Tuning this 3.0 on SUs...

[oranngetang]

Words of caution; the widebands will make you look at an engine that's running fine and decide it's got WAY more potential, or isn't running fine at all. 

 

Chuckles

Edited April 26, 2015 by oranngetang

[oranngetang]

Comparing the SM against the SS and RB needles (what seems to be popular stock), using mintylamb's charting has got me wondering. Both needles seem to decrease radius at about the same point mine do and continue to do so, just slightly less aggressively.

 

[oranngetang]

A pair of SS needles jumped in the mail from APT this morning. From the chart I posted, looks like a richer needle with cruise efficiency considered. SUmidel never got back to me, and with current events in CA going on this week I doubt I'll hear from zTherapy until Friday or the following Monday.

Placed some nuts in pistons around the damper reservoir to limit overall piston rise around for an experiment. Greatly leaning out the AFR at WOT and cruise, but with obvious flow restrictions. Interesting to see how this balance can be manipulated.

Quite interested to see how stock and SS grinds will behave.

Edited April 28, 2015 by oranngetang

[Stanley]

Some stuff from the '72 engine manual (also available elsewhere on site):

1. 1/2 turn of idle adjust nut stroke = 0.5 mm (0.0191") Fig. EF-48

2. Jet needle: N-54 (and in the emission section,jet dia. = 2.5mm(0.100") needle N-58)

Got early (4-screw) nozzles and N-27's (for my 3-screws)from MSA in 2013. N-27 is only stock needle for 4-screws as far as I know. According to MSA, per phone call and this: http://www.thezstore.com/page/TZS/PROD/classic17a04/11-2532, '72 (3-screw) nozzles are NLA, and you can't use early needles with the later nozzles.

I wonder why. Could it have something to do with why I have to run it with the mix nuts 5 turns down (even with SM's and modified N-27's), when FSM says 2.5 turns for my altitude and temperature?

Edited April 28, 2015 by Stanley

[oranngetang]

I did a couple of hours of reading yesterday as to what the difference would be. Honestly, everyone is quick to point out the 70-71 needle and the 72 needle (s). I can't find any evidence that the jets or needle diameters/lengths are any different. ZTherapy even seems to say all nozzles are 0.100" as are the needle bases, and the nozzles are are a one size fits, though they offer plus or minus sizes.

APT emailed me today in reply to my needle questions to state that only k&n air filters are interchangeable between SU, nothing else.

Seems to be some confusion between various sources.

I ordered those needles prior to the reply, so if they fit, I'll have to let them know.

Edited April 30, 2015 by oranngetang

[oranngetang]

APT's SS needles showed up today, they're about 1/8" shorter than the needles that I have in there but fit like a glove so far. Engine fired right up and idle mixture works well with them, as did prelim 4K RPM without load in the garage. Snowing out... I'll attempt some go-pro/AFR and whatnot someday when it's dry out.

[240260280z]

Sell your research back to Rebello who should have done this years ago.

[oranngetang]

Agreed. Stanley, did you try a thicker oil or what? From what you've described, it should help with your WOT transition.

[oranngetang]

It does not seem these engines require nearly an aggressive needle as what these SS are. I still havn't heard back from zTherapy, but I'm thinking a stock needle might actually perform better than SS or Rebello at this point, seeing as I also need to lean out the mixture screws to the point of idle problems in order to get an acceptable cruising fuel ratio.

 

Currently I'm able to idle ~20-23 AFR, cruise at ~15, accel at ~14, but as soon as I'm close to WOT, ~11, 10, 9... 

 

I was ambitious enough to set up a GoPro to review some data this afternoon, but upon reviewing my footage I see the camera was not at all happy with the AFR gauge LCD refresh time. I'll have to play with some FPS settings to see if I can get a reading on that gauge while recording, rather than 1/4 of the display randomly flashing.

[240260280z]

I bet customizing stock needles in a drill press will be worth doing.

[oranngetang]

I think that's where I'm going to end up. Hopefully I can get my hands on 3 or 4 pairs, and work my way to something that works well. 

[Stanley]

I changed dashpot oil to 30 wt. a few months ago and it helped reduce the miss at transition to WOT, but didn't eliminate it entirely. I had the N27's polished, and that made a further improvement, but still not 100%. Installed the SM's a few weeks ago. I like the peppy low end they're providing but I still can't get on it unless I make it too rich at idle. Got the N-27's polished some more last week, will reinstall them in a few days, and see. When I put them back in I'll take the SM's in for polishing, and see what's better.

 

Also bought a high-flow fuel filter (for 400+ HP engines) to install by the tank, instead of WIX can there now, below the level of the outlet (doesn't make it easier) as the manufacturer recommends. Overkill probably, but it might provide more flow. I saw fuel pressure go up about 0.1 to 0.2 psi when I tossed the glass fuel filter. Sometimes there's a combination of problems.

 

A good digital micrometer might make it easier to keep track of the needle mods. Wonder if my $10 Harbor Freight micrometer would be up to it. The ones from Japan look OK.

 

If carbs are modified to flow more air, stock needles might be too lean. Don't give back too much of that 285 HP just for drivability.

Edited May 7, 2015 by Stanley