Carburetor adjustment

Tony_V

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Hi.

What can be a good starting point for carburetor adjustment.
Number of turns for the idle mixture and the additional mixture screw.

It's for a 3.0 csa -75.

Rgds/Tony
 

bill

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I replaced my Zeniths with Webers on my '74 long ago primarily to avoid having to fiddle with two mixture screws...I don't remember what the settings were, but try starting with 1.5 turns each and see what happens. Then adjust in or out from there until you get a good idle. To adjust these carbs, you really need to have a CO meter (I guess you know that), another reason why I removed the Zeniths. Good luck.
 

Stevehose

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I've had webers, and I have Zenith's, I prefer the Zenith's when properly adjusted so I am curious to get this info also, as well as a step by step adjustment procedure starting from ground zero all the way to final syncing.
 

61porsche

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Assuming you have carbs with mixture bypass ( two adjustment screws, parts 15 and 17 on the exploded carb diagram, on the throttle plate) 1,1/2 to 2 turns from closed as the starting point for both sets. Euro carbs by engine design do idle slightly higher by 100 rpm or so. As Bill mentioned, some emissions requirements are important. But that's dependent on where you are. I take a slightly different view- first tune for best running, then emissions.

The factory did issue a supplemental instruction manual for Zeniths for techs. It was located in the original CS Registry that is in the process of being put on this site. I think I can locate my hard copy, if someone wants a scan- pm me please.

61Porsche
 

Stevehose

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PM sent thanks.

Assuming you have carbs with mixture bypass ( two adjustment screws, parts 15 and 17 on the exploded carb diagram, on the throttle plate) 1,1/2 to 2 turns from closed as the starting point for both sets. Euro carbs by engine design do idle slightly higher by 100 rpm or so. As Bill mentioned, some emissions requirements are important. But that's dependent on where you are. I take a slightly different view- first tune for best running, then emissions.

The factory did issue a supplemental instruction manual for Zeniths for techs. It was located in the original CS Registry that is in the process of being put on this site. I think I can locate my hard copy, if someone wants a scan- pm me please.

61Porsche
 

bill

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Well, to be honest I never paid much attention to emissions...the PO removed all the emission stuff anyway, and in NJ I can register the car as an historic so I don't need to worry about passing emission inspection. The Webers have only one mixture adjustment screw and were much less prone to vacuum leaks than the Zeniths, another reason I replaced them. I was also trying to diagnose a misfire problem with the Zeniths which I thought was carb related ...it wasn't. I had a leaky cyl. head gasket and didn't find that out until after I switched to Webers. Live and learn (but it is all a labor of love.)
 

Tony_V

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Saw in a list that there are a lot of different variations of carburetors used over the years.
It is different for automatic and manual,,, what's the difference?
From 74, it's more adjustment possibilities,,, it is an advantage or disadvantage to have the newer version?
 

61porsche

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Carbs Continued

Tony,

The difference with an automatic is the idle air bleed is slightly larger.( presumably to help the transition to drive, not unlike the accelerator pumps)

As to all the other differences- it mainly had to do with emissions getting tougher with some minor refinements. ( Capped idle screws) For example, the idle screws where the last sets had two screws. It was thought at the time running hotter and leaner helped, but as we now know it caused or added to problems with heads, overheating, etc. and from an air quality- is just as bad. Sweden ( as did Italy) had it's own version of carbs and not much is known about country differences that I've seen than perhaps a minor jet size or so.( Altitiude tuning?) Most all of those problems are gone by now... better(thicker water jackets) heads... faster burning blended gas...no visual inspections...changing to electonic points, etc.

Is one version better? The only one that maybe fits that description was a version I've never seen. That set had access to the jets from the top( somewhat like a weber) so you didn't have to take the choke section off to get to the jet section for cleaning. Second would be idle valve add from early carbs to stop run on. The factory felt that the vent change was better ( perhaps closer to the throat...) and the choke diaphram adjustment cover.... easier to adjust the earlier version.

Maybe someone else has a different take?
 

DougE

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Carb Adjustment

These are the Redline adjustment instructions, I would also consider gettting a Syncrometer for setting the idle. You can get a rubber adapter that is molded for the 32/36 or 38/38 air horn. This makes setting the idle very easy. I like the Syncrometer better than the UniSyn it's much easier to read.

