JD 425 carb rebuild followup-HELP!

This post is a followup to a post from about 6 days ago:

I thoroughly cleaned out the carb on my '97 425 after running poorly. I removed seemingly everything that was plastic or rubber before soaking carb body in Berryman's cleaner. I also removed and cleaned jets, choke shaft, throttle shaft, idle mixture screw, etc. In other words, I removed everything that could be removed, cleaned them, blew everything out with air and re-assembled.

My problem is this: Even though I can see that the throttle plate is closed, I can easily start the engine, but it will race until I shut it off. Moving the throttle lever will open and close the throttle plate properly, but it races like a raped ape until I shut it down(which is immediately).

I tried adjusting the idle mixture screw, even closed it completely, but the engine will still race with the throttle plate closed.

I did replace the gasket between the carb and intake because it was torn. It is not upside down and can really only go on one way. Carb seems to be properly tightened down.

The engine can only race like this if it is getting a lot of air, correct? Am I looking at some sort of leak possibly or?

Thanks for any ideas, the lawn needs a good mowing now!

I should have added that the choke works properly. I need to start it with choke on, but when I open the choke, it races.

Are you sure you put the linkages back in the correct place?

First, make sure the butterfly moves freely and it is not binding up on anything.

Second, make sure the linkages are in the right place. Make sure idle screw for butterfly allows the butterfly to close.

If it did this before the carb rebuild, the governor could be broken inside the engine(I am thinking small engine). If it is a real tractor engine, the governor works a little different.


Third option is to check/adjust the governor. I mention this with caution. Some engines are very finicky about governor adjustments. I find the Tecumseh and Briggs are easier to adjust. Other brands can be complicated. Only check this as a last resort.


I had one engine that did this. It took me a while to figure it out. Someone crashed into a tree or something but didn't dent the hood. The hood hit the engine sheet metal and pushed everything back enough to bind the throttle linkage.

They can surge when there's an air leak somewhere or if the governor is messed up. I'm not familiar with how your motor is
laid out, can you see the linkage between the carb and the governor? If so start it up and watch if the governor- is it
pulling the throttle open causing it to race? If so the problem is in your governor or linkage. Try pulling it closed and
see how much force the governor is pulling the carb open, sometimes things get unhooked and they flop open. I'm not
familiar with the governor on your tractor either but when messing with governors you need a manual unless you've been
trained/taught or have a lot if experience, even with the manual it can be frustrating.

If it's not the governor and it not running so fast you're worried about things on the inside of the block exiting take a
can of carb cleaner and start spraying on the carb and manifold. If you spray an area and the motor starts acting normal
that's where your leak is. I've heard of some folks using propane the same way, spraying propane gas on the engine so the
engine is sucking propane through the leak returning air/fuel mixture to somewhere near normal. I've always been to chicken
to use propane.

What can happen? I bought a snowblower from a co-worker, he said "it sped up real fast, made a loud noise, and then it got
real quiet". I did a post-mortem on the engine, the plastic cage for the governor weights failed, it pulled the throttle
wide open and the motor free-revved- I'm not sure if the rod broke or it seized to the crank and then broke but anyway
broken rod, crank journal with aluminium deposits fused on it and a big hole in the block from rod pieces leaving the
crankcase.

rrobert and wisbaker,

Thanks for responses. The engine is a Kawasaki V-twin 20 horse liquid cooled. I can look down the throat of the carb when it is racing and see that the throttle plate is closed. Now by closed it is actually open about 1/8" on either side. I assume this position is idle as it shuts off with a key. I made sure that the idle screw allows the butterfly to close as far as it can. Working the butterfly open and closed does nothing - it still races.

I don't think the governor comes in to play here as I can physically see the butterfly is closed. Looks like I'll be taking it off again, must be some kind of air leak you think? I've heard of spraying carb cleaner, propane or other things around to check for leaks. Normally if you had a leak and did this, it would cause the engine to speed up, correct? If mine's already racing, I wouldn't want to do this would I?

Thanks,

Dan

Hi,
You might check to see that the governor arm has not slipped on the governor shaft that comes up out of the rear cover. Loosen up the governor arm, the little bolt that holds it is left hand thread if I remember correctly. There is a little hole in the top of the governor shaft, stick something in it to turn that shaft as far as it will go ccw. While holding it as far as it will go ccw, move the governor arm to hold the throttle plate wide open. While holding the parts in these posistions tighten the arm on the shaft. Hope this helps.

I am thinking that your throttle plate is either not installed properly (inside out or upside down) or that you have a linkage problem. The throttle plate should be able to fully close to regulate the air going into the engine and with an unloaded engine 1/8"open is way too much air.

Heywood and t.r.k. good points I will check them after I get home from work tomorrow, thank you

I have been thinking about this problem t.r.k.you may be right about that throttle plate being in there the wrong way.I know a STX38 or a LT133 i can't remember came in running all erratic and one of the screws had backed out holding the throttle plate to the shaft.Anyway Kohler instead of this Kawasaki but it did remind me of this situation.What town do you call home?Biscoe,NC here.Later

an 1/8" is a lot and will cause the racing with no load.

The linkage should allow the plate to almost touch the throat. sounds like linkage binding or misadjustment.

If you can see the butterfly closed,and the engine
is running away i don't know what to tell you my
friend.Believe me i am thinking about you're
problem.Maybe you should come on a fishing trip and
forget about that Kawasaki engine for a bit.

Hi-My 425 acted the same way- I ended up replacing governor,camshaft & anything related to the fiber gears on the front of the engine.

Success!

Thanks to all you guys I figured it out. I feel pretty stupid really, I had the idle adjustment screw in backwards! When I put it back in I referenced the drawing from the manual, but the carb was upside down! Doh!!!! When I mentioned that the plate still had about 1/8" on either side and wasn't really closed, t.r.k. said that was really open enough to allow the engine to race. Well, I took the carb back off, thinking I might have had the plate on backwards. The plate was fine but then I noticed my backwards idle screw.

Put her back on and adjusted the governor (thanks Heywood). She fired right up and idled down appropriately. I noticed she revs pretty high if I let her, so I still need to adjust that. One thing I did notice after the carb clean is that my 60" deck fired right up when I popped the button. Previously, I needed to let her warm up forever before the deck would fire without killing the engine. The governor seems to work fine also,

Thanks again to everyone, you guys are great, thanks for saving my silly butt!

Well Dan that's good to hear.Congrat's