popping through the exhaust at 4500 rpm or so.. HELP!

[Captain Obvious]

Man! What a disappointment...

I saw that you had updated the thread, and I was expecting results!! :ogre:

Haha! The suspense is killing me!! It's like a Z equivalent of a reality show!

[Zedyone_kenobi]

I am sorry Captain. I was in family time mode last night.

I got all the parts safely tucked under the car, and the center console is in but not screwed together. I should have it on the road by Saturday. Monday will be a long data gathering day as I have off work and hopefully it will not rain.

I will say this, at idle with the engine almost warmed up I was reading

15.1:1 at about 600 rpm.

Then I blipped the throttle and it immediately started to stumble at about 450 rpm and wanted to die, but kept itself alive, but the A/F went to 19.7:1. I bet you a million dollars one of my pistons did not drop all the way down and I was starving it. They have been sticking more and more the more I take them apart and mess with them. Not sure why, as I have been careful and marked them F and B on all parts. But the carbs seem to be fighting me right now. They are getting tired of coming apart and going together so many times.

But this little gage is awesome. Install was a snap, worked the first time. Just a lot of soldering to ensure good connections and a lot of heat shrink because I am anal.

Again, I will try to get it completely together tonight, and on the road Saturday. But for SURE monday

[Captain Obvious]

I know, I know... I'm just starved for entertainment. :classic:

So this piston sticking thing. That's new information isn't it? You're talking about the suction pistons in the carbs, right? If the suction pistons are sticking, that'll screw everything up! That's one of the carb's major organs!

There's not a lot of contact between the suction piston and the rest of the carb. In fact, other than the spring, the only thing that is ever supposed to make contact is the polished steel tube in the center that you fill with damper oil. The needle is never supposed to touch the nozzle, and the outer rim of the suction piston is never supposed to touch the inside of the round topped piston housing.

Have you run the "thumb over the damper hole gravity drop test" to see if the pistons are about the same front to back? Maybe you swapped the two of them somewhere along the way. Blue posted a good link to a youtube demo sometime back... I think it was over in the SU specific section.

If you're rubbing the needle on the nozzle with enough force to get that piston to stick, then you've probably ruined the needle or the nozzle or even both by now. I've measured a couple needle and nozzles, and it's amazing how good something can look and how far off spec it can measure.

[steve91tt]

Based on my wideband experience 15:1 at idle is very lean for these cars. Both of my engines seem to like to idle between 12.5:1 and 13.5:1 any leaner or richer and idle suffers. When you get a stumble, expect to see a false lean reading which will be independent of whether you are actually lean or rich. When the engine misfires a slug of unconsumed air hits the sensor. Because it can only measure oxygen, it thinks you are lean. YMMV.

Edited January 13, 2012 by steve91tt

[Zedyone_kenobi]

Captain, I have about 90% success in getting my pistons to drop reliably and steady.

My procedure is as follows...

1) clean the parts religiously, meaning I clean the dome, piston, tube, check valve etc

2) Install them together on the carb dry. I ensure that both pistons rise and fall without any sticking at all and make that lovely 'THWAMP' when they hit down as close to the same time

3) I lift up the piston so the filler tube is level with the dome top as it makes it easier to fill. I drop oil into the tube...I have to do this as if I get any oil at all in between the piston tube and dome bore, the fall rates vary drastically, if I keep them clean they are identical.

4) Here is where it gets tricky. I screw in the little brass check valves into the top of the domes slowly. I then wait until the air bubbles have a chance to move out of the way and begin the drop testing. THIS is where my fall rates start giving me issues. THIS is when I get some minor sticking that I have to just play with to get rid of. I have taken both check valves apart and cleaned them religiously. I have measured them and they are identical as close as I can measure them with my micrometer.

This last time, I knew that I had it a bit sticking on the back carb where it would fall 90% of the way down and then stop and then s-l-o-w-l-y go the rest of the way. This is no doubt causing my sloppy idle issue this time and I am not worried about it. MY SU experience now totally covers this. THe wideband just made the diagnosis that much easier. I already love it.....!!

Just to recap, the piston sticking thing is not new, it is just taking more and more work when I get to step 4 above to get them to fall in perfect sync. Maybe I need to send my carbs back to Bruce and the Z therapy guys for some fine tuning.

Just to make sure needle is not hitting the jet (I am rather sure it is not), but I will do the work without a needle installed, and that will allow me to see if it is the needle dragging or the check valve causing me grief. Since I can get it to fall perfectly without the check valves installed, I do not think I have any needle rubbing issues.

I would think I could also use a black sharpy and color the jet black. Then do a test and see if any of the black rubs off. Alcohol will take off any extra marker residue.

Steve, copy that on the stumble/lean condition, I am ready for that. When data and science come together, only good things can happen.

Edited January 13, 2012 by Zedyone_kenobi

[LeonV]

And people say that triples are a pain!

As much as I'd like to see the issue resolved, I say just get yourself some Webers or Mikunis already, you won't regret it!

[Zedyone_kenobi]

LeonV Make no mistake, I am going to buy a set of triples THIS YEAR. I dearly love playing with carbs, maybe I am a masochistic. I have always wanted a set, and after hearing Steve91tt's MIkunis, I am going to pick up a set of triples for DARN Sure.

However, I still I need to fix this issue for two reasons.

One, if I am to ever sell these SU's, I will want to ensure the buyer that they are perfect. And Two, before I go slapping triples on anything, I want to be sure the engine is healthy and ready to accept them.

I found out the compression is spot on already, so that is good. I will get this problem nailed down soon. I would stake my OEM voltage regulator on it.

[madkaw]

You are aware that sometimes you have to loosen the domes up and retorque the screws if you experience binding. Sometimes you can tighten one of the screws too much on one side which will have your dome sitting on the carb crooked.

[Zedyone_kenobi]

yessiree

That is a fun 'personality' trait with SU's.

[madkaw]

Just checking!!!

[Zedyone_kenobi]

Thanks for trying to help me avoid a rookie mistake though...

[steve91tt]

I find it easier to turn the adjuster knobs all the way in (full lean), then center the dome/piston, do the drop test and then turn the knobs back to where they started. With the adjustment all the way lean during the drop test, the distance between the needle and the seat will be at its minimum. Therefore if you pass the drop test at full lean then the needle will be as close to centered as possible and you stand a better chance of being perfectly aligned once you move the mixture adjustment back to where it was before you started.