hard to start

[wshelton]

I have DD671Ns and have now have an engine that is hard to start when cold(not run for several days). It will not light even after two or three attemps. I have to advance the throttle slightly to make it start and then immediatley throttle back to a confortable rpm to let the engine warm up. No smoke and will run perfect with no other start up problems till engines are cold. Now here is what I think I've done to create this problem. While this engine was idleing, I adjusted a little pen or shaft like thing that moved in and out of a small like round cylinder shaped part that is mounted up on top of the engine near the throttle linkage. This shaft moves in and out so I turned it a few times which lowered the rpms which I wanted to do. Ever since then I have had this problem starting the engine cold. I have looked throught the DD engine manuals and do not see this round cylinder part and I have not attempted to do an idle adjustment dealing with a buffer screw and such as pointed out in the manual. What's up. I have not tried to turn this pen like shaft again either seeking your advice.

 

[Passages]

The problem may not be "in" the engine.

I have a 6-71 with similar symptoms. My engine is well tuned but the dang thing needs to crank for 20 seconds (broken up into 4-5 (4) second bursts) before it will fire. This only happen after a having sit a few days. Fires immediately if it only sat a few hours. There are no visible leaks in the fuel lines.

My best guess is the problem is in the check valve on the return line. Over time , the fuel drains back to the tank and needs to prime itself before firing.

Further pondering led me to believe it's OK left alone. I've read elsewhere a cold pre-start proceedure of cranking with the stop button depressed for 15-20 seconds. Gets the oil circulating so the engine doesn't fire "dry".

I may still replace the check valve, but it's not on my priority list.

 

[Genesis]

Ok, couple of things here.

First, on the governor which you apparently futzed with. There are FOUR "things" on the governor that are "adjustable" without removing the cover or dorking with internal adjustments.

The first is the speed lever. That one is obvious - it is connected to the cable that goes to your throttle control. You set the speed of the engine with this; the governor controls the fuel to result in the speed you select. It is on the SIDE of the governor.

The second is the STOP lever. That's on the TOP of the governor cover, and is pulled to stop the engine. It must be all the way to the RUN position - if it is even a tiny bit towards STOP it will screw with you badly, including producing hard starting. Make absolutely certain it is not binding and goes ALL THE WAY to RUN when not in use to stop the engine. Your problem is likely here as it sounds like you diddled the linkage to the STOP lever from your description. Undo that.

The third is the idle speed screw. This is found on the end of a small cylinder near and behind the throttle lever's shaft and is an allen screw with a locknut around it. You need a small allen key to turn it. It faces AFT. The one facing the side of the engine (usually starboard) is the buffer screw - I'll get to that one. The aft screw adjusts the idle speed ONLY, but beware as the buffer screw interacts with it - procedure follows.

The buffer screw is on the SIDE of the governor case, and is a hex bolt with a locknut around it.

To properly set the idle speed you need a phototach or other ACCURATE means of measuring RPMs. Bridge tachs are not adequate.

To set the IDLE SPEED, warm up the engine, back off the BUFFER SCREW a few turns (3-4 will do) and then loosen the locknut around the idle speed screw. Set the idle speed using a phototach and an allen wrench. 500-600 RPM is recommended for marine engines; I prefer the higher end of the range unless there's a problem with idle speed when set there (on some boats there is.) Holding the idle speed screw, tighten its locknut. This requires both an allen key and open end wrench. As you diddle this you will see that the throttle lever moves slightly - this is normal, as what you're adjusting is the "low side" travel of the throttle lever.

If idle is set too low, you will likely get an engine that fires but won't start when cold, stalls going into gear, and may ring the low oil pressure alarm when going into gear hot, as the RPMs will get too low. Very low idle RPMs are not desireable; you want 500-550 in gear, which usually requires 550-600 in neutral, again, both hot.

NOW, with that done, you must set the buffer screw. Briefly pull and release the STOP LEVER. The engine will likely "hunt" a bit before it settles down. Now turn in the buffer screw slowly until the RPM goes up JUST A TOUCH - NO MORE than 15rpm - just enough to stop the hunting (5-10rpm is usually enough.) Try the "stop lever" test again. IT IS IMPORTANT THAT YOU NOT TURN IN THE BUFFER SCREW MORE THAN 15 RPM! Then lock that one down.

Re-check your idle RPM to make sure nothing moved while you were locking it down. If it did, go back and do it again from the top.

Test going into and coming out of gear; it should smoothly do so without hunting and NOT "dawdle" at the higher "unloaded" RPM when coming out of gear.

DO NOT attempt to adjust the idle speed with the stop lever or with the buffer screw - you have to use the right tool for the right job.

Detroit governors can be flummoxed if toyed with inappropriately and in extreme cases (particularly abusing the buffer screw) you can "lock up" the governor and cause a full-rack runaway.

