Fuel System: Small Backfiring in my 289 V8 1955 Truck

[go-studebaker]

Hi All,
I was working on my 1955 Truck today as the timing needed looking at. It was well advanced and would occasionally back fire, so I have pulled it back to where it feels right.

When I finished with the truck last year I don't remember it ever back firing as it does now on acceleration. It only has a little cough as I take off or maybe get it into 3rd and accelerate gently before getting it into OD

The truck has a 289 in it with stick and OD. Edelbrock 4 barrel carb and a window type later dissy.

I have never tuned the truck and the fuel in the tank may be over a year old but topped up. We have pretty good fuel here in the UK.

Have any of you got any ideas of what the problem may be ? It does seem to accelerate fine, but the occasional light cough is annoying.

Thanks
Greg

[bensherb]

Sounds like it may be a bit lean to me. What does it do when you're going downhill at speed and take your foot off the throttle?

[PackardV8]

You may have diagnosed your own problem.
1. Drain the fuel tank for use in small engines. Refill with fresh fuel. Old fuel causes many similar problems.
2. Do your tune-up. You know you need to. These days, when someone asks my help diagnosing a problem, I won't touch it until there are new spark plugs, points, condensor, cap, rotor and plug wires. Can't tell you how many times a CASO has told me, "I just did all that a while back." and it turns out to have been more than ten 'whiles-back."
3. Set the distributor on "IGN" with a timing light.

jack vines

[Ron Dame]

Except, posibly for a new condenser, it seems the new ones have poor quality control, or so I hear

You may have diagnosed your own problem.
1. Drain the fuel tank for use in small engines. Refill with fresh fuel. Old fuel causes many similar problems.
2. Do your tune-up. You know you need to. These days, when someone asks my help diagnosing a problem, I won't touch it until there are new spark plugs, points, condensor, cap, rotor and plug wires. Can't tell you how many times a CASO has told me, "I just did all that a while back." and it turns out to have been more than ten 'whiles-back."
3. Set the distributor on "IGN" with a timing light.

jack vines

[Mrs K Corbin]

What fuel are you using? I only use NON-Ethanol fuel, as it has a much better TANK-life.

[jclary]

Well...while we are taking a "shotgun" approach of just blasting out suggestions for your problem, let me suggest this...after it gets dark, start your engine, raise your hood, and look for sparks and arcs along your spark plug wires from the distributor cap to the spark plugs. Even wires not very old can still break down and short to ground. Especially look for sparks where the wires go through the small metal brackets at the valve covers and the caps where they connect to your spark plugs. It only takes one cross firing wire to create an errant inconsistent backfire as you describe.

While looking, make sure to vary the engine speed. Sometimes, the electrical path will change with rpm and the variable current resistance that creates. By the way...for some reason...I have a great fondness of the '55 C-cab trucks.

[go-studebaker]

Thanks for your advice guys.
I am going to take it back a step further and check the valve clearance before I start the tuning aspect.
I am sure I have all the parts I need on the shelf over here.
Regards
Greg

[PackardV8]

Recently we had a thread mentioning backfiring. That one was due to a flat cam lobe not opening an exhaust valve, thus having a full charge in the cylinder when the intake valve opened. It's relatively easy to confirm valve lift with a dial indicator.

jack vines

[TWChamp]

I agree with Jack. In the 70's I worked at the GM dealership, and GM had soft cam problems on some V8 engines.
Whenever I drove a car into my stall and it backfired through the carb, I knew it needed a new cam and lifters.

[altair]

I agree with Jack. In the 70's I worked at the GM dealership, and GM had soft cam problems on some V8 engines.
Whenever I drove a car into my stall and it backfired through the carb, I knew it needed a new cam and lifters.

I owned a carbureted GM 305 that had a rough idle, the car was near new (second owner) I checked the intake manifold bolts and they were not torqued, they all went 1/8 - 1/4 turn. The bolts directly under the carburetor could not be tightened without removing the carburetor. I did not retighten the bolts directly under the carburetor and continued to drive the car. With the manifold heat crossover raw exhaust was leaking back in to the crankcase and contaminating the oil and the cam. Carbon grit eventually wore the cam shaft lobes nearly round, you could not tell the lobes from the bearings, I would not consider the cam shaft as soft, it took considerable abuse before it failed, the main problem being the loose bolts, With all the valves almost not opening there was no backfiring just very noisy lifters. I feel the backfiring in the above post is a minor vacuum leak.

[go-studebaker]

Guys,
last week I adjusted the valves. They were pretty much OK. But in the process, there were three spark plugs that seemed a little loose.
A new set of plugs were installed. When I check started the truck it sounded a lot better.

The weather was a bit naff at the back end of last week so I only had it out today for a quick run and it works fine without a cough.

I think it might just have been the loose feeling plugs or a combination of everything.

Thanks for your tips everyone.
Greg

[Skip Lackie]

The weather was a bit naff at the back end of last week so I only had it out today for a quick run and it works fine without a cough.




Greg

Naff? Please define. Origin Oz or UK?

[go-studebaker]

Skip,
Naff is UK English for 'a bit rubbish'

Regards
Greg