280zwitha383 Posted May 10, 2005 Share Posted May 10, 2005 Well, I need a little help. I recently got my 383 going in my 280zx and got the exhaust and pretty much everything worked out minus a leak or two. Anyway, when I'm below lets say 2,500 rpm it surges almost like it is missing but all the plug wires are good as well as plugs (I would assume since they're both new). I'm wondering if the fuel pump is not supplying enough fuel at low speeds. It would seem that it would be the same at high speeds but once I get on it goes quite nicely. I'm running a stock fuel pump (mechanical) and I have the return line plugged off and the line to the vacuum canister open, I have tried them both open and at first I had them connected so they would leak. I have checked firing order, fuel filter, lifters, and distributor. I have used the carburetor before also so I don't think it's the problem. I have a complete running 350 in my truck that could be used to swap parts also. Any advice as to what's causing my problems and what to do with the other lines coming from the fuel tank. Thanks a lot guys. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted May 10, 2005 Share Posted May 10, 2005 What carby is it? Could be the float levels too high? Quote Link to comment Share on other sites More sharing options...
jt1 Posted May 10, 2005 Share Posted May 10, 2005 Try backing some timing out and see if that helps it. If so, you may need to reconfigure the vacumn/mech advance curves to have a little less timing at the rpm the surge occurs. John Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted May 10, 2005 Author Share Posted May 10, 2005 It's a Holley 670 Street Avenger. I've adjusted the floats but I haven't tried dumming the timing down any which I might try. I even thought the timing was not advanced enough. What gets me is you can throw the throttle back and it revs without hesitation. I'm going to try a different fuel pump tomorrow or Thursday because I'm thinking maybe I've got one with lower psi since it doesn't have a return line in it. Quote Link to comment Share on other sites More sharing options...
WickedWild Posted May 10, 2005 Share Posted May 10, 2005 I currently have the same problem with my 305 right now. But mine is because I have a wobble on my crank from the pully. The car is accually going form retarded to advanced in idle but is fine in WOT. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted May 11, 2005 Author Share Posted May 11, 2005 Any chevy buffs know if the fuel pumps without the return line are lower psi? I'm thinking maybe they came on cars with 2 barrel carbs and they don't put out enough.... I guess I'll find out tomorrow when I get the car back from the window shop. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted May 11, 2005 Author Share Posted May 11, 2005 Bingo JT1, thanks for the advice. I just timed it by ear but I guess I hit the second rpm jump instead of the first. Now it runs great Also, just fyi, I have read that the older style pumps without return lines can overpower a lower hp engine since the pressure builds. That was not my problem however. Quote Link to comment Share on other sites More sharing options...
garry Posted May 12, 2005 Share Posted May 12, 2005 what is the carby it sounds like its is to big and you dont have the air speed though the carby to drag the fuel though at low engine speed it is a problem when the carby is to large for the engine regards garry Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted May 12, 2005 Author Share Posted May 12, 2005 Well, if anything the carb is either pretty close or too small. It's a 670cfm Holley Street Avenger rated by them to 400hp. I'm pretty sure with my setup I'm making more than 400hp. Thanks for the suggestion though. The timing was the problem. Quote Link to comment Share on other sites More sharing options...
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