how to reset the carbs

[bmw art car]

i had/have a list if issues with my carbs
mostly i wonder how to set them back to a base setting.
and then balance them from there and all that...
both of my small knuckled screws were tightened on one side down all the way
and it cracked the lower ficture. i took em off and fixed them so that they can
be cranked with the wheel again.
now that would be a base figure as a lenght?
and how can i crank the fuel down and air supply up?
if i turn in the base screw all the way and back it off 1 1/2 turns.
and how about the idle screw what if i turn it all the way out
what will it affect?

 

[DougE]

Carb Settings

i had/have a list if issues with my carbs
mostly i wonder how to set them back to a base setting.
and then balance them from there and all that...
both of my small knuckled screws were tightened on one side down all the way
and it cracked the lower ficture. i took em off and fixed them so that they can
be cranked with the wheel again.
now that would be a base figure as a lenght?
and how can i crank the fuel down and air supply up?
if i turn in the base screw all the way and back it off 1 1/2 turns.
and how about the idle screw what if i turn it all the way out
what will it affect?

If you have Webers, search Redline on the internet, Redline has a really good instruction sheet on setting and balancing your carbs. If you have Zeniths I'm sure someone will chime in with instructions for those.

Doug

 

[61porsche]

Zeniths?

1) now that would be a base figure as a lenght?-

The adjustible throttle shaft rods are set after the basic carb adjustment so they're equal, non binding, and snap on without changes. This means take them off until you're done tuning the carbs and ready to adjust the common linkage.


2)-and how can i crank the fuel down and air supply up?

Mixture is adjusted by the throttle plate screws near the choke ( air by way of the throttle plates). Back them off individually. Then SLOWLY turn them in until the slightest of movement occurs on the cam and roller slot. Do the other side the same. Then move both the same amount to start- 1/4 to 1/3 turn. ( Think motorcycle carbs with very fine adjustment) Start up. Use a tach, unless you like to run around alot to see. Or put on your Obewan Kanobi suit and listen for the force. (The sweet spot, no spitting and smooth.) Then using a 2' piece of hose to listen at the throat of the carbs at the same place, mechanic stethescope without the metal probe, or your favorite unsyn/ air meter and weber cup try to decide which one has less HISS or air. Change the other carb to match with it's air screw. Sometimes it takes a while to feel the force with many tries. I personally like to use a vacumn guage to get to the highest reading on each manifold then back off just a little to get a slightly rich mixture than lean.


3) if i turn in the base screw all the way and back it off 1 1/2 turns.

This screw is a fine adjusment of idle speed and slight mixture of say- 600 to 950rpm only. It's not a Holley. Get your base mixture first to idle at say 600-700. then use both screws the same amount from in... say 2 turns... remember the nasty gas they serve us now... always go a bit rich if you want a little power and no bogs. Get it to idle at 850-950 real smooth. ( Ok -one more tip- I watch a spark plug wire to see how stationary I can tune for. It used to be a silver dollar standing on the valve cover.....)


4) and how about the idle screw what if i turn it all the way out
what will it affect?

It just lets in a little more gas at idle. Too much and your idle circuit will go bye- bye and you're into the jets. Fuel will come out the venturi and you'll be running at 1100 rpm. Stop. Go back. Do it it over.

One more tip- if you're tune isn't up to it... at least check the points, dwell, plugs, etc. as there's NO way the carbs are going to help it out. Probably the single most reason people buy Webers and have for 50 years.

Then you can adjust the dual linkage. No play. Balls snap on without moving anything. Front first. Then back. Then make sure the front one/ plate/ and high idle screw isn't touching from your last timing job or may be it never worked and now's the time to bend it a bit so you won't have to stick a bunch of feeler guages everywhere to get the idle up to timing specs.

There's something wrong if you can't use the adjustments and see any difference.

Most imbalances can be traced back to the other linkage- the small plastic one on the carb.. I cannot say this enough- use a mike. A quarter turn will throw everything off and yes I know it looks terribly simple but deceptively has small threads. Even the German engineers call this one out.

One last thing. I check my entire linkage- down to the motor mount and back. If that area hasn't seen the light of day in 20 years.. a little clean up and grease, straighten any rods, and Most importantly check to make sure you have WOT to scare the neighbor's cat off you're new shiney paint.

 

[bmw art car]

wow porsche so much good info

what do these knurled screws do?
are these the throttle plate screws you speak about?

