68 CST 396 - Need Advice

[story2tell]

I have been working on a 68 Custom Sport Truck, 396, 325 horse, TH-400, no AC, limited slip. The truck belongs to my Fateher-in-law and in the 17 years I've been in the family, the truck has not run right. I recently retired and have spent the last 2 months steadily working on it. The truck has an Edelbrock Performer RPM manifold and Edelbrock Thunder #1806, 650 cfm carb. We installed a mild Edelbrock cam, lifter and spring set. After fixing a bunch of electrical issues, the truck starts fine, idles fine and runs great up to about 3,000 rpm, then sputters and dies. The truck will start right back up most of the time afterwards and then does the same thing again. I have cleaned the carb, adjusted the floats, installed a fuel pressure regulater (set at 6 psi) to make sure it's not blowing fuel by the needle valves and flooding. The fuel pump is putting out 11 psi at idle and 10 psi up to 3,000 rpm. The distributor is a stock points distributor (new points, rotor, cap) with an adjustable vacuum advance which I have hooked to manifold vacuum. The truck makes 12 inches of vacuum at 800 RPM and 15 inches at 1,000 RPM. The vacuum module starts pulling vacuum at 7-8 inches and is all-in by 12 inches with 15 degrees of advance. The mechanical advance is free and working. Initial timing is 8 degrees BTDC and total timing is 42 degrees. In trouble shooting, I have changed coils and by-passed the ignition switch with the same "sputter and die" results. I've done everything I know to do and am totally baffled ...any suggestions appreciated!

[Willys47]

It has been years since i have worked with point, but is there a gap the points need or a dwell angle that it need to be at I think that's what it's called ?

[Willys47]

I found a picture that I hope may help

[story2tell]

Thanks Willys47 for your replys. "Yes" on the dwell. Specs call for 28-32 degrees. I set the dwell at 30 degrees. If the dwell bounces around a bit it is usually caused worn distributor bushings. In my case, the dwell is rock steady at 30 degrees.

[old Chevy guy]

Seems kind of too simple but what about the condencer? The 350 in my 69 Camaro ran great at idle, started fine ,but going down the road if you stuck your foot in it, it would skip and sputer and act like it was going to die. We did plugs wires ,cap,roter points and condencer, tried a diffrent coil,another carb,fuel pump,everthing we could think of. Turned out to be the condencer and even though I put in a new one it too was defective so even though I thought I had eliminated it,it was the problem. Not to much latter I put in an HEI and never had that problem again.

[story2tell]

Thanks old Chevy guy. I put in a new set of points and condensor today (have had your same experience in the past) but it made no difference. HEI is looking better all the time!

[CC69Rat]

Original Distributor? I'm thinking HEI too. Looks like you have covered about everything I can think of on a points type dizzy. It may just be worn (?) HEI would help you a little on the fuel mileage too. (not astronimcal difference .. but just sayin)

[bowtie72]

I would start by checking to see if your loosing fuel or spark. They sell a spark tester that you can hook inline with the wire and see spark. Once you figure out if it's spark or fuel you can go after that system. I have seen fuel filters do kinda of the same thing but need to see which system is causing it to die. Good luck

[Dave]

There's nothing like being in front of the problem and seeing it first hand. However, you might try looking at your fuel pickup/sending unit. Do you still have the fuel tank in the cab?

If it's the original tank it could have sediment in the the tank. When fuel demand is high the sediment will surround that sock/filter on the pickup unit and cause the engine to starve for fuel and die. IMHO.

Hope this helps

[chopnchaneled]

This is probably way out in left field but, i have a vortech sbc with a electric pump in my 68 and when i would throttle it, sounds like the same thing would happen. Went thur the same as you.
Turns out i had bought a new gas cap that was susposed to be vented
and was not and under high demand it would cause a vaccum in the tank,
would do it quicker when the tank was close to full.

Like i said wierd, but now no problems, try taking the cap off and see what happens.

Good luck

[story2tell]

Dave and Bowtie72, thanks for your responses. I took the fuel tank out this week and drained it into a fuel strainer. I was surprised at how clean it was...just a small amount of sediment. Most of it was from the deteriorated sock filter on the pick-up tube. I fasioned a new sock filter from nylon strainer material and zip-tied it to the pick-up tube, blew out all the lines up to the fuel pump and installed a new fuel filter between the fule pump and carb. When I cleaned the carb, the screens at the needle float valves were clean, the needle valves drop open when the floats drop, and fuel pressure is good (10 pounds) all the way up to when the truck sputters out around 3,000 rpm. I've pulled the top off the carb a couple of times immediately after the truck dies and the float bowl have fuel in them. Edelbrock techs thought it might be flooding out, but the pressure regulator set at 6 psi limits the fuel pressure at the needle valves and the carb is not overflowing at the top.

I have a spark test light hooked up to #1 plug. It does seem to lose spark as the engine sputters out. Yesterday, I pulled the distributor, thoroughly cleaned the mechanical advance portion, checked the vacuum advance, installed a new set of hi-performance points and condensor, cap and rotor, set the dwell, timed it, adjusted the idle jets...and same problem. I switched off the coil with a spare one (designed for use with an external resistor or resistor wire) and same thing. The ignition side of the resistor is getting 12+ volts right up through the truck dying (eliminates the ignition switch as the culprit), and I have also jumped the coil right off the battery while trouble shooting with the same result.

Question for those with more alternator/charging experience than me: Is it possible an overcharging alternator could momentarily knock out the coil? I ask because the charging voltage sometimes reaches 15.2 volts when the truck is running. I know max charging should be around 14.2 volts, so I initially took the alternator apart and tested the components which checked out fine. I then took the alternator to a local alternator/motor rebuilder and tested it on his machine, which tested good. Still, 15+ volts seems high and I haven't measured it through the truck dying...I'll do that today and try running the truck up through "dying range" with the alternator disconnected.

[story2tell]

chopnchaneled, any suggestion appreciated! The truck had a new cas cap and when I first started this project the truck had a strong smell of gas inside the cab. When I removed the gas cap the tank was pressurized even though the cap was supposed to be vented. I eventually altered the cap by removing the venting plunger. Now no smell inside the cab and no vacuum lock preventing fuel from flowing to the fuel pump.

[yuccales]

Just a thought, problem with the exhaust system?

[John Fabris]

agreed on exhaust, unbolt the pipe from the exhaust manifold and the start it up. If you get past 3000rpm, then you have something loose in the pipes or mufflers and its time for new exhaust.

I have had this happen with a newer truck where the catalytic converter came apart and would block pipe at higher rpms.