B7100 hard start and over-speed after repairs

[Teenwith318]

Hello everyone, I am new to this forum!

Back in September, I purchased an early Kubota B7100 (manual-shift) tractor with a couple of issues. Unfortunately, it does not have an hour meter and it does look like the machine was well used judging by the original front AG tires which have about 1/4" of tread left on them (rear tires are new). The tractor was maintained regularly and burns no oil (5W40 synthetic Amsoil).

The main problem with the tractor was excessive white/gray smoke (smelled like unburnt fuel) especially during startup or while throttling up. The smoke was never clearing up even after the engine was warm. I have performed the following repairs attempting to fix my issue:
-Removed and cleaned the fuel tank
-Replaced all of the fuel lines
-Replaced the air filter
-Adjusted the valves (they were very loose)
-Replaced the fuel filter and o-rings in the fuel bowl and valve (there was junk in the bottom of the fuel bowl )
-Disassembled and cleaned the injectors VERY CAREFULLY (not mixing up internals) following the instructions in the repair manual.
-I have tested the injectors myself by connecting them to the injection pump with the lines reversed (so that I can see the spray pattern) and they do not appear to leak and have nice uniform spray patterns.
-Bled the fuel system as per the manual.
-I have fresh clean fuel in the tank.

After the repairs, it took me three attempts to start the engine, finally, it started with A LOT of smoke. I purged the injector lines with the engine running and confirmed that it is running on all three cylinders. Once the engine warmed up a bit, the smoke cleared completely and it is running much better than before with quite a bit more power (will pull that 6-foot blade in 6th gear mid throttle without any problem and no smoke). THE MAIN PROBLEM NOW IS THAT THE ENGINE IS VERY DIFFICULT TO START WHEN COLD AND EVEN RESTARTING WHEN WARM REQUIRES GLOW PLUGS. I have tryed purging the injection system multiple times, but it did not seem to help. It takes me about three attempts (and a minute of glow plugs) to get it going after filling my garage up with dense gray smoke which clears completely once the engine warms up. Also, low idle RPMs increased from 750 to 1200 and high idle RPMs increased from 2700 to 3200 (I did not make any adjustments to the governor).

I am not sure how to proceed with the repairs since don't understand what causes the hard start and overspeed issue after my repairs. Any suggestions appreciated!

 

[vic gerbasi]

L3300 very good machine, circulating heater put on it years ago when -20s plug it in starts right away when not quite so cold and no plug in glow plugs x2 starts quickly let it run to warm up.. as I read on this forum start let it run have a coffee then another cup then go to work slowly dont forget tans and hydto oil has to warm up I follow this routinely and it works even at -40

 

[Lencho]

Have you checked the compression? Did it start easy before the repairs?

 

[thepumpguysc]

Its possible the inj. pump control rack is sticking & not going into "starting fuel" & giving u fits while running..{surge in rpm}..
By chance does it have a removable cover below the inj. pump.??
If yes, remove it & see if u can access the pump control rack..disconnected, it needs to slide freely w/ no hesitation..
Good luck,

 

[Teenwith318]

Have you checked the compression? Did it start easily before the repairs?

Yes, it always started very well. Unfurtunently, I don't have a diesel compression tester, but I doubt that its an issue since in the fall when it was warm, it would start even without glowplugs.

Its possible the inj. pump control rack is sticking & not going into "starting fuel" & giving u fits while running..{surge in rpm}..
By chance does it have a removable cover below the inj. pump.??
If yes, remove it & see if u can access the pump control rack..disconnected, it needs to slide freely w/ no hesitation..
Good luck,

Yes, there is a removable cover on the side of the block where the injection pump mounts. I will remove it and see if I can access the rack. Is it possible that a stretched governor spring is not pulling the fuel rack into the "starting fuel" position and cause the overspeed issue?

 

[Teenwith318]

I have removed the cover from the side of the injection pump, and the fuel rack is moving freely without binding. The only thing that I noticed is that when I rapidly push on the throttle lever (from slow idle to full with the engine shut off), the governor does not move the fuel rack very rapidly (takes it about a second to open, but I am not sure if its because the engine is cold and the oil is thick). Also, in the full-throttle position, I can still manually push the fuel rack about 1/8" (toward the front of the tractor) before it actually hits the stop. Can this be an indication of a weak governor spring? Is there only one spring (the one visible under the cover on the side of the pump) or is there a second spring that might be broken?

 

[thepumpguysc]

Your gonna hafta get the book for the spring answer..
IDK about your mdl. but I***8217;ve seen them w 1 or 2..
I don***8217;t pay attention to mdls, cuz a pumps a pump to me..
Unless there***8217;s gov problems I don***8217;t pay attention to mdls.
The lag is prob from a stiff cable & u need to lube it.
The control rack should move total travel, stop to stop.

 

[thepumpguysc]

Sorry for the goofy looking posts.
I***8217;m on my phone.
Do u have anyone to help u?
If yes, start the engine & move the rack manually.

 

[North Idaho Wolfman]

Most likely you have a glow plug failure, glow plugs are used in both the pre heat (backwards of the switch) with indication, and in the crank position without indication.

Do you have an OHM meter, remove the buss wire between all of the glow plugs and test each one.

Report back with what you find.

