Jump to content
kayinsunz

How to tune carbs JUST to get the car running?

Recommended Posts

New to the forum and already feel welcome, thank you for that.

Anyways, thanks to a suggestion Zed Head, I was able to hear my 240z sputter up for time last night. Unfortunatly, it won't stay running for more than 30 seconds. The guy I bought it from said it was running good when he parked it, but then he tried to adjust the carbs and screwed them up. It sputters up after cranking for 10 seconds, and within 15 seconds fuel is pissing from the float intake hose, and soon after starts pissing out of the carburator air horn as the engine misses, backfires, and dies.

What am I missing?

I can already tell this forum is a plethora of information so if there is a similar thread I miss feel free to send me that way. Thank you for any suggestions.

-KS

Share this post


Link to post
Share on other sites

Sounds like the fuel pump pressure is too high or the needle valves in the fuel bowls are no closing.  Check to see what kind of pump is installed on the car.

 

Carbs only need 3  to 4 psi.

 

If you have just the stock pump then take the fuel bowls apart and get the needle valves to work.

 

 

 

Edited by 240260280
  • Like 1

Share this post


Link to post
Share on other sites

Ok cool so I will need to buy a pump with a lower PSI rating. Would that explain why is pissing fuel and sputtering like so?

Share this post


Link to post
Share on other sites

My Z had this issue, what I did was open the float bowl, remove the needle, take it apart and clean, and put back together.

You might need a gasket if the old one is old. Try blowing air through the gas inlet, while lifting the float up to see if it's able to seal correctly.

After you have this all done, turn the page to the service manual and get a base tune.

Might be worthwhile to grab a carb tune. I thought mine was good, but my front was around 13 mmHg while the rear was probably around 7, I had the impression it was running good until I got my hands on the tool, and got them both on an idle around 12, now it's running like butter.

Good luck, ask good questions, read and reread.

  • Like 1

Share this post


Link to post
Share on other sites

Ok so first, I will try to open up the float bowls, check the float bowls, and clean up the needle valve with carb cleaner. Gonna grab my fuel pressure guage from work and test the fuel PSI after the regulator. 

Edited by kayinsunz
off topic
  • Like 1

Share this post


Link to post
Share on other sites

So I tied off the hose I have in an attempt to reduce pressure and it purred like a kitten for about 2 mins untill it flooded the float bowls again. Going to replace the pump with a lower pressure pump, and will post the results. Thank you gentlemen.

Edited by kayinsunz
  • Like 1

Share this post


Link to post
Share on other sites

When you replaced the pump was it with a high pressure unit? Or an OEM equivalent? How did you clean the floats? I had to actually disassemble the valve inside the float and clean the seat.

  • Like 1

Share this post


Link to post
Share on other sites

Hey guys just an update.

Replaced the 5.5-9psi pump with a 2.5-4psi pump. Opened up both of the float bowls and both floats were way out of adjustment. Adjusted the floats to spec, pulled out the needles, and cleaned the seats with carb cleaner and a small wire brush. Just waiting on new gaskets for the float bowls. In the meantime going to adjust the valves.

Quick question, the floats were 'pushed down' really far. The clearance was way over spec on both F/R floats. Could that be the cause 'overwhelming' the floats with high fuel pressure?

Thanks,

KS

Edited by kayinsunz

Share this post


Link to post
Share on other sites

The tangs on my floats were bent up like a roller coaster's first climb.  That caused the bowls to barely have fuel, if I drove up a pretty steep mountain it would stall out from fuel starvation.  I found that having them bent fairly level was a good starting point.

The red circle was for somebody else.

float.png

And try gluing your gaskets onto the lids, it helped me when i was getting them set.  I used black oil and fuel resistant RTV.

20170102_201821.jpg

  • Like 1

Share this post


Link to post
Share on other sites

I see, that would make sense. I think the previous owner tried to adjust the floats and put the needles in backwards. Both needles were facing down (towards the float bowl) and it didn't seem right to me, so I flipped them the other way, facing what I think would be the seat (top side of the float lid). Phone is down right now or I would post pics. It just seemed to be the way it was engineered, the float rises from fuel and closes the needle valve right? By pushing the needle into the seat?

As for the gaskets, they just disintegrated as soon as I removed the lids so I will just wait for them to come in from Zcardepot. Patience is key with my old lady, she's safe in the garage anyway.

IMG_0211.JPG

Edited by kayinsunz

Share this post


Link to post
Share on other sites

How in the world would/could somebody put the needles in upside down??? That seems impossible but I guess not. I've heard it all now of what a previous owner can do. "My word!" is what my Mom would say. 8^)

  • Like 1

Share this post


Link to post
Share on other sites

Anything is possible I guess! He told me in was running when he bought it. Hell when I got the car the coil was wired backwards, firing order off, dizzycap on backwards, 5.5-9psi pump, and now the needles in backwards. I guess he didn't have access to classiczcars.com lmao!

Edited by kayinsunz
  • Like 1

Share this post


Link to post
Share on other sites
57 minutes ago, 240260280 said:

You can photocopy (or scan and print) your lids to felpro gasket paper (at most cars parts stores)  then cut new gaskets with an xacto knife.

 

carb gasket.gif

gonna head to the parts store and try this now actually, give me something to do on my only day off!

Share this post


Link to post
Share on other sites

You may have to scale the above drawing so practice on plain paper until you are happy then throw the gasket paper in the printer.

I filled the drawing up with side-by-side copies so that 1 sheet of gasket paper had 6 or 8 templates printed... just in case I screwed up a few when cutting.

Edited by 240260280
  • Like 1

Share this post


Link to post
Share on other sites

The Parts Department at your local Nissan dealer should be able to get all the float bowl gaskets you need.  Cost was $1.70 each last time I bought some.

Dennis

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.