Adjusting Webers For Mi16

[Saveit 0]

Hi there,

 

Firstly, i have already searched around, but i cant seem to find any info on how to correctly setup and adjust webers for a 205 with an mi16 engine. Secondly my question is more specific so i need an answer from you clever people

 

The thing is, that i have a set of original weber carbs from a 205 1.3 rallye (eurospecs). I am planning on using those on my mi16. I read on the internet, that there are 4 important things to setup on a set of webers. These were; Choke/venturi size (?), Emulsion tubes (?), Main jet and Air corrector.

 

How much do you think has to be changed to use such carbs from a 1.3 rallye on an mi16? What specs are you guys running your carbs on? And lastly, what is the procedure for setting up the carbs with the specific engine (as regards to tuning them in correctly and so on).

 

Thank you!

[hexhamstu 9]

i would have thought the webbersfrom a 1.3 rallye would be way to small to run an mi16 to its full potential.

[edbar 6]

Pretty sure that you would want 45's for an mi-16 engine as 40's are probably going to be restrictive. Dont know what size chokes and jets actually work on an mi but my guess is somewhere around 36mm-38mm chokes, not sure but most people have 45's on the 1.9 and 2.0ltr engines.

[Saveit 0]

I read that whether it is 40's or 45's doesnt really matter. Its the venturi size that matters. I dont know if this is true or not though.

[edbar 6]

being a 40 means it is 40mm bore so you are restricted on what the choke sizes can go up to. Yes the venturi is the bit that matters but its getting one big enough in a 40 dcoe. Again i cant give you a yes or no answer but i spoke to skip browns and des developments and they said i needed 45's for my 1.9 8v and an mi16 engine will want more air than an 8v.

[projectpug 0]

Yes you will definately want 45's for an mi16 engine. You should only really use 40's on a standardish 1.6/1.9 8v.

[andy0075 9 1 Cars]

This answeres all your questions : http://www.geocities.com/MotorCity/9526/carbs.html

 

cheers, Andy

[Saveit 0]

Ahh interesting. But take a look at this:

 

"For example: a two litre engine giving its maximum power at 6000RPM will require a venturi size of 36mm, and therefore an ideal barrel size of 45mm (36 * 1.25), for this application 45 DCOE is the ideal solution, however a 40 DCOE will accommodate a 36mm choke, so if funds are limited and the engine is not going to be tuned further then 40 DCOEs will do the job."

 

And yes, i know that the mi16 not peaks at 6000RPM but about 8000RPM. But its neither a two litre engine. So perhaps if we were to adjust this example a bit so it fits the mi16, i could look something like this:

 

"....a 1900cc engine giving its maximum power at 7000RPM will require a venturi size of 36mm...."

 

Now we still need the last 1000RPM since 36mm venturi probably will restrict above 7000RPM. But then again, how often do you really rev it to a full 8000RPM? And maybe it will not pull perfectly above 7000RPM, but it will still run, maybe just at 80% power. This is just my thoughts.

 

How much driveability do you think i will use by using 36mm venturi in an 40 DCOE on the mi16?

 

(Perhaps we can wind up getting this thread Pinned for the future if we come to any conclusion at some point. Then people will know what to expect and what to look for when doing carb conversion)

[andy0075 9 1 Cars]

On my tuned 1.9 8V i tryed both. 40 and 45 DCOE

The venturisize in the 40 DCOE was 32mm and the engine was very strong at low rpm but

above 5000rpm i felt that the engine would go on but it couldn't :-)

 

With the 45 DCOE and 36mm venturis the engine is stronger at high revs and it

extremely revs up fast to over 8000 rpm.

 

There is a difference if you use a 36mm venturi in a 40 DCOE or a 45 DCOE, because

in a 45 DCOE more air can go through it.

 

The venturi reduce the diameter of the carb in order to accelerate the air. If the

diameter of the venturi and the carb is nearly the same, then this effect is minimized.

