427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

[Skip N.]

Bent Rod 1.jpg

There have been some Tech comments about leaky Holley Carbs & 60s FI units - WELL...I suffered the ultimate failure

Car was sitting for 2 weeks, I started the car and IMMEDIATLY I had ignition ; THEN motor LOCKED up! (diagnosis #2 chamber must have had enough gas sitting to Fuel Lock & the shortened bent rod/piston seized up against the Crank counter weight)

- it was obvious that my 40 yo rebuild needed to be done again
- got lucky as block and crank OK
- New pistons, Rods and balance done (+ other rebuild parts)

Carbs were Holley aftermarket maybe 10 yo
- there have been Tech discussions nytrophil floats sticking causing bowl to leak down

I know from conversations with Fuel & Additive experts that current Premium Fuels do not do well in carbureted engines

My corrective action is to USE a Kill Switch during initial cranking
- hoping any fuel lock stop rotation ; THEN I can pull the plugs
- if engine cranks over THEN turn on the ignition for the start

Any other members suffer similar Fuel Lock???? Skip

[Keith B.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

One trick my dad always taught me that I sometimes fail to do is. If a car has been sitting for a week or so and before you crank it is to check and sniff the dip stick.

[Patrick B.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

Had exactly the same experience with my first Corvette, a 67 L-71, in 1971 shortly after I bought it. The connecting rod did not bend quite as much as yours. But, it bent enough that the bottom of the piston would contact the crank shaft counterweight on each revolution. The engine ran but made a sound I will never forget. It had nothing to do with gasoline compatibility issues. The car was parked facing down a hill, and the needle and seat of one of the carbs simply leaked.

Sniffing the dipstick and noting the oil level is good advice. I did this after the fact and found at least a gallon of gas in the oil pan.

[Skip N.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

Good idea, but in this case I sent the oil from the failed engine to Black Stone Labs ; to see IF there was much Fuel in the oil
- I have the report that says fuel content was LOW (had Joe Gibbs oil with Zinc in the motor for about 1000 miles of driving)

It is unusual for this to happen on a Carb ; BUT I used to hear stories about early FI cars bending 2 or 3 RODS before '62 added the Fuel Leak Down valve.

[Mark M.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

I restored a 67 L68 which ran strong before tear down. When we had the engine apart, it was discovered one of the rods was bent. It was hard to see with the eye but measured wrong. Never knew what caused it but the carbs had recent work on them by previous owner. Yours bent so far I'm glad to hear your block wasn't harmed.

[Gary C.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

If you look at Corvette Restorer Vol 30 #3 (Winter 2004), it has article "Tech Tips from National Discussion Board", talking about when C2 or C3 parked on a hill with full tank of gas and nose pointing down that the fuel level from tank to carbs overload the floats in the front/rear carburetor on tri-power cars allowing gas to get into intake and cylinders. This article saved my bacon on my 69 L89 where our Chapter went to a car show event (Concours in the Hills) and when we were leaving, I spotted that my car was parked exactly with the nose pointing down, and this article rang in my head, dang, you idiot!!! Pulled front spark plug from each side to check and see and fuel poured out both sides. Pulled rest of spark plugs, pulled TI connector, and spun engine to clear cylinders. Checked oil, was ok, level was not higher. Luckily I did not try to start the engine with this condition, it probably wouldn't anyways since it struggled to start after clearing the cylinders, way way too rich of mixture. Changed oil when I got home, just in case. Since then, I watch how I park this car to make sure nose is not down. Recommend all tri-power cars do the same.

Sorry to hear that you bent a rod but good that block was not harmed.

[Larry M.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

If you look at Corvette Restorer Vol 30 #3 (Winter 2004), it has article "Tech Tips from National Discussion Board", talking about when C2 or C3 parked on a hill with full tank of gas and nose pointing down that the fuel level from tank to carbs overload the floats in the front/rear carburetor on tri-power cars allowing gas to get into intake and cylinders. This article saved my bacon on my 69 L89 where our Chapter went to a car show event (Concours in the Hills) and when we were leaving, I spotted that my car was parked exactly with the nose pointing down, and this article rang in my head, dang, you idiot!!! Pulled front spark plug from each side to check and see and fuel poured out both sides. Pulled rest of spark plugs, pulled TI connector, and spun engine to clear cylinders. Checked oil, was ok, level was not higher. Luckily I did not try to start the engine with this condition, it probably wouldn't anyways since it struggled to start after clearing the cylinders, way way too rich of mixture. Changed oil when I got home, just in case. Since then, I watch how I park this car to make sure nose is not down. Recommend all tri-power cars do the same.

Sorry to hear that you bent a rod but good that block was not harmed.

Sage advice.............thank you for posting.

