hunting the carbs problem

[deQuincey]

hunting the carbs problem, zeniths

so, it has been a long time up and down with the carbs

really fed up with them, no way to synchronise both, to get a good and smooth iddle

and when the iddle (thanks to porsche61, and stevehose among others) was reached, the transition (1800 to 2200 rpm´s) was not good, and so on,...

apologies for not translating all this (probably the pics are selfexplaining), if questions, i will be really happy to answer:

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empezamos

sacamos las conexiones electricas y nos rompemos las manos soltando las tuercas del carbur trasero, la buena noticia es que una vez sueltas con la llave, se sacan facil a mano

vacio el refrigerante, y la buena noticia es que sale bastante limpio (un año en el circuito) y sin aceite o porquerias

corto los tubos del circuito del carburador, esto se podria evitar, pero no quiero quitar las cazoletas en el motor, asi que corto y me llevo todo la banco

bomba de gasolina mecanica

suelto vastagos de carbur trasero

y ya esta en la mano

idem delantero

se pulen las bases de los carburadores con lija de agua del 1200, para eliminar cualquier resto, y se pasa un spray de lubricacion para que quede limpio hasta el dia del montaje

suelto bomba del todo

proteger con trapos

 

[deQuincey]

second step

encajonamos los mihura, en cajas de rioja, nada menos

de momento se quedan aqui porque me falta alguna junta y porque necesito hacer sitio en la mesa para ellos, pretendo soltarlos al mismo tiempo en dos mesas, ya veremos

otras mierdillas

sobre todo la bomba gasolina me tiene preocupado

me temo que tendre que aflojar, pues el casquillo de laton del balancin esta en las ultimas, y por lo que he indagado no hay recambios, arregla me paso su bomba y esta todavia peor, asi que prepara la cartera
rehacemos el cajon de mierdillas, soltar, limpiar y engrasar

preparo juntas nuevas para la bomba, y presento la secuencia de montaje
tengo un problema, y es que la bomba debe ir muy bien centrada para que el vastago de impulsion quede en su sitio, pues me faltan los dos casquillos de teflon que debieran ir para esa funcion, asi que me los preparara un amiguete en el torno

presento

primera junta

baquelita

segunda junta, todo hecho a mano

bombon

varilla de mando

 

[deQuincey]

first disassembly, rear carb

hi

yesterday i started with the tear down of the rear carb (be aware in the pics "tras"=rear )

all this was done following the zenith disasemble instruction manual provided by mr. porsche61, thank you very much

i found some holes blocked and some dirty corners, but also a bad assembly of the float valve washers, and a wrong gasket !

do not know the overall influence, but for sure it was not doing any good

preparing new gaskets for ulterior assembly:

start, remove automatic choke, three tiny bolts and careful disingage of the bimetallic spring

disingage the top lever, 1,5 allen headed micro-bolt

undo top perimetric bolts

these are long bolts (only two are longer than the others)

problem at 1 o`clock, take a look at the gasket long hole, it opens a lower channel that should not be communicated, (see later photo comparing gaskets)

error in the gasket (classicgarage) middle is the original worn one (39 year old one), front is the new one (source BMW), below is the classicgarage wrong one, take a look to the 10mm hole situated at 1 o`clock, the old and new gaskets are good, not the one that lays on the table

another mistake, float valve washer 1mm instead of 2mm, and wrong material

good ones, 2 aluminium washers total thickness 2mm + new float valve with built-in springs (source BMW):

tiny holes were blocked with dirty and small paper particles

the evil ! that PIA gasket, has given me all the hole-blocking problems, as the paper has disintegrated particles into the holes, it is a spare from classicgarage, you should use the original baquelite with paper gaskets that will maintain the shape when that area is hot

some penetrating oil to clean and rest to try to remove mounting bolts, very rusty and worn out (that will be done tomorrow, hopefully)

almost cleaned and prepared for re-assembly

 

[Stevehose]

Fantastic - you've outdone yourself with this one! I am reliving my own nightmares with this but it will help future rebuilders. Am looking forward to the finished product(s) and the start up!

