Truck stumbles when floored

[1968CHEVYC10]

I took my truck for a test drive today probably about 3 mi, whenever I tried to floor it or get into the secondaries it lost all it power, It's got a 350 with a Qjet didn't seem to matter what speed of gear.

[kevmic28]

I had the same problem about a week ago. After changing the fuel pump, fuel lines, cap rotor, plugs, adjusted the metering screws, I figured out the plug wires were bad. Two of the wires would intermittantly just stop conducting electricity. Specially when it was hot outside. Like over 95. Oh and I ran some carb cleaner thru the tank.
Wires were only about 6 months old and maybe had 3-4 thousand miles on them. It was the damndest thing I would work on it in the mornings and it would run fine. Jump in it in the afternoon and it would run like crap again. It took a lot of trial and error and throwing parts at it but I figured it out and solved some minors issues along the way. I finally pulled one plug wire at a time and started the truck. Thats how I figured out two wires were back. Because the idle did not change when the two bad wires were disconnected.
Also just remembered i changed the coil and the fuel filter in the carb.

[Hart_Rod]

Accelerator pump needs adjusted???

[1968CHEVYC10]

Well I just replaced the dizzy with a skip white and got new plugs and wires, but probably don't have more than an hour running time since I put them on.

[1968CHEVYC10]

Originally Posted by Hart_Rod

Accelerator pump needs adjusted???

I don't think I know what that is...

[kevmic28]

Have you checked the fuel filter inline in the carb? Might be clogged up. Also check your timing. It may have jumped on you.

[1968CHEVYC10]

I have one of those little clear plastic ones on there now, didn't notice anything.

[kevmic28]

Originally Posted by 1968CHEVYC10

I have one of those little clear plastic ones on there now, didn't notice anything.

Yeah but do you still have the in the carb filter on the it? Qjets have a small filter inside the carb on the inlet side of the carb.

[JRBECK64]

Dont Floor it!!! Just kidding

JRBECK64

To much Beer (These days thats one)

[1968CHEVYC10]

Originally Posted by kevmic28

Yeah but do you still have the in the carb filter on the it? Qjets have a small filter inside the carb on the inlet side of the carb.

Oh ok, actually I'm not sure, I'll have to check

[70cst]

Check the Carb jets size on the carb. Mine are to big and we are going to adjust the jet size... if I have my facts correct. Does your truck run rich?

[1968CHEVYC10]

Originally Posted by 70cst

Check the Carb jets size on the carb. Mine are to big and we are going to adjust the jet size... if I have my facts correct. Does your truck run rich?

I honestly don't know how to tell but I've been told that it does run rich.

[70cst]

Originally Posted by 1968CHEVYC10

I honestly don't know how to tell but I've been told that it does run rich.

I am carb challenged but if the carb is getting to much gas it would have a tendency to to bog down on take off. Mine does and Curt is going to modify the carb. I am sure someone will chip in with more recommendations. Good luck.

[AirSpeed]

I had the same problem with mine awhile back. It turned out my secondaries weren't opening, more specificly the airvalve. I had two problems, first was the airvalve was sticking when I tried to open them manually, they were sticking to the rear edge of the carb opening, I took them out and filed off a little bit of the edge then centered them when I reinstalled them. The second proplem was the auto choke coil wasn't pushing the linkage up far enough to release the butterfly lockout, I took the coil out and bent it a little so it would push the linkage up further. What a massive difference! My truck now hauls butt and the gas milage has definately improved. I used to have to constantly manipulate the accelerator to get it to go up hill, now it flys up hill.

[kevmic28]

Pull one of your spark plugs on each side and take a look at it. If it black with carbon then you are rich I believe.

[1968CHEVYC10]

Originally Posted by AirSpeed

I had the same problem with mine awhile back. It turned out my secondaries weren't opening, more specificly the airvalve. I had two problems, first was the airvalve was sticking when I tried to open them manually, they were sticking to the rear edge of the carb opening, I took them out and filed off a little bit of the edge then centered them when I reinstalled them. The second proplem was the auto choke coil wasn't pushing the linkage up far enough to release the butterfly lockout, I took the coil out and bent it a little so it would push the linkage up further. What a massive difference! My truck now hauls butt and the gas milage has definately improved. I used to have to constantly manipulate the accelerator to get it to go up hill, now it flys up hill.

That might be it, with the air filter off I've messed with them before and it seems like they get kinda stuck.

[1968CHEVYC10]

Originally Posted by kevmic28

Pull one of your spark plugs on each side and take a look at it. If it black with carbon then you are rich I believe.

Ok then yeah I'm def running rich, how do I tune/adjust that?

[Bus Ted Knuckle]

set the clock spring on the secondary butterfly to 7/8ths of a turn past 1st contact. Your secondaries are opening too fast.

[1968CHEVYC10]

Originally Posted by Bus Ted Knuckle

set the clock spring on the secondary butterfly to 7/8ths of a turn past 1st contact. Your secondaries are opening too fast.

Hey thanks for all the help yall!

Sorry I'm pretty dumb when it comes to carbs, If you don't mind could you explain that a little more in depth? Thanks!

[kevmic28]

Ok before you start messing with the carb give us some back story. You said you went for a test drive? How long did the truck sit? It could be clogged jets. Sticking float. Does it fire right up and idle fine or does it take some cranking to get it up and then idles rough? It may be because of the heat and humidity you are experiencing right now that you need to adjust the metering screws.
Did it run just fine till the 3 mile mark when you took it for a test drive? Double check your plug wires to make sure they didnt melt on the exhaust on the 3 mile drive.

[1968CHEVYC10]

Alrighty, the truck hasn't been on the road in twenty years, but its was used on a dear lease and got drove a few times a year, got the truck a year ago, didn't really start messin with the motor till about 2 months ago, and I just recently got the brakes workin good so I could actually drive it. I had taken it out on a few little mile- 2mile drives and it always kinda did the same thing whenever I got on it. At first I thought it was the clutch slipping, but on the last drive it def seemed like it was the motor. I felt the plug wires a few times after driving it and they seemed pretty hot but not melted at all. Oh and it starts right up and idles fine.

When I put the new dizzy in I set the timing by just turning the cap till it idled smooth, I didn't do any of the vacuum advance stuff, could that be an issue? I don't really know how all that works but I've read alot about setting and adjusting the timing throughout the rpm range as I understand it. Thanks for the help yall!

[Shyguy]

One thing I do when I get a car or truck that has not been driven for a while is I put a can of SeaFoam in the tank and fill it with fresh gasoline.

I had a '71 350 with a Q-jet and it had the same symptoms until I ran a tank of fresh gasoline with SeaFoam. It seemed the longer I drove it the better it ran.

Most people set the timing between 10-12 degrees at idle with the vac advance unhooked.

[kevmic28]

Definately put some seafoam in it or replace the carb.

[Ticker]

$20 says the timing is wrong - either the initial or the overall timing curve.

Where is the vacuum advance connected?

[kevmic28]

Id say change the fuel filter in the carb and run some seafoam through it. If it only gets run a few times a year that carb has got to be clogged up something good.