1965 L79 Just started back firing

[Mr. Cricket]

Only owned it a couple of months so only managed a couple of short trips but it ran flawlessly. Then just like flicking a switch it's now difficult to start, to keep running and huge back fires going on so much so I'd be reluctant to drive it to my local garage.

New house and garage and no heat yet in the garage and one day last week the place was ringing wet through with condensation which I've now got a handle on with a small dehumidifier.

Checked all plugs leads are on.
Checked the distributer and no signs of any dampness.
Installed new battery.
Checked the fuel to make sure I hadn't put diesel in and I haven't and can't see any signs of water in the tank.

And thinking back when I discovered the condensation issue I ran this and another Corvette for maybe 40 minutes to get rid of any dampness I couldn't wipe down myself and they ran fine.

Any other ailments that would show as a back fire? Suppose I should check / change the fuel filter?

Stuart

 

[Oneball]

Stuck choke or stuck carb float.

Fuel contamination, dodgy HT leads/plugs etc would cause a misfire not pops and bangs.

 

[Mr. Cricket]

Stuck choke or stuck carb float.

Fuel contamination, dodgy HT leads/plugs etc would cause a misfire not pops and bangs.

What size of hammer would one recommend

Thanks will look into both

 

[Oneball]

What size of hammer would one recommend

Thanks will look into both

The answer is always “the biggest one”.

 

[Roscobbc]

If the distributor has mechanical points I'd be inclined to firstly open them up with a small screwdriver, insert the edge of a piece of clean cloth, release screwdriver and pull cloth to and frow across points to absorb any moisture present. Repeat using a folded piece of fine grade abrasive paper. Repeat finally with clean cloth again.
If the issue persists check out HT leads are not crossed and touching each other - check-out the spark plugs are nice and clean - any high resistance as plug there could create an induced spark on another cylinder if plug leads cross each other.......possibly. Perhaps check-out resistance of each plug lead. Backfiring through exhaust or carb? Unlikely perhaps but have you a sticking exhaust or intake valve. Has the timing 'slipped' ? When the engine is running do all cylinders appear to be firing? - if not are you able to remove one plug lead at a time to identify a non firing (or cause of backfiring) cylinder?

 

[Mr. Cricket]

If the distributor has mechanical points Electronic I'd be inclined to firstly open them up with a small screwdriver, insert the edge of a piece of clean cloth, release screwdriver and pull cloth to and frow across points to absorb any moisture present. Repeat using a folded piece of fine grade abrasive paper. Repeat finally with clean cloth again.
If the issue persists check out HT leads are not crossed and touching each other - check-out the spark plugs are nice and clean - any high resistance as plug there could create an induced spark on another cylinder if plug leads cross each other.......possibly non crossed and it was running sweet. Perhaps check-out resistance of each plug lead. Backfiring through exhaust or carb? Exhaust Unlikely perhaps but have you a sticking exhaust or intake valve. Has the timing 'slipped' ? When the engine is running do all cylinders appear to be firing? - if not are you able to remove one plug lead at a time to identify a non firing (or cause of backfiring) cylinder? It was running on all 8 but with the rough running and noise now difficult to say. I'll check the choke and carb first as that is easier then move on to leads if no improvement.

Thanks,

Stuart

 

[Roscobbc]

Thanks,

Stuart

It might be a bit of a faff - but as you'll know low voltage (12v) and high voltage (hi-tension) electricity can do some really odd things during atmospheric conditions............I could write a whole manual of Vette issue I have experienced.......just simple earthing things like engine and other component 'tails' to the chassis can throw up some really bizarre things........

 

[Mr. Cricket]

I was tempted to go play whack-a-mole but the car is on stands at the moment for new rubber tomorrow so it'll have to wait

 

[Mr. Cricket]

It might be a bit of a faff - but as you'll know low voltage (12v) and high voltage (hi-tension) electricity can do some really odd things during atmospheric conditions............I could write a whole manual of Vette issue I have experienced.......just simple earthing things like engine and other component 'tails' to the chassis can throw up some really bizarre things........