Doug



Base line Settings

Speed Screw 1 to 1-1/2 turns

Mixture Screw 2 turns

Your settings with engine running

Speed Screw______________

Mixture Screw______________


SET UP ADJUSTMENTS

Start set up by confirming carb base line settings. Do not depend on the factory delivered settings. Check them before the carb is installed.

All settings are done with choke disengaged or warmed up so that the choke is fully opened and disengaged. This is done on automatic choke carburetors by first opening the choke butterfly by hand and inserting a wood block or wedge of some kind to hold open while the linkage is cycled (linkage operated through its full movement ) to clear the choke cam. (You will hear a metallic click as the cam is released. You can check the fast Idle screw under the choke assembly to confirm that it is not in contact with the choke fast idle cam.)

Set the Idle stop screw (speed screw see fig 1) by backing out the Idle speed screw until it is not in contact with the throttle stop lever. Cycle the linkage again to be sure that the linkage comes to close without any assistance. (Checking for linkage bind) Now bring screw back into contact with the lever and continue to open or screwing in 1 turn no more than 11/2 turns.

Set the mixture screw (see Fig 1) by first screwing in until the screw stops, bottoms out. DO NOT FORCE OR BIND AS THIS WILL CAUSE DAMAGE TO THE SCREW AND IT’S SEAT IN THE BODY OF CARBURETOR. Back out the screw 2 full turns.

TUNING

BE SURE TO FOLLOW THE NEXT INSTRUCTIONS IN THE PROPER SEQUENCE, DEVIATION WILL CAUSE THE CARBURETOR TO NOT FUNCTION TO ITS IDEAL SPECIFICATIONS AND MAY NOT PROVIDE THE PERFORMANCE AND FUEL ECONOMY AS DESIGNED.
Start the engine, the engine will run very slowly more like a tractor. As long as the engine stays running idle speed is not important at this point.
The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). The engine should pick up speed and begin to smooth out. Back out ½ turn more, or until the screw does nothing or runs worse then turn back to the point where it ran its best.
Use your ear, not a scope or tuning instruments at this point. You want to tune the engine by sound. Adjust to best, fastest and smoothest running point.
Now that the mixture screw is at its best running location, you can adjust the Idle speed the screw. The screw will be sensitive and should only take ¼ to ½ turns to achieve the idle speed you like.
Check and set idle to your driving preference. Put the car in gear and apply slight load, (AC on) and set the Idle as you like it. Don’t set it too high, as this will cause causes excessive clutch and brake wear. The Idle only needs to be 7 to 900 RPM with light load or AC on.
Recheck timing and vacuum hook ups. Recheck mixture screw to lean best idle again. If all is still best and smoothest idle then confirm and note the final settings.
To confirm settings with the engine running. Start by screwing in the mixture screw and count the number of turns it takes to bottom out and note if the engine dies. If Idle Mixture screws are with in ½ turn of base line setting then all is well and have fun. Also check the speed screw and note how many total turns from initial contact. You may have opened (turned in) the speed screw. Your final setting should be under 2 full turns. Reset the screws (back in) to the best final settings (Per your notes) and go on a test drive and have fun. If the settings are other than described then you may want to recalibrate the Idle circuit (low speed circuit) to your engines needs. This is done by following the rule of thumb BELOW.


Simple Rules for low speed calibration

If the mixture screw is more than 2 1/2 turns out turns then the Idle jet is too lean (too Small). When the mixture screw is less than 11/2 then the Idle jet is too rich (too large). These assumptions are based on the fact that the speed screw setting is not opened more than 11/2 turns. If the speed screw has to be opened 2 or more turns then this is also an indication of a lean condition usually requiring greater change. At times it may appear to be showing signs of richness or flooding it is really a lean condition. See pictures and notes in the tech 2 article supplied in the kit instructions, view and please understand the need to keep throttle plate as near to closed as possible so as not to prematurely expose the transition holes. This is what causes the visible rich condition, and confirms the need to increase the jet size. JET KITS are available if needed.