So you can't use a 38mm Venturi in a 40mm Carb. There should be a difference of

aprox. 7mm between the venturi and the carb :

 

40 DCOE - max venturi 34mm

45 DCOE - max venturi 38mm

 

If you have a big venturi the airflow at low rpm is low -> low power, but at high rpm

enough air can get through it to produce maximum power.

If you have a small venturi the airflow at low rpm is high -> high power, but it limits the needed

airflow at high revs.

 

It is your decision what you want and where the power should be.

The MI will definetily run with 40DCOE and 34mm venturis, but 45DCOE and 36-38mm is needed if

you will get all out of your engine

SORRY FOR MY BAD ENGLISH ! IT's NOT MY NATIVE LANGUAGE.

 

Andy

[jplautomotive 0]

just a quick one , has any body ever put 48s on a mi ?

 

sorry for the hijack lol

 

jonny

[Saveit 0]

On my tuned 1.9 8V i tryed both. 40 and 45 DCOE

The venturisize in the 40 DCOE was 32mm and the engine was very strong at low rpm but

above 5000rpm i felt that the engine would go on but it couldn't :-)

 

With the 45 DCOE and 36mm venturis the engine is stronger at high revs and it

extremely revs up fast to over 8000 rpm.

 

There is a difference if you use a 36mm venturi in a 40 DCOE or a 45 DCOE, because

in a 45 DCOE more air can go through it.

 

The venturi reduce the diameter of the carb in order to accelerate the air. If the

diameter of the venturi and the carb is nearly the same, then this effect is minimized.

So you can't use a 38mm Venturi in a 40mm Carb. There should be a difference of

aprox. 7mm between the venturi and the carb :

 

40 DCOE - max venturi 34mm

45 DCOE - max venturi 38mm

 

If you have a big venturi the airflow at low rpm is low -> low power, but at high rpm

enough air can get through it to produce maximum power.

If you have a small venturi the airflow at low rpm is high -> high power, but it limits the needed

airflow at high revs.

 

It is your decision what you want and where the power should be.

The MI will definetily run with 40DCOE and 34mm venturis, but 45DCOE and 36-38mm is needed if

you will get all out of your engine

SORRY FOR MY BAD ENGLISH ! IT's NOT MY NATIVE LANGUAGE.

 

Andy

 

See this is very interesting. Could you tell me which jets and so on you used in your 40 DCOE 34mm venturi mi16 setup? I would like the overall specs of the carb setup.

 

just a quick one , has any body ever put 48s on a mi ?

 

sorry for the hijack lol

 

jonny

 

Hehe no problem

[midnight motorsport 0]

See this is very interesting. Could you tell me which jets and so on you used in your 40 DCOE 34mm venturi mi16 setup? I would like the overall specs of the carb setup.

 

 

 

Hehe no problem

 

See this is very interesting. Could you tell me which jets and so on you used in your 40 DCOE 34mm venturi mi16 setup? I would like the overall specs of the carb setup.

 

 

 

Hehe no problem

 

hi there, i run 45s on my mi quite successfully,

originally i was going to run 40s as i was going to keep the engine standard and 40s will just about cope on a standard engine, you can get 36 mm chokes for a 40dcoe and this is what you would use,

 

as for jetting it really is a bit of an art, as a start point though go with 140 mains, 180 airs, and somthing like f16 emmulsion tubes, on the main circuit, and then id try 45f9 for idle, and 35 pump jets, in either a 45 or a 40, if your engine is standard then use 36 mm chokes in the 40s and the 45s 38s in the 45s will poss get you a few bhp in a slightly modded engine at the top eng, but midrage tractability will be lost,

If you are still looking for carbs, try to get a set of dcoe 152 G the 'G' stands for german spec, and they have another progression hole drilled in them, this was to help with 16v engines as they required more fuel on the progression stage between the change over from the idle/first stage progression circuit, to the main circuit, this was due to the extra low down power/torque that 16v engines natually make,

this makes the low down drivability alot smoother, as you tend to get a lean dip in the fuel curve without this extra progression hole,

Or try to find a set of dellorto dhla carbs as these have an extra progression already too, and are very similar to set up, but harder to find jets for so poss not for you?