 

[bmw art car]

honolulu's procedure - q's about it

i have written my question in bold
The short answer is "Hell Yes! You CAN synch your own carbs." And you should, too. I dunno if you're familiar with multiple carb synchronizing, so here's most of it. It assumes your engine will run at idle.

Cold engine, set valve lash .008 intake, .010 exhaust. Running engine, dwell 35 to 41 degrees (about .014 at points IIRC). Timing per spec on the flywheel ball at 1700 rpm with vacuum hoses disconnected and plugged.

The "poor man's" carb synchronizer is 8 feet of 1/8' diameter clear tubing. Costs about 15 cents per foot. Suck some ATF into it so that when hung in a loop, ends up, the ATF fills a U shape about 8 inches high on each side.

I have used the factory sychronizing device (probably NLA), and have THREE Uni-syn devices (about $30 each if I had paid for them) which have also been experienced with my current 3.0, my old 2500 4-door, and wife's Bavaria, and my old dual-carb '67 VW Type 3. Believe me, the poor man's tubing is just as good as any UniSyn, and BETTER than the factory tool, which works only at idle.

1. Disconnect the front-back carb linkage, at the rear carb, so the two operate independently and are no longer linked together. I also disconnected the link coming up from the bellcrank on the side of the block.

2. Remove the vacuum hoses on the left side of each carb (left is left, facing front of car). Hang the tubing in an "M" shape, from the open hood.
I am supposed to connect both ends of the 'M' to the vacuum hose outlet at the left and right carb?
Put a small weight at the middle of the M so it doesn't blow around too much. Pinch or kink the tubing so that when you start the engine, all the ATF doesn't run into one carb. If it runs away anyway, it won’t hurt, just refill ATF in the hose and set up the M with the engine stopped.
is the hose supposed to stay pinched throughout the procedure?
3. Start the engine, run at idle until warm and chokes are fully opened. If the carbs aren't balanced, the ATF will be higher on one leg of the M than the other. Adjust the idle SPEED screws on each carb linkage to get a 900 rpm idle, with the ATF at equal height on each leg of the M.
whenever i try to un-pinch one side of the 'M' the vacuum sucks it toward one of the carbs

4. Adjust the idle MIX screws at the right side carb bases, to lean best idle. Hint: lay a cloth over the valve cover which will be quite warm.

5. Go back and forth between front and back carbs, adjusting idle mix and idle speed, a couple times till all is well and you have a smooth idle at about 900 rpm. Okay, idle is done.

6. Now reconnect the linkage at the back carb (and bellcrank if disconnected). Idle speed should not change. If it does, adjust the little knurled wheel at the rear carb linkage until the ATF in the M doesn’t change with the carbs linked or no. Don't use other tweaks - just the knurled wheel.

7. Raise the engine rpm to about 2500 using the small vertical screw on the linkage between the front carb and valve cover. If the ATF shows imbalance, even it out using the little knurled wheel at the rear carb linkage

8. After balancing at 2500 rpm, back off the little vertical screw on the linkage until it doesn't touch, i.e., has no effect on engine rpm.

9. Shut off engine, remove M tubing, reconnect vacuum hoses. SMILE you've done it. That wasn't hard, was it? Think about going into business. Think again.

 

[Stevehose]

Jerry's post should be a sticky on carb adjustment. I have spent the last month rebuilding and repairing my carbs with his help and he knows his stuff. The knurled screws are the throttle plate screws. The mixture screws are the ones recessed into the carb base seat and difficult to adjust without a flexible screwdriver and burning the @$!& out of yourself. Turn the mixture screws in till they stop then back out 2 turns. Screw in the throttle plate screws like he says - the idea is to get the car running, then once it is back down the throttle plate screws so that each carb is sucking the same air or vaccum (I use 2 air gauges and a vacuum guage to check manifold) at around 700 rpm. If the car idles too high from the throttle plates you wont get much if any response from the mixture screws. Then adjust mixtures screws as he says - to get it idleing smooth then out a little more to run slightly rich.

 

[61porsche]

knurled screws

The only knurled thing that I think your talking about is the linkage on the throttle shaft. The front is just a fuel rod- two ends, opposite threads and a rod. The rear- similar, but has a knurled wheel.

The lingage on the manifold must have a little play. Sometimes as part of the final throttle common shaft- you can take up a little play if there's slop. ( minor) If the balls and cups are worn- it's best to replace them. But I can see how you can take a little play out.


Some of the later idle mixture screws have a knurled end that's hidden in the small brass fitting.

If I missed the part- describe pls. We could be just calling the same part something different.

