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 Post subject: Speaking of hoses...
PostPosted: Wed Jan 15, 2020 8:34 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 650
Location: Ansonia, CT
I took my Z out last weekend to "stretch its legs" while the weather was cooperating. The Z started right up and ran great until I wound it out it 2nd gear where it just died at about 4500 RPM. I thought the issue may still be related to timing or the something with the distributer but then I discovered what I think has been the real culprit for a while now. After removing the air cleaner and looking closely at each SU carburetor, I noticed that both of the rubber fuel lines that connect the float chambers to the fuel jets were kinked (see picture). I had installed these lines a while ago when I rebuilt the SU's and I believe they have hardened and kinked over time and may even be the wrong length causing fuel starvation under hard acceleration.

I ordered two new SU rebuild kits from MSA which now seem to include braided covered hoses. Hopefully these will remain kink free and flexible. I just can't seem to find a good source for just the new fuel lines. I'll let you know how this works out.

I love the simplicity and ease of maintenance on these SU carburetors. I feel that their only drawback are those vulnerable fuel lines.

I figured I'd post this just in case anyone else running these SU carbs has experienced the same problem during high RPM acceleration.


Attachments:
20200112_134214.jpg
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John Kish
1971 240Z original owner
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 Post subject: Re: Speaking of hoses...
PostPosted: Wed Jan 15, 2020 10:01 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13570
Location: CT
Our member Jimbo Frederick in Florida has (and sells) full sets of braided hoses for every part of the L24 engine. He owns about two doZen perfect, low-number 1969 240Zs and a couple very low number 1970s.

https://youtu.be/zN-Z6Zt8F1U

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 Post subject: Re: Speaking of hoses...
PostPosted: Sat Jan 18, 2020 8:42 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 650
Location: Ansonia, CT
Well, the SU/Hitachi carb fuel hoses were replaced but the acceleration problem still exists. :( Engine revs to about 4500 RPM under load and just flattens out. I'm back to checking out ignition and timing. :roll: I plan to check cam indexing for timing chain stretch as soon as the weather warms up so my garage heater can keep up.

I am glad I replaced the hoses though as the ones I replaced were badly cracked and ready to fail. :thumbs_up:
Don't want gas dripping down on a hot exhaust manifold. :shock:

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John Kish
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 Post subject: Re: Speaking of hoses...
PostPosted: Sun Jan 19, 2020 1:23 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13570
Location: CT
when did you last change your coil?

I misunderstood this initially; I thought you meant the engine died.

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 Post subject: Re: Speaking of hoses...
PostPosted: Sun Jan 19, 2020 10:56 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 650
Location: Ansonia, CT
I changed the coil in May 2018. Nothing changed. I have also:

Rebuilt the distributor (Dec. 2018)
Replaced the points and condenser
Replaced the rotor
Advanced the timing
Retarded the timing
Replaced the plugs
Replaced the spark plug wires
Adjusted the valve lash

This has been an ongoing issue ever since I started asking about changes in the gasoline we are buying a few years ago. When accelerating hard at over 4500 RPM the engine just flattens out. Pressing the accelerator at speed does nothing but make it worse and backfire.

I plan to check the cam timing out to make sure that the timing chain is not stretched beyond allowable tolerances. She is coming up on 200K miles soon. I'm wondering that when I had the head resurfaced (milled less that .005") it changed the cam chain timing any.

Frank, If you remember, she ran pretty well at the Glen this summer but I never had her go much above 5K RPM. She still runs well otherwise.

I may also re-install my Pertronix ignition to see if that helps any.

I'll also do another compression test. The last one I did was back in January 2017, all cylinders looked good then at close to 180psi

If it ain't timing then it might be that time to finally send my SU roundtop carbs to Z Therapy. :roll: I may also bring her over to Vinny's to see what he thinks.

One comment that the fella from Advanced Distributors made when he sent back my rebuilt distributor was that he recommended installing a higher performance set of points. I can't seem to locate any of these hence the pending Pertronix re-install. The aftermarket points may just be floating around at high RPM which I would think could cause this issue.