 

To really set carbs up well, you need an afr (air fuel ratio) meter, (wide band lambda) , and lots of patience, oh and a friend sitting next to you seeing what is going on when you are driving,

 

Basicly the idle jets do most of the fueling up to about 2500-3000 rpm, then the mains take over,

Get the mains sorted first, if you have the fuel rich all the way through come down on the main jet, if its lean go the other way, if you have it so it if fine in the midrage but goes leaner in the upper rev range, go smaller on the air jet.

Basicly the main jet increases/decreases the fuel across the whole rev range from 2500 upwards, The air jets will have a very small effect on the lower rev range but have more of an effect on the upper rev range, ie bigger air will make it go leaner at the top, smaller will make it go richer,

you can also use the pump jet to fine tune the top end, as this becomes a high speed fuel jet once the engine is really going, so if you have it almost rite but it just goes thin at the very top, try the next size pump jet,

Next the idle circuit,

to adjust the idle mixture you use the screws on the top of the flanges that bolt to the inlet manifold, out to richen, in to lean off,

As a start wind them out about 1 turn

A good rule to start with for idle jet size is, if the screws are out about 1 to 1 1/2 turns and the mixture is ok on idle. start from here,

the problem with the idle jets is, they are not really idle jets, they are first stage progression jets, the idle mixture is controlled by the mixture screws as above,

basicly you need to drive around in the lower rev range checking the mixture, if its lean go up a size, rich, go down, you can also fine tune the upper and lower part of the idle mixture, the jets are marked, ie. 45f9, the 45 is the fuel jet the f9 is the air, there are lots of variations, but you can basicly get anysize jet ie 45, 50 55 etc, with any air jet ie f9, f8, f7 etc....

 

But normally an f8 or f9 will do and just jet the idle using the 45, 50.......

remember though if you go up or down on a jet size you will have to adjust the idle mixture screw to compensate for this, as the idle mixture is part of the first stage progression fuel circuit,

 

I hope this is of help to anyone trying to set up these carbs,

But do please remember this is only a few basic steps to setting up a weber, but should get you somewhere closer to running well,

these carbs are a work of art and very fine tunable, if you have the time and can get you head around it,

 

another helpfull thing is a book called Weber Carburettors, by John Passini, very good, and shows all the things in much more detail, well worth the few pounds if you are considering tuning these carbs yourself,

 

regards jay

[Saveit 0]

Thanks Jay! Now i have something to start with. The engine will be used for offroad racing, so whether it runs well or not is not really important. It just has to run good on full throttle. A bit rich in mixture would not hurt Still think i should used the setup that you mentioned or?

[midnight motorsport 0]

Thanks Jay! Now i have something to start with. The engine will be used for offroad racing, so whether it runs well or not is not really important. It just has to run good on full throttle. A bit rich in mixture would not hurt Still think i should used the setup that you mentioned or?

 

Well the problem is, that is just a starting point, really,

Before i go into it more, that info that andy has put up in this post is very good, iv just read it, so use this to help with the carb setting up,

As for the carbs, are you going to use 40s or 45s,?

 

I can tell you what i was using in my set up, but my engine was not stock,

But you should only run richer if so, and this should be ok. sort of, maybe lol!!