 

[bmw art car]

The only knurled thing that I think your talking about is the linkage on the throttle shaft. The front is just a fuel rod- two ends, opposite threads and a rod. The rear- similar, but has a knurled wheel.

The lingage on the manifold must have a little play. Sometimes as part of the final throttle common shaft- you can take up a little play if there's slop. ( minor) If the balls and cups are worn are worn- it's best to replace them. But I can see how you can take a little play out.


Some of the later idle mixture screws have a knurled end that's hidden in the small brass fitting.

If I missed the part- describe pls. We could be just calling the same part something different.

#61 here is what i was talking about... there is one on each carb. apart from a bigger knurled screw

X2 on the screw driver... the front carb is ok to adjust but the linkage is right in the way to do anything to the rear carb.
read all the great answers and run out in the garage to see what i can do

 

[61porsche]

Homemade manometer

Refine Honolulu's by:

1. Buy a cheap yardstick- aluminum ones are nice. Easy to see the marks.

2. Mount it on a 1 by3.

3. Fasten the tubing with clamps.

Drill a hole and hang it up somehow.You're choice.

Do all the things Honolulu's post says.

You can do one carb at a time or both by holding one end in the carb throat or both at the same time.

What's missing in this equation though are the caps. The caps fit over the whole carb with a 3/4 hole and a small fitting for the hose if you want to be totally accurate. The back barrel does has some air going in it that's not evident. It's to keep it from sticking when the vacumn secondaries open. It does effect your mixture.

You can really do this with a rubber hose though. I know plenty of Jag/ Healy/ TR guys who threw the unisyn's away once they understood the principle.

The only thing else about the factory manometer over a home made one is they put restrictions in the hose. Use the yardstick and you should be fine.

Save it for that homemade flow bench when you want to bore out the throats for that 3.8 and add a megaspark and hide it under the air cleaner!

 

[Stevehose]

Sorry I thought you meant the throttle plate screws - the knurled ones you mention are the linkage adjustments and not used for mixture syncing but need to be the same length so both throttles open the same when the pedal is pressed.

Get a 1/4" flexible driver from Sears:

http://www.craftsman.com/shc/s/p_10...rd=flexible&prdNo=10&blockNo=10&blockType=L10

then put a wide screwdriver bit into it and secure with electrical tape so it doesnt fall out - this will bend around the linkage on the back carb and make the front carb easier to adjust as well as minimize skin burning. The mixture screws are soft brass and it doesnt take much to strip them so you want the screwdriver to fit well and not come from an angle.

#61 here is what i was talking about... there is one on each carb. apart from a bigger knurled screw

X2 on the screw driver... the front carb is ok to adjust but the linkage is right in the way to do anything to the rear carb.
read all the great answers and run out in the garage to see what i can do

 

[61porsche]

Carb ID

Part 61- is the part that has a dimension that HAS to be mic'd x 2. The dimension is in the manual. No guessing. Take them both off and do them. Pay attention to how they snap on- orientation of the sockets.

This part gives lineal linkage movement x 2.

Be careful with it too as just a quarter turn off will give you hell. Sometimes you have to turn just one, the other, or both since they only snap on one way and the easy way is to turn one. Don't! Worse than any valve adjustment and no tolerance.

Like Ron Popeil- set it and forget it!

Idle screw- go find a sewing machine screw driver or similar. Put it in the tool box.

 

[deQuincey]

interested in this topic, help

hi

I am absolutely interested in this topic, I have been trying to adjust the carbs in the past weeks, with no excessive luck

I have the hayness book, and a bmw carburetor manual

my basic problem is that my carbs are dated 1971, so they are the oldest version, with only advance hose for the distributor, and when i look to the photos in the books, and the explanations, they are not like mines, so I can not perform the same operations as what the manual is saying

considering this incredible sucession of posts written by experts in the carburetor matters, much better than the manuals, I find another handicap, the language,

it is very difficult for me to:

1- identyfy the screws that you are mentioning

2- understand the expressions you use for the fixing operations

may I ask you to help me identify, in the following pics, the correct screws that have to be fixed ?

here is a general view of that part of my engine, I have a mechanical fuel pump with a pre-filter

here is a detail of carb 1 (left one, nearest to the interior of the car)

I am identifiying the screws as 1(not seen), 2(not seen), and 3(seen through the spring)

and here it is carb 2

the basic problem is that there is not a screw2 in this case, that place is occupied by the advance hose for the distributor
in carb2 you can see the screw1 (similar to that one in carb1, in which photo can not be seen)

question: are these the main fixing screws ?

any other screws needed to adjust carbs ?

regards

 

[61porsche]

Carb Adjustment The sequel.

