So we're doing a 73 restoration project

[Captain Obvious]

Cool! Sounds like great progress.

I don't know what type of rubber they are using for those bowl gasket seals in the rebuild kits, but I've found the same thing you have. They suck. If you never have to take the bowl cover back off, it's fine. But if you're on and off with the cover a couple times, that swelling is a real PITA. I've not found source for the seals loose. The only ones I've seen are in the rebuild kits, and I assume they are all the same crappy material. Look at the bright side... If it swells, it makes a better seal, right?    

12 hours ago, Michaelwk said:

Adjusted the tangs on the floats to get the fuel level into the middle of the window and meet the dimensions from the FSM.  I was surprised how far off they were from the recommended dimensions.  I wonder if the floats were replaced before and just half-arse adjusted. 

See? Waste of time to spend all that time dinking around with precise mechanical measurements with calipers and stuff. Just get it preliminary and then use the sight glass for the real setting. And if you got them close on the bench, then they should be pretty good on the car. You'll still need to verify with a mirror or endoscope, but it should be pretty close.

[Michaelwk]

I just finished the compression test.  Uff da.  We've got 130, 130, 132, 140, 120, and an even 100.  I was not moving super fast, so the last couple could be just because the engine was cooling down, but not even getting to 150 on the first few was unfortunate. Wet compression test improved them all, so I'm concluding the rings are just pretty worn. 

The engine also couldn't idle.  It only ran when the choke >50% open.  I wonder if this is part of the reason the floats were set so high.  Would running it rich make up for poor compression?  My dad had a local mechanic get the car running back in 2003 and doesn't know exactly what he did.  I'm guessing the compression wasn't great back then either since we didn't put many miles on it back then.  It's also seems to have all the original hoses so I there could definitely be vacuum leaks.  Will try to diagnose that this weekend and see if I can get it idling and possibly even take her for a test drive. 

Short video of the car running.  The white smoke went away after it got up to temp.  The throttle was also stuck during this video which is why it didn't die when I pushed the choke down.

[Captain Obvious]

Yeah, those compression numbers aren't stellar. Did you have the throttle blocked to WOT while doing the compression test? I do not believe that running rich would make up for poor compression.

If you're running all the original hoses and stuff, I wouldn't be surprised at all if you've got a whole bunch of little vacuum leaks. Little leaks like that are killer at idle. Much less of a contributor at higher throttle positions, but a real problem at idle. You want every molecule of air passing through the carbs, not around them. The extra hoses and connections and complexity make it more difficult to achieve that with the flat tops.

Also remember than none of the carb systems work great until the engine is up to temp. If you're starting the engine cold and expecting to be able to immediately take the choke off, you're kidding yourself. You'll need some choke (and the associated idle boost it provides) until the engine warms up.

Next, if I were doing this, I would try to simplify the system to get things tuned... Remove the air cleaner and plug the appropriate connections. You should be able to remove and cap the anti-backfire stuff, the idle compensator stuff, and the intake air damper control snout lines. You can temporarily live without any of that stuff and disabling them will remove a bunch of potential leak areas.

[Michaelwk]

I realized I had the choke closed when I did the compression test, which was incorrect.  The directions said have the choke open, and to me that meant "engage the lever", which obviously is wrong and doesn't match what the throttle plate is doing. So that was probably the issue.  I attempted to repeat the test this past weekend but couldn't get the engine started.  After cranking a while the battery died.  Using my other car to jump still didn't get it to fire.  Back when the car was driving, it always needed a lot of cranking to fire, my dad attributed this to the electric fuel pump being shot, but I also read that this could be due to a bad coil.  The coil looked like the it was still the original, so definitely time to replace anyway.

I attempted some trouble shooting prior to replacement but wasn't quite sure if what I was getting was correct.  At key-on, there was ~5V at the coil.  Everything I read said this should be 12V.  But the new coil is giving ~5V too, so I'm now assuming that's correct.

I also replaced the plug wires while I was at it.  I thought about doing the points, condenser, and distributor cap too, but that actually looked really clean.  I am guessing it was replaced in 03/04.

Got the new coil in tonight (with temporary cardboard spacer).  Anyone have a recommendation on a different bracket or proper spacer to use?

Battery was all charged up and it still took a good amount of cranking to fire, but it did eventually go and seemed to run better than before, so I'm pretty happy.

I let it idle with the choke on (closed!) for a while and was able to drop it to about half to 2/3 open eventually, but it still ran a little rough.  The temp gauged climbed a bit high so I shut it off.  I need to top off the coolant before a test drive.

So, took a step backward and didn't make any progress on getting it to idle better.  Thanks for advice on looking for vacuum leaks @Captain Obvious, I will try to tackle that this weekend.  I don't get much time during the week to work which stinks.  It's getting cold in Wisconsin and my winter storage location might give away my spot soon!

Michael

[Captain Obvious]

Yeah, I'm thinking a whole bunch of little vacuum leaks. Can't quite tell from the pic, but one of the rubber tubes leading to your throttle opener device looks questionable. Like it's split down where it connects to the intake manifold? Anyway, everything needs to be airtight. Especially with the flat tops since you cannot simply crank the nozzles down to mask vacuum leak issues like you can with the round tops.

So were you able to retest the compression with the chokes open?

As for the coil voltages... It depends on where the points landed when the engine stopped spinning last time. If the engine stopped with the points open, then you should see 12V on both sides of the coil. However, if the engine stopped with the points closed, then you should see less. Five volts might be appropriate. You end up splitting the battery voltage between the ballast resistor and the coil. Probably fine.

