Nice truck! Here's my $.02 worth - based on the symptoms you mentioned (shakes at idle, doesn't want to accelerate with light throttle, but moves good with lotsa throttle), I would check out the power valve in that carb. Sounds to me like it might be leaking.

Try this - run it for a few minutes to get it warmed up. Then shut it off and let it sit for five minutes or so. Remove the air cleaner and look down into the carb with a flash light. Slowly open the primary throttle blades so you can see the floor of the intake manifold. If the floor of the manifold is wet with fuel, you have a leaking power valve (or the float level is way too high).

 

When we drove it home today. It would hit around 30, and start pinging or knocking. I do not know if it would go faster my husband wanted to take an easy on it.
When in full throttle (sitting still in the garage) done manually under the hood it seemed to even out. To me anyway. But then as soon as we stopped it shakes. The engine shakes, the dual exhaust pipes shake as well. Basically the whole truck I think.
The neighbor guy said it had some blow by.Which was white smoke from behind the carb. (I am not sure if that is a real term used or not)
The spark plugs were replaced. The dist cap, and rotor were replaced. The plugs were checked for spark. He tested them by putting a spark plug in the wire and looking for the spark.
All was ok there.
My dad thought he just bought bad gas and put a fuel treatment in the tank. He then replaced the fuel filter.
today the neighbor also sprayed water down the carburator (with a spray bottle)and pushed full throttle to see if he could loosen a possibly stuck valve. But no luck there. The dist. is stuck so we cannot time it.
The truck had been running great. Just one day after my dad bought gas out of town..on the way home it started acting like that. It has sat for months. The exhaust is also burning clean
Melissa

 

Have you put any great gas in it yet ?

 

The firing order being checked to see if it is correct seems to keep being overlooked. Don't do anything else until this simple thing is confirmed to be in order. If you find the firing order to be correct for this engine then start looking elsewhere for the problem.

You haven't said whether the vacuum hoses have been checked for leaks or just plain disconnected. Is the carburetor loose? are all of the intake bolts tight. Are you positive there isn't a bad (leaking) cylinder head gasket, intake manifold gaskets or carburetor gaskets?

If there is excessive blowby present then run a compression check on each cylinder. If this test shows all cylinders in good shape then you are experiencing a carburetor or fuel problem maybe. You have never stated whether the carburetor is original, rebuilt or if the choke is working properly. If the gas is suspect then just pull the carburetor and save yourself a lot of grief and just disassemble and rebuild it. One of the ports could be clogged in the idle circuit and any engine will run rough at idle but will run fine at higher rpms because at higher rpms the engine is no longer using the idle circuit at that point. I don't recommend looking down the throat of a carburetor while an engine is running since it could be dangerous if an engine backfires into your face. You can however perform an idle circuit check by turning in the idle mixture screw on one side then the other while the engine is idling. If you turn one idle mixture screw all the way in (clockwise) while the engine is running and if the engine doesn't change then reset that screw back to it's original setting. Now perform the same test on the other idle mixture screw. If no change then you have a carburetor problem for sure, but this is not the entire problem. If you performed this test and one idle mixture screw being turned all the way in clockwise caused the engine to change how it is idling, but the other on didn't then there is a partially blocked idle circuit. Both idle mixture screws should cause the same reaction in the way the engine is running while idling. If one idle mixture screw caused a difference at idle but the other did not then rebuild the carburetor and be absolutely sure that the ports and circuits are cleaned and free of blockage.

If this engine has a more hard to detect valve train problem or a blown cylinder head gasket then it may take an experienced mechanic to find it. Pull the valve covers off just to be sure the cam and the rocker arms are doing their jobs and opening the valves while the engine is being cranked with the ignition disabled. You can perform this test while checking the compression (remove all sparkplugs and open the carburetor all the way to perform a compression test). Check each rocker arm for movement. Make sure nothing is out of place (obviously missing, bent or broken). Look for any obviously smaller amount of rocker arm movement on any of the rocker arms while the engine is being cranked as described above in this paragraph.

I will be surprised if the problem isn't weak compression on at least one cylinder if the problem isn't found to be the firing order, valve timing or the carburetor. Maybe you will get lucky and your engine was tuned by someone who just made a simple mistake.