Dequincey my very good E9 friend-

1) You must hook up the wires to the choke and electric idle solenoids. These are powered with ignition. It will never run properly without power.

2.) You have a more modern set. There are earlier versions than yours. Send a picture of the other side of the carb. If it has a rectangular aluminum box on that side- it must be wired in a series from the back carb to the front with all these devices.

3. You definately get points for clean. Que bonito!

Ok here we go........

a) Vac. advance- doesn't matter which carb. Tip- if one carb pulls a little better vacumn- use that one. It will help your total advance at the distributer and driveability.

b) Carb 2 screw one- this screw controls the mixture by opening and closing the throttle plate letting in or taking away air. It must be set at idle as from then on... part throttle the mixture is just linear... and set. This screw on both carbs sets the balance. Tip- get them to run best individualy and then together. As you can imagine- these are small adjustments.

This where carefully listening comes in- the hiss or air movement should be equal by slow movement of this screw.


c.) Idle screws-Screw 3.... under the springs- very small adjustment to riase or lower idle speed. Once you have the idle set at 700 rpm or so- use these to raise the idle to 850-950. Usually these are set at about two turns out- but you can get a little benefit from them if you turn them a bit one way or another to get best running. A small bit. A tach and vaumn guage helps if they're sensitive. Then turn them out an extra bit to run a little rich.

Keep asking.. I'll do my best to help.

Jerry

 

[hans3]

Always an interesting topic.

First off, 61Porsche what do you mean by carb “spitting”? Or does this refer to exhaust spitting? My exhaust “spits” intermittently or frequently depending upon how I have the carbs balanced. Don’t know what the sound means.

Second, deQuincey I believe your distributor vacuum plumbing may not be correct. The Blue books have a very clear diagram of how these should connect. On my 2800 Zenith the distributor advance connects to the port on the very front (forward) side of the front carb. Vacuum connects to the left rear port of the rear carb. The clear Tygon tubing you show in Pic 1 with the 3-way black connector is what I have attached to the vacuum ports on the passenger side of each carb. The 3-way channels vacuum from each carb to the air cleaner housing.

I had trouble balancing using the manometer and vacuum gauge approaches; one carb would exhibit too much vacuum fluctuation at idle. I purchased a round, $2.30 Tupperware bowl at the supermarket that fit the carb top diameter exactly. Next I cut a large hole to accommodate my air synchrometer tool, like the one sold at Pelican Parts:

http://www.pelicanparts.com/cgi-bin...=Mechanical Injection/carburetor Synchrometer


I placed some strip caulk around the Tupperware’s synchrometer opening, just to ensure sealing. With this method, which is similar to the factory top dome tool, I was able to obtain a much steadier car airflow reading. Hence I was able to verify that the carbs were out of sync at idle and make the correction to the throttle plate screw. This homemade tool works at higher revs too.

 

[61porsche]

Hissing , spitting, and bad boys

Hans,

The exhaust spitting after warmup. Naturally, dependent upon temp, humidity, etc. some moisture is expected until the engine and exhaust is up to temp. A by product after would be too much mixture or not enough, sometimes smelled without an analyser or wideband.

I tune for the smoothest sound and then a bit richer.

Vacumn take off location- there is a carb out there that has a port nearer to the idle valve.( fan side) That series would be the last or next to last emission carb with additional features such as jets removable from the top like a weber, a gas vent diaphram, and the choke top being more pointed.

Dequincey's is the earlier one. I assumed the clear lines do something else- dashpot, etc. That's kinda why a picture of the other side is needed.

Tupperware- works for me... but can we ghost some flames on it please? I thought I had something going with Obewan... now maybe the Sith bad guy that looks devilish?

 

[deQuincey]

Dequincey my very good E9 friend-

1) You must hook up the wires to the choke and electric idle solenoids. These are powered with ignition. It will never run properly without power.

2.) You have a more modern set. There are earlier versions than yours. Send a picture of the other side of the carb. If it has a rectangular aluminum box on that side- it must be wired in a series from the back carb to the front with all these devices.

Jerry

vielen danke jerry, thank you for your help giving me so detailed explanations, now I think I have got it,

first point: the electric connections were removed (in the photo) because I was renewing them, :?, they are usually in their place
second: no aluminum box electrically connected

so summarising: screws number 1 in both carbs will give me the mixture air-fuel, and screws 3 in both carbs will fine tune the iddle from 700 to 950

questions:

1- which is the function of screw number 2 (that belongs only to carb 1) ?

