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]

Originally Posted by Hart_Rod

Accelerator pump needs adjusted???

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

[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.

[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.

[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.

[JRBECK64]

Dont Floor it!!! Just kidding

JRBECK64

To much Beer (These days thats one)

[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 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?

[1968CHEVYC10]

Originally Posted by Ticker

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

Where is the vacuum advance connected?

Here's a pic of where I hooked up the vacuum advance.
It's right below here the fuel line comes in.

[youhaveamonkey]

Ok, a few things here. RECHECK YOUR TIMING. Just do it. It is not hard. That is first.

Then the carb. There is a place for a fuel filter it is in the picture that you posted. It says "filter" on the front of the carb. Pull out the flare nut, then take a larger wrench (dont remember what size) and back off the part that the flare nut goes in to. If there is no filter in there, there needs to be one. That would be your first step. If your carb isnt getting enough fuel to allow the secondarys to work, you will effectively lean your mixture each time you push the accelerator down, and bog down the engine.

Check your mixture. Get a vacuum gauge. Set the mixture screw where you have max vacuum.

The carb may need to be rebuilt. There is a book about q-jets. I was not a carb guy either, however, the only way you are ever gonna learn is to do it.
There is a book about rochester q-jets. It is like 20 bucks or something at barnes and noble or borders or what ever. get it. it is worth its weight in gold. With the book and a good re-build kit, you can do it. It is not hard. Just be gentle, follow the directions and get it CLEAN CLEAN CLEAN. the toughest part for me is the end where you are trying to put the two halves of the carb together with the metering rods. It is a bit of slight of hand type of thing, but it really isnt hard. I guess what I am trying to tell you: just do it. Probably needs it anyway. MUCH MUCH MUCH better than a can of Seafoam, but I cant say I disagree with the other guys on here about it....

Good luck!

Cheers!

[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.

[1968CHEVYC10]

Originally Posted by 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.

I took the fuel line off and I didn't see any kind of filter in there, is it kinda far back in the carb? I put some seafoam in there today and ran it for a little while, didn't notice anything but I figure it'll take awhile.