Any help diagnosing this would be appreciated. Purchased KX41 as a project with this condition. Bogging under load - 3300rpm will drop to 1800rpm when any load is added (See Video at bottom) This includes crawling, raising and lowering boom, etc. Seems to get worse as it warms up (drops 300-500rpm when cold but 1300-1500rpm when warm) Doesn't smoke any colour at any time in the process. Here's what I've done so far: emptied and cleaned fuel tank (had water, rust and gunk) replaced fuel filters (clogged with water and gunk from tank) replaced fuel lines (lines were brittle) - had injector pump and injectors tested - tested ok bled injector lines replaced engine oil and oil filter replaced thermostat and coolant (thermostat was stuck open) air filter had already been replaced - exhaust is clear checked governor spring, forks and flyweight. Warn but nothing broken or missing Let me know if there's anything i can add to help diagnose this.
I don't think the rack is making it to full travel or working freely. When you move that lever it should go to 3k RPM instantly, not lazily as it is doing. Same when you remove load, it should instantly spring back up to full RPM. You can check for adequate fuel flow by repiping the return out of the injection pump to where you can watch it. If fuel flow is too low, the return will stop flowing when you load it down, but I don't think that is your problem.
Thanks Birken Vogt. The slider plate on the injector pump has free and full movement. I could try wind the fuel limiter screw out further. Maybe that has been fiddled with. That's the only thing I can think of that could limit it. Regarding the slow RPM movement when adjusting the throttle. Where it is now is a lot better than where it was. Previously it was taking a good 20 seconds to drop from 3000RPM to idle. I got it down to the current 5-10 seconds by setting each of the injector pump barrels slightly clockwise of centre. Previously, pump barrel TWO was sitting centred while pump barrel ONE and THREE were slightly clockwise of centre. Which I'm guessing means that cylinder TWO was being delivered more fuel than the other two.
Agree with BV.!!! That rpm should “snap to” when you move that throttle.. R u absolutely sure the rpm’s should run to 3200.?? Back the throttle down to 2200 and try the test again.. It sounds like the max fuel has been tampered with..there should be a center screw in the max fuel setting.. that’s your torque screw. That lagging rpm is a sign of an issue.. if things aren’t moving freely, you’ll never get the bog out of it.. Remove the pump and shake it to the side.. the control rack in the pump should fall to that side..now the other.. If the rack doesn’t move to its stop limit, u have pump problems..
At the start, it would eventually warm up to about 2800RPM but the throttle response issue was way worse (it would take a good 20-30 seconds to come down from 2800rpm to 1200rpm when the throttle was moved from full to idle). I noted that IP barrel 2 was centred but that other two were slightly clockwise. I theorised that IP2 was trying to keep the rpm higher than the other two and so fighting each other on the way down. I adjusted them all to centre but that resulted in the rpm slowly taking itself to 3000rpm while the throttle was still on idle. So I adjusted them all slightly clockwise. That brought a steady idle and a faster deceleration response time (the 5-10 seconds it is now) but also resulted in max RPM of 3500+. I think the specs say 3000RPM should be max.
Fair chance. Are you suggesting it needs to wound out more (increase max fuel), or wound in? What do you measure when adjusting this? Do you just wind it out in 1/2 turn increments until you hit black smoke and then wind it back in a 1/2 turn?
I have had the pump out and can confirm that the rack slides freely. I have also had the governor shaft out to check movement of the governor forks and all move freely.
So to pursue this some more, if the adjustment of the IP barrel twist improved the throttle response time, maybe it needs some more adjusting. Also, I'm wondering if the fact that the IP barrel 2 had been tweaked, that the previous owners had made the adjustment to compensate for an issue on that cylinder.