2- how can I set the iddle to 700 rpm´s in the beggining of this adjustment operation, let me describe my actual situation:

the car has an erratic behaviour when starting from cold, I am not really worried about that, but when it warms up then I am not happy at all, because the iddle will go up to 1500 rpm´s and will stay there no matter how many kilometers you drive it

the smell of the smoke it is acid and strong, i think the mixture is too rich, but I can not tell anymore

so, my intention is to recover a good iddle of 900 - 950 rpm´s as it was before rebuilding the carbs

3- can I get my objective using only those screws ? or do I have to modify other settings ?

regards

 

[deQuincey]

pics to clarify

some photos:

detail of the admision pipes, you can see that the one for carb 2 (the front one), has a tube for the brake helping suction

front image of both carbs in this side you can see one pipe in each carb, those pipes are interconnected whith a flexible hose and also to the air filter case (it can be seen done in the photos of previous post)

the other side of the carbs, in which all the previously mentioned screws can be seen, take a look to the pipe pointed with a green line, that is the one for the advance of the distributor

 

[Stevehose]

Screw #1 is the throttle plate screw.
Screw #3 is the mixture screw.

You can close both mixture screws (#3) gently. On screws #1, back them out until there is no movement on the throttle plate linkage, then screw back in 2 turns or more, enough so the car starts. Once started then adjust these screws to 700 rpm.

Then open up each mixture screw as per Jerry's instruction to get to best idle/950 rpm. Then open up a little more for running a little rich.

Jerry would know but I bet capping those 2 vacuum ports going to the air filter would give you better mixture to the carbs and smoother idle once syncronized. Also make sure all other vacuum ports are capped if not being used for advance/retard.

so summarising: screws number 1 in both carbs will give me the mixture air-fuel, and screws 3 in both carbs will fine tune the iddle from 700 to 950

questions:

1- which is the function of screw number 2 (that belongs only to carb 1) ?

2- how can I set the iddle to 700 rpm´s in the beggining of this adjustment operation

 

[61porsche]

Gas, fuel, and chokes.

Let's answer your questions:

Screw number 2- together with screw 3 are the small idle adjustments. 2 is air and 3 is fuel. PM me with your email and I'll send you the factory suppliment.

2.- The carbs from your description are running too fast and rich.

a. The chokes-need adjustments. I assume you know how they work normally so let's talk now-

Inside the choke cover, the small stepped cam lever, is not releasing the throttle. Open the cover and move the arm. The idle should drop at each carb by 300 rpm or so. Check the sequence of the serrated washers to make sure you didn't place one incorrectly. All good? No....

b. The throttle plates are too open- screw one counter clockwise 1/8 th turn or more.

c. Take the connecting throttle rods off. ( Make sure no throttles are being held open)

d. The plastic rod on each carb- wrong dimension on both. Too long can hold open the throttle.

e. I assume the choke plates open?

f. Choke idle screws- accessible only at open throttle- turn them out by 1/4".

Any one or more above will do what you describe.

Back to your pictures-

To air filter- take it off and plug. Just adds extra air to upset your very fine running motor up and down the mountains..

Answer to last question- We have to trouble shoot the high idle back to normal first. But yes, once that is normal, the screws will work beautifully.

Keep asking and this will get easy!

 

[deQuincey]

dear Dr. Jerry

let me explain the case

today I have borrowed two hours from my family duties, and I have pleased him with some attentions listening to the carburetor´s air swallowing

I warmed up the car, the iddle was around 1100rpm´s (I closed screws number 3 in both carburetors one turn to get it down from 1500rpm´s (but I can not go lower than that due to the evident aparent risk of getting the engine dead)),

and then oppened the air filter cover, suddenly I was surprised by the hiss sound of air passing onto the carburetors, it was louder than I expected (usually that sound is deadened by the mentioned filter cover so maybe that is the reason for not noticing it before)

the problem is that I do not have an historic record of what that sound should be like

as almost everything in this life is relative, and as I said I have no pattern to compare I did the most sensible thing I could do, this is compare carb 1 and carb 2: and the fact is that the hiss in carb 2 sounds much more louder than in carb 1

so, doctor, what would you recommend ? I suppose that both carburetors should give the same hiss sound level, then:

1- what is better: go for the upper level in both carbs, or go for the lower ? (more hiss sound means more mixture in the engine ?, I am assuming that "venturi" is making more fuel mixing in a bigger air flux, OR is exactly the contrary)

2- which screw will change this ? probably screw 1 ?

thanks for your patience and help

regards