If that doesn't solve the problem you need someone to come out and go through the full tune-up procedure. Not a big deal, but it has to be done "by the book".

 

[wshelton]

Ok, couple of things here.

First, on the governor which you apparently futzed with. There are FOUR "things" on the governor that are "adjustable" without removing the cover or dorking with internal adjustments.

The first is the speed lever. That one is obvious - it is connected to the cable that goes to your throttle control. You set the speed of the engine with this; the governor controls the fuel to result in the speed you select. It is on the SIDE of the governor.

The second is the STOP lever. That's on the TOP of the governor cover, and is pulled to stop the engine. It must be all the way to the RUN position - if it is even a tiny bit towards STOP it will screw with you badly, including producing hard starting. Make absolutely certain it is not binding and goes ALL THE WAY to RUN when not in use to stop the engine. Your problem is likely here as it sounds like you diddled the linkage to the STOP lever from your description. Undo that.

The third is the idle speed screw. This is found on the end of a small cylinder near and behind the throttle lever's shaft and is an allen screw with a locknut around it. You need a small allen key to turn it. It faces AFT. The one facing the side of the engine (usually starboard) is the buffer screw - I'll get to that one. The aft screw adjusts the idle speed ONLY, but beware as the buffer screw interacts with it - procedure follows.

The buffer screw is on the SIDE of the governor case, and is a hex bolt with a locknut around it.

To properly set the idle speed you need a phototach or other ACCURATE means of measuring RPMs. Bridge tachs are not adequate.

To set the IDLE SPEED, warm up the engine, back off the BUFFER SCREW a few turns (3-4 will do) and then loosen the locknut around the idle speed screw. Set the idle speed using a phototach and an allen wrench. 500-600 RPM is recommended for marine engines; I prefer the higher end of the range unless there's a problem with idle speed when set there (on some boats there is.) Holding the idle speed screw, tighten its locknut. This requires both an allen key and open end wrench. As you diddle this you will see that the throttle lever moves slightly - this is normal, as what you're adjusting is the "low side" travel of the throttle lever.

If idle is set too low, you will likely get an engine that fires but won't start when cold, stalls going into gear, and may ring the low oil pressure alarm when going into gear hot, as the RPMs will get too low. Very low idle RPMs are not desireable; you want 500-550 in gear, which usually requires 550-600 in neutral, again, both hot.

NOW, with that done, you must set the buffer screw. Briefly pull and release the STOP LEVER. The engine will likely "hunt" a bit before it settles down. Now turn in the buffer screw slowly until the RPM goes up JUST A TOUCH - NO MORE than 15rpm - just enough to stop the hunting (5-10rpm is usually enough.) Try the "stop lever" test again. IT IS IMPORTANT THAT YOU NOT TURN IN THE BUFFER SCREW MORE THAN 15 RPM! Then lock that one down.

Re-check your idle RPM to make sure nothing moved while you were locking it down. If it did, go back and do it again from the top.

Test going into and coming out of gear; it should smoothly do so without hunting and NOT "dawdle" at the higher "unloaded" RPM when coming out of gear.

DO NOT attempt to adjust the idle speed with the stop lever or with the buffer screw - you have to use the right tool for the right job.

Detroit governors can be flummoxed if toyed with inappropriately and in extreme cases (particularly abusing the buffer screw) you can "lock up" the governor and cause a full-rack runaway.

If that doesn't solve the problem you need someone to come out and go through the full tune-up procedure. Not a big deal, but it has to be done "by the book".

Your explanation here is greatly appreciated, I feel sure I messed with this stop lever. When I try to start the engine, it is does sound as if it is out of fuel--similar to the way it sounds if you've pulled the emergency shut down and not reset it. I think all I need to do is let this engine warm up and un-turn that little pen like shaft thing. I will try this before even comtimplating dealing with the adle adjustment although appreciate your descprition and procedure which is more clear than the book. TKS

 

[Genesis]

No problem.... What you PROBABLY turned was the locknut on either the cable "emergency" shutdown pulls (on the bridge) or the adjustment for the stop solenoid (depending on how your engines are rigged)

That's definitely not what you want to mess with - put it back, then do the idle adjustment the right way if you're unhappy with the idle.

 

[Nonchalant1]

Ok, couple of things here.

First, on the governor which you apparently futzed with. There are FOUR "things" on the governor that are "adjustable" without removing the cover or dorking with internal adjustments.

The first is the speed lever. That one is obvious - it is connected to the cable that goes to your throttle control. You set the speed of the engine with this; the governor controls the fuel to result in the speed you select. It is on the SIDE of the governor.

The second is the STOP lever. That's on the TOP of the governor cover, and is pulled to stop the engine. It must be all the way to the RUN position - if it is even a tiny bit towards STOP it will screw with you badly, including producing hard starting. Make absolutely certain it is not binding and goes ALL THE WAY to RUN when not in use to stop the engine. Your problem is likely here as it sounds like you diddled the linkage to the STOP lever from your description. Undo that.

