The Stovebolt Site Forums The Shop Area Engine Shop 63 305 V6 Bucking

Hi, I have a 63 3/4 4x4 with the 305E that started bucking. I tuned up everything including new points, condenser, cap etc. Had the original Stromberg carb rebuilt and still having issues. I love that it's all original so don't want to do the holly carb thing.

Any feedback appreciated.

Thanks,
Rob

If you didn't check your fuel tank for rust (ethanol and old tanks = rust) and did not replace your fuel filter, the rebuilt carburetor could now have contaminants inside.

Check your fuel pump pressure or replace.

Check for vacuum leaks (carburetor to intake, vacuum lines/hoses, distributor timing advance diaphragm).

Replace coil.

thank you for the quick reply. Yes, did coil, plugs wires, cap, everything and fuel filter when the carb rebuilt. Fuel pump is about two years old but I probably haven't driven 300 miles. I'm no expert but when a pump goers it goes. I also left out that when I start it after she sits, runs perfect and then seems to happen 20 minutes into driving her.

Possible item in fuel tank?

Ed

Crud in the fuel tank moving around occasionally covering the pickup.

It's not a procedure I would recommend without extra precaution to be safe....but....you could rig up a test fuel container and connect to the fuel pump.

The Stromberg WW has a good reputation.

Do you have a vented gas cap?

Stuck heat riser?

Try rigging up a temporary fuel tank, like one for an outboard motor, and be sure it's well vented. Then take a test drive. I'm going to guess you're getting a vacuum in the tank after a few minutes of driving that's causing the engine to surge. You might have the wrong type of gas cap, or a clogged vent tube.
Jerry

I will never ceased to be amazed at experienced Stovebolt folks firing off a bunch of ideas from just the word "bucking".

Ditto. thank you all. Have some homework to do.

bartamos, some of us have tried to ride a full 8 seconds!

It's a guessing game. It's all we can do given the limited info we have. I'm curious to find out who gets it right. Join in! Everyone is welcome to play. Don't expect a prize, though.

Oh, come on, now! Isn't everybody supposed to get a "participation trophy" these days? Getting rewarded for actually accomplishing something is so "1950's"!
Jerry

could it be the clutch binding when it heats up?

my bad clutch will make my truck "buck" when accelerating at low rpms.

OK, I'll join in. Could it be that the town has added speed bumps and you didn't notice?

A mechanic, a plumber, an electrician, doctors, scientist, engineers try not to guess. At least until after many questions, definitions of words and tests. Jerry knows this. So far, some folks have asked for tests. Very few questions. Many guesses.

I, too, am guilty of breaking my own advice.

I truly hope this is not another "fad away" new guy. Hope he stays engaged and checks the post. Some just don't realize that Stovebolt has a massive amount of knowledge that is put forth within minutes. He has 8 same-day responses. Several second day.

1. Does bucking mean the truck is lurching or hesitating or bogging down during driving? Is it rapid or large intervals?
2. Does it mean the motor itself is jumping all around while truck is not moving?
3. Does it do it only while going thru gears using clutch and then settles?
4. If you get up to 30 mph and push clutch in, does it coast with no bucking?.....while motor is revved a little?
5. Do motor mounts look OK? That motor is pushing 900 lbs on two rubber blocks.
6. Was it running good and all of a sudden did this? Was some work done just before this? I realize you did work after.
7. Can you describe bucking....what, when, where, how long. Trying to determine if "bucking" is the motor missing.... or the truck (motor mounts, clutch, tires, brakes, ujoints, wheel bearings and all that stuff). That would really narrow down "bucking".
8. Could you find a place to safely coast with motor off, clutch in?
9. Any modifications like mustang front clip, air bags, lowered, lifted, big tires, wheels, messing with distributor.
10. Those motors run better at more advance than spec now-a-days. Like 8-10 BTDC sometimes. Spec is 5.
11. If you have removed spark plug wires, recheck that you have them clocked for Firing Order 1-6-5-4-3-2 NOT 1-5-3-6-2-4
12. "When a pump goes, it goes". You can't use that theory to eliminate the pump.

Another issue OldGMC1963 is we don't know your mechanical/electrical automotive experience, equipment or ability to test. Sounds like you are no rookie from all the tune up effort you've done. Let us know your approximate experience level. Sounds like a neat truck. I had a 1960 GMC with 305E recently. Yours is first year for coil front suspension and last year for wrap-a-round windshield.

Bartamos is doing this the right way.....asking clarifying questions.

As for myself, I’m just gonna throw some more poo at the wall and see what sticks.

I like the motor mount theory, but the fact that it starts acting up after 20 mins doesn’t jive with that.

A couple other ideas I haven’t seen mentioned:

* I know nothing about the WW carb or what kind of choke it has. Maybe some kind of choke weirdness?

* Some sort of vapor lock thing?

* Perhaps a vacuum leak at the manifold or carb base that develops only once the engine gets to temp and things move around a bit?

I agree that acting up after 20 minutes is a clue. Not too much of a clue. Can mean what others have said, venting, vapor lock, floating tank debris, loss of pump pressure/suction. The WWs I've had all have cable operated chokes. Maybe he will answer the questions in order for us. 50 guesses does not give someone a direction. No info does not give us a chance to use our experience.

The problem with the pump tests, is that 20 minutes. The truck is going to start with any of the pump tests. I have, and others have, run a truck with a hose stuck in a gas container on the passengers floorboard, hose thru the firewall. This way you can drive for 20 minutes to see if pump begins to fail or carb somehow fails. Idling for 20 minutes is not fool proof. Need a load. This is what Jerry already said. That would be a good easy test and give lots of info. It sounds dangerous but what the h e l l.

Anyway, this is all guessing, if it was debris, it would be at the bottom of tank near the pick up, after sitting. A person could say that is when it should "buck"/starve for gas. Not after sloshing....

this can easily be a trans or diff issue as well, though fuel supply is a great place to start. I second the can on the floor method for initial test.

A shot in da dark..... Ignition coil is heating up and failing?

How long do you let it sit?

Second post by OP says new coil. (although if made in China ??)

Opps, speed reading and spun right by it. Well i tried and now i get a prize. Right???