What Happen?

[jvest]

I’ve got a 383 SBC in my 68 Camaro. Just recently it’s started sputtering at wide open throttle and partial throttle while lugging up hill. At first I only noticed it at wot and thought it was bad rev limiter chip in the MSD box, but that wasn’t it. Next I replaced the distributor cap and rotor thinking I had a hairline crack in the cap, but this didn’t help either. It sounds great at an idle and still has very crisp throttle response while sitting in the shop. This setup has run great for over 3 years now without any issues and I only drive it to shows and cruise-ins locally. The only thing I’ve done recently is I added a crankcase evacuation system on it to stop some oil leaks. This is the system that uses the exhaust pressure to pull a vacuum through the valve covers. When I called Barry Grant they stated the Speed Demon 750 mech. secondary was not the correct carb for my application. They said the Speed Demon is running to lean and that I need a Mighty Demon 750. I told them it’s ran great for 3 years and just now started doing this, but they continued to state I need to the Mighty Demon. Does anyone have any thoughts on this issue? Could the crankcase evacuation system cause this issue to pop up? I don’t mine buying the Mighty Demon, if I know that’s my issue. I just hate spending $500-600 and still have the same issue. I listed some motor and car specs below.

Eagle 383 Rotating Assembly
5.7” Rods
2 Valve Relief Flat Top Pistons
XE284H Xtreme Energy Cam (Dur @ 0.050 = 240In & 247Ex / Lift = .507In & .510Ex / Valve timing = .006 / Lobe center 110)
GM Phase III Performance Heads (angle cut to increase compression)
11.75 Static Compression
RPM Performer Intake
MSD 6 Ignition with gutted HEI distributor.
20 deg Initial & 38 deg Total Timing
750 Speed Demon Mech. Secondary
Primary Jetting 72 & Secondary Jetting 79
4.10 Rear Gear
4l80E OD Trans w/3,000 Stall

Thanks,
Jim

[emort]

I had a problem like this, and it was my fuel pump.

[Ollie8974]

What is the possibility that you got a tank of bad gas? Put some gas deicer in the tank to absorb the water.

[Pro Stock]

[QUOTE=jvest;675361]I’ve got a 383 SBC in my 68 Camaro. Just recently it’s started sputtering at wide open throttle and partial throttle while lugging up hill. At first I only noticed it at wot and thought it was bad rev limiter chip in the MSD box, but that wasn’t it. Next I replaced the distributor cap and rotor thinking I had a hairline crack in the cap, but this didn’t help either. It sounds great at an idle and still has very crisp throttle response while sitting in the shop. This setup has run great for over 3 years now without any issues and I only drive it to shows and cruise-ins locally. The only thing I’ve done recently is I added a crankcase evacuation system on it to stop some oil leaks. This is the system that uses the exhaust pressure to pull a vacuum through the valve covers. When I called Barry Grant they stated the Speed Demon 750 mech. secondary was not the correct carb for my application. They said the Speed Demon is running to lean and that I need a Mighty Demon 750. I told them it’s ran great for 3 years and just now started doing this, but they continued to state I need to the Mighty Demon. Does anyone have any thoughts on this issue? Could the crankcase evacuation system cause this issue to pop up? I don’t mine buying the Mighty Demon, if I know that’s my issue. I just hate spending $500-600 and still have the same issue. I listed some motor and car specs below.

Eagle 383 Rotating Assembly
5.7” Rods
2 Valve Relief Flat Top Pistons
XE284H Xtreme Energy Cam (Dur @ 0.050 = 240In & 247Ex / Lift = .507In & .510Ex / Valve timing = .006 / Lobe center 110)
GM Phase III Performance Heads (angle cut to increase compression)
11.75 Static Compression
RPM Performer Intake
MSD 6 Ignition with gutted HEI distributor.
20 deg Initial & 38 deg Total Timing
750 Speed Demon Mech. Secondary
Primary Jetting 72 & Secondary Jetting 79
4.10 Rear Gear
4l80E OD Trans w/3,000 Stall

Thanks,
Jim[/QUOTE

You don't need another carb, it sounds like a fuel pressure problem to me, it's probably a fuel pump starting to go bad and not keeping the float bowls full, the vacuum that you added to the engine would not have caused this problem, if anything it would have had the opposite effect by incresing ring seal which would create a little more manifold vac and booster draw. Look for another problem related to the fuel system, fuel pump, regulator, ect. Also test the power valve to see if it is working correctly, they sometimes go bad.

Dale

[TT302Z28]

I have had a 383 in both a camaro and a 77 Chevy 3/4 ton. Both ran great on a 3310 Holley and is a 750 also.

You have gotten some great advice. Look at fuel pump pressure and also look at spark plugs / wires. I have had a fouled plug and a cracked wire also do exactly what your describing.