 

[deQuincey]

continue carb overhauling

after undoing the 4 big bolts, using the circular brush i cleaned the surfaces

finish with sand paper no.1200

clean the threads with tools and fat

overview of the working area with the educational USA carbs

detailed cleaning of tiny holes with ortodoncial brush, works fine!

choke, diaphgram:

problem with gasket, not ok, see vaccum-hole position

big intermediate spacer (baquelite), and paper seals

advice on this issue, there is a reported problem about clogging of these small holes, so i decided to increase the size of the spacer holes by 0.5mm, and the paper holes by 1mm:

for the spacer use drill:

for the paper, cutting tools

second stage diaphragm
old:

check 66mm distance

to be continued

 

[deQuincey]

continuation, rear carb finished

sand paper finish

one tip for gasket positioning: introduce a little all the bolts while moving slightly the carb body in order to let the bolts put the gasket in its place

take into account that in this pic there will be only two bolts left, the central ones, so the perimetral ones will be taken away

iddle shut off valve

iddle screw

ne gasket for choke heater housing

connect both joints

views

end

 

[deQuincey]

a peculiar thing, learning !

there is a fact, the first carb overhauling lasted for 2 weeks, the second one was done in two days

that is learning process !:mrgreen:

 

[61porsche]

Very well done!

Bakelite- if you ever do this again- counter bore for O-ring like factory solution. ( Half the thickness of the ring.)

Caution- throttle butterflys and shafts- the butterflys are matched and bevel edged to the bores. make sure you mark them well and take the time to make sure they are centered and extremely secure by the screws. I have found two carbs so far that appeared fine, screws were tight, but the butterfly could be shifted on the shaft! No moving allowed.

P.S. I have never found throttle shaft wear. Never. But if you do, there are ball bearing type replacements with teflon seals that a machine shop can put in. But then there's another tale on how to make a Zenith into a race carb..........

 

[deQuincey]

Very well done!
thanks, it is a pleasure to work with detail without hurry

Bakelite- if you ever do this again- counter bore for O-ring like factory solution. ( Half the thickness of the ring.)
i knew this, but it has been impossible to find spares in that way, in my first overhauling (8 months ago) i used the spare from classicgarage, IT WAS S**T !, a very bad gasket altogether made in neopren, it was even unable to maintain the shape and thickness...
so this time i decided to sand-paper and clean the old bakelites, together with paper gaskets, the traditional solution, but bearing in mind the clogging problem, with a little renewal of the design ;-)

Caution- throttle butterflys and shafts- the butterflys are matched and bevel edged to the bores. make sure you mark them well and take the time to make sure they are centered and extremely secure by the screws. I have found two carbs so far that appeared fine, screws were tight, but the butterfly could be shifted on the shaft! No moving allowed.
remark: i didn´t touch the butterfly-shaft assemblies, it seemed dangerous ! (now you gave me the reason for my guessing), ha, ha

P.S. I have never found throttle shaft wear. Never. But if you do, there are ball bearing type replacements with teflon seals that a machine shop can put in. But then there's another tale on how to make a Zenith into a race carb..........

thanks again

 

[deQuincey]

closing the renewal

only pending basic settings in the table, and then into the car, plus synchro,..., i am still studying the manuals, and some threads from this forum:roll:

happy to come to an end with satisfaction

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take a look to the scrap pile (how to get 2 good carbs out of 4 regular ones)

 

[deQuincey]

fixing the carbs in the table following the manuals: settings

table settings of the two carbs (before going to the car with them)

the following will be done with the throttle screw always in the high position of the cam (see point 1 in the first pic)

first step:

adjust the throttle butterfly in closed position while maintaning a gap of 1,5mm (see point 2 in blue) between the actuator (point 3) and the diaphgram rod

in this position the throttle buterfly rod must be fixed using the allen screw that can be seen in the right side of the previous pic



second step:

adjust a 3mm gap in the throttle butterfly while pushing the diaphragm rod up (see red displacement in next pic), to allow this displacement, prior to the fitting the nut and bolt should be undone (refer to two pics later to see the nut in question (marked as 2 in green colour))

the 3mm gap will be placed using a 3mm drill (number 1 in red), introduced in the throttle butterfly
set this position for the diaphgram using the bolt and fix it with the nut (number 2 in green in next pic)

you will need your finger to raise up the diaphgram rod (see 3 blue)

do not forget to maintain the throttle screw in the high position of the cam (see number 2 green in the next pic)

these are the basic settings for the carbs

now close the throttle mechanism box and prepare the place for the carbs in the car, prepare gaskets, nuts, hoses, ...

another setting very nice to do while they are on the table, is to close the iddle screws and undo 1 and 1/2 turn, so then they will be prepared for the synchronization

 

[deQuincey]

lets go to the car with the carbs

new teflon centers for the pump

see new ends (white caps) of the action bar

connect the accelerator bar end

connect water coolant hoses

connect oil pressure sender, old and new for vdo instruments

accelerator bars and plates cleaned and greased

new gasket, old style hand made in 1mm thick oiled paper

rear carb landing in its place

set of new washers and nuts

installation, the rear one is a PIA !

