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I just finished installing my L28 into my 240z, and did not change out the needles, and it seems to me to be running lean, it backfires a little through the carbs when it is going oh, 40mph in 5th gear. (1900rpm???) I think the needles are running a little lean for the bigger displacement, what needles are you guys running??? thanks!
 

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Hi Andrew--------------The place to start correcting for a lean running condition is not the needles. Start by checking the float level in each carb and adjust them to specs first. Then check the needle height relative to the bottom of the vacuum piston. When you have established this baseline you will be ready to consider changes in the needles. You can find info on these procedures in the "Just SU's" video sold by Z Therapy (www.ztherapy.com), the factory manual or even the Haynes manual will help you.

In answer to your question, I've been running the SM needles in my carbs. I have an L-26 engine in my 240, and these needles definitely increased the car's performance and decreased my gas mileage. They come on above about 2500 rpm's and provide plenty of gas all the way to 6500. I see no reason why they wouldn't do the same for an L-28.

Roadman
Gulfport, MS
 

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Check your distributor/timing!!!

had similar problems and found out mechanical advance was not functioning. would idle nice and rev from 0 to 2500 rpms smoothly and then backfire and stutter terribly from there.

check initial timing and both vacuum and mechanical advance first before fooling around with anything else. once i had a functional distributor installed i couldn't make it backfire no matter how much i screwed around with the carbs.

search the archives, there is a lot of good material on this subject.
 
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