Detroit 6-71 idle rpm

[micky]

Guy's what's the idle rpm for a detroit 6-71n?? Right now mine are set to 400 rpm per the tachometer but I know that's too low. Thanks

 

[lisaann]

mine idle at 550 i think thats about right, hows your oil pressure at that rpm i got about 10lbs hot at 550 the alarm goes off at 7lbs.

 

[Genesis]

Most people set them up at 500-550. Some people like 'em slower for easier low-speed maneuvering and that's ok provided (1) you don't ring the low-pressure alarms when hot and (2) you don't get stalls when you go into gear.

 

[micky]

That's what's happening when I put it in gear one of the engine shuts off.

 

[Genesis]

Note that you need to set the buffer screw any time you mess with the idle speed and in addition the booster spring pivot point and tension will probably need adjusted as well.

The procedure is (assuming the rest of the tune is ok):

1. Unlock and back out the buffer screw enough so that it is not contacting the governor lever at all and disconnect the throttle cable linkage so you know the lever is free and all the way to the idle stop. Hold the speed lever at idle and start the engine. (Make sure nothing can get caught on rotating parts, nothing can get sucked into an intake, etc.)

2. Unlock the idle speed screw (loosen the locknut) while holding the screw with a hex wrench, set the idle speed, then re-lock the screw's position with the locknut. Verify that the idle speed is where you want with your phototach after locking the nut.

3. Turn in the buffer screw JUST ENOUGH to stop idle roll and lock it. ("Roll" is a hunt in the idle speed when you return the throttle lever to idle, or when the engine is just sitting at idle. There should be none; the buffer screw acts as a small dampening force to stop overshoots in the governor.) This can result in NO MORE than a 15rpm increase from where you set the speed -- if you need more than that to stabilize the idle your rack is out of balance or something else is wrong (something's sticking, etc.) Find the other other problem and fix it. If everything in the tune (rack balance, etc) is spot-on you should be able to get in the range of 0-5 rpm increase while still avoiding roll in the idle.

4. Stop the engine. Adjust the booster spring pivot point (by moving it in the slot on the throttle lever) so it is just barely overcenter with the throttle lever held at idle and lock it down. Re-start the engine and set the booster spring tension so the throttle lever moves easily over its full range with the engine running and the lever returns to idle on its own without delay when released from any position from just off-idle to full throttle. If it seems to be impossible to come up with a booster spring tension that achieves both goals stop the engine and check the pivot point again (it's off.)

5. Stop the engine and re-connect the cable; you're done.

Note that ALL of these steps need to be repeated any time you change the idle speed; the booster spring pivot location changes slightly with the throttle lever position which changes with the idle stop screw setting and the buffer screw's plunger changes relationship to the internal governor operating lever with idle speed as well. These are all inter-related so you must back them all off and then check and adjust all of them when idle speed is changed.

You need a phototach for this; the bridge tachs are not accurate enough. Detroit recommends 550 rpm for idle speed although some people consider that too high for decent close-quarter maneuvering. So long as you get no oil pressure alarm at hot idle and do not stall when going into gear setting the idle lower is ok. If you like the lower idle you have now but are having stalling problems I'd move it up in 50rpm increments until the misbehavior stops. I ran mine at 550; I had no particular complaints with low-speed maneuverability with them set there.