nice tools made life easy

electric connections

fuel hoses

probably tomorrow we will try to start it

 

[deQuincey]

start and syncro

today was "the day"

it was supposed to be the "easy" part, but that assumption was a mistake, new tricks and terrors were prepared for me in the mechanical jungle

i prepared everything, including a new spark-cables-tube, new sparks, check levels, battery,...

you can see my "invented device" for letting the gases from the head go to their appropriated place

so i start the engine, once, again, again,.... and nothing !

ok i considered correct that some time would be need to fill the carbs with fuel, but,...

so i checked the fuel pump, it was no suction, so i suddenly realize that a pump usually "must be fed", then i prepared this device, a reservoir with a transparent hose full with petrol and hanging from the hood

e voila !

so the engine runs at high iddle, but i saw that the pump was leaking a lot of fuel, i stopped at once, and i changed the pump for the old style model (rubber membrane)

then i checked everything for leaks, and so on and i restarted the engine

1700 rpm´s until the engine warmed up, a touch of the accel, and fall until 800 rpm´s

so a piece of hose in my ear, and i started synchronization

sounds good, so a little drove around the street, and,...that´s it !

done !

tomorrow i will check again the fast iddle in the automatic start, and warming up process, i will try to place a video

regards

 

[Stevehose]

Nice work but your engine isn't clean enough! :mrgreen:

 

[deQuincey]

Nice work but your engine isn't clean enough! :mrgreen:

ha,ha,ha,...
from now on it will be worse !
i am going to get it dirty, dirty, dirty !
...,the smell, you know,...that road, smelled like,....victory !

 

[eriknetherlands]

i found .......and a wrong gasket !

do not know the overall influence, but for sure it was not doing any good

disingage the top lever, 1,5 allen headed micro-bolt

undo top perimetric bolts

these are long bolts (only two are longer than the others)

problem at 1 o`clock, take a look at the gasket long hole, it opens a lower channel that should not be communicated, (see later photo comparing gaskets)

error in the gasket (classicgarage) middle is the original worn one (39 year old one), front is the new one (source BMW), below is the classicgarage wrong one, take a look to the 10mm hole situated at 1 o`clock, the old and new gaskets are good, not the one that lays on the table

another mistake, float valve washer 1mm instead of 2mm, and wrong material

As this thread is the best on our site detailing the steps to do your own carb rebuild, I thought I'd aid in improving it a bit ( hardly possible as it's already near perfect)
@deQuincey reported improper gaskets in a kit. This seems to have an explanation:
In my '76 dated dutch bmw service manual the difference of the gaskets is explained: it links the gasket shape to the type of top cap (float chamber ventilation) that you have, see enclosed picture of the book.

Translation of the text:
For vent tower A you can use both gaskets A and B.
For vent tower with side pipe B you can use gasket B, or you can use a modified gasket A to create the oblong hole.
The gasket on the table in DeQ's post wasn't wrong after all.

If you rebuild a set, choosing the gasket B with the oval hole will work for sure. Gasket A also works, but if you have vent tower with side pipe B you just need to elongate the round hole, see dimensions in drawing.

 

[eriknetherlands]

Another aspect: I have 8 dead carbs as spares, and in most of them a gasket was missing, likely by previous owner interference; the rubber ring gasket on the idle shot off valve. Also in the pics of DeQ above they are missing.

Note how in the picture there is a metal ring, and a rubber ring to seal the idle shut off valve to the throttle valve body.
I think that a missing rubber seal may lead to additional false air being sucked in.

I'll add some dimensions of the parts later on, so other are able to source something similar.

 

[deQuincey]

Another aspect: I have 8 dead carbs as spares, and in most of them a gasket was missing, likely by previous owner interference; the rubber ring gasket on the idle shot off valve. Also in the pics of DeQ above they are missing.

Note how in the picture there is a metal ring, and a rubber ring to seal the idle shut off valve to the throttle valve body.
I think that a missing rubber seal may lead to additional false air being sucked in.

I'll add some dimensions of the parts later on, so other are able to source something similar.

it is interesting , but you can easily replace it using some light loctite in the thread, it will seal

 

[Belgiumbarry]

i admire your courage to restore those over complex Zenith's.... i would have dumped them from minute one for a pair of webers.

 

[deQuincey]

i admire your courage to restore those over complex Zenith's.... i would have dumped them from minute one for a pair of webers.

first time is scary, yes, but once you learn how to do it, you can do blind eyed

and they are so good carbs