Larry

PS: I have always been reluctant to fill my gas tank to the top with an infrequently driven/ stored car. I try to keep it about 1/2 to 2/3 max. Never any problems so far in 27 years.

[Donald S.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

Welcome to the "club"! I had the same issue with my 69 L-71 after winter storage. Hit the key and it locked up.
It's currently wall art....learned my lesson and installed a valve by the gas tank and shut the fuel off any time the car sits for any extended period of time.
Don
rod.jpg

[Skip N.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

Thanks all,

I like the idea of a Fuel Shut Off
- maybe this can be done by extending the rubber line between the Fuel Pump and Fuel line from the tank?

- that way the shut down and start up procedure can all be done under the hood 100% of the time

Like an Airplane START Procedure
1) turn on Fuel (off after every shut down)
2) Turn on Kill Switch; allowing no spark
3) Crank the motor (it wont crank if any cylinder has 60CC+ of Fuel - requiring pulling plugs to purge fuel)
4) Turn OFF Kill Switch & Crank to start

CONTACT!!

I refuse to Bend another ROD after all this rebuild work!

[Richard L.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

On a tripower car maybe fuel can flow from carbs (only center one?) into the cylinders under certain conditions (parking downhill) and cause lock-ups as attested by the pics above, but is this catastrophe really possible when the car is parked on a flat surface such as garage? One of the great advantages of the mechanical fuel pump of course is that it does not push fuel into the carbs when the engine is shut off. It would have to be an internal leak in one of the carburetors--if not all three--which would explain the steep forward angle parking situation affecting all three carbs equally. Which makes me ask: a) how much fuel is in those carbs at shut down, b) how much fuel would it take to cause a catastrophic lock up (bent connecting rod[s]), c) wouldn't fuel evaporate (time, engine heat, etc) so as to lessen the possibility of mayhem?, and d) do we really need to install an in-line fuel shut off valve to be rid of this worry?
Not just curious since I have a 67 tripower that I do like very much though it doesn't get driven frequently (see my post above regarding a leaky center carb--externally thankfully!).
Ric

[Skip N.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

My Tri-Power was parked in a flat garage floor for maybe 2 weeks with 1/2 tank full ; when it Fuel Locked at start up
- any of the 3 carbs that have the seat partially open can drain down to open valves
- IF added pressure from car parked downhill will be worse

Typical combustion chamber is 50 to 70CC (depending on head/chamber size & piston dome size)
- fuel will last a long time sitting in a combustion chamber with a partially open intake valve

SO...any fuel over that amount will cause a bent rod - IF the 1-2 cylinders fire before the fuel loaded cylinder (think I only have ONE loaded cylinder)
- motor has more than enough inertia to bend the rod (per pics)
- I DOUBT the starter by itself has enough Torque to bend a rod while cranking (ignition off); any EXPERT Opinion on IF Starter could bend a rod ; or would just stop cranking over????????????

[Donald S.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

My understanding is that the gas tank is higher than the carburetors and gravity can create enough pressure to get past the fuel pump. Any leak within the carbs will allow gas to find it's way into the cylinders and cause hydrolock upon start.
Don

[Richard L.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

Not being a wise guy but, if it's possible for whatever reason for fuel to leak from carbs internally into cylinders and cause bent rods by locking up, can this condition be prevented by simply parking with the front wheels on a couple of 2x6's and thus elevating the front end and keeping the gas tank below the carburetor level? How much of an incline would be needed for this easy solution to work? Any others that would not necessitate a shut off valve from tank to pump to carbs?
Ric

[Larry M.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

My understanding is that the gas tank is higher than the carburetors and gravity can create enough pressure to get past the fuel pump. Any leak within the carbs will allow gas to find it's way into the cylinders and cause hydrolock upon start.
Don

Use a tape measure and check your car.

For my 1967 327/350 HP car, the top of the fuel tank is still an inch or so below the carb inlet. If you run 1/2 tank gas, there should be about 6-8 inches freeboard. But liquid gas can and will find a way into the engine if it can. Temperature changes could account for some instances from a stored car.

[Donald S.]

Re: 427 L68 Tri-Power Engine Failure - leaking carb Fuel Lock

I went probably 30 years with no issues; the only leaks I had were typically Holley external leaks over the years. Over the winter I make sure the tank is full to reduce any condensation; parked on a level lift. It happened with that first start and I don't remember if it had a chance to fire, it just "clicked" and my first thought is that the starter was the problem. Needless to say, after checking my oil level which was quite a bit higher than full, smelled of gas, I knew the issue wasn't going to be a simple fix. Looking back at the time, I had a slight odor of gas in the garage over the winter that I caulked up to the snow blower; I should have checked it further.
I have a new "ritual" I follow in the Fall and Spring with the fuel valve installed and haven't had an issue since. I think if one checks the oil level and use your sense of smell, you should be good.
Don