Maybe it needs re-jetting, but first you should determine if the governor system is connected and working. Engine off and air filter out; see that the governor spring is holding the air vane all the way over so the throttle plate is wide open; the air vane should move freely and snap back to wide open; a small spring should be connected from the base of the vane to the sliding throttle member on top of the air box - this member must move left and right when the throttle lever is operated.
If it's all connected and apparently working, tension on the governor spring may be too light; turn the adjusting collar clockwise two clicks or more at a time to see if it stabilizes. This is a fine adjustment for engine RPM. If you can improve it's running this way, try it in some thick grass to see if the engine settles down with a load on it.

Sometimes the surging just shows up at the right atmospheric conditions. My commercial has been a great runner for years, but with the high humidity and cooler temps lately it surged badly the last mowing. Most of the time the surge goes away very soon or doesnt appear at all. You got a great deal for a couple bucks.

Couple being 2 twenties. I pulled out the pilot jet. It may be a stupid question, but it had 3 holes on the side and one microscopic little hole in the carb end base. Is it this tiny hole that would be oversized?

That tiny hole is the one. Just drill it until the small hole intercepts the cross drilled holes. Don't go out through the other end. Easy does it as the jet is soft brass and the drill bit will tend to grab and you don't want to end up with a broken bit stuck in the jet.

For lots of Lawnboy answers, come here.

Here is a link that might be useful: Link

Just to bump bc my original question wasn't answered. Is there another main jet replacement (and part number) that I can use rather than drilling oversize? I don't have the bits and have the carb apart for cleaning and would rather take care of this all at once. tHanks very much.

The pilot jet from a Suzuki 2-cycle will fit a DuraForce carburetor. It's orifice is slightly larger in diameter than the one on stock jet (40.5 vs. 37.5), which makes it a good alternative to drilling the stock jet.

The Toro part number for the Suzuki pilot jet is 94-1684. It was still available a few years ago, but it might not be available now. (I haven't checked lately.)

Hope this helps.

Orangedotfever....give it up already. I read your same comments on other posts. Provide advice, not advertising another site.

Tarheelman, thanks, but I already ordered the replacement alternative pilot jet from the R-Tek carb (42.5). I was looking for an alternative to drilling the main jet.

I'll see how it runs with the replacement pilot when it arrives. I cleaned out the carb, replaced the plug, put in an inline filter and cut off valve, and new carb gaskets. It started on the first pull. It seemed ok, was surging a little, but it was too late to try it under load.

droc:

Sorry about the info on the pilot jet---that's what I get for replying to a post after skimming it rather than *reading* it. :(

Since you cleaned out the carburetor, installed new gaskets, and installed an inline fuel filter, replacing the pilot jet might be all you need to do to cure the surging.

Good luck and keep us posted.

If your surging isn't bad I would try dirlling the pilot jet first. It's an easy job, an increase of just 0.001" over stock should do the job. The drilling instructions in this thread are correct - drill from the engine side using a wire gage drill (you can find the complete instructions on this web site as to the size) drill only to the cross holes and not the whole way through. I'm betting your engine will run 100% better my Gold Pro 10550 sure did! I just clamped the drill vertically in a vise, and by hand, very carefully, turned the pilot jet down over the drill with my fingers, however it's best mount the drill in a pin vise if you have one. -- Spray out the brass shavings with carb cleaner or WD 40 -- works perfectly! The drill you need can be bought on line for about $3.

MisMike, thanks for the reply. I ordered the R-Tek 42.5 replacement pilot jet - which was just 4 dollars. If I have to wait for the bit, I might as well get the new jet instead. Hopefully, it will run great.I'm just waiting for it to arrive. I can't wait. I also ordered the mulch plate on ebay and waiting for that. I was very pleased when the compression readings were 120 plus, which means the engine is like new. Now I have to search on posts about repainting the deck. Thanks.

I got a chance to run it today and it was bad. I have so far, cleaned the tank, replaced the fuel with a fresh mix, put an inline fuel filter and shut off valve, replaced the plug, checked the exhaust ports (clean), checked the governor spring (appears to work fine), cleaned out the carb and stock jets, and replaced the gaskets. I didn't replace the float, but I adjusted it to 1/2 inch. It starts right up on choke, but once out of choke revs up and down and eventually stalls. Under load of cutting the same. I'm hoping the new pilot jet improves this, but I think there might be another issue. I wasn't able to cut the lawn with this machine. Any other ideas other than the re-jet? Thanks.

Since it acts the same under load, I think you're right---there's another issue. Surging due to lean jetting doesn't cause the engine to stall eventually.

According to the Toro E Engine Service Manual (available as a free download on Lawn-Boy's website), possible causes for surging are:

1. Fouled idle circuit (Remedy is to clean it)
2. Air leak (Remedy is to check sealing surfaces, oil seals, & gaskets)
3. Restricted fuel flow (Remedy is to check filters and fuel line)
4. Engine RPM too low (Remedy is to increase governor spring tension slightly)
5. Air vane sticking (Remedy is to clean or replace)

You've cleaned the fuel tank, cleaned the carburetor, and replaced the carburetor gaskets. That leaves cleaning the idle circuit, checking the crankcase seal, the head gasket, and the oil seals, and cleaning the air vane.

Hope this helps.

I have that manual. I can't find anything in there about cleaning the idle circuit. Anything you can point to for a tip on this?

Unfortunately, I don't know of any source for information on how to clean the idle circuit. Hopefully, someone else on here does.

Anybody know what this means? Still trying to get this duraforce mower going

Fouled idle circuit (Remedy is to clean it)

It just means to clean the passages within the carburetor. I would remove the carb. remove the jets and needle and seat and use a good quality spray carburetor cleaner into every orifice, which there arent many on that little carb. Clean the jets good and the screen and any debris in the float housing. Inspect the carb gasgets for breaks or cracks and/or if possible replace the gasgets. Clean and reoil the filter too.

I finally got my parts and installed a new governor spring and put in the R-Tek 42.5 pilot jet. I have mowed twice now and it seems to run pretty good now. It's weird that the high speed setting for the mower is actually when the throttle plate is partially closed and the turtle idle setting is with it open. This is opposite of what I am used to on a car carb. I also noticed when installing the new pilot jet, that the 37.5 hole was much bigger than the new 42.5. I had oversized it, but maybe somebody else had already done it and now it was too big. I am reading the manual about setting the spring. It says a good starting point is four clicks. At this setting there is almost no tension on the spring. What tool can I use to measure the rpm's? Can I use a tach that I used to use on a car to set the idle speed?

Read my post again and check the air vane/throttle position. Also, you don't set the idle speed. The throttle has a RANGE OF MOTION. A higher high speed will also produce a higher low speed. Four clicks is not a 'starting point' - it's the usual amount of adjustment. If four clicks doesn't produce enough spring tension for high speed, turn it four more - repeat as-needed. As long as you have a blade and mulch fan on the crank, you can't really overspeed it. You will have to adjust it to not exceed the max blade tip speed of 3400 RPM for a 21".

Thanks Saxman. I think if I turn it up anymore, I'll see a couple of for sale signs pop up on my neighbors houses. This mower is so loud. I'll check that it is wide open with the engine off and air filter out.