I have looked around quite a bit to try and find my problem. I still can't figure out what is wrong. I have an L28 with a header, N42 head and belltop SU carbs. I was told there is a cam in the engine(but you know how that goes ). I believe I am currently running N55 needles. Which is probably part of my troubles. I am thinking of going with SM's. I set up a dual air fuel ratio gauge (each reads from a carb with my dual collector header). The only way to prevent backfire when the engine is under load is to richen the mixture up quite a bit. Another trouble is that I can't get the rear carburetor to lean out at idle. The choke isn't stuck. The only problem i can find is the gas getting too hot and boiling. This is definatly something i will fix very soon. But could this cause the "always rich" condition. I have tried to adjust the float many times. I recently got some clear tubing and adjusted the level 27mm below the gasket surface. I can't figure much out. I am hoping to get a Z-therapy rebuild kit as soon as i have the cash.

Thanks for taking the time to read this. Let me know if you have any ideas.

Tyler , You dident include where you are that you are having trouble with boiling fuel . You most likely have 54 needles . I am running them as well in my ZX280 engine , milled head , headers and 2 1/2'' plumbing and cam . My engine runs strong and I have no rich problem . This is in my '73 240 Z . I suggest that you readjust the mixture . If you are having backfireing through the carbs , this could also be caused by a lean condition , however you said you are running rich. If the engine is running so rich that it is backfireing out the exhost do recheck the chokes . Some times the nozzles will stick down when the choke is returned to off positon and this will cause a vary rich mixture . Gary

The fuel was boiling out thru the hose that i was using to adjust my float level. The problem is not that the i am running too rich. This is just the only solution i have found to the backfiring. At idle i can get the mixture to where it should be but it isn't drivable because it backfires with even the smalllest load. Even under very slow acceleration it will backfire.

I only get around 10 mpg when the carbs are adjusted so that it will run. Thats the biggest problem.

Thanks for replying.

Have you adjusted the valves? Checked the timing? What shape are the distributor cap, plug wires and spark plugs in?