Mep 831a black smoke won't rev up and shooting flames out the exhaust

[Captainscall]

Have you ever seen it run without black smoke? I.e. could an oil seal be missing on a valve?

This is how it has ran since I got it. Nothing I have tried has made any difference at all. If the remaining steps on the fuel system are done I will start tearing into the motor itself.


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[Captainscall]

I would have sold you a known good injection pump for $30. Yanmar. Hope you got a good deal.

Forgive me if some of this has been suggested, but gears are turning...

The low pressure side getting air would make it starve for fuel. I have run them with a hose pressed on & air definitely getting in. With the electric pump on the MEP 831A, it will just leak vs pull in air. Easiest way to eliminate anything in the low pressure side is to remove the fuel inlet & gravity feed a fuel line from a funnel.

Are you sure the electric pump is moving the proper amount of fuel?

Did you try running it with the electronic speed controller linkage removed so it will just run at 3600RPM? How about something like 1300 RPM? And use the manual knob to stop it? Be sure to remember where it is at before loosening so you can put it back.

Did you confirm all the springs are present & on the linkage are where they belong on the governor? There are quite a few. TM will tell you the right holes to be in. This would all be behind the black knob area.

I had ordered a Chinese clone before I saw your post. If that fixes it I will definitely take you up on the offer. I appreciate it!! I hate throwing parts at this but not sure what else to do at this point.

I will definitely try the gravity feed just to eliminate air on the suction side of the pump.

I drained about 3 gallons of fuel using the pump. Just disconnected the low pressure line to the IP and put it in a can. It has really good flow.

It runs so bad that within a few seconds it has an error and disables the speed controller. I have manually ran the throttle linkage and it runs bad at all rpm.

I went and re watched all your series on the 831a hoping I have missed something but the issue I have appears to be different than anything you ran across in your videos.


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[Captainscall]

Years ago I had an issue with a Kubota 1.5l 3-cyl diesel genset. Those motors are legendarily indestructible. So it was missing and spitting and blowing diesel and would run OK then stutter..... After doing a bunch of fuel related stuff I finally pulled the unit off the mountain location and back to the shop for a tear down. It belonged to a bunch of hippy kids growing dope. Stuff is legal here and what do I care I don't smoke it I just fix stuff for a living.... Anyways I never did get a good story of what happened until I took it apart.

Turns out at some point the idiots had way overfilled it with oil. This bent one of the rods. Hydrolocked it. Just one of the three. Then they corrected the level before I got there. It was plain as day when I put the rods next to each other one was crooked as hell. Actually I could tell right away when I took the head off, rotated the motor, and you could see one of the pistons didn't rise as far as the others. I still have it kicking around the shop as a story piece. Guess those kids were smoking too much of their stuff while trying to do their PM's!

So I put a new rod in, then took the leads as spec, and it ran like new. If I was you I would go ahead and pull the head and squish some lead. Sounds like inadequate compression could be on the menu.

Thanks for the info. Once I finish checking the fuel side of things I definitely plan to year in to the motor if it is not fixed.


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[DieselAddict]

Were there any signs that anyone had worked on the unit before?

 

[CallMeColt]

I had ordered a Chinese clone before I saw your post. If that fixes it I will definitely take you up on the offer. I appreciate it!! I hate throwing parts at this but not sure what else to do at this point.

I will definitely try the gravity feed just to eliminate air on the suction side of the pump.

I drained about 3 gallons of fuel using the pump. Just disconnected the low pressure line to the IP and put it in a can. It has really good flow.

It runs so bad that within a few seconds it has an error and disables the speed controller. I have manually ran the throttle linkage and it runs bad at all rpm.

I went and re watched all your series on the 831a hoping I have missed something but the issue I have appears to be different than anything you ran across in your videos.


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Again, sorry if I repeated myself. I follow a bunch of threads & also have 3 different things going myself, but know the feeling when you just can't something.

