misfiring engine issue

[Mshimy]

Hi everyone,

I have a 72’ 240z that I bought 4 months ago, and have put on the road since early February and recently I’ve encountered a problem.

Problem: Backfiring out of carbs under load in the med/high rpm range. Issue is absent with the choke on. Points, condenser, cap and leads replaced. Issue has got progressively worse after ~500 miles of driving since buying the car. N58 needles used with a slight ridge formed due to wear. Once the problem became severe the oil was found to be at the minimum level. Suspect valve clearances or needles to be potential cause, but it's probably a carburettor related issue.

The car is a US import being driven in the UK

I would appreciate any help possible, I'm desperate to get it back on the road

Thanks a lot!

Moe

[Miles]

Back firing through the carbs is the sign of a too lean mixture.  Do you know about the mixture adjustment nuts on the bottom of each carb?

 

 

You will need to learn how to tune and maintain SU carbs.

 

If you are new to SU carbs then you need to buy the "Just SUs" video at

 

http://www.ztherapy.com/

 

After viewing this video you will be able to maintain, adjust and repair SU carbs. 

 

Ztherapy also carries parts for SU carbs.

 

 

 

If you Google SU carb adjustment  or SU repair  you should get many how to work with SUs write ups by Z car owners.

 

For example:   http://www.nicoclub.com/archives/2-write-ups-on-tuning-su-carbs.html

 

 

Also, search Hybridz  and classiczcars.com  as there are many posts on maintaining SU carbs.

 

In addition to the video, download a pdf copy of the factory service manual (FSM)  for your year Z from the Links forum.

 

Look here too: http://atlanticz.ca/...bs/su/index.htm

Edited March 25, 2015 by Miles