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425 slowing/power question- just purchased

3198 Views 14 Replies 8 Participants Last post by  jcolegrove
Hi all,
great forum... thanks!
long time JD owner (110, 112, 318, 214, 325), first time 425 owner and poster. Just got a 425 w/ 900 hrs. and 54" deck. I purchased b/c I wanted something bigger/ more powerful than my 325. I'm surprised that at wot, when I engage the deck, engine speed drops maybe 10-15%. when i then go forward, it drops again a bit and is dependent on if going up hills on how much it drops. mowing medium grass and stopping/ starting forward, engine speed varies a bit in that probably 10-15% area.

my question is: do other 425 owners experience this? is this normal? my 325 could maintain engine speed under those conditions, and so could the 214, 112, etc. i know it's running on both cylinders and compression is 185psi in each cylinder. would think that this big engine could keep wot rpm's constant.

thank you!
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Check linkages and such for binding. Also, is there a fuel filter? How old is it?
maint. was just done. do you mean governer/ throttle linkages for bindage? i assume so...
Yep. Exactly.

Not sure precisely how the governor works on that tractor, but I think that is the first place I would start looking.
As far as going up hills, the engine should sound different (ie meaner), but not seem like its burdened. The trans might whine a bit.

Regarding the PTO engaging, I don't know of a tractor that doesn't bog a tiny bit (10-15%) when first engaged. Even diesels...

I agree with the governor or carb out of whack. If running too lean, it may cause this as well.

So far you have gotten some good advice..

What will tell the tale is to:

A) Remove and Read your Spark Plugs! Nothing will tell you more about what is going on with your engine than that.. If the plugs are OK-

B) Check Compression. The Kaw FD620D engine in that should be pretty high if things are right.. ~190 PSI and fairly equal on both cylinders.

C) The deck AND the travel speed share a common bond: The transmission! Lift the seat up and check the level/ appearance of your fluid. A plugging tranny filter may also cause your trouble and even worse it can starve your pump! If it's whining- Service the thing pronto before you have a costly problem on your hands..

Fire back with any more questions.. :fing32:
Ditto to WNYTT, Start off with new fluids and filters. Engaging the PTO is akin to starting your car, hammering the gas pedal and putting it in drive. At low rpm's engage PTO (no load) and throttle up.
thank you all-- i hear what you're saying.
just to clarify though-- it has new trans filter and fluid, etc.

i know that when first engaging pto, every engine/tractor will bog- all my prior ones did, as listed. but this is different, it never recovers to full wot, unloaded, rpm. either when just sitting still running pto w/ wot; or even w/o running pto, but simply somewhat aggressively starting out, and certainly going up an incline.

i have not checked the linkage yet, but will. will also check plugs when i get home. very curious if other 425 owners have similar issue of it not being able to hold wot rpm when under load. it's close- probably 85-90% of wot rpm, but never recovers. thanks!
For initial PTO engagement I have to have things turning pretty good.. About 1/2 throttle and it just about kills the engine.. Once the deck is warmed up the PTO starts up easily at lower speeds. All the bearings are new and the gear box is fine, freshly lubed & serviced. It just is a bear for that 20HP Kawi to move all at once and keep things going. Once the thing is turning I go to WOT and the thing rocks right along and doesn't miss a beat and will blow right through deep grass! If your's doesn't I'd suspect you need help in the engine dept. or Governor / carb. settings to make things run @ the proper power levels.. (provided your deck isn't binding up!) :goodl:

Here's a manual:
Verify that it's running on both cylinders.
I have a 425 and if I do not let the motor warm up just a bit when I engage the PTO for deck, it will kill the motor or really bog it down. Also if I hit super thick grass and the previous row's cuttings it can bog things down unless I go slow. Going up hills, I always lose traction before the engine feels the load and I have ag tires on the back. I am not sure of the true hours on my engine because it is a replacement engine a previous owner had installed. I am guessing around 700-800 hours since the total tractor time is over 1500 and it's a 1993.

So some of your symptoms sound relatively normal (at least too me). Working extra hard going up hill doesn't sound very normal to me, but you have to remember it's a small 20hp motor so it isn't super big on torque.

Like others have said, I would check the fuel flow first since you said the compression is good. You can also check the foot pedals to make sure you have full range of motion but I seriously doubt it is that. If you are concerned about the hydro, I would get a pressure gauge and check it. That would tell you the health of that hydro.
I bought a 425 with a bad engine (Camgear) and rebuilt it. I had the same problem with a lack of power. I tried to adjust the governor a couple times but it still was not right.

The governor spring looked like it was stretched a little so I replaced it. The engine now is a real powerhouse. The spring is PN M76110 and cost $3.18.

Re: 425 slowing/power question- just purchased- FIXED!

thanks to all... after verifying it was running on all cylinders, i had a feeling the engine was over-revving. this just from experience in owning others, etc. got out tach and sure enough, a unloaded wot, rpm was 4400! that 800 over max. so adjusted governor per book and now it runs perfectly.

so... problem was that it sure WAS running slower when loaded at all, but it was just going from 4400 rpm down to where it should have been, about 3600 rpm.

now can run full speed through anything w/ blades on and engine doesn't bog a bit.

my only concern... how bad did the engine get hurt by running at 4300-4400 at wot unloaded and how long had the previous owner been doing that... doh!
You may want to check the valves and see if they are adjusted right. That's usually the first thing to start having issues if you over rev something. I would check the lash and then if you have the ability to check valve spring pressure. You are probably fine though if it runs like a top, now that you adjusted the rpm's. Glad you figure it out.
thanks again... all checks out now except i'm going through oil like crazy. seems to be both leaking and burning as I can see it all over a formerly clean engine and it smells like crazy with white smoke most of the time. very good power though and compression.... any thoughts?
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