And just to poke a little, the flat top cars I've worked on start pretty much instantly even when cold. You don't have to crank and crank. Second or third compression cylinder and it pops. So while that's not really a legitimate comparison to where you are yet, it's at least a goal.  

[w3wilkes]

2 hours ago, Captain Obvious said:

And just to poke a little, the flat top cars I've worked on start pretty much instantly even when cold. You don't have to crank and crank. Second or third compression cylinder and it pops. So while that's not really a legitimate comparison to where you are yet, it's at least a goal.  

Wow! My 73 with flat tops always required a lot of cranking to get it to fire when cold for the ~20 years I drove it. When warm it would fire instantly as long as I wasn't in vapor lock territory. I had both mech and electric fuel pumps and that made no difference. If I let the electric run for a bit before I tried to start it would be easier, but still needed some cranking.

EDIT: When I say cold I'm referring to winter time with temps at or below freezing which is a typical northern Utah morning winter temp.

Edited November 15, 2018 by w3wilkes

[Captain Obvious]

Yeah, you're right. There's the possibility I was looking at the starting issue with somewhat rose colored glasses. I've not used a flat top car in the dead of Pennsylvania weather. The Z's were always fair weather cars. So, I'll temper my statement above to point out that I've had great experience with starting the flat tops from Spring through Fall. Cold fall, but fall none-the-less.

And I'm sure the winters are way colder in Fitchburg, Wisconsin than they are here. Thanks for keeping me honest!

[Michaelwk]

Ok, sorry again for the long delay between updates.  I haven't had much time the past few weeks with Thanksgiving and some traveling for work.  But good news, I took the Z on it's first drive since 06 yesterday!

There was indeed one major vacuum leak in the braided, curved hose going from the anti-backfire valve to the manifold.  I found a hose at Autozone that worked, although it was not metric, so it's a bit oversized and it wasn't quite the same curve, so it's running over the top of stuff instead of under.  Will try to find a proper replacement later. 

I'm guessing some the other hoses are not completely air-tight at the connections.  I did try to address that with some zip ties and hose clamps, but again, I just need new hoses.  Will address that next spring.

On 11/15/2018 at 9:43 AM, Captain Obvious said:

Can't quite tell from the pic, but one of the rubber tubes leading to your throttle opener device looks questionable. Like it's split down where it connects to the intake manifold?

Yeah, I see where you're looking.  It's actually just really thick parting line flash on that hose.

I also continued to have problems getting it started, even with the new coiled.  Turned out this was fuel.  For some reason the new mechanical pump cannot pull anything from the tank without priming.  Took me a while to figure this out, which was frustrating, but once it's primed, it runs pretty well.  I stopped and started it several times and it fired right up once warm.  I'm going to start it again tonight and see if that is still a problem.  If so, I'll definitely be swapping in the electric pump first thing next spring. I never did the compression test again, will save that for spring as well.

Getting up to temp definitely made things better.  The idle wasn't great, so I have the idle screwed turned in one turn. 

I drove it around the block and then to the gas station to put some fuel in.  Was so much fun to drive (even at only 35 mph), I'm sad that it's going right into storage.  But really was fun to cruise around a little bit (even with the window down in 25 degree weather)

[Captain Obvious]

That first short run out on the road is a blast isn't it? I remember the first time I took the 260 around the big country block after it had been sitting for so many years. Half ecstatic, and half terrified.      

Good work on the project so far and hope it continues to come together!

[Michaelwk]

32 minutes ago, Captain Obvious said:

That first short run out on the road is a blast isn't it?

Absolutely!  I'm so bummed that it took me until December to get to this point, but glad it's moving.

And thanks a lot Captain for all your help! 

[jayhawk]

On 10/21/2018 at 5:40 PM, Michaelwk said:

Got the carbs off today… managed to only damage one hose, so I’m calling it a success.  Not looking forward to trying to get them back on and get all the hoses in the right place, but that’s a future-me problem.  .

Looking at the bowls, I appear to have 74 model carb I think.  Worst of the worst?  Haha. There’s 7 screws rather than 6 like the manual shows, and my float pin is only accessible from behind an external screw (the one that's half was out on the upper left of the carb in the pic below.  The only marking I could find was a number 2 stamped on both carbs.  From the Clymer, it says 73s had HMB46W-1 and 74s had HMB46W-4.  It also claims that only thing you can do with a 74 is open the float chamber cover, implying that you cannot take out the floats or needle valve.  Found another thread from a while back that talks about the same thing and it sounds like his was a 74.

Michael

 

Michael,  per your comment eariler in this thread:  If I read my copy of the 1973 1974 Fuel Modification document correctly, I think that the -2 carb you have IS for the 1973 Z.   That document is available here on classiczcars. If I'm reading it correctly, 1973 carbs came as either a -1 without the Float Hinge plug, or a -2, that does have the Float Hinge plug.  Since my '73 was early production (10/72), I think I had the -1 carbs, but your -2 seems to match the description  for a '73. 

I am not at all sure how the 1973 -2 carbs differ from the  -4 used on the 260Z.  (and where did they use -3 carbs?...)

Here is a link to the copy at classiczcars:

 

[Michaelwk]

Well, as I tried to drive it off to storage today, I had the same fuel issue.  It actually fired right up but then died about 2 minutes later. I found that the fuel filter, which was replaced when I started this work, had caught a fair amount of crud.  I didn't notice much, if any, before I drove it Sunday, and that day was probably 15-20 minutes of idling and 20 minutes of driving. 

I blew some air back into the tank and that did the trick.  Started up and ran fine.

Would it be a bad idea to drive it again?  The storage place is ~20 minutes away.  If I do clog it again, I can always do the same thing again I assume. 

And obviously first thing to do in spring is drop the tank and get it properly cleaned.