EXAMPLE With the speed screw set at no more than (1 1/2) turns in after contact with the stop lever; and the best idle occurring with the mixture screw set at 3 turns from bottom, indicates the need for a larger Idle jet. Achieving the best idle at under 2 turns indicates the need for a smaller idle jet.

The secret to understanding the critical nature of the carburetor set up and the advantages of a WEBER over other carburetors is the Idle circuit. Referred to as the low speed circuit by Weber, this circuit is responsible for 80% of the driving operation. This is the reason that the Weber should give a fuel economy improvement over most factory carbs along with significant performance gains. In the worst case you should not see a significant fuel economy loss over stock, while improving HP & Drivability.

The Weber Carburetor is a sequentially timed device to the motor like the distributor. Time taken in the setup will provide more fun later.

If you should need to call REDLINE for technical assistance we will need to know your final settings to help. Technical assistance is free for the first 60 days of purchase. Units in service over 60 days may be assessed a service fee. All charges will be noted up front after a brief consultation to determine any possible defect. If the carb is out of the warranty period and no defect is determined we will estimate the possible cost of tech support or recommend literature available that may help.

ALL WARRANTIES ARE HANDLED DIRECTLY THROUGH REDLINE NOT THE RETAILER. DO NOT SEND PARTS TO MANUFACTURER WITHOUT CALLING FOR TUNING CONSULTATION AND WARRANTY CONFIRMATION OR INSPECTION RETURN AUTHORIZATION. PARTS RETURNED WITHOUT AUTHORIZATION NUMBERS WILL BE REFUSED AND RETURNED FREIGHT COLLECT.

PARTS RETURNED FOR INSPECTION AND WARRANTY CONSIDERATION AND NOT FOUND TO BE DEFECTIVE WILL BE CHARGED A MINIMUM INSPECTION AND ADJUSTMENT CHARGE OF $35.00 AND RETURNED FREIGHT COLLECT.

Contact REDLINE at 1 800 733 2277 ex 7457 Monday thru Friday 8:00 to 5:00 Pacific Standard Time

Non warranty Tech support is on a fee for services basis with minimum charge of 35.00 per problem resolution . With tech support calibration and tuning parts will be available at discount pricing as well as access to technical support documents and mailings
 

JhwShark

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Doug,
Great stuff should be very helpful...our cars are instruments (like music) and tunning by ear can be acheived...though I do use a timing light, coupe's sure do sound good when they're in-tune.

On my MGB the UniSynch is fine (I own it) but I do prefer the Synchrometer (just don't have one)...
Jon
 

Zibsnis

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Hi there,
I am rebuilding my Zeniths now and trying to find some manual for earlier versions (no vent chimneys, no adjustment screw for Diaphragm pull rod). Any ideas where to get those, or someone can just advice on this? Thanks!
 

deQuincey

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Zibsnis

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Thanks a lot for detailed instructions. Have already finished tear down on both carbs, inspected all the elements, cleaned and now waiting for some parts to arrive to reassemble everything. Actually, it seems this is the job I really enjoyed (like a sand therapy for kids, just another thing for big boys) instead of doing all of the sheet metal works, so thrilled of the result.
I noticed that your carbs had those diaphragm adjustment screws on top (see 2 in the picture of yours attached), so this is the only headache I have left for adjustments. Will still try to dig on the web or look for another cap for diaphragm that would have this adjustment possible. Attached also the pic of the carb I have.
carn_2.jpg
IMG_7832.JPG
 

Stevehose

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Zibsnis, make sure the sections and tops of the carb bodies are not warped, I sanded mine flush on a straight piece of granite, this will ensure no vacuum leaks. This was often the cause of so many Zeniths getting swapped back in the day.
 

zinz

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Your Zenith looks great! Like you, I enjoy working on carbs.

If you want them to keep that fresh appearance, I suggest wiping them down with Penetrol (available at Lowes, in the paint dept). Apply lightly with a cheap, bristle brush and after about 5 minutes you can wipe them down with a cloth (otherwise, the Penetrol will remain somewhat tacky). I treat all my exposed, underhood aluminum and such with a red ScotchBrite pad, then blast the part with Brake Cleaner, then wipe it with Penetrol. You can even use it on rubber bits, like the hoses. It keeps them shiny.

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680 solexes mounted II.jpg



Ed
 
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