BJ-8 Engine run-on

[Legal Bill]

Is it usually the carbs that cause the BJ-8 to run on after you switch off the car? My sprites would do this when the timing needed to be advanced. But form what I read, the idle speed and mixture in the BJ-8s are more likely the problem.

 

[RAC68]

Hi Bill,

As far as I have experienced, run-on can be caused by a number of things. Improper timing, glowing carbon in the combustion chamber, leaking jet or even an overly rich carb setting. If the pin is not closing off fuel and/or the butterfly is slightly open to allow fuel and air to pas into the combustion chamber where the glowing carbon or even heat from the engine will igniting it.

Check your carburetor settings and timing and adjust if necessary. Also, check to see if something is hanging up the butterflies from closing. However, since run-on cannot happen without something igniting the fuel, check your fuel and de-carbon if necessary.

Good luck,
Ray (64BJ8P1)

 

[Keoke]

----YES:
All those things mentioned as well as overheating

 

[vette]

Hot Engine, Residual Fuel in the intake track, HD carburators on BJ8 are suppose to be idling with the throttle plates completely closed. Your slow run adjuster screw is used to set Idle and it is a by-pass circuit to pass the mixture around the throttle plates. If you are idling your engine by screwing down the throttle plate screws there-by opening the throttle a little, that will lead to engine run-on when turning off the ignition.

 

[why]

The carbon deposits heat up and glow red so when you switch off power, the glow makes it like a diesel and ignites the fuel for a few beats. In the old days a fix along with carboned plugs was an "Italian tune-up" meaning run it in any gear at high RPM 4-5K which should burn off carbon. The carbon is just like the soot on a plug used to diagnose a rich fuel mixture, (I will forgo the lecture on stoichiometry and gas air mixture [hint hint google]) and that it is why it is also associated with hot running (Etype runs on only when very hot) which gets the carbon lit up. So most probably a slight leaning out of carb should do the trick, but the existing carbon unless burned up will continue to cause the problem when shut off very hot. Maybe Italian trick or fuel additive, probably not worth taking head off as run-on not known to do major damage.
Jay '65 3000

 

[Michael Oritt]

The old trick is to put the transmission in gear and then when turning off the ignition drop the clutch slightly. The strain overcomes any tendency for the engine to keep spinning.

 

[Keoke]

The old trick is to put the transmission in gear and then when turning off the ignition drop the clutch slightly. The strain overcomes any tendency for the engine to keep spinning.

Be sure you have your foot on the brake too.--:excitement:

 

[Michael Oritt]

Be sure you have your foot on the brake too.--:excitement:

That too...

 

[jjbank]

Bill,

Before adjusting the carburetors, do you use Shell 93 in your car? I only use Shell 93 and about every 2 or three fill-ups I put about 1/2 bottle of Octane boost. Bardahl's and Lucas make good octane boost.The main cause of run-on or dieseling is carbon deposits on the cylinder walls. The higher octane will help clean the walls by burning out those deposits. I had this problem with my BJ8 Ph 1 when I first started driving it back in 97 but the Shell 93 and periodic 1/2 bottle of Octane boost has solved the problem the last 15 years.

John B

 

[RAC68]

Hi Bill,

First, due to arrogance and inexperience in my younger days, In the late '60s my BJ8's compression was raised when I ignored the machinist's correction and had the head shaved 0.06 rather then 0.006. On result of this higher compression requires the use of high octane premium fuel or pre-ignition will be experienced. Another condition that, I believe, resulted from this increase in compression was run-on as a result of carbon build-up.

Since my Healey was new, I have had a tendency to wind the engine and shift close or, on rare situations, beyond red line. Although I can't prove this practice has eliminated the build-up of carbon (the engine combustion chamber has never been opened since the head was shaved), after the valve job and compression increase, when I babied the car and shifted at low RPMs (around 3500), I experienced run-on quite often. However, after adopting the practice of shifting at 5K RPMs, run-on stopped and I haven't had it return.

Hope this helps,
Ray (64BJ8P1)

 

[Legal Bill]

Ok, I started with some easy stuff. A full tank of fresh shell gas and a few runs up to 5K rpm and shut it off with my foot on the clutch pedal. Is seems a lot better. On four shut-offs it only ran-on once for about 1 second before it shut off. I'll give this a few more tries.

 

[TodE]

My car also runs on after shutdown, but also does the following: if you get on the gas at cruise the car "pings" (I am using 93 octane fuel), runs normal temp, but after shutting down with the car ilding for 20 minutes it over heated.

Retard timing or increase timing??

 

[healeyblue]

My car also runs on after shutdown, but also does the following: if you get on the gas at cruise the car "pings" (I am using 93 octane fuel), runs normal temp, but after shutting down with the car ilding for 20 minutes it over heated.

Retard timing or increase timing??

sounds like carbon build up on the piston tops or in the combustion chamber

 

[bdcvg]

Sounds like a job for Sea Foam!

 

[victoriacoffees]

Sounds like a job for Sea Foam!

I'm on my second can of Sea Foam. Along with adjusting the timing, changing plugs, tuning carbs, better gas, and adjusting the idle, the run-on has improved. I can't say for sure if SF has played a role but what I have noticed is less soot on my drive way after ignition.

 

[RAC68]

Bill,

One last thought. Check the carburetor pin and seat to make sure the piston is dropping the pin and closing the flow of fuel. This condition, in combination with a slightly open butterfly, could allow some fuel to leak past and vaporize into the hot cylinders and potentially fire.

Ray (64BJ8P1)

 

[AUSMHLY]

Sounds like a job for Sea Foam!

What about adding a bottle Chevron Techron.

 

[Legal Bill]

Bill,

One last thought. Check the carburetor pin and seat to make sure the piston is dropping the pin and closing the flow of fuel. This condition, in combination with a slightly open butterfly, could allow some fuel to leak past and vaporize into the hot cylinders and potentially fire.

Ray (64BJ8P1)

By pin do you mean the needle?

 

[RAC68]

Hi Bill,

Yes, needles. I appreciate the possibility of a leaking needle being the underlying cause of your run-on may be a little on the far side, but I thought I would present it just in case it fits with a subtle observation you may be having.

Good luck,
Ray (64BJ8P1)

 

[BOBBYR]

Hi Bill, I've read this post a couple times and I was wondering if anyone has directed you to pull the power lead to your distributor when this condition exists . Run on was extremely common back when these car were being built but in most cases , we fixed the the problem by adjusting engine timing . If your engine runs on after the key is turned off , I would try shut it off by pulling off the distributor lead as a test of the primary ignition circuit and also check your timing again . Keoke also pointed out that your engine temp could be too high and that is also a common problem that creates run on or post ignition. Hope this helps.
Bobby R