zenith carb question - PeachParts Mercedes-Benz Forum

Necrosavant · #1 03-09-2009, 12:59 PM

i have a 1968 280s with dual carb.. car cranks right up will run till choke opens up and will stall unless i push in accelerator car will even drive but will not idle with choke open.....thinking of overhauling them but before i go that far does anyone have a pic of the carb labeling the idle air bore or other important air passages to clear out..

bwostosh · #2 03-09-2009, 03:45 PM

With this engine there many factors to getting the idle correct.
They can run perfect when all are correct.

#1 adjust valves
#2 cam chain check-up
#3 compression test
#4 electrical tune-up

then ask for the secrets
my 280S runs perfect

Necrosavant · #3 03-09-2009, 03:56 PM

deffinetly a carb prob..car runs great otherwise car will even idle if i keep choke closed about 80%..

Mike D · #4 03-09-2009, 04:17 PM

Vacuum leak

bwostosh · #5 03-10-2009, 11:19 AM

Are these the big Zeniths, which accomplish the idle adjustment by holding the throttle plates open and adjusting thru the bottom of the choke?
Then (after setting timing correctly), turn up the idle air slightly, re-set the idle fuel mixture.
Balance both by listening to the air hissing with a shop vac hose.

(what is a "necrosavant") or should I just guess?
Is that someone who specializes in dead benzes LOL

flacollect · #6 03-10-2009, 11:39 AM

This is weird, cuzz mine does this exact same thing.. and I rebuilt my carbs....If you find what it is....I'LL pay 20 bucks for the correct answer.. I
have had mine tuned perfect..timing spot on..new vacuum lines..rebuilt carbs....compression tests......new pertronix ignition....all the goodies it needed......cleaned out the gas tank.....new fuel lines....... and it still dies when I put it in gear. I've adjusted and re adjusted till I'm blue in the face. Anyway..if you find it email me, and I'll buy you a beer

Dave

1967 - 250 S

JMela · #7 03-10-2009, 12:18 PM

Carbs also need to be synced perfectly or weird things happen. Also, if the linkage rods are sloppy that can be cause problems.

Necrosavant · #8 03-10-2009, 12:29 PM

Quote:

Originally Posted by bwostosh

(what is a "necrosavant") or should I just guess?
Is that someone who specializes in dead benzes LOL

HMM kinda like that definition lets go by that..heh

todds · #9 03-10-2009, 05:36 PM

Does it die when you put it in gear or just idling in neutral? I agree with making sure everything else is 100% first. You'll never get em' tuned right otherwise, they idle based on a few different things.

jaimekop · #10 03-10-2009, 09:02 PM

My trusty carb manual is still online....
http://www.jaimekop.com/CarbManual/

Enjoy.
Jaime

wbain5280 · #11 03-11-2009, 12:51 AM

It's a good carb manual too. Thanks!

Necrosavant · #12 03-11-2009, 08:43 AM

Quote:

Originally Posted by todds

Does it die when you put it in gear or just idling in neutral? I agree with making sure everything else is 100% first. You'll never get em' tuned right otherwise, they idle based on a few different things.

mine just dies as soon as choke opens all the way idling in or out of gear

todds · #13 03-11-2009, 10:34 AM

Well if it is regardless of idle speed then I think you're on the right track with the idle passages. Is it idling at 850-900 or so in P after the fast idle cam comes off completely and the choke is still partially shut, or held that way?

Necrosavant · #14 03-11-2009, 11:03 AM

Quote:

Originally Posted by todds

Well if it is regardless of idle speed then I think you're on the right track with the idle passages. Is it idling at 850-900 or so in P after the fast idle cam comes off completely and the choke is still partially shut, or held that way?

i didnt hook it up to rpm guage yet but sounds about in that range..ill bring home a guage tonight and make sure

todds · #15 03-11-2009, 02:01 PM

Well it just has to be in that ballpark for diagnostic purposes, if it goes reasonably faster than that then it probably IS a vacuum leak somewhere. If it's in that range then it's simply not getting fuel at idle (blocked passages or idle mix screws way off), if it's much slower and barely running or varying in speed and sputtering then the carbs are way out of balance or your plugs or points are bad or something. Compression and condition of the plugs might be a worthwhile thing to check, at least it'll give you peace of mind.

If it's running more or less steady at a good speed when you do the choke thing, your carb passages are probably plugged up. Mine were full of sludgy rust that turned to powder once dry, it's a common problem on old cars. If that's the case then check your filter and gas tank. You'll have to pull at least the top couple layers off the Zeniths, better study up! (if you end up doing this then don't forget the little slotted screw in the middle under the air cleaner stud) I don't believe you necessarily have to entirely remove the carbs to check the condition of the bowls. The top layer gaskets will likely crumble apart in your hands tho...