I keep thinking it is a valve issue. The reason being, is these little engines are savages, and will attempt to run is the worst conditions. I think it combusting with the exhaust valve open.

In my videos for the MEP 831A, I was lucky that the engine itself had no problems. Just everything else was messed up.

I did have a Yanmar L100V that for the life of me, would not run right. I did everything. Time = money, & I finally gave up as the "v" models have slightly different parts, making them even more annoying to get. It ran fine at first, than for no reason acted like it was starving for fuel. Everything was replaced on it at some point in the injections system & compression test done. Finally, I just sold it to someone who wanted to take it on.

I've learned a lot more since then & I think my issue was valves. These little Yanmar engines are picky with the valve clearance. And even though they give a spec, I think that is to get you in the area. In my example above, I think it was a little tight, so it wasn't getting enough air.

In your case, messing with the valves is a really easy thing to do. Go a few steps on the gauge in each direction, start it, and see what it does. Can't be any worse than what you have now! When I rebuilt the L48 in the older videos, my valve adjustment was way off and it ran, but really bad. It looked like one of those old wind up toys that would try to do a backflip as it unwound. That also, needed to be slightly off-spec if I recall. At the time, I thought I just didn't know what I was doing. Maybe I still don't, but make things work?

Don't give up! I'm rooting for you.

 

[Captainscall]

Again, sorry if I repeated myself. I follow a bunch of threads & also have 3 different things going myself, but know the feeling when you just can't something.

I keep thinking it is a valve issue. The reason being, is these little engines are savages, and will attempt to run is the worst conditions. I think it combusting with the exhaust valve open.

In my videos for the MEP 831A, I was lucky that the engine itself had no problems. Just everything else was messed up.

I did have a Yanmar L100V that for the life of me, would not run right. I did everything. Time = money, & I finally gave up as the "v" models have slightly different parts, making them even more annoying to get. It ran fine at first, than for no reason acted like it was starving for fuel. Everything was replaced on it at some point in the injections system & compression test done. Finally, I just sold it to someone who wanted to take it on.

I've learned a lot more since then & I think my issue was valves. These little Yanmar engines are picky with the valve clearance. And even though they give a spec, I think that is to get you in the area. In my example above, I think it was a little tight, so it wasn't getting enough air.

In your case, messing with the valves is a really easy thing to do. Go a few steps on the gauge in each direction, start it, and see what it does. Can't be any worse than what you have now! When I rebuilt the L48 in the older videos, my valve adjustment was way off and it ran, but really bad. It looked like one of those old wind up toys that would try to do a backflip as it unwound. That also, needed to be slightly off-spec if I recall. At the time, I thought I just didn't know what I was doing. Maybe I still don't, but make things work?

Don't give up! I'm rooting for you.

Thanks for all your help! I will not give up. I did check the valve clearances when I first got it. They were a little loose compared to the spec so I tightened them up to spec with no change in how it runs. Once I finish the fuel system I will tear into the engine if I have to. Just wish it was warmer out or I had a heated garage. It’s not fun working out there when it is 10 degrees but I will get this figured out eventually!!

My plan was to fix and sell this one to be able to buy an 802a or 803a at auction. My goal is to end up with an 803a which should be the perfect size to run my house.


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[Captainscall]

Were there any signs that anyone had worked on the unit before?

Yes. The more I look at the machine it’s obvious Someone before me has definitely been in there before.


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[DieselAddict]

Yes. The more I look at the machine it’s obvious Someone before me has definitely been in there before.


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Ug, all bets are off then. You need to start from square one. The first thing I would do is pull the valve cover and check your valve action and timing.

 

[Captainscall]

Hi group. Have an update but it is not much of one.

Received the new injection pump. It made no difference at all. Just like everything else I have done. I drained off some of the engine oil and lowered it down to the bottom of the dipstick with no change. I added and removed injection pump shims and it ran worse both ways.

