Needle Modification for L20b SU's

[Sealik]

What is this you speak of?

 

 

Here you go......good price.

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=331025944562&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

 

A/F ratios from 7.35 to 22.4

Oh so tempted..........fried my last Innovate

[KlassicMotion]

Here you go......good price.

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=331025944562&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

 

A/F ratios from 7.35 to 22.4

Oh so tempted..........fried my last Innovate

 

Thanks!

[Just Joel]

at some point i really need to get around to installing the pyrometers I picked up. I'm going to do cylinders 1 and 4. this will finally, for me, settle the question of how lean is too lean by resolving what the exhaust gas temp is, correlated to mixture.

 

I have also contemplated doing this for ultimate tune but haven't yet...

 

What are your engine specs? Head and mods? Stock l20b internals? Are you having trouble with your wot numbers or just the typical lean cruise condition?

[mtngoat]

N66 head I think, open chamber. stock cam,  040 overbore, 38mm SUs, pertronix dizzy

 

yes, the typical lean cruise. way lean. i have to drive it around town at 10-13 to stay under 15 when i'm on the freeway with a headwind. idle pegged at 10. 

 

I plotted up my work from last night, and found that i'd basically thinned the entire needle by accident. since it doesn't take much up top and you spend a long time on the middle and at the bottom of the needle, it must have been just touching the sandpaper now and then above station 6. my profile looked like the beginning, except a few thou thinner with not much additional taper towards the end.

 

I tried em and couldn't detect much of a change. I decided it wasn't radical enough. 

 

So I calculated up a new set of numbers with a more aggressive progression of 0.0004 per station instead of 0.0003, and had at it again. this time I put masking tape over the paper for stations 5 and above. no more accidental thinning up top. 

 

here are the new numbers..

 

station thickness 0 0.087 1 0.085 2 0.082 3 0.080 4 0.078 5 0.076 6 0.075 7 0.072 8 0.070 9 0.067 10 0.065 11 0.063 12 0.060 13 0.058 14 0.055

 

 

Now it definitely behaves differently. I just did a couple miles out and back, out and back with a modest hill on the highway providing a loaded cruise segment. It doesn't get nearly as lean while cruising when in steady state, but i haven't really put any miles in for real to tell. Once I do some runs on the highway for real and tweak the knobs till get a nice 14ish at cruise, i'll pay closer attention to the low speed cruise numbers and idle. I did notice it now idles at 10.5 with the rough tune, and I never saw it that lean before at idle!

[KlassicMotion]

I can't wait to hear more!

[Just Joel]

That's funny your idle is so rich... at 2-1/2 turns out (approximately) I run between low 11's and mid 12's (as lean as these motors want to get for best idle, anything above 12-1/2 and it will start to get rough) are you sure you dont have worn nozzles?

[Just Joel]

Also, I've found that out door air temperature plays a huge difference with mixer. What typical air temps are you running at right now? Here in central Oregon, we can see (and is often the case) 50º of temperature change in a 24 hour period. These air temperature changes can influence my afr numbers + or - 1.5 points so it's important to do your tuning at the mid point of your potential temperature range of operation.

[mtngoat]

The needles and nozzles are only a couple years old, I got the kit when I redid the motor.

 

It's been about 50 in the morning and 75 in the afternoons for the last few days so that seems reasonable.

 

One of the environmental conditions which does bedevil me here is wind. Living in the Gorge you do a LOT of driving up or down river, and a howling tail or headwind is the norm. Yesterday i did a common trip for me, 85 miles east for work then back W in the evening. Coming back I had my typical 20 mph headwind the entire way, and as you can imagine to maintain 65 you have your foot mostly buried and if it's going to run lean this is the time.

[Just Joel]

Interesting, the only lean condition I experience is when I'm at very light throttle. If I'm into the peddle, the mixture drops almost immediately. That being said, i rarely experience such condition and with the high end power of my engine, i rarely need anything but light throttle to even climb the numerous mountain passes indicative of my area... leading to my lean cruise/light throttle condition.

[Just Joel]

Also, are your nozzles z therapy? Considering there attention to detail when profiling their so called m66 needle sets, I wouldn't be surprised if the nozzles are potentially off a bit as well. ;) might want to check against factory spec just to be sure.

[mtngoat]

Yup, it's all Z therapy stuff.

 

The drive in to work today went well enough, I never pulled anything higher than 15, but idle and 2nd gear in town still nets me 10-12 or so. I may go back in for another round of thinning and move the start up another station, but for now I'll give it a few weeks and tweaks to the knobs, and see what I think.

 

I was terrified to start sanding these things at the outset, but my second go last nite had me treating it like old hat. I decided to stick with the drill press, which turns out to be running at 620 RPM. It seems to take 5 seconds and a good press to remove about 0.001, so it's plenty controllable.

 

It's actually kind of fun.

 

It took a fair bit to get the last few stations down below .060.  Systematic is the way to go. After a few initial rough out passes, I simply began checking off stations, from top to bottom when I was within .001 above the mark, counting on hitting the next station to remove the last bit from the one above it. This works pretty well until you get down to where the larger amounts come off.

