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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: 516
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.


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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: 13350
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: 516
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
1971 240Z original owner


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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: 13350
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: 516
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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John Kish
1971 240Z original owner


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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: 13350
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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