Lawn Boy Gold Pro DuraForce 10525 with no throttle control/response

Picked up a 1998 Lawn Boy Gold Pro DuraForce 6.5 Model #10525 for about $40 since it wouldn't run. I could tell someone has already been into the thing so please keep in mind I have no running configuration to work with. It had the completely wrong plug, was missing a couple pieces, and had been someone creatively assembled in certain areas. I got all of that straightened out and just need to heli-coil one CDI mount point and it'll be all good then.

The problem I still have is no throttle control and it seems to surge. With the throttle on 'slow' vs 'high' I can't tell a difference in engine note/rpm. When I push it into choke I can hear the engine note changing and the RPM lowers a little but it doesn't chug. I have not checked the butterfly in the carb to see if it's 3/32 or not. Since I don't have any throttle and it surges all the time I think I probably have an air leak somewhere in the gaskets that sandwhich the carb to the head/reeds.

When I was pulling the carb off the 2 gaskets that bolt the carb to the heat shield and then the heat shield to the head ripped or separated. I used some regular gasket material like what you would user on a carb to intake gasket on a car and cut new ones but I don't think they're sealing correctly. I ordered new gaskets for the Air Box to Carb, Carb to Heat Shield, and Heat Shield to Intake but the Heat Shield to Intake gasket was wrong. The one that was on the mower was a square port gasket and the one I received was a round gasket like what you would put on the carb to airbox. The part # was 94-5795 and I ordered it from partstree.com. I'll double check how my home-made gasket sealed when I pull the carb back off this weekend. If it looks like it sealed good and no indications of it leaks then I'll throw it back on. I might find some spray gasket prep/tacky stuff just to make sure.

In my quest to get the throttle to respond to 'high' vs 'low' I adjusted the governor up and down a couple clicks. Eventually I got it to where it ran at a relatively high RPM all the time but the throttle still did nothing. I think I have to adjust that down a few clicks as I think it's over-revving and bouncing off the governor now too. Either way once it got to the point where it was running on high RPM's I fed it some grass and it seemed to run pretty good. It barely dropped RPM unless you went into 6" tall grass and even then it was good until the grass balled up under it. It did smooth out some when I hit the tall grass but I could still tell it was surging.

So, where should I proceed from here?

Things I've done so far:
- Replaced incorrect spark plug with an Autolite 2976 (couldn't find the NGK locally) $4
- Rebuilt/Cleaned carb $4
- Replaced 37.5 Pilot Jet with a 42.5 Pilot Jet (Briggs 803801) $6
- Replaced CDI with an identical looking one $15
- Replaced Air Filter $8
- New 21" gator-style blade $24

Things I've yet to do:
- Check butterfly in carb to make sure it's 3/32" hole
- Replace home-made carb gaskets with OE gaskets except the intake to heat shield gasket
- Helicoil one of the coil mount points that stripped
- Pressure wash it good


I will say that it has some pretty impressive power. Considering my old home despot special mower would bog down if you hit much of a thick patch of grass this thing was going through foot tall lawn like it was nothing. Can't wait to get it right.

Hello,

Did you drill out the main jet with a #67 (.032') drill?

Regarding the stripped CDI mount, is it possible to just drill and tap to the next size larger? Not sure if the holes in the coil will accept a next size bigger bolt.

Make sure the primer line isn't interfering with the governor operation. There should be a small white plastic clip that holds the fuel line and primer line together. If it's missing a zip tie works well in holding the primer line away from the governor.

It's odd the throttle has no effect on RPM,,,everything hooked up correctly?

When you move the air vane by hand, is there any binding? Any of the spray on gasket material get on the governor shaft?

Regards

Jeff

jp1961 said:

Hello,
Did you drill out the main jet with a #67 (.032') drill?

Click to expand...

Not yet. I am borrowing a buddy's mini drill kit. I've got somewhat conflicting information on drilling the main jet. Some say a #67 and some say a #68. Not sure which one but I'll probably start with the smaller one first. I'd rather error small since I can always go bigger.

jp1961 said:

Hello,
Regarding the stripped CDI mount, is it possible to just drill and tap to the next size larger? Not sure if the holes in the coil will accept a next size bigger bolt.

Click to expand...

The original bolt looks pretty tight in there to begin with. A helicoil should be fine in there plus I'm going to give it a dab of blue loctite to help it deal with the vibrations. Although now that I think about it the bolt that was in there was pretty short. Maybe it's not the original bolt and that was the problem to begin with. It possible it was too short and wasn't able to grab enough threads to be tightened down. When I dig back into it tonight I'll check the thread depth in the head and see if there's a different bolt that might still work. I usually prefer timeserts but buying a kit to do one mount point is a little drastic. The mower ran fine with just one bolt in the CDI so I think a helicoil will hold up just fine.

jp1961 said:

Hello,
Make sure the primer line isn't interfering with the governor operation. There should be a small white plastic clip that holds the fuel line and primer line together. If it's missing a zip tie works well in holding the primer line away from the governor.

Click to expand...

Funny you mention that, it was one of the parts that was missing when I got the mower. When I ordered the carb gaskets I also ordered it since it was $1.07. I do have one question on routing the primer line. I currently have it going up and over the throttle arm that the spring for the governor hooks to. I am thinking that when I re-do the carb I should route it so that it goes under the throttle arm. I have verified that the primer line does not hit the air vane but it still didn't seem quite right to me. If you could let me know how it came OEM that would be great!

jp1961 said:

Hello,
It's odd the throttle has no effect on RPM,,,everything hooked up correctly?

When you move the air vane by hand, is there any binding?

Click to expand...

