection and then snake it around and up to the cam cover hose. Once your intake system is tight you can do some meaningful work.

The fuel return line connects to the fuel return valve on most models. This valve screws into the metering body of the front carb and has a needle valve that opens and closes to allow excess fuel to return to the tank.

Your description of backing out the idle screws to get it to run is telling...these screws add fuel to the idle circuit. The spray and general excess of fuel seems indicative of possibly incorrect basic float settings and two carbs mal-adjusted to the point they working against each other. Make sure your floats are set about the right height. The float should be about level when you hold the metering body upside down. The sealing washer in most kits will place the level just about right. Never use more than one washer, don't stack them seeking prefect level. The usual thickness is 1mm more or less. The inlet valve should be snugged against the sealing washer.

Once you have this set you can try to get the basic setting for starting and running. Disconnect the link between the carbs. Each carb has another link, about 2 inches long with ball connections at each end and an adjustment in the middle. This small link connects each primary throttle with the main carb linkage bell crank so you can convert front-back motion into up-down motion. Set the length of these small links so the primary throttle is fully closed and just about to open. Then open each one-half turn. Set idle mixture screws evenly at 2 turns open. This is the basic setting so you can start and run the car.

Marc, diagnosing from a distance is almost a lost cause. Get yourself a manual, study it and I know you can figure this out. My attempt to describe things for you may not even be helpful if you don't have a picture to relate the words to.

But be confident about this: you can fix this; if your rebuild parts were good you only need to check the accuracy of installation and then move on to set-up. It all works when the front and rear carbs are working together and not against each other. There is a reason most folks hate these carbs, they are not easy to set up, and it is very easy to screw them up.

The 114/115 CD ROM has almost the full factory carb manual in it. The 108/109/110 CD ROM also has excellent data. Send me your email and I can probably send you some PDFs if you cannot locate these manuals. The Chilton and Haynes manuals are pretty good too.

Good luck for now,

230/8

[Blue 72 250]

230/8 is correct on his pointers. If you have not seen the post with a diagram of the inat here is a link




The needle valve has two specs. in the jamie koop manual. One is for a valve that has solid pin, one for a valve that has a pin with ball. Make sure that you have the correct washer for the type of pin that you have. Better too low (bowl fuel level) at this point. That would mean there would be a thicker washer then a smaller washer.

Hope this helps.

[Blue 72 250]

Originally Posted by 230/8

Marc:


Once you have this set you can try to get the basic setting for starting and running. Disconnect the link between the carbs. Each carb has another link, about 2 inches long (#67) with ball connections at each end and an adjustment in the middle. This small link connects each primary throttle with the main carb linkage bell crank so you can convert front-back motion into up-down motion. Set the length of these small links so the primary throttle is fully closed and just about to open. Then open each one-half turn. Set idle mixture screws evenly at 2 turns open. This is the basic setting so you can start and run the car.



230/8

Just so we are all on the same page. If she can't run at this point, you have other problems with the build or the ignition.

[MunichTaxi]

when you tune an old Mercedes to the book specs, it will run very poorly. Happened to me.

Try setting the Timing by ear. How did you set the Dwell?

[Neubie]

Well here's the progress so far...

I think I have the excess fuel problem down, when I changed over the float valves to the new pin style, I was using the old washers. The ID on these is just larger than the ones that came with the rebuild kit. Perhaps just enough to let some fuel slip by them? Installed the appropriate washers and tightened the valves good n snug, and it seems to have done the trick, although when revved high, I still get some fuel spurting out the barrels...

I found the inlet to the intake manifold 230/8 was talking about, someone has capped it off so theres no leak there.

There is no fuel return valve on my setup, just a bolt with holes in it that connects to a hose that runs back to I am assuming the gas tank?

I've got the carbs adjusted to where they are pulling evenly, It seems to run if I nurse the throttle, but it still won't idle on its own for more than a few seconds. It is missing quite a bit. After getting Carbs as good as I could, went to check timing (I know its backwards, but had to get it running well enough first) Where it runs the best, is about 40 BTDC @ 1500 which is a good 20 degrees past where it should be. And it only gets worse as the RPM's go up. Any attempt to move the distributor results in it running worse, or not at all.

I found a thread that delt with the cam/crank/valve timing, and wondered if that might be off? I Pulled the valve cover to look for timing marks, I can see one on the tower by the sprocket, but for the life of me can't find one on the cam sprocket that corresponds. In the post is mentioned that at TDC (00 matching up with the pointer right?) The rotor should be pointing at the mark on the distributor which corresponds with the #1 spark plug wire.(about 1 o'clock in my case) My rotor in that position is pointing at like 9 o'clock, not even close, like 120 degrees off. I started checking this because in getting the cam sprocket back on after head gasket replacement, Im not absolutely sure it went back in the exact place, but sure its very very close. The car has run since it went back together, and before all these problems so if it is off, I know its not enough to totally shut the car down. neither cam lobe appears to be pushing on a valve in this position, IE they are at the 9 and 3 position, rather than 6.



thats all I've got, not sure what any of it means, or how to go about fixing it, but it feels like some small measure of progress anyway. As usual, any help or ideas may help me get further down the path. Thanks!!

Marc

[Blue 72 250]

I would look at the distributor next. Do you have a clean reading on the timing? or is it bouncing around with weak signal?

Again, I can't stress enough the need to have perfect spark all the time. I spent months going back and forth with my carbs and timing. It turns out that my transistor switch gear was acting flakey. The best $100 I spent was on a crane optical upgrade and dumped the points. Now she runs like a top.

There is no reason to suspect the mechanical timing at this point.