Detroit 6-71T Won’t Idle Without Manual Control of Rack

[Meghan]

Hey there.

Having some trouble getting a Detroit 6-71T in-line to run at idle without manual control of the injector rack.

I am aware that this particular thread is for trucks, but I am resurrecting a pair of Johnson & Towers Detroit Diesel 6-71T engines in a sportfish boat. The boat sunk back in 2017, was salvaged, engines were drained and restarted, and then it was left semi-winterized until I took it over this year.

The port side engine was stuck when I first started working on her. Wouldn’t budge. I removed the valve cover, pulled the injectors and poured a mixture of diesel and Marvel Mystery oil into the injector holes until the engine was filled. After soaking, I was able to free things up and turn her over.

Before first start, I cleaned and tested each injector to ensure proper functionality before reseating them. I disconnected the fuel rod and put a pair of vice grips on the injector bar. I was able to fire up the engine and control throttle manually. Since that worked out and the engine wasn’t knocking or sucking air, I tried to reconnect the fuel rod linkage to see if I could get things idling without manual control.

I made sure the throttle was in idle position and hit the starter. The injectors sat in the full fuel position and the engine instantly tried to rev up out of control. I had left the vice grips on and was able to kill the fuel before things got out of hand.

Upon further inspection of the governor and throttle, it appears that the throttle lever barely moves the fuel rod. With all linkage connected, the stop lever will move the injector rack significantly more than the throttle.

I’ve tried running the rack and the adjusting the gap in the governor but didn’t make any difference. All parts seem to be intact.

Engine: JT Detroit Diesel 6-71T
Governor: 5183314 Single weight variable speed
Injectors: Reliabuilt M15 (all move freely)

I’d be extremely grateful for some help! Any ideas on what to try next?

 

[Former Wrench]

Without being present, I would put my money on something rusted or gummed up in the gov. When not running the injector rods should be in full fuel until the engine starts and the gov takes over control of engine speed. I suggest removing the pin connecting the rack to the gov rod and make sure it is free with no resistance. If free, pull, disassemble, inspect, clean, and reassemble the gov. These engines are simple, but sensitive. A little dirt, rust, or salt water residue goes a long way down a bad path.

 

[Birken Vogt]

You probably already know this, but even if you get it to run do not trust the gov and rack for a long while. Always have a way to shut down the air.

 

[Meghan]

Without being present, I would put my money on something rusted or gummed up in the gov. When not running the injector rods should be in full fuel until the engine starts and the gov takes over control of engine speed. I suggest removing the pin connecting the rack to the gov rod and make sure it is free with no resistance. If free, pull, disassemble, inspect, clean, and reassemble the gov. These engines are simple, but sensitive. A little dirt, rust, or salt water residue goes a long way down a bad path.

Thank you. I’ll have a deeper look at the gov.
The fuel rod was easily disconnected and freely moving with the stop lever. Minimal movement of the rod with throttle. Internal components of the gov seem to be greased and freely moving otherwise.
I’ll be disassembling today to see if I can find anything gumming up.

 

[Meghan]

You probably already know this, but even if you get it to run do not trust the gov and rack for a long while. Always have a way to shut down the air.

Will do. Thanks for the heads up.
So far, I still have manual control of the rack with the valve cover off. But also have the emergency blower flap and a temporary quick release connection on the fuel line to the injectors as backup.

 

[Delmer]

So you have two engines, and only one has this problem, and one works like it should? Easiest thing for me to do is look at them side to side to see what's happening differently. If it was smaller, I'd even swap components, but that shouldn't be needed here. this should be visible.

 

[Vetech63]

It would help to know which governor the engine has. Pics of it and its tag?

 

[cfherrman]

Gov is in the post.

Your just way out of adjustment.

Back out the buffer. Back out the idle a lot till it has nothing on it. You might see the fuel rod move closer to no fuel when you do this. Then set up the rack again.

Get a optical tach and start and set the idle to 600, then check the no load speed

There might be a starting aid screw you might have to back out, I don't know jack about since it's a t, I had a n.

 

[Vetech63]

Since this was underwater for a time and sat afterwards, I'm wondering if the thrust bearing for the governor yoke failed on startup.

 

[56wrench]

Do you have a DD service manual for a 6-71T? It will cover the procedure for setting the VS governor unless someone has bastardized it which is entirely possible given the multitude of different configurations

 

[Vetech63]

Do you have a DD service manual for a 6-71T? It will cover the procedure for setting the VS governor unless someone has bastardized it which is entirely possible given the multitude of different configurations

That’s why I asked for pics. A lot of marine governors were open link.

 

[Former Wrench]

Not sure if this applies, but disconnect the linkage between the hand throttle and the gov. Could there be something that is manually pulling the RPM's into high idle?

 

[Vetech63]

Guess its fixed?