my z suddenly lost all engine power

[danny41972]

OK. here is a problem that has me baffled and really upset. First let me tell you my engine configuration. I put a 280ZX engine with flat top pistons in my 240z. I put the E88 head on top of that engine. I also put a mild performance cam on that head. SU carbs. I know that this will yeild a high compression ratio but I thought it would be acceptable.

This engine was running great for about 2 weeks I was having fun and then all of a sudden while I was accelerating the engine became very weak. If I step on the gas hard it backfires. When I accelerate the exhaust sounds funny it kinda sounds like a rattle out of the exhaust(not muffler rattling against frame). Now when this car is not in gear it runs and sounds normal and I can easily rev it up. But when I try to drive it, it is just very very sluggish.

Timing is correct. Replaced fuel filters. Spark plugs and wires. Compression is good. I tried a different mechanical fuel pump.No change. I dont have an electric fuel pump. I had a crane ignition on and I changed it back to the old points and condenser ignition. Same problem.

Any ideas would be appreciated.

[Brett240]

ive had this problem before. im mine the jets were worn out in the carbies becouse the needles were not set in the carby pistons properly, it took a little while to show symptoms but it eventually started loosing significant power in the way you describe. did you recently change the needles?

[danny41972]

About 2 years ago I took these carbs apart cleaned them up put em back together. I did not change the needles. But I did change the setting of the needles. When I took them apart the shoulder of the needle was even with the bottom of the piston. When I put them back together I put the shoulder of the needle even with the groove in the bottom of the piston. I heard somewhere that this was the correct way to set them. Is that the correct way to set them? Brett, it sounds like you nailed this problem down, I hope, because I tried just about every other thing I could think of. Where can I get new jets? Do I need to replace needles too? If so where do I get new needles?

[beandip]

Unless you have just changed the position of the needles before the problen stated leave them alone at least for the time being. If the engine was working and all of a sudden , as you indicated , you experienced a loss of power , unless the needles came loose or something like that I seriously doubt that is the trouble. Back fire through the carbs can either be a lean pop or timing. Have you checked the filters that are in the carbs? Since you have changed the main one what about them? How about the vacume advance on the dist. you stated that you installed the different ignition with no change , is this right? Since you have done this and checked the timing , look to the fuel as the cause. Did this happen right after refueling ? Maby you got a bad load of fuel and some of the crap got by the first filter and has done a number on the filters at the inlets of the carbs them selves and causing a lean situation. This would account for the smooth idle and poor performance. thats my thoughts Gary Another thought Have you checked the oil in the carbs ? this normally wouldent cause this problem out of the blue , but it is easy to check and fix if needed.

[danny41972]

Brett240, you were right it was the jets in the carbs. I bought a set of carbs on ebay. rebuilt them, put them on and it runs great. Thank you for your help.