your carbs are way too clean!
rough iddle issue again
- Thread starter deQuincey
- Start date
the diaphragm is ok, and a new spring has been placed also conviniently
yesterday was a fine day, i will try to repeat it today, you never know if it is a wistle blow !, something that happens once, and never repeats, so today (as it is sunny and cold and dry again) will be a 200km ride to check everything one second time
i get your point on the long explanation, it might has been that way, but i will re-check in a month time or so
also i will try to make a syncronising device like yours, just one question:
when you place the two cups on the carbs to check the suction, that is ok, i can understand, but: what are you doing with the pipe that is in the top of the head case ?, in the manual it says that you have to place another fake tool there to produce the effect of the air filter, what do you place there instead ?
yeap !, i try to maintain things clean ! it is the best way to check problems, think that i im using the car when i go to work, an usually i have to check things in the engine area with my suit on, so clean and tidyness is essential, ha, ha
Air cleaner tool 130000
For me, I have that connection capped at the manifolds.
I beleive it to be an early attempt at positive crankcase ventilation and emissions that carried on to fuel injection. Using it does require that the engine and items such as the dipstick be sealed so as not to introduce unwanted air/ leaks into the combustion process.
Since we know the result of the adapter is to lower the rpms by 100 or so, the pipe or tool must have a very small opening that restricts enough air for the end result.
A suitable piece of hose or pipe, the diameter of the nipple on the valve cover, a small tap for connecting the vacumn lines, and a cap of sorts ( beaker cap) with a hole of a diameter to reproduce the drop in rpm would reproduce the result. I beleive the assumption is that if that vacumn connection from the front of the manifolds is left open it introduces enough air to raise the idle.
Since there are at least two versions of syncrometers, it appears this hose/ line is hooked on to the meter which must have a calibrated air bleed hole.
That's my theory. Anxious to hear from others that have had one in thier hand.
For me, I have that connection capped at the manifolds.
I beleive it to be an early attempt at positive crankcase ventilation and emissions that carried on to fuel injection. Using it does require that the engine and items such as the dipstick be sealed so as not to introduce unwanted air/ leaks into the combustion process.
Since we know the result of the adapter is to lower the rpms by 100 or so, the pipe or tool must have a very small opening that restricts enough air for the end result.
A suitable piece of hose or pipe, the diameter of the nipple on the valve cover, a small tap for connecting the vacumn lines, and a cap of sorts ( beaker cap) with a hole of a diameter to reproduce the drop in rpm would reproduce the result. I beleive the assumption is that if that vacumn connection from the front of the manifolds is left open it introduces enough air to raise the idle.
Since there are at least two versions of syncrometers, it appears this hose/ line is hooked on to the meter which must have a calibrated air bleed hole.
That's my theory. Anxious to hear from others that have had one in thier hand.
I have not used the simulator as the book suggests, I just set my idle a little higher than I want and it drops when I put the air cleaner back on.
For me, I have that connection capped at the manifolds.
thank you very much for all the infos
by the way, when it suits you, can you pic some photos of this as it is in your car ?
a new question on the same topic
hi
i have one long question again
the car seems to have an acceptable iddle, and somehow i have got a suction equilibrium between both carbs, but i am worried about the iddle screw position, it is ALMOST closed !, surprised, is this normal ?
because when i look to the manual it says that 1&1/2 to 2 turns open is the normal thing
i have found that even when i close the mentioned screw totally, the iddle goes well, and on the contrary when i open that screw the revs go up or the engine starts to be unstable (lack of syncronisation)
knowing that to run an engine there must be fuel somewhere, i was anxious to see where was the gasoline coming from, and i found this:
when the engine is iddling, you can clearly see a tiny drop of gasoline getting out from this red arrowed small hole (is this a brass pipe ?)
so there is for sure a contribution to the mixture that is comming from this point, and what it comes out from the iddle screw is an addition
is this right ?
please advise !
hi
i have one long question again
the car seems to have an acceptable iddle, and somehow i have got a suction equilibrium between both carbs, but i am worried about the iddle screw position, it is ALMOST closed !, surprised, is this normal ?
because when i look to the manual it says that 1&1/2 to 2 turns open is the normal thing
i have found that even when i close the mentioned screw totally, the iddle goes well, and on the contrary when i open that screw the revs go up or the engine starts to be unstable (lack of syncronisation)
knowing that to run an engine there must be fuel somewhere, i was anxious to see where was the gasoline coming from, and i found this:
when the engine is iddling, you can clearly see a tiny drop of gasoline getting out from this red arrowed small hole (is this a brass pipe ?)
so there is for sure a contribution to the mixture that is comming from this point, and what it comes out from the iddle screw is an addition
is this right ?
please advise !
Carb tips continued..