 

Yes we checked the firing order yesterday as well. We used the Haynes book to check that the wires were on in the right order.
Since the truck was redone years ago, I have no idea what was redone. On the carb..I think it is original by the look of it. I also belive my dad said the choke was working correctly.
I do not think the vaccume hoses have been checked.
Thanks,
Melissa

 

Melissa, this sounds to me like a timing issue. Maybe one of the timing advance springs in the distributor has broken. A broken spring would allow full timing advance to come in at idle, and it would run very poorly at lower rpms. This could be easily checked with a timing light.

Don

 

I concur with Don. The first order of business here is to get that distributor unstuck.

 

this may sound stupid..
But what is a timing light??
~Melissa

 

Also would it have that blowby if it was a timing issue?
I have some guy that is suppose to call me tomorrow. To supposedly come look at it. My husband is at work, and I am wanting to get this fixed badly. My hubby does not know much about cars.
The neighbor guy tried to unstick that dist. but he said the air conditioning is in the way. And he could not get to it.
I feel like going out there and doing it myself...HAHA
I don't know the first thing about cars or trucks.
~Melissa

 

This truck also has 3 gas tanks. So if the fuel was a issue wouldn't the problem go away when the tanks are switched?
~Mel

 

I am thinking more of a carb problem. I had a stock 2 barrell on my 390, i got a edelbrok carb and intake, runs like a champ now. I would check it wil a timing light, never jurts to check something. Take the dist. apart and take off the rotor, there should be a spring down in there, and a thing that turns and advances the timing. I would also check vaccumm leaks. Might even be the power brake booster. There are not many vaccumm lines on the old trucks, the only ones i can think of would be your brake booster, vaccumm advance, cruise if you have it, pcv valve, might have one going to the transmission, if an automatic.

 

Right, if it's because of bad gas it would go away if you switch to a tank with good gas. But all 3 tanks might have been filled with the same bad gas...

Marty

 

Does anyone know how to get that distributer unstuck??
My dad said it is not the screw that is stuck, but the distributer itself. It will not turn at all. A guy we know who use to be a mechanic told my dad if the distributer was stuck it unlikely was out of time. But common sense tells me, what if it was out of time and then stuck.
The mechanic guy I called yesterday said he would call me today. but the jirk did not call or anything.
I wish he would have just said he was not interested so I could have found someone else. Hey does anyone here live in Oregon??
HAHA.
I have a feeling it is something stupid wrong with it, easy to fix.
I just wish I knew what it was.
~Melissa

 

Melissa, if it started running bad all at once, I don' t think it's out of time unless a distributor spring is broken. A stuck distributor is common on these old trucks, and there's many posts on how to unstick them.

Here's an easy way to check the distributor advance springs: Unclip the two hold-down clips on the distributor cap. Remove the cap. The first thing you'll see underneath the cap is the rotor. Turn the rotor CW, and see if it springs back into place. If it does, the springs are OK. If it dosen't and feels loose when you move it back and forth, then chances are the spring(s) are broken or have slipped off.

 

originally posted by
RHunt64


If this engine has a more hard to detect valve train problem or a blown cylinder head gasket then it may take an experienced mechanic to find it. Pull the valve covers off just to be sure the cam and the rocker arms are doing their jobs and opening the valves while the engine is being cranked with the ignition disabled. You can perform this test while checking the compression (remove all sparkplugs and open the carburetor all the way to perform a compression test). Check each rocker arm for movement. Make sure nothing is out of place (obviously missing, bent or broken). Look for any obviously smaller amount of rocker arm movement on any of the rocker arms while the engine is being cranked as described above in this paragraph


Hello,
Well my brother in-laws mechanic friend has finally looked at the truck.
He came over to our house, and in about 5 minutes he told me it was missing on 1 or 2 cylinders, and that it might be a burnt valve. So I made a appointment with him for the next day.
Yesterday he did a compression test at his house. He called me last night with the results, and it actually has 3 dead cylinders.
So now today he is taking apart the engine to see why.
I am so hoping that it is only burnt valves, or bad head gaskets.
He says it is odd that 3 are out. He is hoping it is not rings, and needs a new engine.
I hope it does not need a new engine, the other one only has around 50,000 miles on it. not to mention the expense.
Keep your fingers crossed!!
Thanks
Melissa