Weber selection and initial jet tuning

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In comparing the 3 E tubes with the same main and air (figure 1)  the shapes are not very different however the a/f offset seems to match the tube's diameter.

The F16 is a fat tube at 8.2mm and blocks off most of the well.  This seems to cause a leaning across the full band

The F11 is a medium diameter tube at 8.0mm

The F2 is a thin tube at 7.5mm and does very little blocking/braking

 

The F2 and F11 E tubes 2 have nearly the same drillings in the side and have may more up-higher than in the F16 however the curves do not seem to be much different.

-  The f16 does dip more into richness as it approaches  7000rpm

- The F2 is richer at cruise before the lean gasp spike

- The lean gasp spike is similar in magnitude  for all 3 tubes

 

[Figure 1]

 

 

In figure 2 below, the plot for each tube is normalized to the middle lean peak. Using this technique we can see the subtle relative differences:

[Figure 2]

 

There is minimal difference between the 3 tubes.

The F16 (with fewer high drillings) drops off more in the higher rpm range

The F2 is the flattest after the gasp up to 700orpm. It also dips the least after the gasp.

The F2's lean gasp is largest and cruise a/f is leanest relative to its WOT a/f

The F16's cruise a/f is richest relative to its WOT a/f

 

 

From this data it seems:

• Fewer holes up top in F16  causes the very high RPM range to get richer
• The difference between cruise a/f and WOT a/f seems to be proportional to tube diameter rather than drillings. A fatter tube brings the two closer
• Drilling some holes in the top of F16 e-tubes may reduce the highest rpm dip.

 

 

Comparison of E-tubes:

 

Edited August 10, 2018 by 240260280

[240260280]

Here is interesting F16-like E-tube at 8.2mm but with deeper internal cavity and more drillings.  It also continues its fat 8.2mm thickness nearly to the top so no puddle of fuel outside the tube at cruise or start of acceleration.

Maybe this puddle is what causes the very rich burst at the start of the runs right after the gasp? It is the same puddle for all 3 tubes we have tested so far.  i.e. this puddle is gulped at start of WOT run and is not emulsified very well causing the rich dip in nearly every 45DCOE A/F plot.

Maybe the F19 it can change the curve shape and flatten the hump as it is significantly different from F2/F11 AND because it does not have a thin region near the top where a fuel puddle can occur between the well wall and the side of the jet?  I'll try to source 6 of this strange e-tube.

 

 

Edited August 10, 2018 by 240260280

[blodi]

Thanks again for the great analysis!  I was out of town the last couple days but had a bit of time tonight and through in the F11 and did the 155/185 combo with the following result...same as last time with the down a entrance ramp and then flatter run second.

81218-1 by blodi, on Flickr

81218-2 by blodi, on Flickr

I might throw in that F16 165/215 combo in an retest tomorrow.  The carb is not bigger in diameter than the intake. I think it's either equal or has a slight step if I remember correctly, but I can scope it and find out. 

 

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Thanks a million for that F11 data!  We do not have much on that.

I'll plot the data now.

For the DCOE throat to manifold runner, that is fine.  I just wanted to ensure there was no step from large diameter to smaller.

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Here is F11 155/185

 

Here is blink comparison of F11 155/185 to F16 155/185

No big change in shape between the tubes  8.2mm F16 is ~ 0.5 point  leaner across the band

 

I checked with one F19 supplier.  Price is high.  I'll try to find another or make custom 8.2mm tubes on my lathe.

[blodi]

Here is F16 165/215 again...  

81318 by blodi, on Flickr

[240260280]

 

Thanks again for the data.

Here are the same F16 165/215configurations captured to date.

There is some variance in all so I will have to step back and reconsider what to look for in these plots and all of the others.

I overlaid some lines and data points that may be significant. Please double check my assumptions:

 

1. The left most a/f (13.5, 11.7, 13.3) is at cruise before punching WOT. It seems to vary.  It could be related to atmospherics or velocity.

2. The WOT peaks (13.5, 13.0, 12.5) occur at different points on the x axis because the x axis is time rather than rpm.

3. The delta between lower WOT  dip and middle-ish WOT peak (1.7, 1.8, 2.0) is fairly repeatable though the slopes change due to the x axis being time.

4. The delta between lower middle-ish WOT peak and the highest WOT point (1.0, 1.1, 1.1) is fairly repeatable though the slopes change due to the x axis being time.

5. The peak A/F in the middle WOT hump (13.5, 13.0, 12.5)  varies.  This is a bit troublesome.  It could be related to atmospherics however the range is large.

 

 

[blodi]

I should say that the log last night was down an entrance ramp for what it's worth.  Also I checked my fuel height and it's at 28mm +/- .3 mm in all three carbs.  I may have been closer to 29mm last summer which might be why it's a bit richer now. 

I can try another log on this setup just to confirm. 

 

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Great.  That is appreciated,  If you use the same flat area and punch the throttle at the same cruise speed  for all runs that would help reduce any variables. 

If you still peak at 12.5 on your new runs then a run on the 160 main jet would be nice to have too.

[blodi]

F16 165/215  again on flat ground.  I also received  and installed F9 70 idle jets this evening. Driveablility seems much better at lower speeds. I am going to re calibrate the O2 sensor when I have a chance as well as I haven't done it in a while. 

81418 by blodi, on Flickr

[240260280]

No big difference (which is good). The middle peak is moved but that is artifact of X axis as time.

It is still rich. A calibration or 160 or 155 main will fix that.

 

Edited August 15, 2018 by 240260280

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@blodi

Heads Up!  F19 tubes enroute to you from Europe ?

Edited August 18, 2018 by 240260280