Any suggestions are WELCOME!

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 Post subject: Re: Speaking of hoses...
PostPosted: Mon Jan 20, 2020 5:49 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13570
Location: CT
Back in the OHV pushrod days that would have described valve float, but you would have probably heard it rattle when it happened.

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 Post subject: Re: Speaking of hoses...
PostPosted: Fri Jan 24, 2020 3:08 pm 
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Joined: Fri Dec 25, 2015 7:39 pm
Posts: 539
Location: Long Island, N.Y.
You mentioned that the distributor was rebuilt. Did that include a new set of springs? Maybe you need to experiment with different springs with a different tension rating. And maybe they're already maxed out at 5k and can't give you anymore timing advance??? I don't know if that makes any senZe or not. I'm just a weekend mechanic without that much knowledge.

Good luck John.

Howard J

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 Post subject: Re: Speaking of hoses...
PostPosted: Fri Jan 24, 2020 10:43 pm 
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Posts: 650
Location: Ansonia, CT
Howie, you bring up a good point.

Supposedly my original distributor (which was rebuilt by Advanced Distributors) was put on an old SUN machine which they use to check the timing curve on these older distributors. And yes, the springs were replaced by AD. My gut is telling me (and I have a big one) that it is still a timing issue. I will be checking the ignition timing advance again shortly, but have no way of really checking it under a real load. I do know that both the mechanical (spring) advance and vacuum advance do work, just don't know what the total timing is at the high end revs under load. :roll:

It's good hearing from my fellow LAWNG ISLAND buddy and thanks for the input!

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 Post subject: Re: Speaking of hoses...
PostPosted: Sat Jan 25, 2020 12:46 pm 
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Joined: Fri Dec 25, 2015 7:39 pm
Posts: 539
Location: Long Island, N.Y.
John: Other thought(s)/brain surges. :lol:

Can you be loosing vacuum to the vacuum advance at 4500+ rpm? Like the old windshield wipers? Can you trace the vacuum line back to its supply? Pipe cleaners to clean vacuum ports? Carbon/oil fume buildup/restriction? Maybe if you can connect a vacuum gauge at this source (using a VERY long hose), and plugging up the vacuum advance hose and then a road test/load test to 4500 rpm to see if you're still pulling a vacuum and see if you still have the flat spot? :wink: :?: :?: :?:

Just shoot'n in the dark. :wink: :wink:

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 Post subject: Re: Speaking of hoses...
PostPosted: Sat Jan 25, 2020 9:51 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 650
Location: Ansonia, CT
I'll add that to my check list Howie. Thanks!

It's a short run from the vacuum advance diaphragm to the vacuum source located at the forward SU Carb. See picture. Hose is new, no leaks, but I will see what vacuum it pulls at high RPM and also plan to check high RPM timing again as well.


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John Kish
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 Post subject: Re: Speaking of hoses...
PostPosted: Sun Jan 26, 2020 1:28 pm 
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Joined: Fri Dec 25, 2015 7:39 pm
Posts: 539
Location: Long Island, N.Y.
Love your clean engine compartment. Sweet! :mrgreen: :thumbs_up:

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 Post subject: Re: Speaking of hoses...
PostPosted: Sun Jan 26, 2020 1:36 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13570
Location: CT
Be sure you're not using the top float bowl vent as a vacuum port; there's nothing going on there...... :?
Also, I can't read the settings on your airbox intake vent but as the weather cools they generally like to be closed a little more.

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 Post subject: Re: Speaking of hoses...
PostPosted: Sun Jan 26, 2020 4:20 pm 
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Joined: Mon Jun 30, 2008 2:16 pm
Posts: 650
Location: Ansonia, CT
Its hooked up properly to the vacuum port right next to the round top on front carb. The summer/winter airbox flapper never worked on my car as the dealer literally sawed off the connector piece to make room for the dealer installed AC compressor (AC since removed).

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