 

then at the end I do a single, very light pass with very light pressure with 2000 grit from top to bottom.

[Just Joel]

With my current set, I see 15's and low occasional 16's at the worst cruise condition. Around town I'm 13's and 14's with idle between 11 and 12 but 10's when it gets real hot. I'll pull one this weekend and measure to compare specs.

[Just Joel]

Great thread btw... this needs to be discussed and hopefully we can recruit some talented contributors to the discussion.

[mtngoat]

Well I just got word I'm the winning bidder on a new astronomy toy listed on CL, I'm headed into Portland after work to pick it up. You can bet I'll be keeping a close eye on the mixture and we'll see how the (double) modified M66's work out.

[mtngoat]

The changes are a winner. The drive went great and I seemed to have a very nice improvement in mileage on the way into town, likely because it runs noticeably leaner when lifting throttle on downhill grades and similar part throttle conditions? I never saw the peaky 15-16 behavior on slight grades with a headwind I used to see.

 

I made it 75 miles with the gas needle dropping very little, but then on the return hit a half hour of stop and go, which eats fuel regardless. Upon my return home I still have more fuel than I think I usually do.

 

So far I'm pretty thrilled. I can't believe I put off doing this for so long. It's so simple and really less fussy than I expected. The W02 system is essential for feedback on your work, but beyond that all it takes is a tiny bit of prep, a stable drill platform to act as your lathe, and a bit of patience

[Just Joel]

I'm inspired to finish mine... Will profile my current needle set for comparison this weekend and modify some more :) I'll test them out breaking in the new lsd :p

[mtngoat]

I tickled to death so far. Plan now is to run them for a while, see what I think. I think starting at station 6 was a good move, I may richen the entire lower range a bit more to close the gap between idle and low speeds relative to freeway cruise. I'd sure like to see idle numbers above 12 without having that force me to 16s at cruise.

[Just Joel]

Keep removing material until you can set the idle where you need it ;) I'm pretty deep in mine (compared to m66) and I'm not quite there yet.

[Just Joel]

Alright, as promised here are the needle profiles I have been using and others referenced here in this thread so far. You can see my first "conservative" modified needle set and mtngoats modified set side by side. My set is not done yet and needs further narrowing between region 2 and 7 (as described by the DQ article as "midrange") to better my lean cruise/steady state scenario. My WOT numbers are well into the 13's and 12's (as measured by my WB02) where I feel comfortable for now so I don't plan to narrow below region 7 as of yet. Also, my idle numbers are easily maintained in the 11.5 to 12.5 range (depending on outside temps/air density) so station 0 through 2 will also remain unchanged.

 

 

I obviously have a lot more material to remove... need to quit being a pussy and put paper to brass!

[loungin112]

Sigh....i need to do this at some point too. But first i need to learn more about the su‘s to feel smart enough to take this on. Do either of you have a blown up schematic of the su carbs? Ive sesrched around and cant seem to find one. Im still in the process of identifying everything that has already been done to my car (previous owner was a tool that just parked the car in his driveway and let it sit for years.)

[Just Joel]

Alright, round two!

 

I decided to started with the z therapy m66 needles... why? Because I wasn't using them and they seemed like a good starting profile. Like I said before, my feeling based on research is that my cruise/steady state lean condition is as a result of stations 2-7. My idle and WOT numbers seem fine for now so I'm only going to modify what I think I need. We'll see how it goes after I can test and report back.

 

 

So I did the math and decided on a new set of numbers. I started at station 2 and worked up to station 9 to make sure that the taper would be consistent and smooth while reducing the diameter enough to make a difference in my fuel map (hopefully) To help keep track of the stations, I made a scale drawing that I can use as a template. Seeing as how I had a set group of stations I wanted to modify, I decided to only make the sand paper as wide as it needs to be and glued it to the back of the reference card.

 

 

 

I then chucked the needle up in the drill press and reduced the speed to about 200 rpm for the initial cut.

 

 

I found it easier to mark the stations on the needle for measuring between passes.

 

 

And about two hours later, I had matching needles with my new profile. 

 

 

So here we are now... this is the original table I made but I've added my new sizes to the chart.

 

 

Still need to install and test them before I can know if I made the right mods but I'll report back one way or the other :)

[Just Joel]

I should also add my motor specs for future reference.

 

L20B

W53 closed head, ported and matched, larger valves (not sure of how much though, machine shop did the swap)

38mm dome top "SU's"

L20B/SSS cam

[Just Joel]

Because its semi on topic I will add the exploded view pic but please reserve this thread to advance needle tuning questions and comments ;)

 

And don't let this scare you... they aren't nearly as complicated as the pic makes them out to be.

[mtngoat]

That's good stuff Joel! nice and thorough!

[mtngoat]

Here's a plot of the profiles reported, using the numbers compiled by Joel, and I of course double checked mine. 

 

Curiously, Moya's reporting tracks Joel's for the M66, and both are very similar to the M76. 

Both our measurements of the Z therapy "M66" needles come in close to each other. 

 

 

Another view minus the M76