Dequincey,
Fuel dripping from where you indicated means:
1. Fuel level too high, gasket under the float valve loose, float hanging up.
It is adjusted by the thickness of the washer under the valve. But can only be adjusted by the thickness limit of 2mm otherwise the float swing will be interrupted.
I have also found carbs that the fuel section gasket is wrong and hits/ scrapes the float.( There are several that come in the kit and using the wrong one is easy. If the gasket extends over into the fuel bowl , it's the wrong one. It can be modified though.)
2. Way too much air- meaning the throttle plates ( butterflys) need to be closed slightly.
3. The choke venturi- ( where you pointed to fuel drip) there are gaskets. The large brass nut on the side holds tension on this part which has a small rubber gasket that must seal it to the body. If leaking it is possible for vacumn to pull fuel up and out the seal vs. the hole.
Yes, number three or your pointer in your last photo has a brass insert.
No, no fuel at idle is to come from there.
Fuel mixture at idle comes from a small hole below the butterfly. The amount of fuel comes from the idle screw when warm. But the carb should be able to run the car at a low rpm- 550-600 with the mixture screws closed which means not all the fuel comes from the mixture screws.
Fix the dripping fuel. You will be amazed at how smooth you can make it run. I find the idle screw settings with modern gas ( 10% ethenaol, premium) to be more open than the factory. I also find that the setting is different for each carb rather than the manual procedure. (I tune each carb for a bank of cylinders corresponding to the intake manifold.)
The butterfly adjustment- what I do is start from closed then slowly turn till the linkage moves slightly. But you have to use some method to determine how equal that is.... hose, manometer, air flow meter...etc.
With the fuel dripping, even a bit, it will make the idle rough.
Dequincey,
Fuel dripping from where you indicated means:
1. Fuel level too high, gasket under the float valve loose, float hanging up.
It is adjusted by the thickness of the washer under the valve. But can only be adjusted by the thickness limit of 2mm otherwise the float swing will be interrupted.
I have also found carbs that the fuel section gasket is wrong and hits/ scrapes the float.( There are several that come in the kit and using the wrong one is easy. If the gasket extends over into the fuel bowl , it's the wrong one. It can be modified though.)
2. Way too much air- meaning the throttle plates ( butterflys) need to be closed slightly.
3. The choke venturi- ( where you pointed to fuel drip) there are gaskets. The large brass nut on the side holds tension on this part which has a small rubber gasket that must seal it to the body. If leaking it is possible for vacumn to pull fuel up and out the seal vs. the hole.
Yes, number three or your pointer in your last photo has a brass insert.
No, no fuel at idle is to come from there.
Fuel mixture at idle comes from a small hole below the butterfly. The amount of fuel comes from the idle screw when warm. But the carb should be able to run the car at a low rpm- 550-600 with the mixture screws closed which means not all the fuel comes from the mixture screws.
Fix the dripping fuel. You will be amazed at how smooth you can make it run. I find the idle screw settings with modern gas ( 10% ethenaol, premium) to be more open than the factory. I also find that the setting is different for each carb rather than the manual procedure. (I tune each carb for a bank of cylinders corresponding to the intake manifold.)
The butterfly adjustment- what I do is start from closed then slowly turn till the linkage moves slightly. But you have to use some method to determine how equal that is.... hose, manometer, air flow meter...etc.
With the fuel dripping, even a bit, it will make the idle rough.
I had this problem - like Jerry says it is either the float level leaking or more likely too much air through the butteflys which sucks the fuel out of the tube and makes the idle mixture adjustments not work as much if at all. Back off the butterfly screws until idle almost dies and see if A) you don't drip fuel anymore and B) your idle mixture screws work again and by opening them up your idle goes back up. Let us know.
thanks
thank you both jerry and steve,
today i have been fixing the carbs only adjusting the screws (not opening them)
i reached a fine smooth iddle at 900 rpm´s, but the way to get it has been closing the butterflies, and also closing the iddle screw of the front carb,
i proceed like this:
1- with the engine warmed up, stop the engine, i removed the air filter assembly
2-and then i closed the two iddle screws of both carbs completely, and then oppened the screws 1+1/2 turn each one, then started the engine again
3-the iddle was terrible, the engine was running very instable. i tried to smooth it a bit by tighthening the screw that opens the butterflies in each carb, the revs went up, so i started closing the iddle screws a bit until i got 1100rpm´s, but it was unstable
4-then i closed the iddle screw in the front carb, and progresively the iddle became smoother, then i touched a little bit the air butterfly of that front carb, until it was fine
5-i closed the air filter assembly, and run a car for a mile, went back and check: result by now:
- perfect and smooth iddle at 900 rpm´s
- no leaks in the choke venturi
6- but a new problem arised: the engine becomes very rough at 1800 until 2200 rpm´s , from 2200 and up (rpm´s) no problem, it is smooth again
?????, any idea ????
