ZD21 smoke on start-up

[GMCRanch]

Hey all, new here but a 6 year Kubota owner. Love their machines. Recently purchased a 2006 (so I'm told) ZD21F from a friend of mine. He recently replaced a laundry list of parts on it and it smokes on startup for about 5-8 seconds when it's cold and clears right up after. It is a blueish white smoke and smells like raw fuel. Once it's warmed up it just emits the typical small poof of black smoke when re started. Even on hard acceleration or under load it barely smokes otherwise and if it does its black. He replaced the fuel pump and filters and rebuilt the injection pump and replaced the injectors and says he turned it up a little for more power. How do I adjust it back a little? I hate getting gassed out of the shed. I don't know much about the D782 that's in it so I wanted to ask here before taking it to the shop. I also noticed the pump seems to be very slightly wet with diesel fuel. I need to triple check the bolts to make sure it's all tight but nothing seemed loose the other night when I cleaned it after mowing.
Thanks and I appreciate it! Lots more questions to come I'm sure.

 

[lmichael]

My D782 emits a small puff of black smoke when it starts up. Just a small amount. If I start it without using the glow plugs it emits a little more. Never to the point though it smokes me outta the garage when I fire it up. Gotta wonder what it means "tuned it for more power". Has me scratching my head

 

[Roadworthy]

Your friend messing with the power is probably the cause of your smoke. He could have altered the timing or increased the fuel injected. The dealer can probably solve your problem but to do it yourself you would probably need the shop manual as nobody here will have any idea what he did.

 

[GMCRanch]

Ok, thank you. Sort-of what I anticipated not knowing myself. I wasn't entirely sure what to think either other than an injector hanging open or too much fuel. I'd like it to produce as little smoke as possible of course. I'll call the dealer and see what their theory is and go from there. Thanks!

 

[GMCRanch]

I have a follow up question on the fuel pump, I'd read they can shim them to adjust the fuel timing and there is an adjustment bolt on it as well. Wasnt sure if there were stock specs on it somewhere in the service manual maybe?

It also needs a water pump and I'd like to flush the coolant system, it's a little merky like they ran too much water and not enough coolant or it's just old. I saw the drain on the radiator with the rubber cap on it and also saw a drain cock on the side of the engine next to the oil dipstick. Which is best to flush the system with assuming the drain cock goes into the water jacket on the engine? Might as well flush it since I'll have to drain it and refill it for the new water pump. I'm sure this machine had a harder life than they led on when he got it from the church that had it new and whatever he did to it before I got it from him.

 

[lmichael]

Don't be surprised if the drain on the engine does not flow. I had to take mine off and clean out all the sediment. I suspect (possibly) very hard tap water was used in the machine. I gave it a thorough flushing with distilled water and then filled it with good green type antifreeze mixed to proper ratio. So far engine is doing just fine. System holds pressure well, does not leak a drop.

 

[GMCRanch]

Don't be surprised if the drain on the engine does not flow. I had to take mine off and clean out all the sediment. I suspect (possibly) very hard tap water was used in the machine. I gave it a thorough flushing with distilled water and then filled it with good green type antifreeze mixed to proper ratio. So far engine is doing just fine. System holds pressure well, does not leak a drop.

I'd venture to guess this will be the same way. I noticed rusty water blown back from the engine fan and saw the water pump was wet. I have the Prestone flush concentration to run through it most likely while I cut my grass later this week when it's not 100° outside. Be a good test to see if it overheats tho. I ordered an OEM water pump and gasket, the thermostat and gasket, and the upper and lower hoses also. I will most likely replace the radiator cap and the belt while I'm in there too. It's a new radiator at least so hopefully it will at least drain. I plan to run it with the flush concentration in it then let it cool then drain the system and pit my garden hose into the radiator and let it idle with the hose running until it runs clean and clear then pour the premix antifreeze (also Prestone) until it just starts to leak green to ensure the water is out and fill the system. Hopefully that takes care of any future issues.

Then I'll hopefully get the smoke issue fixed.

