SU Troubles

[VaGuS510]

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.

[beandip]

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

[VaGuS510]

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.

[kenz240z]

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