stuttering while the engine is at high idle

[marandall]

I have a 79 chevy k-20 with a v8 350 under the hood. The problem I am having is that while you are trying to bring the engine to a high rpm to shift into the next  gear or if you just want to cruise at a high rpm the engine starts to stutter and it will keep stuttering until you bring the rpm back down and stay under 50 mph. I have the timing set at 8 degrees btdc, a reman quadrajet carb on top and a new in line fuel filter. This problem is pretty confusing because it only stutters when you are driving but if you were to sit still you can hold it to the floor all day with no problem.   

[frotosride]

I only had one thought when I read high rpm and that's spark. Check the power to the coil first and make sure everything is tight. It wouldn't be the first time that the extra movement of the engine under load made a loose connection start to fail. From there I would continue with the coil and distributor inspections, what style of distributor do you have? Still got points? I know that most were phased out in '75 but I also know that these trucks lagged behind technology because they were not marketed as family vehicles until the mid to late '80. If you still got them check the condition of the points. They will have wear of them which is normal due to small sparks from the magnetic field collapsing when the points open. I think that the normal point gap is .019" and if you plan to keep points assuming you have them you can set the dwell at the low range which will keep them in range as the points wear.

On the other hand, if you have an HEI ignition, I would check the internals of the distributor to ensure the the advance has full range and don't forget the cap for cracks because a small crack will be the same as an improper timing adjustment and will cause spark scatter. And then on to the usual rotor button and points on the cap, wires etc. I always start basic because that's where the majority of the problems are and saves a lot of money. good luck and a little more on the engine will likely prompt more responses, like type of ignition, total advance. Oh and spark plugs, how long have they been setting fires?

[marandall]

I have the hei distributor. the engine was purchased from a friend of a friend so the spark plugs have been in there for over 5 years but they still have plenty or electrode on them with the right gap as well. I have noticed that one of the spark plug wires has some of its insulation missing from it but nothing is showing. but I do have a question about total advance what's the proper way of setting the total advance. because I am feeling that I am doing it wrong   

[rich weyand]

To set total advance, unhook the vacuum advance and plug the port on the carb, then run the engine up to 3000 rpm and read the timing in the usual fashion with timing light.  I say 3000 rpm because by then all the mechanical advance will be well in; it should come in closer to 2500.  Total timing should be in the 36 degrees range.

But I don't think it's timing, I think it's fuel starvation.  Maximum fuel consumption will occur at high rpm under load, which is where you are having problems.  Timing would affect high rpm whether it's under load or not, but that's not what you are seeing.  If the fuel pump is marginal and can't keep up, or the filter is clogged, you will get the same results you are seeing.

You say you have a new in-line fuel filter.  Did you remove the filter in the Qjet, or did you change it?

[454Man]

X2 on the fuel starvation.

What's under the hood??? If you have to ask maybe we shouldn't race...

[marandall]

the reman qjet that I purchased should have a filter in it. I haven't taken anything off of it I just removed the old carbuerator and installed the qjet.

[rich weyand]

Fuel starvation at high rpm under load: possible causes, starting at the carb and working back:
- Clogged secondary jet(s) or passages.
- Clogged fuel filter (either in-line filter or the filter in the Qjet).
- Kinked or collapsed fuel line anywhere from the carb all the way back to the tank (hinted at by your rotted vacuum lines).
- Fuel pump cam lever wear or fuel pump internal leaking (How old is the fuel pump?).
- Clogged sock on the pipe down into the tank from the sender unit (Look here last, it's a bugger to check).
- Failure in the evaporative emissions system causing excessive vacuum in the fuel tank (Do a test drive with the cap loose.)

[rich weyand]

the reman qjet that I purchased should have a filter in it. I haven't taken anything off of it I just removed the old carbuerator and installed the qjet.

Replace (or remove) the filter in the Qjet.  You have an in-line filter, so you can remove it, at least for testing.  Simple, fast, cheap.

[marandall]

alright I will go threw the list and report what I come up with. thank you for your help rich I very much appreciate it.

[rich weyand]

De nada.  Let us know what you find out.