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First off. I just installed a F54 with an e31 head into my '71 240z. The block has been bored .050 and the head completely reworked. I"m using the original 3 screw SUs with SM needles and a Mallory ignition. The car has lots of power and pulls strong.

Until...about 4000 rpms in 4th gear and 4500 in 3rd gear. The thought is that maybe the fuel pump isn't getting enough fuel to keep the bowls full. The SUs have been rebuilt and they are working great. Once I get to 4000 the car stops pulling and i have to wait and then power returns.

Any thoughts?
 
G

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I apologize for not having a direct answer to your question. The other day I was reading a post and the individual mentioned the exact same problem. He cited adjusting the needles as his solution. I believe the post was under the search section regarding coils. Someone said their Z was breaking up at a higher rpm and thought it was the coil. This was a recent post within the last few days. If I see it again I will contact you with the information. Good luck. John
 

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It does sound fuel related. What pump are you using now? On my race car I use a Holly blue pump that puts ton's of volume up to the bowls. Also, I installed a larger capacity line between the tank and the regulator. You might try just a larger line at first.
 

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Hi tdignj-----------------With the SM needles, the SU's use a lot more gas, especially at higher revs. I agree with ITS racer--the Holly blue pump is plenty strong enough and will get all the fuel to the carbs that they can use. Good advice on line upgrade, too.

Before you do this mod, it might be worth your while to check all the filters, if you haven't already done this. Don't forget the little ones in the banjo fitting on both carbs.

Roadman
Gulfport, MS
 

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Has the tank ever been cleaned out? The tank and pickup screen were a mess on my '80 and that's 9 years newer than yours. Dirt on the pickup screen can seriously reduce the fuel flow to the engine.

Dave
 
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