[B7500] Frequent loss of RPM (almost stall)

CBearse · Mar 5, 2015

So on our B7500 Kubota, we've been having some type of fuel problem (i assume). after the engine has warmed up and when we're working at cruising RPM's (2.7k) it will suddenly drop to under 500RPM, then raise back up again. Sometimes as frequently as every 20-30 seconds and other times only once or twice in an hour. it idles fine.

We've changed the fuel filter multiple times. changed the fuel pump. we have a replacement air filter, but the old one doesn't seem too bad.

i'm wondering if anyone else has had this problem, or has any tips.
if you need any more information that i left out, let me know.

Any help would be greatly appreciated,
Thanks.

2002 or 2003 Kubota B7500 series 21hp 3.0L 4x4

rentthis · Mar 5, 2015

It could be as simple as cleaning out the fuel tank. You may have an algae bloom blocking the line or more likely something in the tank blocking the fuel pickup or water. Sometimes you get trash that will move off and back on the pickup causing the problem to be intermittent. Check it with your flashlight. You will probably have to drain the tank to see. When draining the tank, if the fuel is slow to run out of the fuel line, that points to one of these problems.

Dave_eng · Mar 5, 2015

CBearse said:
So on our B7500 Kubota, we've been having some type of fuel problem (i assume).

If it has been near 0 F then gelling of the diesel fuel could be your problem.
This is a situation where, at cold temps, wax crystals being to form in the fuel and the first symptom is from the blocking of the fuel filter which sees the crystals as being like dirt particles. Water in the fuel from condensation is also possible as it freezes and restricts or blocks flow.
Is it possible you are trying to run on fuel that was purchased when the weather was much milder?
The solution comes in several forms:
Drain all fuel from the tank and filter, refill with diesel from a truck stop where lots of diesel is sold as this fuel is going to be a cold weather blend. Next you need to ensure the filter is full by bleeding any air out. Finally, get the tractor somewhere warm and give it time to sit there to ensure everything is fully warm. Immediately start and use the tractor to get the new fuel throughout the system.
An alternative is to look in truck stops or auto parts shops for special additives designed to deal with fuel gelling. You need to get the tractor warm and then use it to ensure the additive is circulated throughout the system.
Southern truckers who head into the northern states can have this problem as they don't have a suitable fuel on board. When the truck sits overnight they don't want to start.
It is possible that the vent for your fuel tank is plugging. Try loosing the cap when the tractor starts doing this to see if it will cure it.
Dave M7040

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[B7500] Frequent loss of RPM (almost stall)

CBearse

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rentthis

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Dave_eng

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