Guest zfan Posted January 6, 2001 Share Posted January 6, 2001 I AM CURRENTLY RUNNING A 350 SBC RPM SETUP. APPROX. 420 HP. MY PROBLEM IS THE CAR STAGGERS OFF THE LINE WHEN I JUMP ON IT OR HIT SECOND HARD. I AM CURRENTLY RUNNING A STOCK MECH. FUEL PUMP WITH 5/16 FUEL LINE, FUEL PRESSURE REGULATOR SET AT 5 LBS. I KEEP THE GAS TANK 3/4 FULL, SO IT IS NOT FUEL SLOSH TO THE BACK OF THE TANK. I AM LOOKING AT GOING WITH A BLUE HOLLEY ELECTRIC FUEL PUMP STREET OR STRIP WITH 3/8 ALLUMINUM OR STEEL FUEL LINE. WOULD A HIGH PREFORMANCE MECHANICAL PUMP WORK JUST AS WELL. I HAVE HEARD ELECTRIC PUMPS ARE VERY NOISY. ANY SUGGESTIONS, IDEAS HINTS ETC... WOULD BE APPRECIATED. THANKS IN ADVANCE FOR YOUR HELP. ZFAN...MIKE Quote Link to comment Share on other sites More sharing options...
pparaska Posted January 7, 2001 Share Posted January 7, 2001 I really doubt that a stagger off the line is from too little fuel volume. I'd go after the accelerator pump adjustments. Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted January 7, 2001 Share Posted January 7, 2001 I agree that a hesitation at launch is not a delivery problem. What carb are you running? Q-Jet,double pumper,vac sec,or AVS type? They all have different tuning methods to cure your problem. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 7, 2001 Share Posted January 7, 2001 THE CARBURATOR IM RUNNING IS A EDLEBROCK 750 PERFORMER RPM TYPE. MANUAL CHOKE. I BELIEVE IT IS A MODEL 1407. HEY GUYS SPEAKING FROM EXPERIENCE DO ANY OF YOU HAVE PREFERENCES RE: HIGH OUTPUT MECHANICAL FUEL PUMPS VS. AFTER MARKET PERFORMANCE ELECTRIC PUMPS OR USING THE COMBINATION OF THE TWO?? ALSO IVE BEEN TOLD TO NOT USE RUBBER FUEL LINE FROM TANK TO CARB AS THEY CONTACT AND EXPAND THUS CAUSING PRESSURE FLUCTUATIONS??? THANKS Z/FAN...MIKE Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted January 7, 2001 Share Posted January 7, 2001 You probably need to adjust the pump shot on you RPM carb. This is easily done on that model by putting the pump linkage in the hole closest to the pivot. This will give a larger shot. Check the float level first though. With the power you have 3/8" lines would be good but 1/2" would be better. The stock mechanical pump won't get it done at higher RPM with your power level either. There are some very good mechanical pumps on the market,Holly Pro Series for one,and they will work well for you. But a good high pressure electric mounted near the tank regulated to 5-6 psi at the carb will do the job and prevent vapor lock. Use your 5/16" line as a return to the tank and you should be good to go. Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted January 8, 2001 Share Posted January 8, 2001 quote: Originally posted by Tom Scala: You probably need to adjust the pump shot on you RPM carb. This is easily done on that model by putting the pump linkage in the hole closest to the pivot. This will give a larger shot. Yes that's one possibility. If you change it the first spot and that makes no or little difference go back the prior location and then alter your the springs on your metering rods. Do you have the tuning kit? I'd guess you do....if not a good investment. Jump to the softest or stiffest (don't recall/tuning book has it as does website) spring. If that fixes it then back up one increment(spring set) at a time until it starts getting worse, go back to your last pair and that's optimum for your setup. Your timing can also play a v. vital/big part in that. Try a few more degrees initial if it doesn't knock your total up too high and you may be very pleasantly surprised:-) Quote Link to comment Share on other sites More sharing options...
MYRON Posted January 8, 2001 Share Posted January 8, 2001 ZFAN, Myron here. If your running 400+ hp you may want to run 1/2 inch line and #8 an fittings from the tank all the way to the regulator. Then branch off with #6 an lines to the carb.. As for your hesitation, I had the exact same "stumble" right when you hit the gas. I have the MSD pro billet HEI distributor and that unit has both vaccume and mechanical advance. I had the timing set using both advances and when I disconnected the vaccume advance the problem went away. I am assuming the the timing was swinging way too advanced off idle causing the hesitation... You can also try different accelerator pump "cams". they are color coded and the cam lobe changes the volume of fuel and rpm (throttle position) that you get the "squirt"... Myron Quote Link to comment Share on other sites More sharing options...
JFryer Posted January 9, 2001 Share Posted January 9, 2001 MYRON Not to confuse the issue but normally Vac advance is at it's least under WOT/ low manifold vac conditions and high(advanced) under low throttle high vac conditions. That is why you disconnect and plug the vac line when setting the advance. It sounds like what is happening is that there is not enough initial advance. so what is happening is that as you stepped on the gas hard the vac advance unit retards' the advance causing the engine to bog until ether the mech advance kick's in or manifold vac increases again. Good thing Z's are very light for most V-8's if it were a normal car 3500-4000lbs the stumble would be very pronounced. Quote Link to comment Share on other sites More sharing options...
Guest EPS Posted January 27, 2001 Share Posted January 27, 2001 Mike, I had the same stumble but not directly off the line, it came on at about 2500 rpm. Setting the timing on the dyno to 32 degrees from 36 seemed to take care of it, however it was about this time that I installed the MSD 6AL so perhaps that was the cure. I doubt it is fuel pressure and you are right, the electric fuel pumps are nosey and I have tried several. I'd welcome anyone's idea on that problem. The electric pumps on the Z car don't have that problem, strange! [This message has been edited by EPS (edited January 27, 2001).] Quote Link to comment Share on other sites More sharing options...
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