1970 round top, sticking rear float valve

[Oceanzide]

Greetingz!

Since starting my Z recently - after 10-15 years of mostly sitting - it hasn't been idling well. At first I tried starting the car on 10-15 year old gas and quickly discovered the fuel line was clogged because the tank was full of rust. The gas tank has been cleaned/treated, and I'm using fresh 91 octane fuel. The first indication it was a rear-carb problem was that starter fluid had almost no effect on the rear carb.  Then gas came out of the rear-bowl overflow; I rapped the bowl with a screwdriver handle, that stopped the gas pouring out, but the next time I pulled off the air-cleaner, there was gas pooled at the bottom of the carb's air-inlet. Motor runs great when I accelerate, it's just difficult to start and has rough idle. So, I plan to pull apart the rear float-bowl check-valve (yet again) and, this time, focus on the inlet side aluminum cylinder and seat (part of cover).

Does anybody have any tips regarding "refurbishing" these check-valves?  I've seen several threads regarding stuck check-valves, but not much on how to refurbish the old parts.

[Mark Maras]

I've either cleaned them or replaced them if the needle tip shows wear. The problem is likely crud in the needle and seat. Check the filter in the banjo fitting while you're disassembling things again. Have you made any carb adjustments since the problem started?

[Oceanzide]

36 minutes ago, Mark Maras said:

I've either cleaned them or replaced them if the needle tip shows wear. The problem is likely crud in the needle and seat. Check the filter in the banjo fitting while you're disassembling things again. Have you made any carb adjustments since the problem started?

Thanks Mark,

Dismantled the brass check-valve including spring-clip which retains a tiny spring and "plunger". Squirted everything with WD40, Swabbed-out brass seat with Q-tip. Bent float-tab slightly to lower float. Assembled. Still hard to start and idles like crap.

Re: Adjustments:  At this point I've disconnected the rear fast-idle(AKA"choke") which (as far as I could tell) wasn't pushing on anything anyway.  I've twisted the mixture adjustment and put them both 3/4 turns clockwise from bottom (near where I found them). I've seen posts that advise a coarse tuning of 2.5 turns clockwise from bottom, but mine only have about 2.5 turns total adjustment!(?)  I've now changed the float level in the rear bowl. Now the front carb seems more prone to cough/backfire than it has on the last couple weekends.  That is, when trying to start the engine - on front 3 cylinders. 

[siteunseen]

It's 2.5 from the top. Turn them clockwise until they snug then go counterclockwise down two and a half.

[Oceanzide]

5 hours ago, siteunseen said:

It's 2.5 from the top. Turn them clockwise until they snug then go counterclockwise down two and a half.

Thanks for catching that!?

[Mark Maras]

 You didn't mention if you found any foreign matter in the rear float bowl chamber or the needle and seat. My thought on the front carb acting up is, it has now picked up some crud like the back one. I'd start by cleaning the float chamber in the front carb, reset the floats to the recommended level, reset the nozzles to 2 1/2 turns down, use a Uni-Syn to balance the carbs. As it's been running kinda poorly, I'd also change the plugs, and reset the valve clearance too. Basically, a complete tune-up to eliminate any other possibilities. It's also possible that the nozzles are sticking in the down position when the choke is off. With the choke lever off, reach under the carbs and push up on the nozzles. If you feel the nozzles move up, lube the outside of them with some lithium grease. It may start better, for now, by using no choke and part to full throttle to compensate for the extra gas.

[siteunseen]

I had sticky nozzles that wouldn't come up plus bad out adjustment on the valves. The PO had used 1/4" fuel line (if I remember right) for the hose from the float chamber to the nozzles. That does not work very well. Bought the thin wall hose from ztherapy, adjusted the valves and boom, new car.

Edited January 27, 2019 by siteunseen

[Oceanzide]

On 1/27/2019 at 6:39 AM, Mark Maras said:

 You didn't mention if you found any foreign matter in the rear float bowl chamber or the needle and seat. My thought on the front carb acting up is, it has now picked up some crud like the back one. I'd start by cleaning the float chamber in the front carb, reset the floats to the recommended level, reset the nozzles to 2 1/2 turns down, use a Uni-Syn to balance the carbs. As it's been running kinda poorly, I'd also change the plugs, and reset the valve clearance too. Basically, a complete tune-up to eliminate any other possibilities. It's also possible that the nozzles are sticking in the down position when the choke is off. With the choke lever off, reach under the carbs and push up on the nozzles. If you feel the nozzles move up, lube the outside of them with some lithium grease. It may start better, for now, by using no choke and part to full throttle to compensate for the extra gas.

Thanks guys. Last couple of weekends have been cool and wet here, so I didn't work on it until today.  I checked the three  (rear)  plugs, which looked a little dark brown, but otherwise practically new. Gap was OK on all.

The front bowl was clean last time I looked, but there's usually a fine dust at the bottom of the rear bowl. 

Re: nozzles, Huge THANKS for mentioning it! Rear nozzle was _really_ stuck.

Re: valves, I have heard some valve noise (tapping under valve cover), so was considering this too.

I balanced the carbs a few weeks ago.

I'll focus on mixture-adjustment again, next weekend, weather conducive.

Thanks/Cheers.

Edited February 11, 2019 by Oceanzide

[siteunseen]

If you remove it and sand all the old fuel/varnish off the shaft it should work fine. Good luck.

Ps make sure those hoses are still pliable and soft that go from the nozzle to the float chamber. I've got some new ones from nissan if you need the p/n. They're J shaped thin wall hoses. Nothing else will work very well.

 

 

 

 

 

[Oceanzide]

Just wanted to follow-up, as the engine is idling smoothly now. Turns out the front-carb nozzle was quite stuck as well.

The main problem with idle was that I'd managed to completely back-off the rear throttle adjusting screw while trying to balance carbs (with both nozzles stuck). By turning rear throttle-adjust clockwise a few turns, the idle smoothed-out considerably.  I'll need to go through the carb-balancing again.

By the way, the default mixture adjustment of 2.5 turns down seemed OK for the front carb but seemed to be way (2+turns) off for the rear (as indicated by a Colortune).  I'm not sure whether to worry about the apparent lack of symmetry.

[Mark Maras]

 The lack of symmetry is likely in the float settings. That's what I'd check first.

[Oceanzide]

15 hours ago, Mark Maras said:

 The lack of symmetry is likely in the float settings. That's what I'd check first.

Thank you for that - will certainly check the float setting. I know there's a robust attachment being sold for dynamically monitoring the bowl/fuel level, but I'm thinking about temporarily inserting a "T" or "Y" between bowl and nozzle, using a clear tube on 3rd branch (which will just be suspended above the bowl). It kinda depends on how easy it is to remove the stock tube (which I don't want to cut).