743b (kubota v1702) starts missing at around half throttle

[rogerh]

All, hope someone can give me some help: Have a 743b with kubota v1702. Engine starts immediately and runs perfectly up to a little less than half throttle. But after accelerating the throttle to about midway, it starts missing really badly. It doesn't smoke abnormally that I can tell, only a small bit of blueish/white smoke when it starts missing. I have changed the fuel filter but (obviously since I'm asking here) that did not clear it up. Any help or advice is greatly appreciated, Roger

 

[SkidRoe]

Hi Roger, it could be a lot of things. Is it missing randomly or does it seem to be on one cylinder only? If you can isolate it to 1 or 2 cylinders that, might help. You can do that by cracking individual injector lines while it is exhibiting these conditions. I had a VW diesel do this to me once and it turned out to be insufficient valve clearance on one cylinder. Hope this helps - SR

 

[foton]

Hi Roger, it could be a lot of things. Is it missing randomly or does it seem to be on one cylinder only? If you can isolate it to 1 or 2 cylinders that, might help. You can do that by cracking individual injector lines while it is exhibiting these conditions. I had a VW diesel do this to me once and it turned out to be insufficient valve clearance on one cylinder. Hope this helps - SR

maybe the lift pump is starting to go bad and letting it slightly fuel starve. But I would think that if it runs good at lower rpms it almost has to be lack of fuel flow. check parts diagram to see if there is a in tank filter screen, I do not know if there is one off hand.

 

[bobbie-g]

maybe the lift pump is starting to go bad and letting it slightly fuel starve. But I would think that if it runs good at lower rpms it almost has to be lack of fuel flow. check parts diagram to see if there is a in tank filter screen, I do not know if there is one off hand.

rogerh, any resolution on this yet? ---Bobbie-G

 

[rogerh]

rogerh, any resolution on this yet? ---Bobbie-G

Sorry for my lack of feedback until now, I had some extra time today so did a little trouble-shooting. I checked the fuel pickup tube screen and it was clean and looked almost new so don't think fuel is being restricted from there. I loosened 3 of the injector lines(one at a time) to see if I could isolate an injector and could tell the engine ran even rougher when they were loosened, so don't think its one of those injectors. Didn't do the last injector line because it was harder to get to. Also, loosening the injectors made the resulting engine miss very obvious and even more severe than the problem I'm noticing ... so not even sure its worth trying the 4th one. Because I had the machine inside a barn I was able to see better the smoke that is being generated when it starts missing ... its black with some white ... not sure what that means. The engine still cranks effortlessly (in less than 3 seconds after 15 seconds of glow plug) and it runs fine with good power until about 1/2 throttle then starts running rough and blowing smoke and lacks power

 

[rogerh]

Sorry for my lack of feedback until now, I had some extra time today so did a little trouble-shooting. I checked the fuel pickup tube screen and it was clean and looked almost new so don't think fuel is being restricted from there. I loosened 3 of the injector lines(one at a time) to see if I could isolate an injector and could tell the engine ran even rougher when they were loosened, so don't think its one of those injectors. Didn't do the last injector line because it was harder to get to. Also, loosening the injectors made the resulting engine miss very obvious and even more severe than the problem I'm noticing ... so not even sure its worth trying the 4th one. Because I had the machine inside a barn I was able to see better the smoke that is being generated when it starts missing ... its black with some white ... not sure what that means. The engine still cranks effortlessly (in less than 3 seconds after 15 seconds of glow plug) and it runs fine with good power until about 1/2 throttle then starts running rough and blowing smoke and lacks power

not to bet a dead horse, but was thinking if I could describe the miss I'm hearing better: I would say it sounds more like a "flutter", not a complete miss but more of a "dull" miss with smoke.

 

[foton]

not to bet a dead horse, but was thinking if I could describe the miss I'm hearing better: I would say it sounds more like a "flutter", not a complete miss but more of a "dull" miss with smoke.

white smoke indicates a coolant leak , maybe a head gasket or cracked head has the engine been overheated? look at your engine oil make sure it does not look like a milkshake. and look for excess turbulence in the cooling system from compression bypass into coolant.

 

[rogerh]

white smoke indicates a coolant leak , maybe a head gasket or cracked head has the engine been overheated? look at your engine oil make sure it does not look like a milkshake. and look for excess turbulence in the cooling system from compression bypass into coolant.

I don't see any sign of coolant in oil (head gasket/head was/is my concern as well).

 

[Thomas1]

I don't see any sign of coolant in oil (head gasket/head was/is my concern as well).

ROGER, HAVE YOU CHECKED THE AIR FILTER? NOT SURE IF A PARTIALLY BLOCKED FILTER WOULD MAKE IT MISS BUT MAY ACCOUNT FOR THE SMOKE...

 

[rogerh]

ROGER, HAVE YOU CHECKED THE AIR FILTER? NOT SURE IF A PARTIALLY BLOCKED FILTER WOULD MAKE IT MISS BUT MAY ACCOUNT FOR THE SMOKE...

Thanks to everyone that donated some input ... well, as the saying goes, "a blind squirrel finds a nut every now and then". Checked the air filters today and the inner filter was almost completely covered in black soot ... removed it, reinstalled outer filter and machine runs perfectly, turned it off immediately ... as typical, the easiest thing to check, I checked last and it was the fix. To be honest, I didn't think it could be the filters because they had been replaced less than 100 hours ago. But here's the culprit (I think), I had to install a new exhaust pipe from exhaust manifold over to muffler about same time new filters were installed... of course the new pipe did not fit as snuggly with the muffler as it should have which resulted in a small (may not so small) exhaust leak right above the breather ... I'm assuming the leaking exhaust was being sucked directly into the breather. At least I know now the inner filter will trap those small particles. Getting a new filter and will do my best to makes sure the exhaust leak is fixed ... I feel relatively lucky, maybe the cheapest fix I've ever had on this particular machine, Thanks again to all.

 

[farmshop]

Thanks to everyone that donated some input ... well, as the saying goes, "a blind squirrel finds a nut every now and then". Checked the air filters today and the inner filter was almost completely covered in black soot ... removed it, reinstalled outer filter and machine runs perfectly, turned it off immediately ... as typical, the easiest thing to check, I checked last and it was the fix. To be honest, I didn't think it could be the filters because they had been replaced less than 100 hours ago. But here's the culprit (I think), I had to install a new exhaust pipe from exhaust manifold over to muffler about same time new filters were installed... of course the new pipe did not fit as snuggly with the muffler as it should have which resulted in a small (may not so small) exhaust leak right above the breather ... I'm assuming the leaking exhaust was being sucked directly into the breather. At least I know now the inner filter will trap those small particles. Getting a new filter and will do my best to makes sure the exhaust leak is fixed ... I feel relatively lucky, maybe the cheapest fix I've ever had on this particular machine, Thanks again to all.

While it can be frustrating overlooking the simple things expecting the worse cheap fixes are always a welcome sight. Might try some red high temp rtv when you slide that pipe on or they do make some exhaust system sealer that is more like a clay base

 

[foton]

While it can be frustrating overlooking the simple things expecting the worse cheap fixes are always a welcome sight. Might try some red high temp rtv when you slide that pipe on or they do make some exhaust system sealer that is more like a clay base

glad you figured out what it was but confused how you saw white smoke , will have to think on that. but I have had good luck with the muffler bandage stuff for a semi good fix.