rough iddle issue again

[deQuincey]

butterfly question

regarding the bottom buterflies, i want to know which position should i expect when i make the following actions,

i want to know if they must be closed, a little open, or fully opened when:

1- before i start a cold engine from the begining without pushing the accelerator pedal:

butterfly 1 should be:
butterfly 2 should be:

2- before start the car, but after pressing the accelerator pedal to enable cold start mechanism:

butterfly 1 should be:
butterfly 2 should be:

3- when car started but the engine still cold and rpm´s in high iddle speed, i assume the position of butterflies will be like in point "2", right ?

4- when car is warm, i push accelerator pedal, and get low iddle speed, then:

butterfly 1 should be:
butterfly 2 should be:

 

[deQuincey]

The head gasket I used was from Elring. The torque instructions are:
1st. step: tighten to 60+/-2Nm
Wait 15 mins.
2nd step:torque angle 33+/-3 degrees
warm up engine 25 mins.
3rd step:torque angle 35+/-5 degrees

I followed this procedure and haven't had any problems after 1000 miles of driving (so far...) Retightening is not necessary with the Elring gasket.

hi

i have to say that i haven´t ever seen that procedure, instead, the procedure i found in HAYNES, and in the car original manual:

tighten of cylinder head bolts (engine cold), in three stages:
1- 35 to 45 N.m
2- 60 to 65 N.m
3- 68 to 72 N.m

after 1000 km, with engine cold, slacken off the head bolts a bit and tighten them down to final torque setting in the sequence pattern specified

 

[61porsche]

Throttle plate operation

Condition 1:

Both butterfly plates are slightly open.

Plate1 ( Primary) is open by the amount of the screw on top.

Plate 2 ( Secondary) is preset to have a small opening by another screw that is at the top of your picture and beneath. ( See manual for exact preset)

Neither plate, when held to a light is completely closed. This is why the balance caps are necessary. If you use this method, the plastic cap that covers the choke linkage must be in place also.

Condition 2:

Plate 2 Same as above.

Plate 1: The pushing of the accelerator sets this butterfly open more. Inside the choke housing and connected to the shaft is a stepped cam, spring loaded that opens the shaft and in turn opens the butterfly by about 1/8". That cam is hooked onto a thermostatic and electric spring that when heats up puts tension on the cam towards it's closing position.
When you tap the accelerator, the cam resumes it's normal running position and idle drops from 1800 to 850 rpm or so. There are two other actions which effect this action. The choke daiphram which sets a range and the action of the choke rod to aid in setting the cam to the 1800 rpm.

3. Yes.

4. Like condition 1.

The setting of butterfly 2 is very important for idle and syncronizing. The opening can be checked with a feeler guage in addition to the linkage preload. Both carburators should be equal.

Trick- since we know that this butterfly is slightly open, I put the palm of my hand over it very briefly to see if one carb is pulling more by feel. Make every effort to get them open the same amount and not too much since 80% of the action is on the other butterfly.

P.S. Your picture- the choke diaphram cap- the one with the screw/ nut is better than the closed cap. This screw- the amount of threads showing should be equal to both carbs.

 

[61porsche]

Head bolt retorqe

Not recommended.

Oil finds it's way into the threads and holes, then solidifies.

M30s are prone to develope cracks in these areas. It is very important to check and chase out these when rebuilding or head work.

 

[bill]

Bolt torque

Just to clarify, the bolt tightening procedures I followed were those recommended by the gasket manufacturer (Elring.) I hadn't heard of the "degree" procedure either (always used the 3 stage torque sequence previously.) Again, Elring does not recommend re-torquing (although the Blue Book does) after 1000 km.

 

[deQuincey]

hello,

i am happy, yes today i have done a nice job

i have not checked the iddle, but i have been taken a deep look to both carbs, trying to compare one with the other, and,...

i found in the second stage vacuum box a slight difference, when i pressed the back of the diaphragm, in the front carb, the vacuum was audible, and when released the air comes out by the tiny hole in the carb body, but when i did it in the rear carb, nothing, the diaphragm was very difficult to press and no sound of air going out, so,... a difference !

i removed both vacuum boxes from the carbs and compared them

in the case of the rear carb, the air could not pass because the holes and pipes were blocked, and the gasket was almost destroyed , so i cleaned everything and installed a new gasket, ...but that was not everything

i checked the diaphgram assembly and i found that the length of the rod was incorrect, it was 75mm instead of 66mm (I FOUND THIS IN THE NICE MANUAL THAT STEVEHOSE SENT ME, THANKS)

so i modify to the correct leght, clean it (it was almost blocked), greased it with a spray oil, and reassemble everything

i have not checked it but, can you tell me if i will find any difference ?

 

[deQuincey]

Just to clarify, the bolt tightening procedures I followed were those recommended by the gasket manufacturer (Elring.) I hadn't heard of the "degree" procedure either (always used the 3 stage torque sequence previously.) Again, Elring does not recommend re-torquing (although the Blue Book does) after 1000 km.

sorry do not know elring, my gasket was goetze, and it did not include instructions

interesting information that one that you provide us with

thanks

 

[61porsche]

Vacumn Box

Weeeeeeeeeee! It means that you've just added to your driving experience at speed!

