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  #1  
Old 10-22-2006, 04:16 PM
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Its the carbs I tell you...

Hey all,
Long delay of life getting in the way of wrenching, and somehow the elves didnt make it around to fixing my car while I was gone....

quick synopsis of the problem. 230/8, stalls under load, ie dropping in gear, stop signs. wheel cranked full stop (although sometimes after driving a half hour or so it does ok....) Have changed plugs distributor cap, condenser, (points coming they are slightly pitted but ok) set dwell and timing. checked for vacuum leaks and have found none (not ruling out the possibility that I missed one, but for the moment...) considering replacing vac lines just out of spite..

I know the carbs are out of whack just from me tinkering, and while this may not be the whole of the problem, my gut tells me it will help. I got a flow meter, and while it needs a gasket to fully seal, What I have found is that the front carb is pulling very little, the rear carb maxes out the guage. also when restricting the airflow over the aft carb, the idle races. Not so with the front one. The idle screws are maxed on high just to keep the thing from stalling, I can adjust them down a bit but not much or it wont hold the idle.

My understanding is to adjust the carbs one does something with the linkage between the two? the flow meter directions recommend setting individually without the linkage then attaching the linkage so it doesnt affect the balance. How does one adjust the individual carbs besides the idle screws? I need to lower the flow in the aft and increase in the front..any suggestions?

Also have noticed the carbs arent so much spraying fuel, more like dribbling it into the throats, the aft producing a larger dribble than the fore...


Thanks so much for all the help, just a little more and I think I'll be there!

Marc

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  #2  
Old 10-22-2006, 04:26 PM
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Location: Evansville, Indiana
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Yup, unbalanced carbs.

Heres the lowdown -- you MUST adjust the carbs to pull the same amount of air. This is supposing you have a good engine and proper valve adjustment, etc.

Unhook the link between the carbs and set basic throttle position to exactly the same opening on both carbs. You can use your flow meter or just block the air bleed and check speed drop, either works, but if you have a decent meter, it helps.

Your front carb has the throttle plate too far closed at idle, the rear is too far open.

Once you get that set, you must get the idle mixture set correctly on BOTH carbs. Blocking the idle air orifice must give the same idle speed change on both carbs.

Idle speed must be set equally on both carbs -- turn the screw EXACTLY the same amount on each. Your flow meter will come in handy here, too. I believe the idle speed adjuster is a vertical screw/nut combination on those carbs, but I'm not sure, dont' have a manual any more.

Re-install the link between the carbs so that it fits without pulling either way (otherwise the front carb will be off).

This should get you bad up and running.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #3  
Old 10-22-2006, 04:40 PM
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Ok, will do, but one clarification, setting the basic throttle position....the butterfly flaps on top of the carb? I can push those around manually without a whole lot of change in the way it runs, till the aft one gets quite close to completely closed. how do I lock them into position?

correct on the idle speed adjuster, vertical screw/coil spring thingy

Sorry for the basic questions, Im a boatbuilder not a mechanic

Marc
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  #4  
Old 10-22-2006, 04:50 PM
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Well, there are some similarities -- they have to be done correctly and nothing is exactly cheap...

Those are the chokes. Probably electrically heated, check the wiring and make sure the heaters work. Should, like any automatic choke, snap shut when below 70 F or so, open some at full throttle position, and open up slowly as the engine heats up. They must be fully open while you adjust the carbs, of course.

Some of them were water jacked heated, but I believe the Zeniths were all electric. Check linkage to make sure someone hasn't fiddled them to "fix" a bad heater issue.

Also verify that the manifold heat risers under the carbs aren't stuck. They usually stick open, roasting the carbs and can actually warp them. I'd lock them closed myself.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 10-22-2006, 05:22 PM
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Yep, nothing is cheap in the marine world!

I went out and adjusted the throttle linkage, hysically extending the rod that pushed the front carb open and giving it a little more, adjusting the middle rod that connects the two to compensate. seems to have made an improvement, I dropped it in gear and it didnt stall! Blocking the little hole on the top of the carb didnt drop the RPM on either carb, in fact it accelerated it when the aft one was blocked, much like putting a hand over the choke butterfly (thanks). still a large difference in the flow meter readings though


What do the heat risers look like? will check that next.

Thanks!!

Marc

Last edited by Neubie; 10-22-2006 at 05:23 PM. Reason: additional info
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  #6  
Old 10-22-2006, 06:14 PM
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The heat risers are bimetallic spring operated flaps that direct exhaust up onto the bottom of the intake manifold when open. Should have a bimetallic spring visible, or under a sheetmetal cover on the exhaust under the carbs.