i went for a longer ride and the iddle maintained always smooth at 900 rpm´s when i stopped, but in the transition through 1800-2200 rpm´s the engine is unstable and stumbles
remark: remember that i reached the iddle by closing the iddle screw more in the front carb than the one in the rear, when i checked the fine tuning tip (jerry´s tip, inserting a thin cable) it happens this:
1-the front carb revs up the engine
2-the rear carb dies the engine
i have checked the hiss sound in both carbs with a home made sthetoscope and it seems similar sound
thank you both jerry and steve,
today i have been fixing the carbs only adjusting the screws (not opening them)
i reached a fine smooth iddle at 900 rpm´s, but the way to get it has been closing the butterflies, and also closing the iddle screw of the front carb,
i proceed like this:
1- with the engine warmed up, stop the engine, i removed the air filter assembly
2-and then i closed the two iddle screws of both carbs completely, and then oppened the screws 1+1/2 turn each one, then started the engine again
3-the iddle was terrible, the engine was running very instable. i tried to smooth it a bit by tighthening the screw that opens the butterflies in each carb, the revs went up, so i started closing the iddle screws a bit until i got 1100rpm´s, but it was unstable
4-then i closed the iddle screw in the front carb, and progresively the iddle became smoother, then i touched a little bit the air butterfly of that front carb, until it was fine
5-i closed the air filter assembly, and run a car for a mile, went back and check: result by now:
- perfect and smooth iddle at 900 rpm´s
- no leaks in the choke venturi
6- but a new problem arised: the engine becomes very rough at 1800 until 2200 rpm´s , from 2200 and up (rpm´s) no problem, it is smooth again
?????, any idea ????
i went for a longer ride and the iddle maintained always smooth at 900 rpm´s when i stopped, but in the transition through 1800-2200 rpm´s the engine is unstable and stumbles
remark: remember that i reached the iddle by closing the iddle screw more in the front carb than the one in the rear, when i checked the fine tuning tip (jerry´s tip, inserting a thin cable) it happens this:
1-the front carb revs up the engine
2-the rear carb dies the engine
i have checked the hiss sound in both carbs with a home made sthetoscope and it seems similar sound
Last edited:
Condition one response:
The front carb is too lean. Caused by the butterfly being a bit too open close it a bit or the idle screw needs turned out a bit more.
Condition two response:
The back carb is too rich. Open the butterfly up a touch. Or screw the idle screw in a bit more.
When using the tip of partially inserting a wire, etc. in the idle air hole, the carbs should give the same reaction to speed or stumble.
The hose method- is an aquired skill. Because the other secondary butterfly is slightly open there is air coming in from there.
If all is close, there is a direct relationship where the idle screws, opening position of the butterflies all are small adjustments. This mixture at idle effects the transition at 1800-2000. From there on the main jet takes over which is why it smooths out again.
You're getting closer.. keep at it in small increments and be patient.
The front carb is too lean. Caused by the butterfly being a bit too open close it a bit or the idle screw needs turned out a bit more.
Condition two response:
The back carb is too rich. Open the butterfly up a touch. Or screw the idle screw in a bit more.
When using the tip of partially inserting a wire, etc. in the idle air hole, the carbs should give the same reaction to speed or stumble.
The hose method- is an aquired skill. Because the other secondary butterfly is slightly open there is air coming in from there.
If all is close, there is a direct relationship where the idle screws, opening position of the butterflies all are small adjustments. This mixture at idle effects the transition at 1800-2000. From there on the main jet takes over which is why it smooths out again.
You're getting closer.. keep at it in small increments and be patient.
MMercury
Well-Known Member
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As you are aware, carburetor tuning can be more of an art than a science. At best, it is a compromise between idle and wide-open throttle. What you may be describing is sometimes referred to as a progression or transition issue. You may have gotten the idle to where you want it, but it sounds like your fuel mixture is leaning out when you are transitioning to or operating at part-throttle.
Your idle settings influence both idle and part-throttle engine operation. This means that your adjustments and jetting are necessarily compromised, as they serve both idle and low speed part-throttle operation. As you crack the throttle/s from the closed "idle position," the throttle plates expose small ports in the venturi. In theory, as those tiny ports are uncovered, the existing vacuum signals the carburetor/s to feed more fuel to the engine. By screwing in the mixture screws, you are leaning out the idle mixture on one or both carbs at the expense of the part-throttle operation. Adding multiple carburetors merely increases the chances of upsetting the mixture balance from off-throttle to part-throttle. Per 61P's observations, you may have one carb leaner than its sister carburetor.
You are not the first person to experience this or similar carb-related problems. This thread may give you some ideas: :wink: http://www.e9coupe.com/forum/showthread.php?t=6275
And of course, looking at this could never hurt: http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/13000040.html#refertoc