 

[Teenwith318]

Here is a video of it starting up.
I never knew that the glow plugs are also on while the ignition switch is in the crank position! I will check that out tomorrow!

https://www.youtube.com/watch?v=kiPZv-TrgV4

 

[Dave_eng]

Here is a video of it starting up.
I never knew that the glow plugs are also on while the ignition switch is in the crank position! I will check that out tomorrow!

https://www.youtube.com/watch?v=kiPZv-TrgV4

You need to do the GP resistance check suggested by NIW.

Your testing may have damaged the GP's. GP's need the mass of the cylinder head to control how fast they heat up. Testing them in open air without being secured in say a vice allows the temp to rise too fast.

Applying 12 volts directly to the GP's is also a bad practice. The GP indicator is used to moderate the voltage the GP's experience. When the GP's are being heated in the start position of the key switch, the battery voltage is already being drawn down by the starter motor.

Looiing forward to seeing a video of your loader in operation.

Dave

 

[Teenwith318]

You need to do the GP resistance check suggested by NIW.

Your testing may have damaged the GP's. GP's need the mass of the cylinder head to control how fast they heat up. Testing them in open air without being secured in say a vice allows the temp to rise too fast.

Applying 12 volts directly to the GP's is also a bad practice. The GP indicator is used to moderate the voltage the GP's experience. When the GP's are being heated in the start position of the key switch, the battery voltage is already being drawn down by the starter motor.

Looiing forward to seeing a video of your loader in operation.

Dave

I will check the resistance tomorrow and report back.
I did visual check the glowplugs while they were in the cylinder head when I removed the injectors. They were clearly visible through the injector ports. It took them about 20-25 seconds to get bright red (with the ignition key in the glowplug position) and all three of them were heating up pretty evenly (cyl 2 appeared to heat up a little bit slower than the others).

 

[freewheel3]

Try doing the same cold start tomorrow, but only push the throttle open about a quarter of the way, instead of full throttle. See what happens.

 

[Teenwith318]

Try doing the same cold start tomorrow, but only push the throttle open about a quarter of the way, instead of full throttle. See what happens.

No difference at all. Smokes just as bad since the governor holds the fuel rack in the open position. Tried starting it at idle, there is less smoke, but it takes quite a bit more cranking.

 

[Russell King]

Looking at your video, the safety police want you to block the FEL up so it won’t crush you if it falls. It may already be blocked but not showing up in the video.


Sent from my iPad using Tapatalk

 

[torch]

Have you bled the lines to the injectors?

If you crack each connection in turn with the engine running, cylinders that are firing will cause the engine to lose rpm. Cylinders that are not firing will have little or no effect on rpm when the fuel line is cracked. If the line blows some bubbles then the rpm picks up and smooths out when re-tightened, that one had air in the line.

 

[North Idaho Wolfman]

STOP Running it!

You are dumping fuel into the engine and will cause damage if you haven't already.

The injectors are misassembled or damaged.

Pull them and either take them to an injection shop and have them tested and rebuilt or get a quality set of injectors to replace them.

Do not but cheap injectors off of ebay, or amazon or any of the sort of sellers as there most likely going to be bad injectors.

 

[Teenwith318]

I do have the loader blocked up when I work on it.

Injector lines where bled MULTIPLE TIMES and all of the cylinders are firing properly. The engine changes the sound exactly the same when I loosen any one of the injection lines.

The smoke clears completely once the engine is warm, it is not overheating (from too much fuel being injected).

I will get my injectors pop tested next week.

 

[Teenwith318]

***UPDATE***

The hard starting issue was caused by the glowplugs! When I measured the voltage on each one of them I discovered that #3 had 10.2 volts as it should and then #1 and #2 had around 6 volts. Turns out there was a bad connection at the #3 glowplug which did not supply enough current to #1 and #2. I think that the issue was caused by diesel fuel that got into the glowplug contacts while I was purging the injector lines. I removed all of the cables from the glowplugs and cleaned the contacts. Now I have 10.2 volts on all of them. The resistance of the glowplugs measured at 1.7-1.9 ohms which I believe is in spec.

Now I just have to figure out why is the engine misfiring. It will misfire before reaching full operating temp running over half throttle (misfires REALLY BAD for about 20 secs right after startup). Each misfire is accompanied by a puff of white smoke. Strangely enough, the misfire goes away completely if I loosen ANY ONE of the injector lines. I have also tried loosening two injector lines at a time and the engine will continue to run on just ONE cylinder (I tested all cylinders this way and the engine runs the same exact way on each of them). Maybe the added load from one or two cylinders not firing causes the governor to open the injection pump to push more fuel through the injectors making them fire properly? I am trying to determine if this is caused by sticky injectors or the injection pump itself... I will get the injectors tested on Friday and report back.

Thanks for your help!

 

[thepumpguysc]

That sure sounds like air in the system..
Have u tried PRESSURIZING the fuel system.??
THAT'LL show u something.. either dry all the lines w. brakekleener, sprinkle baby powder along the lines & bowl assembly & put a few lb's in the fuel tank & look for the wet spots.
OR just spray everything down w/ a soap & water & solution, pressurize the tank & look for bubbles..
Its best to have a helper.. that way they can spray while u run the air..
U DONT wanna blow up your tank so be careful.