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Using new AFR meter and tuning 32/36 Weber


7502

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Been playing w/ my new air fuel ratio wide band O2 meter today.  Meter confirms that I have been running rich so I have made a few small jet changes, but gauge still shows a reading of 11.2 at 3000 rpm cruising down the road. When I  take my foot off the gas AFR goes up to about 14 so I think that's fairly normal behavior. As of today I dialed in the fuel mixture screw to read 13.2 at idle. Incidentally, should I lean it out at idle a bit more?  Purrs like a kitten now but I bet I could lean it out more.

 

Here's my current jet set up:

 

PRIMARY                 SECONDARY

Idle 60                      Idle 50

Main 140                  Main 170

Air 160                     Air 170

 

I believe I have F50 emulsion tubes based on my notebook.  Does anybody else think the naming of the primary and secondary throats is counter intuitive? Seems to me the primary side would be the one that is employed for initial and normal throttle positions. The primary doesn't even begin to open up until about 2/3 petal movement.

 

Appreciate any ideas on leaning it out. Should I target something under 14.7 ? 

 

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25 minutes ago, 7502 said:

Does anybody else think the naming of the primary and secondary throats is counter intuitive? Seems to me the primary side would be the one that is employed for initial and normal throttle positions. The primary doesn't even begin to open up until about 2/3 petal movement.

 

I think you have them backwards in your brain.  The primary is on the passenger's side.

 

Does this mean you need to swap jets side to side?

     

 

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Yep, brain is backwards. Probably why I always walk the opposite direction when trying to leave a new building.  But in my defense I was working from this neat drawing.

 

I will have to swap jets sis to side. I should also probably check my float level, might be too high.

DSC_5281.JPG

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That is a pretty drawing alright... misleading though it is. 

 

My car idles best down around 12.5, so I think you're doing well with it as lean as it is.  I'm new to all of this though.

 

Remember that brass and plastic floats get set at different heights.  Brass around 40 and plastic around 35 mm I believe.

 

Give the auxiliary venturies a wiggle to make sure they are snugly pressed in.  Sometimes they need a little shimming to be tight. 

That looks like a brand new carb though, so they're probably fine.

     

 

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5 minutes ago, '76mintgrün'02 said:

Give the auxiliary venturies a wiggle to make sure they are snugly pressed in.  Sometimes they need a little shimming to be tight. 

That looks like a brand new carb though, so they're probably fine.

 

I was going to mention the ventureis do seem loose. I'll try to shim them up and check the floats again, then switch back all the jets and figure out where I am. I have that drawing on my garage wall and just grabbed it for reference.  Think I got it from Google Images.

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3 minutes ago, '76mintgrün'02 said:

My car idles best down around 12.5

Yep, I agree, most old BMWs I've played with tend to be happier running rather rich at idle.  Mid-12s is what I tend to aim for as well.  If your happy with your idle in the low-13s that's fine too, but I certainly wouldn't suggest going any leaner.  11.2 is definitely rich for cruising though, 14-15 is where you want to be there for fuel economy, and wouldn't recommend letting it get above 16 anywhere.  For safety against detonation you ideally want slightly richer at the higher revs, even in the cruising zone, say 13-14 above 4000 RPM. Full throttle target is 12-13. Last thing, remember at low throttle openings (off idle and cruise), you're pulling a lot of the fuel mixture through the progression holes.  So while you can tweak this with the idle jet and then re-adjust idle with the mixture screws, because the progression holes are a fixed size it can be easy to get stuck chasing your tail here, and you may need to compromise a little between the two.  Hope that all makes sense and helps some!

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10 minutes ago, AustrianVespaGuy said:

Yep, I agree, most old BMWs I've played with tend to be happier running rather rich at idle.  Mid-12s is what I tend to aim for as well.  If your happy with your idle in the low-13s that's fine too, but I certainly wouldn't suggest going any leaner.  11.2 is definitely rich for cruising though, 14-15 is where you want to be there for fuel economy, and wouldn't recommend letting it get above 16 anywhere.  For safety against detonation you ideally want slightly richer at the higher revs, even in the cruising zone, say 13-14 above 4000 RPM. Full throttle target is 12-13. Last thing, remember at low throttle openings (off idle and cruise), you're pulling a lot of the fuel mixture through the progression holes.  So while you can tweak this with the idle jet and then re-adjust idle with the mixture screws, because the progression holes are a fixed size it can be easy to get stuck chasing your tail here, and you may need to compromise a little between the two.  Hope that all makes sense and helps some!

Thanks AVG, that's helpful. Tomorrow I'll get back in the garage.

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13 hours ago, '76mintgrün'02 said:

 

I think you have them backwards in your brain.  The primary is on the passenger's side.

 

Does this mean you need to swap jets side to side?

 

EDIT: I see his carb is a G series but still curious. 

 

Will a 32/36 DFV/DFAV/DFEV fit a 2002? That might explain some reverse-ery.

Edited by Jimmy
Clarification
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1 hour ago, Jimmy said:

Will a 32/36 DFV/DFAV/DFEV fit a 2002? That might explain some reverse-ery.

 

The DFEV can be used in air cooled VWs (but not the DFAV, since there is no Acqua).

 

Since Eric has a Ghia, I'm guessing that might have something to do with the revers-ery.

 

 

To be used on a 2002, the DFV carbs would need to have a cable actuated throttle, since the throttle shaft would be facing forward.

Either that, or the primary and secondary would be sitting over mismatched hole sizes on the intake and throttle shaft alignment would probably be offset.  Perhaps a peanut-holed manifold could be used though... I don't know.  The throttle plates might also rotate the opposite direction... I've forgotten.

 

The shape of the inlet on top of the carb is oval-ish-ly shaped on the DF series, not rectangular-ish, like on the DG models.

 

I had a DFV carb and intake for a bug, but sold it a few years ago.  I never ran it.  The problem they have in that application is that most of the intake manifolds are not heated well enough and they ice up.  The manifold I had was the typical crappy kind.

 

I wish I still had that carb now, so I could share some photos of it on an M10 intake.  I dug a bit, but could not find my old photos.

 

Tom

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I think that line drawing of the reversed carburetor I was working on may have been taken from the VW Idiot Book by John Muir. The style and fonts are very familiar.  I never had a Weber on any of my VWs just Solex and Bocars. 

 

Back at it this morning. I switched my jets around, shimmed up the venturies w/ an 0.002 feeler gauge and checked the floats.

 

Checked every one and wrote them down for posterity :

PRIMARY                 SECONDARY

Idle 60                      Idle 50

Main 140                  Main 170

Air 150                     Air 170

 

Pretty happy with it, thinking I will bump up the Primary air correction to 160 or maybe 165 if I have one. 

AFR Gauge gives me the following reading, 

 

13.0 at warm idle 850 rpm

12.0 at 3000 rpm

12.5 at 3500 rpm

13.0 at 4000 rpm

On decel it rises to about 14

 

Fun little project.

 

 

 

 

 

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I messed with this carb for about 6 months, including customizing the emulsion tubes.  I could never get it to be 12.5, without hitting 14+ over 4500 rpm.  I was able to smooth out that curve with soldering up the holes on the emulsion tubes.  There is a great video on the tuning of this carb, he is a Mini guru but pretty awesome.   This is why I went to EFI, and most people know my struggle on this forum with this.  It did however smooth out my AFR curve.   

 

The trick is the emulsion tube in straightening out the AFR curve.  Just got sick of messing around, knowing that I was going to go EFI and now forced induction (soon). 

 

 

 

 

 

 

 

 

"Goosed" 1975 BMW 2002

 

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