I am at a loss here. Before I tear the engine apart to check cam timing I am going to get a small section of clear fuel line to rule out any air in the fuel and change the oil. Any other ideas?

To recap I have changed the injector, injection pump. Disconnected exhaust to rule out restriction in exhaust. Pulled air cleaner to check for intake restrictions. I have checked valve clearance. Checked pump timing by removing and adding shins.

I know I’ll figure it out eventually but I’m really lost as to what it could be. It starts fine. The rpm’s will go up and down. When it’s revving up thick black smoke. When the rpm’s are going down it’s thick white smoke. Once it has been running for a few minutes the muffler glows orange and it backfires out the exhaust with a flame and gunshot sound at the same time.

Thanks!!!


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[CallMeColt]

Has this been adjusted? There should be a wire with lead on it to show if it's been tampered with. Would need to be cut if so. The example picture here shows it WITHOUT the wire.

 

[CallMeColt]

Are you sure it is not just very wetstacked? Have you tried just running it under some load to see if it cleans up if it otherwise runs okay?

 

[Captainscall]

Has this been adjusted? There should be a wire with lead on it to show if it's been tampered with. Would need to be cut if so. The example picture here shows it WITHOUT the wire.
View attachment 939683

I have checked that several times and the wire is still intact. Thanks!!


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[Captainscall]

Are you sure it is not just very wetstacked? Have you tried just running it under some load to see if it cleans up if it otherwise runs okay?

Kind of. It runs so bad that it is hard to get it to stop throwing the short light on which stops the governor controller from controlling the engine and kicks the inverter off. I was able to run a 1500w heater for a minute or so but got scared when the exhaust started glowing and the backfires were so loud I figured my neighbors would call the police.

I still have a feeling it is air in the fuel but have no clue where it would be getting in. I plan to get a section of clear fuel line to put between the injection pump and the first metal T where the return line from the injector connects. I did replace the fuel line from the return of the injector to that T because I broke it disconnecting and reconnecting it so much.

I’m reading up on the fuel system to make sure the person before me didn’t mess it up. I find it weird that the return line from the injector T’s off. One side goes back to the T on the fuel line to the injection pump. The other side takes a small line all the way to the back of the machine where it t’s into a large fuel line at the filler neck which I think is a vent . That large fuel line that I think is a vent goes all the way around to the front of the machine and enters the fuel tank which would kinda make sense as the return. Just seems weird and over complicated?? Or maybe it’s wrong??


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[CallMeColt]

Should be a fuel flow schematic on the generator. If not, in the TM. Don't recall off the top of my head.

 

[Captainscall]

Should be a fuel flow schematic on the generator. If not, in the TM. Don't recall off the top of my head.

I did a quick look on my phone but could not find a flow diagram. I did find diagrams but they were just sections of the system. So far everything looks to be hooked up properly.

I’m not giving up but I really wanted to get this one done and sold because I just won an 802a at auction and hope to pick it up next week


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[2Pbfeet]

Kind of. It runs so bad that it is hard to get it to stop throwing the short light on which stops the governor controller from controlling the engine and kicks the inverter off. I was able to run a 1500w heater for a minute or so but got scared when the exhaust started glowing and the backfires were so loud I figured my neighbors would call the police.

I still have a feeling it is air in the fuel but have no clue where it would be getting in. I plan to get a section of clear fuel line to put between the injection pump and the first metal T where the return line from the injector connects. I did replace the fuel line from the return of the injector to that T because I broke it disconnecting and reconnecting it so much.

I’m reading up on the fuel system to make sure the person before me didn’t mess it up. I find it weird that the return line from the injector T’s off. One side goes back to the T on the fuel line to the injection pump. The other side takes a small line all the way to the back of the machine where it t’s into a large fuel line at the filler neck which I think is a vent . That large fuel line that I think is a vent goes all the way around to the front of the machine and enters the fuel tank which would kinda make sense as the return. Just seems weird and over complicated?? Or maybe it’s wrong??