 

45 dcoe

135 mains

165 airs

36 mm chokes

f16 emulsion tubes

60f8 idles ( these are huge!! but mine had lean surge so these were to over come this) id go for 45-50 f8 in yours

35 pump jets.

this will def work, but i cant say it will be right, as that is just impossible

 

Although you say you only care about full throttle, surely with off road driving you will be constantly on and off the throttle, and this means you will really want the rest of the fueling to be fairly good, or it will be a real dog to drive,

 

It is really hard to get the fueling right without an afr meter, you can get a feel for if it is running somewhere right, but you cant get much better without the meter,

You can set up the idle and first stage without, as you can listen to wheather it poping through the inlet(lean) or poping through the exhaust (rich) but the main circuit is not so easy,

 

You could just try from a certain jet size. say135 main and 165 air, see how it goes, then go up a size on the main jet(richen), say 145-150mains, and see how that goes, if it feels more sluggish in the mid range but goes better top end,

Because the midrage has gone sluggish you know that it is now going too rich, but the top end is better so this wanted more fuel,

So now go back down to the original main jet, and then put a smaller air jet in it, say 155, this will keep the midrange similar but make the top end richer, now see how that goes,

now you can try making the mains smaller, then see if it goes better still, if it does, you will have to come right down on the air jets, as you already know that the top end wanted more fuel and you have now put a smaller main jet in, so you will have to come down quite a bit on the air jet to get the top end fuel up!!

and so it goes on............... and just keep trying different jets till you get somthing that feels good,

remember change one jet at a time, go in a fairly big step (ie, jets go up in 5's, 135-140-145, etc.... 145-150 wont make a massive difference so go in slightly bigger steps say 145-160, ect.. this should make a noticable difference)

and see what results you get, then work out what you need to do to get the rest of it right, once you feel like you have got the midrage felling really good, then try to fine tune the high revs with air jets in a similar way!

 

This is quite hard to do , but if you can get your head around it, it can be done, also you can do plug cuts to see how it is running, you need to drive it for a bit, then floor it, and cut the engine at the point you want to check. then look at the plug colour, to get an idea,

 

i hope you can make sense of that, iv just tried to get the theory of it accross,

 

feeeeeeeeeewwww!!!! lol

[Saveit 0]

Thank you very much. Will look in to it!

[andy0075 9 1 Cars]

midnight motorsport really explained the tuning of a carb very well !!

Do it that way and you will get the engine running.

 

But you definitively have to go for a wide band lambda to adjust

the settings. Without you will damage your engine.

 

setup on my 8V ( engine not stock !! ) :

 

DCOE 45

venturisize : 34mm

mains : 150

aircorrection : 180

emulsion tubes : F2

pump jets : 35

 

But to get the engine running it doesn't really matter what setup you

have in your carbs. I really tryed everything :

 

venturis from 30mm to 38mm

mains from 125 to 170

aircorrection from 160 to 220

 

and the engine was running with every single setup.

To poor or to rich ? - that will tell you the wide band lambda :-))

 

Take all the different jets in your car, drive it 5 min and monitor the

wide band lambda, stop your car, change the mains or airs ( 3 min job )

to become leaner or richer and drive again. In two hours my engine was running really well.

 

Always go with the 5th gear from low rpm to high rpm. Then you will see the difference very good.

 

Your AFR (air fuel ratio ) should be :

 

13,0 : 1 at rpm where you have your torque maximum

12,5 : 1 at rpm where you have your hp maximum

13,0 : 1 idle (maybe reacher if you have a very hot cam )

 

15 - 16,5:1 when cruising with low rpm ( 2000-3500 )

 

Andy

[Saveit 0]

What is an wideband lambda?

[Saveit 0]

Admin! This would probaly an idea for a Pinned thread. There is some very good info en how to adjust webers for both gti 8v and mi16.

[andy0075 9 1 Cars]

here you can see/buy a wide band lamba for example :

 

http://www.innovatemotorsports.com/xcart/p...=262&page=1

[midnight motorsport 0]

midnight motorsport really explained the tuning of a carb very well !!

Do it that way and you will get the engine running.

 

But you definitively have to go for a wide band lambda to adjust

the settings. Without you will damage your engine.

