Might have something to do with the governor.

Scott the governor actually controls the carb, and it sounds as if it's bouncing off of the governor due to a lean condition. Todays engines are set up so lean that they are barely stoichiometric. Add a little piece of debris that found its way into a jet or nozzle and you're all done. Beside soaking the carb and using compressed air, run a wire (I use the wife's floral wire) through every opening you can see. You may not find the obstruction until after the fact however it usually works on the Walbro's, Mikuni's, and Nikkei's.

I guess I forgot to mention that I did run a wire though every opening after I broke it down. This was the last thing I tried. There was what appeared to be a very very slight buildup in some of the holes but all of that is gone now and it still surges. Is there a way of riching the mixture or checking the governor?

Scott

I only have experience on the older Deere's. When this happened with mine I changed all the fuel lines. They were 20 yrs old. There could be a clog in the fuel tank where the fuel gets picked up. Or in the line between the fuel tank and filter. Attach a foot pump and blow out the line back from the carb. Realize I am not familar with your tractor. This may not be the right thing to do.

Hold the throttle linkage stationary (fight against the governor) and see if the engine smoothes out. If you hold the plate still and the engine runs smooth, it's in the governor. If not, it's in the carb/intake/heads. Good trick to narrow it down.

Okay, I'll try to hold the linkage stationary, tomorrow. I think I know what you are talking about. I know I have done something like this before. It definitely helps, I just can't remember to what extent. If I remember correctly it stops the surge completely and the engine runs smooth. I seem to recall thinking that maybe something needed tightening or a spring was loose. That was when I did some research on surging and came to the conclusion that it was most likely the carb. So lets say it is the governor. What would I need to do or look for?

BTW, all the springs look in good condition. The tractor has about 100 hours on it but has always been keep in a clean, dry shed.

Scott

I suggested it might be the governor, but I confess that I don't really know just how a governor works or how to fix one. I do know that it can require opening up an engine in some cases. I have an old Snapper LT11 that suffers from the same surging problem. It was strange. One minute it was fine and the next it wasn't. The first thing it did was to start running wide open when I was really trying to shut it down. I had been out mowing for about an hour and when I was ready to stop - the engine just took off. I could not get it to respond to the throttle and just shut it down. From that time on it started to surge. I watched what was happening. The governor would start opening the throttle until it was really revved up, and then it would let go and the engine would slow down, and then it would do it again, and again. I put a wire on the governor that let it go only so far, and that seemed to work.
The funny part was that even before I put the wire on it would stop surging under load. The mechanic at the Snapper dealer told me he thought a part of the governor had come off inside the engine. Wanted about $150 to find out. It's still not fixed, but I don't really need it anymore.

Good luck!

If it is the gov, normally just a simple external adjustment is all that's needed.

First off, thanks for all the replies so far. I think I am on the right track. I started the engine, immediately started to surge, let it warm up for a few minutes, still surging. I can stick a screwdriver under the governor linkage and apply very slight upward or downward pressure and it will stop surging immediately. At WOT, if I keep the linkage from bouncing up and down for a few seconds and slowly let go, it will not surge for 20-30 seconds. It then starts surging very little but quickly ramps up to the full on surge in a matter of a couple of seconds. Keep in mind the surge from high to low and back to high is less than a second.

I observed a few other things. It doesn't surge at idle, but starts at about half throttle. The spring from the throttle to the governor, at idle, has a slight amount of tension. The only adjustment I can see making, on the governor, is actually repositioning the linkage either up or down on the shaft that comes out of the governor. Would this be my next step?

I like my JD dealer but I don't want to think about how much he would charge. Especially, since he has to come get it or I have to rent a trailer.

Scott

anyone???

try weekendfreedommachines- all deere all the time

From your description I would be concerned first about the fuel delivery. Verify good fuel flow to and through the pump. Ensure the pulse line is firmly in place and fuel line ends seal well. If the one screw isn't doing anything, it could be due to the above or an issue in the carb itself. On parts breakdown, it shows that yours is a simpler form of these KAw carbs. Some had two little removable brass jets - one in the venturi that you would see with the carb on the machine. Did yours have these? (They are not shown) They physically can be switched but are not the same. Next, take some carb spray and look for vacuum leaks around where the carb mounts and the end of the intake manifold mounts while you are at it. If you haven't replaced the bowl seal and float valve do it along with the carb to intake gaskets.

The governor adjustment is how the arm is clocked to to the shaft. Not up/down. Sounds like a gov adjustment may be needed - but I have to say that is rare.

Does it surge if the deck is engaged and you are mowing? Honestly, if it doesn't surge under load the engine will do what's it's supposed to do (work). Try running some fuel injector cleaner through it and maybe it will work itself out if that's the case.

Yes, it surges while mowing. But it will stop if in really really heavy stuff.

There is that possibility of changing out one of the jets and also the float valve but they look perfect. I do need to check for leaks. Is there a trick to this using the carb spray?

Scott

The "trick" is: This works because the carb cleaner acts as "an extra shot of fuel". Have the engine idling as slowly as you can (without the engine dying). Now, spray along the seam or joint where the intake manifold attaches to the cylinder head (spraying with the little "straw" tube that comes on the can of carb cleaner). Rest the tip of the straw right against the seam and spray as little as you can and work along the seam. If you have a vacuum leak, you will hear a noticable increase of RPM from the engine when you "find" the leak. Also spray along the seam where the carb attaches to the intake manifold and listen for RPM increase. It is important to have the air filter in place while doing this to sort of "restrict" the air coming into the carb the normal way. The slight restriction created by the air filter makes it more likely for any vacuum leak sources to inhale the carb cleaner through the leak point (it also minimizes the chance of the carb cleaner being inhaled through the carb throat and giving you a "false indication" of a leak.

Thank you for that detailed description. I am going to try this out on Thursday or Friday.

Scott

FWIW I took out my Honda GXV530 powered Pro 150 today to do a final mow and suck up some leaves and pine needles before heading to the dump. The 16 hp twin roared to life with a flip of the key, only to die, buck, surge, etc. I drained a gallon of faint smelling fuel out of the tank and added fresh w/ sea foam, straightened right out. I probably haven't used the Gravely since July, and usually mix stabilizer right in when I get a fresh can full. Perhaps CRS* set in but the gas turns rapidly today, certainly something that shouldn't be overlooked.

*crs=Can't remember stuff

Well it looks like I have fixed the surge. There is a long rod and long very light weight spring that goes from the carb to the governor. I simply twisted the spring 180 degrees and inserted in the other side of the hole on the carb linkage. This gave it just a slight amount of added tension. Surging gone...

Given that this spring is so light weight, I wonder if it simply lost some tension? This can't be hurting anything can it?

Scott