Has anyone had any luck adjusting the parking brakes on these? It feels like the right drive wheel is hanging up compared to the left and the brake doesn't hold the machine. Like it should. Its kind of a PITA to use as well but that's most likely me not fully understanding the manuals instructions on using it. I just hope the drive motor isn't on its way out which is possible. The mower has the super udt in it and it's crystal clear in both drives and the transaxle. I just replaced the filter and topped everything off with more super udt and will change the fluids completely in the fall before I store it for the winter.

 

[Joe Messmer]

I've adjusted the brake on my ZD21, just followed the details in the manual, in fact I think I've adjusted it twice in the 18 years I've owned it. Without consulting the manual I couldn't tell you how to do it but I remember it being simple to do.

 

[lmichael]

I plan to run it with the flush concentration in it then let it cool then drain the system and pit my garden hose into the radiator and let it idle with the hose running until it runs clean and clear then pour the premix antifreeze (also Prestone) until it just starts to leak green to ensure the water is out and fill the system. Hopefully that takes care of any future issues.

Be VERY careful. Doing this can cause the engine to overheat in spots due to the cold tap water artificially keeping the T/Stat closed. It's not like the old days any more. The only way that is "safe" to do is to remove the T/Stat than continuously run clean water through. Than drain and fill with distilled and coolant at proper mix. But DO NOT do that with the t/stat in the engine. Drain it, fill it with distilled water, run and bleed it on the plain distilled. Drain and repeat until all is clear. Than fully drain it and repeat until you get perfectly clear water. Then fully drain it one last time and refill it with either premix or buy concentrate and mix your own with distilled water. Distilled water is so cheap there is no excuse to not use it.

 

[GMCRanch]

Lmicheal, That's good to know, I'm glad I didn't proceed without caution and potentially split my block unknowingly. What was more concerning is my local dealer mechanic mentioned that being one of the methods they use and he didn't mention the thermostat removal. So that's what I will do then since using hose water will most likely just counteract what I'm trying to do if I understand your post fully.
Do you not suggest using the flushing concentrate? I've used it in vehicles before but wasn't sure if it's a waste of time in this application or not. My end goal is to try and get this mower cleaned out and back to as new condition as I can get it and go through the machine as much as possible. Get it mechanically sound and hopefully get many more years of service out of it.

 

[GeoHorn]

As a former auto mechanic for 30+ years I can only say that EVERY TIME I used a cooling system flush chemical the water pump failed shortly thereafter.
I see you plan to replace the pump anyway after your flush so I guess it makes no difference in your case.
I recommend you do NOT actually WORK your machine with flush-chemicals in it…and after you do flush it per the chemical instructions… drain it while it’s hot rather than wait for it to cool down. IMO.
The fastest way to drain it with vigor is to open the lower radiator hose.

 

[lmichael]

I am not a fan at all of chemical flushes unless the cooling system is so fouled up there is no flow. Modern coolants hold corrosion and stuff down pretty well and even moderate care prevents serious restrictions. Good ol' plain distilled water, run as needed followed up by a full drain and mix of whatever coolant is required. I drive only Toyota's so I only use their pink HOAT type of coolant. Apparently good ol' plain green is fine on these Kubota's or I guess the All Makes All Brands type i.e. Prestone Yellow (and there others). I only used concentrate on my G2160 for two reasons. I had a jug of brand new Mopar coolant left from the days my buddy and I had our repair business (we specialized in Chrysler mini vans), and because I flushed it with distilled water I did not know for sure how much water would remain in the block afterward even with a full drain. So I premixed the concentrate at 60/40 rather 50/50 just to be sure the end result in the engine was as close to optimum 50/50 as I could be. When I know for sure an engine is good and has only used proper coolant (i.e. like my Toyota(s)) I do a simple drain and fill with the proper premix in my case Toyota pink. Next time I do the Kubota I will fully drain and use a quality premix as well

 

[GMCRanch]

Ok cool, I'll shelf the concentrate then and just wash it out with the distilled like you all suggested. Guess I don't know as much as I thought I did, but, that's why I asked and signed up here. That would be my luck trying to do the best thing to take care of an older machine and in turn hurt it worse unknowingly. I was just thinking about getting the rust out of the block but I'm sure flushing it until it's clear will achieve the same thing.