 

setup on my 8V ( engine not stock !! ) :

 

DCOE 45

venturisize : 34mm

mains : 150

aircorrection : 180

emulsion tubes : F2

pump jets : 35

 

But to get the engine running it doesn't really matter what setup you

have in your carbs. I really tryed everything :

 

venturis from 30mm to 38mm

mains from 125 to 170

aircorrection from 160 to 220

 

and the engine was running with every single setup.

To poor or to rich ? - that will tell you the wide band lambda :-))

 

Take all the different jets in your car, drive it 5 min and monitor the

wide band lambda, stop your car, change the mains or airs ( 3 min job )

to become leaner or richer and drive again. In two hours my engine was running really well.

 

Always go with the 5th gear from low rpm to high rpm. Then you will see the difference very good.

 

Your AFR (air fuel ratio ) should be :

 

13,0 : 1 at rpm where you have your torque maximum

12,5 : 1 at rpm where you have your hp maximum

13,0 : 1 idle (maybe reacher if you have a very hot cam )

 

15 - 16,5:1 when cruising with low rpm ( 2000-3500 )

 

Andy

 

Thanks andy,

I totally agree about the wideband lambda (afr) meter, its a must to get the max performance out of any car being self tuned!

Again i agree, any jet/choke will make a car run, but how well it runs is another thing,

 

Probably should of said, someone with experience could prob get the carbs set up somewhere near/safe with its fueling,

But really, anyone can try going up/down on jet sizes and see if the car goes better or worse, then just do plug cuts to see how it is running, you can get it somewhere near, but experience helps, and wideband is spot on!! lol

 

Just one other thing, when im setting up my afr i normally use these

 

Idle- 12-13:1 depending on cams

Light load up to about 1/3 throttle- 13-13.8:1

Max load 12.6:1 sometimes a little bit lower, and lower for turbo/supercharged engines

Cruising- 14.7 -15:1

 

I dont normally run any leaner on cruising, 14.7 is what they say is optimum but up to 15 is ok,

and i normally say that full throttle should be 12.6 -12:1 everywhere in the rev range after about 3000rpm,

You really should have max fuel to make max torque and max hp

normally if you get max fuel correct, the rest sort of just works,

then just set the idle and part load mixtures

 

lean cruising light load max load/power <-------leaner / richer------->

15:1-14.7:1 -> 14.7:1-13:1 -> 12.6:1-12:1 15:1------------12:1

 

please dont think i am going against what you have put andy, this is just what i use, and hope this may be able to help you? and others in a similar position as Sav.

 

once i get the time i will try to put some more info up

one quick thing as well

getting the carbs balanced is another major part of getting twin carbs to work properly/nicely.

but this is another post me thinks!! lol

[midnight motorsport 0]

What is an wideband lambda?

 

hi sav.

 

a wide band lamda, afr meter, is a tuning aid,

basicly all modern cars have lambda sensors as a final (fine tuning) sensor, most have a narrow band sensor this only comes into action on light load and cruising to keep fuel as lean as possible to make the car as fuel efficient as possible, this also helps preserve the cat,

some higher performance cars have wide band lambda sensors, these monitor the fueling accross the whole rev range to keep the car at its optimum performace/econemy

 

so what some helpful companies have done is used a wide band lambda sensor, and connected it to a box of tricks, so people like ourselves can plug it in to our cars, and monitor/set up our carbs/throttle boddies etc

 

ive got to go out, but i will edit this post with a link to aa afr meter, its called innovate lm1 but they have other products in thier range too

 

cheers, jay

[Saveit 0]

Hi jay. Okay ill look in to it. And dont worry about editing the post - i have already looked at the innovate lm1 Just dont want to spend that much money on an wide bank lambda, since i am not going to be using it more than a couple of times (i think ). Some autoshops and mechanics may have a wide band lamda that i can rent perhaps?