The secondary butterfly or barrel will now open. The new rod length will mean it will open more.

 

[deQuincey]

Weeeeeeeeeee! It means that you've just added to your driving experience at speed!

The secondary butterfly or barrel will now open. The new rod length will mean it will open more.

and that means, .....speed ? power ?

 

[61porsche]

yes. yes. and the use of more petrol.:-D

 

[Stevehose]

it means when you press hard on the accelerator pedal your secondaries will open, producing an audible roar/suction sound, followed by increased acceleration and smiles. One of the payoffs of a carb induced car.

 

[deQuincey]

to mr. porsche: i checked the jets

you might remember this conversation in another thread in which you presented the famous tip for carbs

"In DQ's picture, I would usually see 80 on the primary and 4or6n on the secondary. Auto equipped cars had 100 on the primary for 2800s. But that's about it.
The same size jets were used on the Mercedes Zeniths.
I tried the 100 from another set I had, didn't help me."

ok, as promised some time ago, I have checked the numbers in the carbs that are installed in the car, and this is the answer:

you can see 80 and 120, which is the primary ?

and what does this mean ?

remark: i have 4 carbs, 2 in the car, and 2 on the shelf (USA version carbs) i use these 2 for learning and spares

 

[deQuincey]

it means when you press hard on the accelerator pedal your secondaries will open, producing an audible roar/suction sound, followed by increased acceleration and smiles. One of the payoffs of a carb induced car.

ok, but nothing that will help to solve my rough iddle issue :cry:

the only point on this is that i am begining to take apart the fear of touching the carbs (and this is due to having 2 spare carbs for learning and as a safe "B-plan")

 

[Stevehose]

Before tearing into your carbs, retrace your steps, what happened to cause the poor idle? Are you getting spark on each plug? Check for vacuum/gasket leaks at idle. Did you find a meter?

ok, but nothing that will help to solve my rough iddle issue :cry:

the only point on this is that i am begining to take apart the fear of touching the carbs (and this is due to having 2 spare carbs for learning and as a safe "B-plan")

 

[deQuincey]

Before tearing into your carbs, retrace your steps, what happened to cause the poor idle? Are you getting spark on each plug? Check for vacuum/gasket leaks at idle. Did you find a meter?

no i am afraid not, i do not have a meter, and that will take time (i will answer your mail in due time, i have to check your links)

i do not mean that i am going to tear down the carbs, do not worry ;-)
what i am saying is that my new procedure is: when i see something different in the carbs, or something strange, first i go to the "learning carb" and i try to disassemble it there, when i see that is possible, and easy, and no collateral effects, i go back to the car

and it works !

 

[61porsche]

Vacumn box

Replacing the bad diaphram will help the idle some amount. There no longer is a leak from that component.

Did you by chance notice the amount ( number ) of coils on the spring acting on the diaphram? 8,9, or 10.?

 

[deQuincey]

Replacing the bad diaphram will help the idle some amount. There no longer is a leak from that component.

Did you by chance notice the amount ( number ) of coils on the spring acting on the diaphram? 8,9, or 10.?

hi

they are 10 coils in each spring ! is it ok ? i have read that they can be cut down to 9 or 8, what for ?

--------

by the way, have you checked a post two or three before this one ? i posted a photo of my jets, they are numbers: 80 and 120,

what can you tell me from that ? also interested if they are well positioned, 1st and 2nd ?

thanks

 

[61porsche]

Carb Answers

1. The ten coils or spring windings are correct. The spring has an effect on the timing of the opening for the secondary. Less coils, faster opening ( 2800s had the fastest opening) . Most important is that they are equal for both carbs.

If an owner's goal was for slightly better performance than gas mileage or a larger displacement and modified engine is used, less coils on this part would make the engine more responsive by opening the secondary sooner which results in more and faster fuel flow.

2. Jets: These are correct for air jets and position. The rule is the smaller number jet goes in the primary side. This barrel is the smaller one and has the choke flap. It is also the side closest to the cylinder head. Your arrow number 1, for reference.

 

[deQuincey]

flying in heaven !

i am very happy !
i want to thank steve and 61porsche
smooth iddle has returned !
i have done a little more work:

i have set this two at 40mm, precisely

and i have update this diaphragm-choke system

then, some adjustment, and voilá, fine and smooth iddle, at 1000rpm´s, i have tried to slow down a little, but it is not as smooth, so i will let it there !

thanks

remark:

when i opened the old diapghram choke boxes i found this oily, dirty "liquid", it seemed gasoline mixed with oil and dirt, can you tell me why ?

 

[61porsche]

Oh happy days!

Glad to hear it runs better for you.:-D

Oil on the choke diaphram... probably from your valve issue in the past. Pls. make sure that diaphram is in tact. (Without holes and flexible.) There is a very small spring on top not in your photo.

Long explanation- The engine is an air pump. If a cylinder isn't firing correctly, too much advance, backfiring, etc. the resultant intake charge as well as the exhaust goes to the path of least resistance depending on the cycles. This mixture of oil and gas can go out the exhaust, out the top of the carb, and into the passages of the carb with the results you've shown in the photos.