I've verified that the throttle cable moves, that the mount tab on the throttle cable is securely mounted to the airbox on the inner most position towards the center-line of the carb, and that it does engage the choke butterfly. As far as I can tell that all is working properly. When I originally got it back together it wasn't engaging the choke right and I had to slide the cable mount in further. When in the 'choke' position the choke butterfly is approximately half closed. Hopefully that sounds correct. If the choke butterfly should be completely (or mostly) closed when choke is on then no, I do not have the throttle cable set-up right and I will need to figure that out. Hopefully someone can let me know!

jp1961 said:

Hello,
Any of the spray on gasket material get on the governor shaft?

Click to expand...

I haven't used any but was contemplating it. I usually don't like using the stuff as it for sure destroys the gaskets if you ever have to take things apart. It also means you have to spend a bit of time cleaning things and it's a pain to get off. It's 100% the way to go when sealing flanges or light weight things that tend to warp. I'm probably going to skip this and might try rubbing a light film of 30w oil on the gaskets to help them soften and seal. I am going to use my MAPP torch to test for a leak. Just turn it on without being lit and poke it around the heat shield to see if the engine RPMs or note changes. If it does then I found my leak. Acetylene works better but I don't have access to a blue tip wrench anymore.


I have been thinking about it a bit and I think one of the problems is that the governor spring lost all tension when I removed it. I think the issue might be that it just needs to be wound a turn or so to help preload it properly. Does anyone else believe this theory or am I just over-thinking it? If the spring tension was so low that every time it tried to rev it got cut off that would for sure generate surging behavior as well as make the throttle never respond. By default, how 'snappy' should the governor vane be? Should you be able to push it back with a business card laid flat against it? Should you be able to move it just by blowing on it? What kind of tension should I be looking for?


So list of things to do as of now are:
- Check butterfly in carb to make sure it's 3/32" hole
- Drill main jet to #67, optionally #68
- Retension or check tension the spring on the governor
- Replace home-made carb gaskets with OE gaskets except the intake to heat shield gasket
- Helicoil one of the coil mount points that stripped
- Test carb base/heatshield for leak with MAPP gas
- Pressure wash it good

Hello,

I'd replace the governor spring too, it's 1.06.

The choke butterfly should close completely. You more than likely, you need to adjust the throttle cable at the air filter box, pushing the cable towards the carb.

FWIW, I remove the carb and air cleaner as an assembly, after letting the aluminum heat shield drop down. The governor spring is quite fragile and you have to be careful not to bend it.

The airvane can be adjusted to get the factory spec of 3100 RPM. Turning it counterclockwise decreases engine speed. Try 2-3 clicks at first, if the engine is really screaming.

You can download a repair manual of the Duraforce engine on the web.

Regards

Jeff

Well it's up and running good now. I don't really have a tach to set the engine speed so I just did it by ear. It sounds pretty mean like it'd take your leg off without thinking twice so I'm calling it good. I might adjust it a little more after I mow the lawn. One things for sure you are pretty much speed walking if you put it in third gear. I've never seen a push mower cut grass at 5mph.

Turns out the throttle issue was what I thought it was. The adjuster was HALF A TURN out of place. Figured that out when I put it on the air box to see how much tension the air vane had. Was pretty obvious when it had none and the spring would bind if I tried to pull it around another turn. The spring still looked OK but I might still order a new one. I read in a few places that some guys put two springs on the governor in order to open the engine up more. I'll see how mowing the lawn goes today but I don't think I'll have any issue with power. Still for $1.06 I might get it just in case.

Put a drop of oil on the choke and throttle shafts and adjusted the cable. Choke closes mostly shut now. I'll probably try to inject some WD40 down all 3 control cables for good measure. I think the last bit of choke I'm missing is the control cables sticking in the jackets.

Turns out I had hooked the primer line up wrong. It was hooked to a hard plastic nub on the very top of the carb. So basically I had no primer at all. No wonder the damn thing was hard to start the other day and needed starting fluid. Don't worry, this wasn't my first, and surely won't be my last screw up.

Throttle plate was the correct 3/32 size. At least I had that going for me.

Drilled the main jet to #67 with no problems.

My intake to heat shield gasket sealed nicely. In fact it even remained attached to the head holding the heat shield in place for me. I decided to leave it alone since it was happy. I went ahead and replaced the rest of the carb gaskets with the new ones like planned. I verified nothing leaked since the MAPP gas had no effect on the engines RPM or note. I did get an interesting look from the neighbor when he saw me poking around a running lawn mower with a torch. I assured him it was off. Nice guy, pretty nosy though.

So only thing left to do is helicoil the one ignition mount, or re-tap it, and bolt it down. Then after I mow the lawn break out the pressure washer and clean it good.

I'm sure I'll have a few more questions after that. Thanks for all the help so far!

jp1961 said:

Hello,

I'd replace the governor spring too, it's 1.06.

The choke butterfly should close completely. You more than likely, you need to adjust the throttle cable at the air filter box, pushing the cable towards the carb.

FWIW, I remove the carb and air cleaner as an assembly, after letting the aluminum heat shield drop down. The governor spring is quite fragile and you have to be careful not to bend it.

The airvane can be adjusted to get the factory spec of 3100 RPM. Turning it counterclockwise decreases engine speed. Try 2-3 clicks at first, if the engine is really screaming.

You can download a repair manual of the Duraforce engine on the web.

Regards

Jeff

Click to expand...

Good to hear you got it running. :thumbsup:

That gator blade sucked. All it seemed to do what catch the grass and sling it in the mower. I ordered an OE-style replacement. Also found out it was missing the fan so I got one of those too.

First 5 minutes of mowing a 6" long bolt fell out of the muffler. I'm going to have to get a sticker that says "Honk if parts fall off" now. LOL

I think that was just for the heat shield though. I'll put it back when I change the blade.