You should adjust the idle on the carbs to draw equal air with the link between them off, then adjust the link so that the idle and air flow don't change when it's re-installed.

Glad it's working better -- that twin carb setup is great when it works, and a huge PITA when it doesn't!

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #7  
Old 10-22-2006, 08:06 PM
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Well, at the end of the day, I think all I managed to do is eliminate balanced carbs as the source of the issue. Had it idling nicely, even not stalling in gear at one point, but it wasn't consistent. now back to starting point i think. Nice that I know how to do it though. Will go get new vacuum tubing this week and do that on principal, seems to be everyones fallback diagnosis, although I cant seem to locate a leak anywhere.

Heat risers, couldnt see anything that fit the description, although on the front carb there is a metallic coil/spring that is obviously broken/out of place. will look closer into that on the next go round....

hmmmarrghhhh....

Thanks for the assistance though, nice to have suggestions and info!

Marc
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  #8  
Old 10-22-2006, 09:11 PM
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The heat risers are down on the exhaust manifold and are most likely seized. I do not have a gas car parked by my computor but for arguments sake probably five inches lower than the base of the carb. Getting a cheap manual even if off ebay might help you a lot. Usually they have at least a reasonable article on setting up the zenith carbs incorporated in them. Also go into the archives on site. You are not exactly the first person to have some difficulty in this area. There are also other areas of the car that might benifit later by owning the manual as well. . When you said you eliminated vacuum leaks did you do it by spraying wd 40 around the bases of those cabs etc? As soon as you mentioned your idle needles are a long way out I suspected very dirty carbs or lots of air leaks.
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  #9  
Old 10-22-2006, 09:42 PM
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Location: Evansville, Indiana
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Don't forget the brake booster and any vac powered door locks, etc if applicable -- the booster can leak quite a bit and still work normaly, for instance.

If you have to have the idle screws all the way out to get it to idle and it still dies when you put it in gear, my very first thought is of a large vac leak -- it's too lean, won't stay running under load.

It's possible that you have a fuel delivery problem as well (perhaps a flaky fuel pump or a plugged screen), but most likely you have air getting in somewhere besides down the carbs.

Keep at it, you'll find the problem sooner or later.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #10  
Old 10-23-2006, 12:03 PM
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I suspect most of what you need to know is readily available at this site under the heading "Carb Manual"

http://www.jaimekop.com/

It is the Zenith factory manual and should help you balance the little rascals. The mixture screws, part #15, are not what you use to set the speed. You need to adjust speed on each carb with link #12 shown on the parts view. If the carbs are reasonably in balance you do not need to remove the linkage connecting the front and rear carbs. With yours, however, I suggest you do remove it. Once the balance is set you can carefully re-attach it after first checking the connection can be made without altering the balance; i.e. too long a link pushes the rear carb open while too short a link pulls the front carb open. This may be tricky and if it does change a slight amount just leave it attached and correct the imbalance via further adjustment of link #12 to obtain perfection. You can tell which carb was affected by observing which one is now sucking more air.

Bear in mind that all the balancing must be done with the dashpot, #24, fully backed off so it does not touch the linkage. You back it off via the threaded screw and the adjusting screw on the spring. Use the screw first. Your final adjustments will be to set the dashpot to give proper function with AC on and the car in gear (automatic transmissions).

Also, there are many posts on this site with helpful information for this issue. Search under Zenith and/or balancing carbs.

230/8
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  #11  
Old 10-23-2006, 08:54 PM
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Hey all, thankks for the responses!

Not using the mixture screws to set speed, rather as you suggested part #12. initial balance done with linkage removed, and that seems fine. Didnt disconnect dashpot tho, will recheck with that off.

Fuel delivery system has been checked and is in good order.

Didn't eliminate vacuum leaks, just never found any by spraying wd40 around. not ruling out that possibility, but cant confirm it either. No power door locks/windows.

Will do further recon into heat risers.

Thanks!

Marc
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  #12  
Old 10-23-2006, 10:41 PM
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If you were not able to change the idle by plugging the air hole, then you either have plugged idle circuits or vacuum leaks around the top plate that make it easier for the air to take that route. That's why you see the dripping - the engine can't get air and fuel through the idle circuit and pulls it through the main circuit.

Try a CTH hand job. Hold the rpm's at about 2500 and close off the carbs one at a time with your hand until the engine almost dies. Sometimes that will suck the junk out of the idle circuit.
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  #13  
Old 10-24-2006, 10:19 AM
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So, this is NOT about going on the Atkins Diet?

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