‘71 sputters going uphill

[shoehorn_hands]

Hi fellow Z lovers,

I recently bought a ‘71 and am using it as a daily driver. The car is generally in pretty good condition and runs well for the most part but sputters/jerks/misfires(?) while going uphill.  This usually happens while within 10% of 65 MPH/3500 RPM. So far it hasn’t completely died yet but it doesn’t feel, sound, or look good when it happens. I’m worried about it.

The car has a rebuilt, non-original L24 with about 45k post re-build.

What should I be looking out for?

[Tweeds]

Might be the carbs - have you tuned them? They might not be balanced, or the mixture could be off. I had similar issues, and a good tune helped a lot. Though I never had sputters from hills and hills alone - it was more a rpm/throttle input thing in general. My mixture was off, I reckon. Sputters are much rarer now that I've gotten things pretty dialed in.

[siteunseen]

I had the same problem going up steep inclines. The front carb would run dry and then it only ran on the back 3 cylinders. I could roll the car backwards and cut the wheel making it perpendicular in the road, let the front carb fill back up and it ran fine for another mile or two. My floats were way off but once I got those adjusted properly I went straight back to Cheaha Mountain and "tested" it. Pulled up that thing like a mule, no sputter whatsoever.

The quick and easy way to get an idea where your's are is the clear hose method.

Edited September 4, 2021 by siteunseen

[madkaw]

1 hour ago, siteunseen said:

I had the same problem going up steep inclines. The front carb would run dry and then it only ran on the back 3 cylinders. I could roll the car backwards and cut the wheel making it perpendicular in the road, let the front carb fill back up and it ran fine for another mile or two. My floats were way off but once I got those adjusted properly I went straight back to Cheaha Mountain and "tested" it. Pulled up that thing like a mule, no sputter whatsoever.

The quick and easy way to get an idea where your's are is the clear hose method.

So you would do half a K turn and block traffic while your carb refilled - lol

[madkaw]

Heavy loading as in going up a hill can also put a strain on your ignition coil . Maybe another thing to check 

[Mark Maras]

Sputtering at 3500 rpms while climbing a hill sounds like fuel starvation to me. Especially if it will rev to high rpms in neutral (no load). Fuel filters, float levels, carb balance, fuel pressure, and fuel volume, are where I'd start looking.

[shoehorn_hands]

Thanks for the help! What is a good source for information on how to tune the carbs?

[SteveJ]

8 minutes ago, shoehorn_hands said:

Thanks for the help! What is a good source for information on how to tune the carbs?

ZTherapy sells a video: https://ztherapy.com/products/videos/just_SU.htm

Here is their main page: https://ztherapy.com/

[Tweeds]

11 minutes ago, shoehorn_hands said:

Thanks for the help! What is a good source for information on how to tune the carbs?

https://www.youtube.com/watch?v=F4JVwqu8dgo&t=343s&ab_channel=LivingWithAClassic and https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/ The video and guide are how I learned. I was running in circles for a while on my first tune, then everything kinda clicked. 

 

[siteunseen]

This got me straight. After doing it once it clicked for me too, like Tweeds says. You can print it out and keep fuel off your computer/phone.

 

[shoehorn_hands]

Thanks everyone!

[shoehorn_hands]

On 9/4/2021 at 4:25 AM, siteunseen said:

I had the same problem going up steep inclines. The front carb would run dry and then it only ran on the back 3 cylinders. I could roll the car backwards and cut the wheel making it perpendicular in the road, let the front carb fill back up and it ran fine for another mile or two. My floats were way off but once I got those adjusted properly I went straight back to Cheaha Mountain and "tested" it. Pulled up that thing like a mule, no sputter whatsoever.

The quick and easy way to get an idea where your's are is the clear hose method.

Where does one find a clear fuel hose like this?