Just the pistons. I want super rigorous about testing their drop rates like the ZTherapy dvd recommends, but they seemed roughly ok. 

1 hour ago, 240260280 said:

Beware! Some 240z repair kits with gaskets and needles sold for early 240z are too rich.  The needles may be made for later 240z with flat tops or even another SU application such as the roadster. Both @Captain Obvious and I had these. The rest of the kit was ok.

Was that the "black dragon" kit I remember reading a bunch of crap about?

4 minutes ago, rcv said:

Just the pistons. I want super rigorous about testing their drop rates like the ZTherapy dvd recommends, but they seemed roughly ok. 

 Are the drop rates still ok with unmatched pistons and tops?

Yeah, it sounds like you're definitely in the market for a new pair of needles, and maybe a pair of nozzles as well.

Material removed by corrosion will wreak havoc on your idle mixture. And if there's pitting on the needle, it's certainly possible there's the same kind of corrosion on the nozzle. That may explain why the needles fixed one carb, but not the other.

As an example... Here's a pair of nozzles. One enlarged by corrosion and another with an accurate original sized hole. The corrosion ate away so much of the material that I can see the difference with the naked eye. At idle, it takes a very small gap to make a huge difference.

So...... Weren't your carbs rebuilt? Sold to you in good working order? Slap-em on and go? Might there be some negotiation and relief there?

And as for swapping and mixing and matching parts between carbs... I think it's OK as a test (like you've done), but I would want to keep the original pistons and chambers together with the carb body they came from. You could possibly move the pair (both piston and chamber) over to a different carb body, but you would have to re-align the nozzle. I wouldn't trust that it would line up after moving to a different body. But the best thing would be to just keep them together on the same body.

I should go into the carb rebuild business.    

14 hours ago, Mark Maras said:

 Are the drop rates still ok with unmatched pistons and tops?

 

Yeah, but I really just eyeballed them separately.  I'm mostly concerned about getting the engine to idle correctly right now as an experiment, so I figured that the drop rates wouldn't be too big of an issue until I start fluctuating the throttle.  I'm keeping things organized on my bench so that it will be easy to re-match things once I feel like I have an idea of what's going on.

 

13 hours ago, Captain Obvious said:

So...... Weren't your carbs rebuilt? Sold to you in good working order? Slap-em on and go? Might there be some negotiation and relief there?

Absolutely - I texted Jeff already but I'm planning on giving him a call in the next day or so when I get a moment.  He advertises a "1 year warranty" and I bought the carbs last October, but I'm hoping he'll be reasonable about it.  Let me know if you decide to incorporate BruceTech - I may be in the market soon. 

Edited December 22, 20204 yr by rcv

Well good luck with sorting the carb details out and I'll keep you posted if I offer up public services. I've currently got carbs all over the workshop, but none of it is paying work.  Haha!!          As with most things I do, the money always seems to go the wrong direction!  Haha!

Just a quick update - I bought some new SM needles from Joe Curto over at British Superior and dropped them in.  The car immediately runs much better.  I think I've got it tuned just about right - the ColorTune is showing a nice blue color, and slightly raising the piston by pressing on the little maintenance pin makes the revs go slightly up and then back down.

 

I'm occasionally hearing a "rattling" sound from the engine now.  At first I thought it was just all of the tools/WD-40/junk I had on the fenders, but I cleaned that all off and I still occasionally hear it.  I've tried to track down where it's coming from, but I haven't found any loose bolts or anything else that looks like culprit.  I've heard that detonation can sound like "a ball rattling around an empty spray paint can" so now I'm paranoid that I'm getting detonation.  Can one of you experts give this a listen towards the end and let me know if I should be worried or not?

 

 

Really hard to diagnose sounds like that over video. I would expect pinging at idle to coincide with the compression cycles, and the noise I hear is an intermittent buzzy kind of thing that is not at the same interval as the compressions. If I had to guess over the internets, I would look at your driven accessories first. Water pump, alternator... That sort of stuff.

In any event, glad to hear you're doing better than you were. Those old needles really looked terrible and I'm glad the SM's have helped.

So have you been out on the road yet? Idling is one thing... Engine under a real load is another.

What oil are you running in the dampers?

Yeah, I'm really hoping it's just the exhaust hitting some resonant frequency and banging into something occasionally.  I've got a big piece of 1.5" tube that I've been putting to my ear and trying to hunt down the sound - I'm sure my neighbors think I'm a crazy person.  I haven't been able to pinpoint it yet, but it's comforting to not hear you say "that sounds like pinging and your engine is about to blow up."

I'm still waiting for the DMV title transfer to go through, but I've been on a few questionably legal burns up and down my street and it feels great. It feels like there's plenty of power, and there's no hesitation as far as I can tell.  I'm hoping I'll have legit plates and registration in a few weeks, and I'm really looking forward to working up to a drive down Mulholland here in LA.

I'm running the "SU Carburetor Oil" from MSA right now - it's advertised as "the best dampening fluid for SU carburetors" but I have no idea what it actually is.  Probably just plain 20W oil. 

 

I'm with CO.  In the first vid, you can clear hear the rattle that I think you are describing. I can't imagine a scenario where that'd be detonation,  especially at low rpm and no load.

Since it's periodic, I'd suspect something running near engine rpm, but either faster or slower, so you're hearing a harmonic which syncs and "unsyncs" with engine rpm sounds (water pump, fan, alt).

All of that said, the sound is peculiar in that it is particularly metallic, and is not suggestive of those components as they don't seem to have the "brass" to make those sounds.  What a lot of help, right?

Look beyond the motor!

 

6 hours ago, ETI4K said:

Since it's periodic, I'd suspect something running near engine rpm, but either faster or slower, so you're hearing a harmonic which syncs and "unsyncs" with engine rpm sounds (water pump, fan, alt).

Exactly, perhaps the heat shield vibrating where a bolt is missing,  a bolt or washer that isn't fully tightened.  A loose clamp on the exhaust pipe or a loose nut in the pocket where the header pipes meet.

1 hour ago, grannyknot said:

a loose nut in the pocket where the header pipes meet

I was up at 5 this morning thinking exhaust!  I used to have a Porsche with a cat converter that the catalyst material broke loose inside the can.  It made a similar metallic sound.