The third is the idle speed screw. This is found on the end of a small cylinder near and behind the throttle lever's shaft and is an allen screw with a locknut around it. You need a small allen key to turn it. It faces AFT. The one facing the side of the engine (usually starboard) is the buffer screw - I'll get to that one. The aft screw adjusts the idle speed ONLY, but beware as the buffer screw interacts with it - procedure follows.

The buffer screw is on the SIDE of the governor case, and is a hex bolt with a locknut around it.

To properly set the idle speed you need a phototach or other ACCURATE means of measuring RPMs. Bridge tachs are not adequate.

To set the IDLE SPEED, warm up the engine, back off the BUFFER SCREW a few turns (3-4 will do) and then loosen the locknut around the idle speed screw. Set the idle speed using a phototach and an allen wrench. 500-600 RPM is recommended for marine engines; I prefer the higher end of the range unless there's a problem with idle speed when set there (on some boats there is.) Holding the idle speed screw, tighten its locknut. This requires both an allen key and open end wrench. As you diddle this you will see that the throttle lever moves slightly - this is normal, as what you're adjusting is the "low side" travel of the throttle lever.

If idle is set too low, you will likely get an engine that fires but won't start when cold, stalls going into gear, and may ring the low oil pressure alarm when going into gear hot, as the RPMs will get too low. Very low idle RPMs are not desireable; you want 500-550 in gear, which usually requires 550-600 in neutral, again, both hot.

NOW, with that done, you must set the buffer screw. Briefly pull and release the STOP LEVER. The engine will likely "hunt" a bit before it settles down. Now turn in the buffer screw slowly until the RPM goes up JUST A TOUCH - NO MORE than 15rpm - just enough to stop the hunting (5-10rpm is usually enough.) Try the "stop lever" test again. IT IS IMPORTANT THAT YOU NOT TURN IN THE BUFFER SCREW MORE THAN 15 RPM! Then lock that one down.

Re-check your idle RPM to make sure nothing moved while you were locking it down. If it did, go back and do it again from the top.

Test going into and coming out of gear; it should smoothly do so without hunting and NOT "dawdle" at the higher "unloaded" RPM when coming out of gear.

DO NOT attempt to adjust the idle speed with the stop lever or with the buffer screw - you have to use the right tool for the right job.

Detroit governors can be flummoxed if toyed with inappropriately and in extreme cases (particularly abusing the buffer screw) you can "lock up" the governor and cause a full-rack runaway.

If that doesn't solve the problem you need someone to come out and go through the full tune-up procedure. Not a big deal, but it has to be done "by the book".

Another Genesis mini-course that I printed and saved in my little file on engines. I hope 8V71's have the same governor if I need to set my idle. Thanks Karl! Gotta love your answers........

Doug

 

[Genesis]

They do Doug.....

Virtually all Detroit marine engines have variable-speed governors. You set the SPEED of the engine with the lever, the governor controls the fuel.

If you've wondered why when you put the throttles at the halfway mark you get a given RPM (within reasonably tight tolerances), no matter how much fuel you have in the boat and how many people are on board, or even if you're in or out of gear, now you know why that happens. That's exactly how its supposed to work. This is why if you put the throttles at half with the engine out of gear you don't get full high-idle RPMs - you only get that if you put the throttle at "full".

Road engines have a different set up, and continuous-RPM engines (e.g. for gensets) have yet another, although the third is kinda-sorta (internally) like what a boat has.

Note that this applies to non-DDEC engines. DDEC engines don't have governors per-se - they control all this with electronics.

The basic tuneup procedure isn't terribly difficult but it requires running the engine with the valve covers removed, use of feeler gauges and a couple of special tools (including a pin gauge for injector timing) along with the potential for having very bad things happen if you are not cautious.

Setting the idle speed is pretty fool-proof; I'm not too worried about someone screwing that up too badly. About the only place you can really hurt yourself (and that can be VERY bad, as I noted) is by trying to use the buffer screw as an idle adjustment.

Of course there are always risks working on running machinery (your body parts will NOT stop a rotating camshaft or crankshaft pulley!), but if you're willing to go down in the engine room with the engines running then you're already taking that risk in your daily use of the boat.....

If you go at this and it doesn't make sense, don't change things. STOP and post here or PM me, and I'll try to help.

 

[Nonchalant1]

Karl,

Thanks. My engines have always idled at about 655 RPM port side and 695 RPM starboard. I'll probably just let 'em go like that since they seem to be otherwise happy. If I need them idling the same, I just engage the sync, but mostly it doesn't affect operation.

Doug

 

[Scott Mather]

A source of great info on this is to get a 6-71 detroit service manual. Not the manual supplied with the boat, get the one the service tech's use, its a couple of inches thick but some great reading for minor to major work on these motors.