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Factory Yanmar L70 engines have those tees. However, in my experience, not much fuel ever comes off the injector low pressure line, and if I had an air leak, I would look at that whole return fuel segment as being a potential source of an air leak. If it were me, I would use new hose to run temporary lines from the filter to the IP, and a new hose to return the excess to the tank. Simplify your troubleshooting.

All the best,

2Pbfeet

 

[Captainscall]

Another update. It warmed up today so I went out and put clear fuel line on the injection pump. There are no air bubbles. And went ahead and changed the oil. As usual, no improvement or changes.

Unless anyone else has any other ideas I am going to start tearing into the engine itself to look at cam timing marks and anything else I can. I am completely dumbfounded on this one. I would think if the cam timing was off it would not build enough compression or run at all due to the injection pump timing being way off I can’t think of a single reason that I have not already checked that would cause this.

Thanks!!


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[2Pbfeet]

Another update. It warmed up today so I went out and put clear fuel line on the injection pump. There are no air bubbles. And went ahead and changed the oil. As usual, no improvement or changes.

Unless anyone else has any other ideas I am going to start tearing into the engine itself to look at cam timing marks and anything else I can. I am completely dumbfounded on this one. I would think if the cam timing was off it would not build enough compression or run at all due to the injection pump timing being way off I can’t think of a single reason that I have not already checked that would cause this.

Thanks!!


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The symptoms that you have been describing sound like overfueling, but low compression might also do it. I would start with the head to check valves and cylinder walls, and to see how much carbon might be in there.

Keep us posted on what you find deeper into the engine.

All the best,

2Pbfeet

 

[Captainscall]

Good Update!!!

First of all I would like to thank each and every one of you for all of your help and suggestions. You are all the best!!

I was preparing to remove and disassemble the engine. I pulled the valve cover just to take one more peek. I swear the first thing I did when I got this machine was check valve clearance. This was before I found Steel Soldiers and before I knew what a TM was. I do not recall what spec I clearances the valves to but it was obviously wrong. They were super tight. I clearanced them to .15 and the machine came to life. Little smoke which i assume is lots of unburnt fuel in the exhaust. Ran great made power. No backfires and no glowing orange muffler. I feel like a complete moron that it was the valve clearance this whole time but I swear it was the first thing I checked. Well, I learned a lot on this machine.

So now it runs well and makes power. Next step will be a load test. One question though. Neither of the fans came on other than the one inside the inverter box. Are the 2 external fans on a temp switch or should they always be on?

I can’t thank you all enough for everything!!


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[CallMeColt]

Good Update!!!

First of all I would like to thank each and every one of you for all of your help and suggestions. You are all the best!!

I was preparing to remove and disassemble the engine. I pulled the valve cover just to take one more peek. I swear the first thing I did when I got this machine was check valve clearance. This was before I found Steel Soldiers and before I knew what a TM was. I do not recall what spec I clearances the valves to but it was obviously wrong. They were super tight. I clearanced them to .15 and the machine came to life. Little smoke which i assume is lots of unburnt fuel in the exhaust. Ran great made power. No backfires and no glowing orange muffler. I feel like a complete moron that it was the valve clearance this whole time but I swear it was the first thing I checked. Well, I learned a lot on this machine.

So now it runs well and makes power. Next step will be a load test. One question though. Neither of the fans came on other than the one inside the inverter box. Are the 2 external fans on a temp switch or should they always be on?

I can’t thank you all enough for everything!!


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I knew it was valves! It very well could have been you adjust them, and when you tightened, they moved. VERY easy to do that on these. Trust me, I know... makes you realize how stubborn these little engines are to just run even when they shouldn't.

Yes, there are thermal switches for the fans. You want the box warm to help with wet stacking so it waits. Each fan is different as well.