6-71 Detroit stuck at full throttle

What you have pics of is the governor. Pull the valve cover, I bet you’ve got an injector stuck. If one sticks....they all stick. Common issue with the old 2 strokes.

Ok can it just be freed up? The governor sure wasn't working. Never heard one run that FAST.

Pull the valve cover, rack tube sits on Gov side of head, HAS to Float freely and each injector "Rack" has to be as free floating. Is a fine art to setting the rack if have to R&R one with a frozen rack/plunger pinion.

oarwhat said:

Ok can it just be freed up? The governor sure wasn't working. Never heard one run that FAST.

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Well there are many that will say to use stuff like Gumout carb cleaner, WD-40 and so on but it it has been sitting for 6 or more years I would not personally take a chance on it.

Governor was probably working it's butt off trying to pull it back to idle but if on injector plunger was stuck for bad fuel or rust from water in fuel there is no way the governor could move it. Like DMiller says pull valve cover an look at the injectors, can just about guarantee you are going to find one that the plunger is stuck down. Might have to turn engine over by hand to find which one but if there is any clearance between the top of injector and the rocker arm you have found it!

First thing I would be doing is to learn how the emergency shut down flapper works on that engine. It's in the housing that bolt to the top of the blower, well being a inline guess you might call that the side of the blower!

And if you don't know anything about Detroits I would be looking for some old fart who does and have them replace at the bare minimum that stuck injector. As when you replace that you are going to need to know how to make a few other adjustments and one mistake and things will get very exciting fast!

I'm assuming your engine has some thing like this bolted to the blower with the air filter or piping to air filter connected to the top.


Take a picture of that and I or someone can explain how it is suppose to work.
I would strongly suggest that you not even turn the engine over by hand until you know this works and how to activate it in an emergency.

Have not EVER put stock in trusting one of those, have witness blower seals get sucked and engine ran on until out of oil.

A piece of plywood slapped on the blower intakes works.
I would vote for the stuck injector.

Thanks for the help guys. I knew about the shutdown on Detroit's but with all that noise I couldn't think straight and find it. I saw the rubber fuel line and cut it with my knife. I will know where it is and how to use it next time! I'll pull the valve cover when I get time and report back. Anyone know how many RPM'S an ungoverned Detroit will reach? It was crazy. We've owned 4 detroit's and never heard one like that.

Critical mass was demonstrated at a DD Education class I took in the 70s, engines could reach around 4500-5G where the moving mass could not move any faster leading to grenade. 2500-3G sounds like 9000 on a 2 stroke.

Was astraddle a 6v53 that skyrocketed, no idea how fast it hit, co-worker smothered it with a co2 extinguisher. They roar off rather instantly. Self feeding watermelons, Faster they climb the more fuel they feed to climb faster.

Seen one go to 6gs. A 6V71 and was lying on its side. Oh in a grader at that.

I've seen them go off on U tube before but first hand is a whole different experience.

I went to look at one early this year, owner says "needs a little work and it should run", found one injector plunger > 1/2" from the rocker, rack on full, would wiggle about the distance of the little c-hook on the end of an injector rack rod. I said this thing is prime for runaway, old man said, I know that, I'll fix it and then we'll run it and look at it.

I said fine, you fix it, just let me get off the property first and call when it is running.

DMiller said:

Critical mass was demonstrated at a DD Education class I took in the 70s, engines could reach around 4500-5G where the moving mass could not move any faster leading to grenade. 2500-3G sounds like 9000 on a 2 stroke.

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Seems I recall a Detroit class where they said that the flywheel can disintegrate at around 5,000 rpm, but that might depend a great deal on the flywheel/clutch design.

DMiller said:

Have not EVER put stock in trusting one of those, have witness blower seals get sucked and engine ran on until out of oil.

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Understand but still worth a try, it just might restrict air flow a bit to keep RPMs below critical mass speed long enough kill it some other way.

One problem I have seen with those E-shut downs is they are not always adjusted when installed, sometime you need to bend the flappers a bit to get them to seal off the intake. Another thing is if not worked once in a while they also get gummed up and won't close at all. Don't need to use them to kill the engine just trip them once in a while to make sure they are free and release latch moves!

Cutting fuel line would not work on most of the engines I worked on because 95% of them had Aeroquip 1503 medium pressure hose for fuel lines. That stuff is hard to cut with a hacksaw and it would laugh at a pocket knife!

6V-53's run at 2650 RPM's to begin with. Would be real scary at almost double that.

Up front and personal is IMPRESSIVE.

start at the top Mr oarwot I have never trusted or used those flapper valve things. you are more than likely going to suck in a blower seal and then she really lights up with excess fuel and lube oil. Keep a set spanner handy to crack the fuel line where it goes into the head from the transfer pump, crack that if the revs start to build and that drops the fuel to the injector units. best of luck.

I had one injector stuck bad but it freed up. Another is sticky and will not totally free up. It runs but gets stuck . The grader is in rough overall I thought if I got it running someone might be interested. I think it will go for scrap.

Hard choices for tentative machines
Some just are not worth the efforts.