I've had and got a few Ross but I've never seen something turn so quickly. An issue in the carb as Oneball (always makes me cringe typing that!) says would explain the dramatic turn from Princess into a 'Megan'

 

[Roscobbc]

I've had and got a few Ross but I've never seen something turn so quickly. An issue in the carb as Oneball (always makes me cringe typing that!) says would explain the dramatic turn from Princess into a 'Megan'

Does it backfire when you press the accelerater pedal - once up to a specific rpm (and when warmed-up) does the backfiring stop? - have you observed the action of the accelerator pump nozzles? - are the primaries 'squirting' a nice equal and even flow?

 

[Chuffer]

The answer is always “the biggest one”.

Plus a can of WD40 , if big `ammer and WD40 won`t fix it , it`s completely buggered !!!

 

[Mr. Cricket]

Does it backfire when you press the accelerater pedal - once up to a specific rpm (and when warmed-up) does the backfiring stop? - have you observed the action of the accelerator pump nozzles? - are the primaries 'squirting' a nice equal and even flow?

Backfire starts after a couple of minutes running and at higher revs. Not had chance to observe carb / fuel action yet. It was turn the key and off she went at high idle now I have to feather the gas to keep it going but as like yesterday I shut it down when the backfire reared its ugly head.

 

[Forrest Gump]

Backfire starts after a couple of minutes running and at higher revs. Not had chance to observe carb / fuel action yet. It was turn the key and off she went at high idle now I have to feather the gas to keep it going but as like yesterday I shut it down when the backfire reared its ugly head.

I’d suspect the coil in that case. Spark is failing and then getting unburnt fuel going into the exhaust.

 

[Roscobbc]

What is the carb? - Holley, Rochester? - carb gaskets can start to brake-up when subject to fuels with ethanol - tiny particals get in to float valves and possibly jets and create issues. Accelerator pump discharge check valves can block up and/or gaskets/'O' rings break-up either perhaps flooding things or blocking-up.

 

[teamzr1]

Have you tested the gas ?

Use a clear glass that has measurements on it

First put gas in it, shake it and let sit for a few minutes
Since water is heaver than the gas it will fall to the bottom, and you would see the point the water level is to the gas contents

If thinking maybe too much Ethanol, do the same and then measure as below

 

[Mr. Cricket]

What is the carb? - Holley, Rochester? - carb gaskets can start to brake-up when subject to fuels with ethanol - tiny particals get in to float valves and possibly jets and create issues. Accelerator pump discharge check valves can block up and/or gaskets/'O' rings break-up either perhaps flooding things or blocking-up.

Holley 4 b. I have an Esso 'round the corner so use their supreme but who knows what came before the two months I've owned it?

 

[Mr. Cricket]

Have you tested the gas ?

Use a clear glass that has measurements on it

First put gas in it, shake it and let sit for a few minutes
Since water is heaver than the gas it will fall to the bottom, and you would see the point the water level is to the gas contents

If thinking maybe too much Ethanol, do the same and then measure as below

View attachment 20757

I drew some out yesterday and it's completely clear with a slight pink tinge. Esso Supreme is 1% ethanol at most but previous owner may have used who knows what?

 

[antijam]

I guessing nowadays it's got some ethanol in the tank? Has the car been sitting for a while and is the fuel tank full? A full fuel load helps prevent moisture condensing in the tank - and ethanol loves moisture. Water then sits at the bottom of the tank and gets drawn into the carb giving rise to all sorts of problems including poor running and backfiring.
Edit; Sorry posted this before reading previous reply.

 

[Mr. Cricket]

I guessing nowadays it's got some ethanol in the tank? Has the car been sitting for a while and is the fuel tank full? A full fuel load helps prevent moisture condensing in the tank - and ethanol loves moisture. Water then sits at the bottom of the tank and gets drawn into the carb giving rise to all sorts of problems including poor running and backfiring.

A couple of weeks only and I use Shell super or Esso Supreme.

 

[Mr. Cricket]

I’d suspect the coil in that case. Spark is failing and then getting unburnt fuel going into the exhaust.

Has a flame thrower. Any good and can they be tested? I have multi meters