BIGJIM Posted March 16, 2007 Share Posted March 16, 2007 Im helping a friend with his 383 powered 280z. The engine is a fresh 383, has a crane cam (not sure of the specs but it does have a nice lopey idle) Holley 750 carbs with vaccume secondaries, air gap intake, ported cast heads with 64cc chambers and roller rockers, flat top pistons, accell distributor, headman headers, hughs 3000 stall converter and a th350 trans. We have been messing with this beast for a few weeks now. It purrrrrrrs like a kitten and comes to life like a lion when its sitting still. Soon as you take it up the street and hammer it it falls flat on its face. Seems to bog and miss, wont rev up or get going at all. As soon as you stop the car and rev it all is fine again. I am totally stumped! Any advice on where to look would be appreciated and save my sanity. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted March 16, 2007 Share Posted March 16, 2007 As far as putting a load on the 383, it sounds like a fuel delivery problem. Check fuel pressure and floats. What do you have the timing set at? Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted March 16, 2007 Share Posted March 16, 2007 Check your timing, I 12-16 degrees is a good starting point for static timing. What type of fuel pump is being used? What if, instead of pulling into the street and "hammering it", you just smoothly and slowly open the throttle. Does it run OK when you do that? If it does, make sure the accelerator pump on the carb is working properly. If you look down the primaries and open the throttle, you should see 2 strong streams of fuel coming out of the nozzles. If its working properly, start playing with cams and larger nozzles. Does this carb have the 35cc pump or the 50 cc pump. i would upgrade to the 50cc pump. Quote Link to comment Share on other sites More sharing options...
Georgia Flash Posted March 16, 2007 Share Posted March 16, 2007 Timing is where I would start. I had a similar problem with my Z (V8) after I installed the new MSD components. My timing was off the mark. Quote Link to comment Share on other sites More sharing options...
BIGJIM Posted March 18, 2007 Author Share Posted March 18, 2007 Check your timing, I 12-16 degrees is a good starting point for static timing. What type of fuel pump is being used? What if, instead of pulling into the street and "hammering it", you just smoothly and slowly open the throttle. Does it run OK when you do that? If it does, make sure the accelerator pump on the carb is working properly. If you look down the primaries and open the throttle, you should see 2 strong streams of fuel coming out of the nozzles. If its working properly, start playing with cams and larger nozzles. Does this carb have the 35cc pump or the 50 cc pump. i would upgrade to the 50cc pump. Even if i ease into it the stumble and lack of acceleration is there. It has one of those mechanical aftermarket fuel pump. I think its a holley, so im sure its pumping tons of fuel. Ive moved the timing all over the place with no improvment. Ill have to check on the 35cc or 50cc pump as im not at home right now. He also has some type of fuel pressure regulator on it. Im gona pull it off and see what it does without it. Thanks for the help, any other suggestions are appreciated. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted March 18, 2007 Share Posted March 18, 2007 The accelerator pump will not do (all of) what you're describing. Put a fuel pressure guage on it and see what it tells you. Does the car smoke or anything when you get on it? Do you have the floats set right? It is possible that your regulator is not set right and that you're either not getting enough fuel or you're making too much pressure and overpowering your floats. If it's not smoking and hurting your eyes I would just say that it's leaning out. One very likely thing I can think of right now is the firing order. It is possible to swap some wires and hardly tell the difference until you put a load on it. Quote Link to comment Share on other sites More sharing options...
jt1 Posted March 18, 2007 Share Posted March 18, 2007 Sounds like a big vacumn leak to me. John Quote Link to comment Share on other sites More sharing options...
Forces Posted March 18, 2007 Share Posted March 18, 2007 I too had a similar problem with my 383. It's not totally up to par yet, but when I added an MSD 6AL, new wires/ plugs, and an in-cap MSD HEI coil it seemed to run much better, but like I said, not 100% quite yet. I know that edlebrock carbs' secondaries only open up when under a load, your Holley MIGHT be the same. I am not certain. Also, I know this sounds stupid, but double check your plug gaps and vlave adjustment. Quote Link to comment Share on other sites More sharing options...
icewtr Posted March 19, 2007 Share Posted March 19, 2007 I had this same thing on mine when i went from 350 to a 383.. the accelerator pump squirters had to go up to a 37 front and 35 rear and also went about 4 jets larger all the way around.. and it went away i could sit in neutral and rev fine all day as soon as ya tried to stomp on it in gear it bogged down and didn't wanna go .. so if the timing is ok start there Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted March 19, 2007 Share Posted March 19, 2007 Icewtr, was that with a 750? Quote Link to comment Share on other sites More sharing options...
icewtr Posted March 19, 2007 Share Posted March 19, 2007 Icewtr, was that with a 750? Yes it is a 750 i am running a proform 750 double pumper with mechanical secondaries ...and the jetting i have now would be a 78 main jets and 84 secondaries with no power valve in the rear and the carb actually has adjustable idle air bleeds and high speed air bleeds Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted March 20, 2007 Share Posted March 20, 2007 So did it have the stock jetting when you were having the problems? I just can't imagine a stock 750dp running that lean. Quote Link to comment Share on other sites More sharing options...
Turbo Meister Posted March 21, 2007 Share Posted March 21, 2007 Yes it is a 750 i am running a proform 750 double pumper with mechanical secondaries ...and the jetting i have now would be a 78 main jets and 84 secondaries with no power valve in the rear and the carb actually has adjustable idle air bleeds and high speed air bleeds When I first got my Proform 750 dp the engine experienced a very damaging violent lean backfire. That's when I determined that the hi speed air bleeds are extremely lean. Although this does not apply to you, I had to replace the boosters to get enough fuel for my turbos. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted March 21, 2007 Share Posted March 21, 2007 I also am running a Proform 750 dp'er on my 383 sbc. My Jetting is almost the same as yours. I had some issues with power valves and float levels. Make sure and check fuel pressure, do not have it above 7.5 lbs and check to see that your maintaining fuel presssure under load as well. Quote Link to comment Share on other sites More sharing options...
icewtr Posted March 21, 2007 Share Posted March 21, 2007 I actually use a Uego1000 wide band to tune with .. kinda made it simple .. press pedal going down street see 15.1 air fuel know it is lean ..lol i actually have it at 14.7 in gear at idle and most of cruising and at 12.6 at wide open throttle and on the NOS it is jetted to be at 12.4 made tuning so simple was well worth the 300 bucks for it .... Quote Link to comment Share on other sites More sharing options...
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