Hi! I was mowing with my tractor when it started losing RPMs gradually. Eventually, it idled down and then stalled completely. I replaced and bled the fuel system, but it still won’t run properly. It starts briefly, but then dies out as if it’s starving for fuel. After leaving it sitting for a few weeks, I tried it again, and it will idle with the throttle pulled back, but won’t go above 800-900 RPM. The lift pump is old, but it seems to be pumping fuel. Based on these symptoms, what do you think could be the issue? Any suggestions would be greatly appreciated! Also, I meant to say that I changed the filters and bled the system.
It sounds like you’re dealing with the classic “flex ring” issue. Here’s a quick way to check: remove the return line at the top of the injection pump, then take out all the fittings down to the aluminum cover. Start the tractor without the fittings and line. Does it run and rev up? If so, the fitting might be clogged—clean it out, as it contains a ball and spring that can get blocked with debris, causing the engine to shut down.
If it’s indeed a flex ring problem, the engine will continue shutting down, and you’ll need to have the pump repaired. I can help with that if you need it. The 4020 models used two different “Rossa Master” pumps: a CBC and a JDB. If yours is a JDB, follow the steps I mentioned.
I’ve removed the input line and fittings and cleaned the screen in the fitting, but I haven’t done anything with the return line yet. The return line is on the side of the pump, while the input is on top. Is there also a screen inside the return line for this type of pump?
Thanks for your response, and I appreciate any additional information you can provide.
Yes, it’s on the ‘side’—actually, it’s on the top, the brass fitting.
Great suggestion on the return line plug! I removed the line, found the debris you mentioned, cleaned it out, and ran the tractor with the line removed. Afterward, I hooked up the bush hog again and mowed for about an hour, but then it started losing power just like before. It stalled before I could get back to the shop, so I pulled the line in the middle of the field. While I didn’t notice any obvious blockage, it fired right back up, and I was able to mow for a couple more hours without any issues.
You mentioned a flex ring—what exactly is that? I’m still having trouble with the throttle not responding properly. When I push it up to idle, the engine wants to die, but if I pull the throttle back just a little, it revs up much higher than it should—WAY higher! I’m thinking a pump overhaul might be in my future.
Any additional thoughts or advice would be greatly appreciated! And by the way, thanks a million for all your help so far!!
There’s a lot of information out there on this issue, but it’s important to be cautious. Some websites might suggest this is a DIY fix, but I strongly advise against it unless you have significant wrenching experience. The problem you’re describing is often due to a broken flex ring inside the injection pump. There is an updated part that replaces the original plastic flex ring, but it does come at an additional cost.
Running the tractor with this issue, especially with throttle and governor problems, is risky. If the flex ring is broken, it can cause the RPMs to rise uncontrollably, leading to a runaway engine that could result in serious damage, like a rod going through the block.
As for the repair itself, the pump is relatively easy to remove. First, make sure to shut off the fuel and disconnect all the fuel lines and linkages. Then, remove the side cover on the pump using two flathead screws and drain any remaining fuel. You’ll see two lines underneath the side cover—one is stationary, and the other rotates. Rotate the engine until both lines align. After that, remove the nuts holding the pump in place, and you should be able to pull the pump out.
Just be aware, this is a job that requires careful handling and knowledge of your equipment. If you’re not comfortable with this level of work, it’s best to consult a professional injector pump rebuilder.
Just wanted to give a quick update. I took the tractor to a local shop that’s worked on my equipment before, and they rebuilt the injection pump. After dealing with another bit of debris blocking the return line, it’s all cleared up now. The old girl is running like new!
