Tuning this 3.0 on SUs...

[madkaw]

I would try a different starter first or just try the reduction starter. Definitely check all connections .

[Stanley]

Still using the SS needles? From the chart posted, looks like they have an interesting profile, like custom needles, going richer at top end (where it needs more gas, and bottom (for when you suddenly floor it from cruise and the piston drops due to reduced vacuum). 

 

Can't find data on stock N27's. Measured them with my $10 micrometer, but would like to compare with the official numbers.

 

Recently installed a vacuum gauge under the dash, it's interesting to watch what is does while driving. Makes it easier to understand what the SU experts are talking about (Blue's SU mod thread, for example). Since the SU piston and needle position depends on vacuum, watching the gauge allows me accelerate without the engine missing or popping. When I see the vacuum drop to about 5 in/hg (with SM needles) I back off the throttle a little, since that's where it happens. When the revs are high, the vac stays high, and throttle position has less effect on vacuum. Obviously, this isn't what most drivers get from a vacuum gauge (hope to eventually learn that stuff too). Since 5 in/hg is lower than the vac at idle (about 15) maybe I can figure where that is on the needle (probably very close to the base) and polish that down, to tune out the miss and still not be too rich at cruise and idle.

 

Regarding the hard starting, maybe more friction in engine in the first half of break-in period?

[Kurbycar32]

I pulled my needles and took some pictures for you. My needles are modified but look way better than what you showed us. Only one side is flattened and it's a nice even taper. I can't comment on how well they work but at least this looks like a nice intentional grind. Has Rebello commented on this yet?

[oranngetang]

I have a gear reduction starter in the mail just to see. My thoughts are compression is higher in a hot cylinder. When it refuses to roll over and you let off the starter, the engine pretty well kicks backwards with some serious authority.

I have the SS needles in right now. They work well for driving around town and idle well, but the taper is too aggressive further down.

Waiting on a couple of other needles, SM and something else... W02 perhaps. I can't recall, from APT.

I'll try ZTherapy on Monday again for the stock needles, no luck so far.

[oranngetang]

Kurby, those look WAY nicer than mine, no lumpy ridges or dips, and straight.

[240260280z]

In another thread I posted an idea of running a cable from the fast idle lever in the cabin to the mechanical vacuum advance lever on the Z. the idea would be to pull the lever to reduce advance at start, then push it forward to increase advance once started. This would reduce the kick back on the piston when starting and the piston is moving to slow to reach TDC before the explosion pushes it.

[Kurbycar32]

Did your gear reduction starter show up yet?  I have my motor cranking and it cranks hard and fast, though i have a highly concerning clunk noise that i now have to investigate.  Heres the crank video:

 

[oranngetang]

I do not know. Is there oil in the engine? I do have my gear reduction starter in. I'm out of town right now but may skip by the house when I run in for groceries. I'll record a video of mine if able for comparison.

Someone with some experience will chime in. Did it come with the flywheel and clutch installed or did you bolt that stuff on?

[Kurbycar32]

Rather than threadjack your carb tuning thread my motor clunking thread can be found here:  http://www.classiczcars.com/topic/48675-just-ordered-my-rebello-30-now-what/page-10#entry470655

 

That gear reduction starter should crank that motor hard with a decent battery.

[oranngetang]

Hey no worries. The starter is an amazing difference. It's quick and even when everything is warmed up it'll kick that engine over like nothing.

[oranngetang]

OK... It's been a while, lots of vacation time lately! Put a couple of thousand km on the car the past week with a new to me 5 speed.

 

Currently installed in these carbs are SM needles from APT. I tried a (TL?) needle as well but they were SUPER lean. 

 

Honestly the SM is a very good performer. I'm getting even, usable mixtures between both carbs at just about every throttle point and any speed. Gear selection comes into play with these a little more as there isn't nearly any power at all below 3000 rpm, and the pull up to about 4500 rpm leaves a LOT to be desired. With that said, highway cruising achieved me ~23 MPG (US) or 10 L/100 KM over the past 1,800 highway kilometers with an indicated AFR of around 14.5. A Pull from 4,500 to 7,000 rpm is good with an indicated AFR of around 13.3. Leaning the mixture ever so slightly can increase a cruise to 15-16 AFR, but I'm finding the engine needs that ~13 point at WOT and high revs to make power. Richer seems to rob a little power, and leaner seems to be a little risky. I wouldn't say this engine enjoys a load at anything over 14. 

 

Next step with these needles will be some playing around with timing. I'll try to get my hands on a 0-60 1/4 mile box to gather some imaginary dyno data from the changes I make. Once timing is at a point that makes good peak power, I'll re-visit the needles. I may incorporate the final half of the SM profile into a leaner needle to the top end right and then try some customization based on a minty-lambs style chart vs my butt-dyno figures. 

 

In other news, I received an envelope from zTherapy with some used core needles in it. It looks to be 4 pairs, though it could in fact be 8 randoms. Can't wait to give them a try. I'll attempt to verify with calipers at another time. As of now, I havn't been able to get a hold of Steve by phone, email or through Bruce regarding these needles or carbs yet. It's just me and you guys on this one for now.

 

BTW, that rear-end vibration is enormous but I don't know how any of you get past the exhaust smell in the cab... What a downer! Side-exit exhaust?

[oranngetang]

Timing data from mechanical advance starting from zero. Timing light rpm vs tach rpm....

1000 RPM / -0 / 1300 RPM

1500 RPM / -5 / 1800 RPM

2000 RPM / -13 / 2400 RPM

2500 RPM / -18 / 2800 RPM

3000 RPM / -25 / 3400 RPM

3500 RPM / -28 / 4200 RPM

4000 RPM / -30 / 4500 RPM

4500 RPM / -31 / 5200 RPM

Set base to -5 BTDC and confirmed -36 at 5000 RPM as per Rebello dyno sheet number.

This is pretty well exactly where timing was set when the engine shipped to me. I marked the dizzy at that point.

What might cause the massive difference between tach and timing light? 700 rpm at 4500... also the placement of the inductive pickup for the timing light was sensitive to placement. In some cases the advance on the light would not move the beam despite showing it was doing so on the display. I'm wondering if the 700 dollar investment in a programmable (123) dizzy would be beneficial, if not just more stuff for me to geek out with.

Edited July 13, 2015 by oranngetang