 

[lmichael]

Don't get me wrong. Sometimes you gotta do it. But I have seen chemical flushes do some harm. I have seen the old timers (people who got in the wrenching gig long before I did in the late 60s) use a little TSP in the flush water (basically dishwasher soap like Cascade or such) but back then engines were all cast iron. No aluminum and nothing to get eaten up. If you use chemical, I would say go REALLY easy with it

 

[Barry Moules]

Hey all, new here but a 6 year Kubota owner. Love their machines. Recently purchased a 2006 (so I'm told) ZD21F from a friend of mine. He recently replaced a laundry list of parts on it and it smokes on startup for about 5-8 seconds when it's cold and clears right up after. It is a blueish white smoke and smells like raw fuel. Once it's warmed up it just emits the typical small poof of black smoke when re started. Even on hard acceleration or under load it barely smokes otherwise and if it does its black. He replaced the fuel pump and filters and rebuilt the injection pump and replaced the injectors and says he turned it up a little for more power. How do I adjust it back a little? I hate getting gassed out of the shed. I don't know much about the D782 that's in it so I wanted to ask here before taking it to the shop. I also noticed the pump seems to be very slightly wet with diesel fuel. I need to triple check the bolts to make sure it's all tight but nothing seemed loose the other night when I cleaned it after mowing.
Thanks and I appreciate it! Lots more questions to come I'm sure.

 

[Barry Moules]

Check your glow plug relay

 

[GMCRanch]

Check your glow plug relay

If the relay isn't functioning properly will the glow plug light come on and then time out after a few seconds? That part appears to work properly at least. It doesn't hesitate to start it just seems like it's got excess fuel sitting in the combustion chambers. But I'm not 100% sure on either.

 

[whitetiger]

Check your glow plug relay

There is no glow plug relay on a ZD21.

 

[GMCRanch]

Sorry for the delay I've been a lot busier than I wanted to be but I did get the water pump replaced on the ZD21 and the coolant system flushed. It was nasty for sure but it's got new everything at this point. Replaced the hoses, thermostat, of course the water pump and respective gaskets, and the belt since I was already in there and it was shot. I cleaned everything out as best I could and filled it with fresh 50/50. It seems a lot happier than it was for sure and the Temps are holding on the cool side of the gauge. I mowed with it some today (nice 97°) day to see if it was going to leak or overflow/overheat etc and no issues. I let it cool and checked the coolant I the reservoir and the radiator and both were nice and green so I think I got the rust out without using the chemical flush like we had discussed.

I also replaced the fuel sending unit so now the fuel gauge works again. While fixing the broken air cleaner bracket I noticed the soft fuel lines that run under the hard lines for the injectors and behind the stop solenoid were cracked and ever so slightly leaking so I replaced those as well. It definitely seems to start much easier but it still smokes more than I'd like it to and seems to stutter a little for the first 5-10 seconds it's running while cold. I checked all the bolts on the reman pump and what appear to be either new or reman injectors that the previous owner installed, everything was tight. Bit frustrating not being able to fix that myself. I filled it up with fuel and added some injector cleaner into the tank (probably snake oil but I thought maybe its just a dirty injector) so that might help, or if one is hanging up but I plan to take it to the dealer for a full once over after mowing season this fall. I appreciate your input and pointers and hopefully I will be problem free with this mower for a long time to come. Or at least I hope so.

 

[lugbolt]

make sure to ask the dealer to do a compression test before doing anything else. That'll give you an idea of the condition of the engine's internals.

Then ask them to do a valve adjustment just for kicks and giggles. Ask them for a worksheet. In other words, have them log the clearance before and after adjustment. I'd be surprised if they are much more than .02-.05mm off either way of spec. Then have 'em do a compression test again after adjusting the valves. These little diesels (well anything smaller than about 2.0L of displacement) are really sensitive to compression gas leaks, in other words it don't take much to bleed off enough air to make them run like poo. The usual complaint is that they're hard to start and/or smoky/rough starts. It just gets worse over time to the point where that cylinder will just not run at all. Diesels need to compress air to a pressure high enough that there is sufficient heat for the fuel to ignite almost instantaneously, on most of the Kubota's, typically 400 psi or greater. They'll run at lower pressures but again they get smoky and loss of power becomes an issue.