The Stovebolt Site Forums The Shop Area Engine Shop Need help with '73 Chevy Truck

Need help from all you great Chevy mechanics out there with a problem I am having with my '73 C20 pickup.

This truck is a 350 V8 with a Quadrajet 4 bbl carb. This truck sat for about 10 years and I got it going again to work on the farm about 5 years ago. It has always been flakey and sometimes unreliable. Over the last 4 months it has gotten worse and worse. It is hard to start, belches black smoke and sometimes backfires. I put a rebuilt carb on it last summer. In the last 2 weeks, I have replace the plugs, points, cap, rotor, plug wires, fuel filter and coil. A few days ago I started it up and drove it over to the gas tank and filled it up. I left it running and when it was full I jumped in and put it in reverse. As soon as I pushed down on the accelerator, it bogged down and had no power. It would barely backup and then die. I could restart it and it would bog down and die again. I finally had to get a tractor out and push it out of the way.

Now it won't start at all. It tries real hard and you can hear it firing but it won't kick over. It has fuel to the carb. The carb sprays gas when you open the butterfly and it has spark to the plugs. I have regapped the points to .019 and made sure the distributer was timed to top dead center on #1.

The timing just seems off somehow but everything looks good. The carb may be flooding it but it is less than a year old. I'm looking for suggestions, hints or thing to try and test. Please let me know what you think.

Thanks,

BigMac
Thanks Dan.

Sounds like it has jumped time. Probably time to check out the timing gears and chain. Chances are they are worn. From what you said about the smoking problem, there is probably a considerable amount of ring wear and valve train problems. You may need to consider getting a remanufactured engine. It is much more economical than going the rebuild route.

First thought (because of the dieing when you step on the throttle) was the fuel filter in the front of the carb is plugged with crud. The choke is obviously sticking and causing the black smoke and choking/back-fire.

Thanks for the replies.

The truck only has 52,000 original miles on it so I don't think there is that much wear. It does not burn oil and runs well when it wants to. I had thought about the timing chain jumping but that usually occurs on higher mileage engines. I would have to dismantle half the front end of the truck just to rule that possibility out.

The in-carb fuel filter is brand new and it has good fuel pressure from the pump. When I crank the engine it seems to fire on about 3 or 4 of the 8 cylinders.

The Q-jet carb(s) have always been a problem. The original started leaking real bad so I got a rebuild for it last year. It ran well for about 3 months with the new carb.

I checked the plugs again today and they were all wet with gas but a random test showed that they had a good spark. Kind of looks like it is drowning out with too much gas. I don't want to spend another $150.00 on a carb just to rule it out.

Any other suggestions?

BigMac
Thanks Dan

WHere did you get the plugs? Hopefully not at any place that has them in bubble-packs(the ones made of plastic and card-board).

Luke,

They are real AC Delco plugs(R44T) out of real boxes from a real NAPA store.

Even in today's economy, I never get auto parts from Walmart. You get what you pay for.

BigMac
Thanks Dan

Check the choke valve and make sure it is wide open. You may need to block it open to get it cleaned out. Try pulling all 8 plugs and letting the cylinders dry.

After reading my '73 shop manual, all your specs. look good, .019" points, .032" plug gap, 30* dwell, 12* timming.

You might try adding a fuel regulator to the fuel line. Turn the pressure down to 2-3psi and see if it helps the problem. For some reason its getting to much fuel or not enough spark to light it off. All of the new ignition parts should of took care of the problem. Have you pull the top off of a Q-jet? They come off pretty easy. The float may be fuel soaked or set to high. I know it's only a year old but things can go wrong. Joe

Joe,

I took the carb off this morning and it appears to have a seepage on the drivers side through the idle circuit. The drivers side of the intake had fuel puddled up in it. The passenger side looked drier. I think the pressure regulator is a good idea. When I disconnected the fuel line from the pump, it sprayed with pretty good pressure.

This kind of explains why the engine was running like it was hitting on four cylinders. Half of them were drowned out

I think I am going to proceed with the assumption that my problem is fuel delivery related rather than ignition related.

I have had nothing but problems with the Q-jet carb on this truck since I got the truck from my Pop years ago. I find it kind of ironic that Pop was an instructor for 17 years at Delco Rochester traveling the Midwest teaching mechanics how to rebuild and tune these carbs.I lost Pop in January and he left without teaching me about them.

Thanks everyone for the help.

BigMac
Thanks Dan
I sure could use you now Pop. I miss you.

Sorry for your loss, a good Q-jet mechanic tough to find. They are easy to work on. Sounds like dirt in one of the idle circuits. Try some carb cleaner with a spray tube on it. Look in the primary side ( Front of carb ) and you will see some small ports. Spray down them to try and clean out what ever is in there.

The engine creates vacuum that pulls air and fuel through the carburator passages. If the air vent is plugged all it pulls is fuel. This would explain the rich condition you are having. Joe

definately sounds like its getting too much fuel to me.