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DuraForce Exhaust Question

1348 Views 6 Replies 6 Participants Last post by  dougmac
I recently acquired a 1999 model 10323. It surges like crazy, so I have cleaned and rejetted the carb. Before firing it up I decided to check out the exhaust to see if it needs cleaning. I took off the access cover underneath the mower and a LOT of dark (nearly black) fuel came out. I would say around 1/4 of a cup.

Is this typical or is this a sign of something bad?

Everything else down there looks fine and the exhaust ports, from what I can see, look clean. I just can't figure why there would be so much unburned fuel inside the exhaust cover. I seems like this would be a major fire hazard, but maybe it's just a special DuraForce feature. :p

Any suggestions or insight would be greatly appreciated. Thanks!
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Welcome to the forum.

Ive pulled them off before and i found it to be unburnt oil. More than one. They run fine but over time they fill up

Check out this recent thread. I did everything to my duraforce but it appears this was the problem.
I read that thread and measured the throttle plate to be sure I had the right one, and it is. Hopefully drilling the main jet to a #66 bit and installing a new 42.5 pilot jet will have this thing running like it should.

It sounds like the exhaust access area gets fuel/oil in it, so I'm going to just clean it out and put it back together.

Thanks for the help!!

Check out this recent thread. I did everything to my duraforce but it appears this was the problem.
You might have a leaking inlet valve in your carb that is leaking fuel mix into the engine and then down into the exhaust cleanout chamber. Do you have a fuel line shutoff valve and if so do you use it? I let my DF run out of fuel if I intend to quit mowing for the day by shuting off the fuel valve and letting it run out of fuel. Does it smoke alot when it is surging? If so it may have a rich surge condtion instead of a lean surge. They sound the same the only difference is the rich surge smokes a lot. If the DF has a bad surge then I open up the main one size and give it a try, if it still has a bad surge then I go the next size drill. If the first drill size makes a big difference then maybe you can open up the low speed one size to finish it off. Be sure to let it fully warm up before increasing the jett size as it can take up to 15 minutes to get fully warmed up. If you just open up the low speed jett then you run the risk of being too rich on the low throttle settings, which can cause it to "Load Up" if you let it idle for a bit. Make sure there are not gasket or seal leaks that can cause the surging conditon due to sucking air past the gasket/seal. Good luck! Your efforts will be rewarded!
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It's called "DuraForce Exhaust Syrup".....pretty common
The 10525 I recently got had the oily "Syrup" inside as have others in the past, but the 10247 I just gave a tune up to this past weekend had that "dark fuel" pour out of it. Probably not quite a 1/4 cup, but it did catch me off guard and made a mess !!

When I last serviced this mower (3 yrs ago), I put a new float / needle & seat in it as well as a shut-off valve and the owner claims she uses the shut-off regularly. I had previously jetted this mower (#66 drilled main & "40" pilot) so I thought maybe I had it running too rich and this was why the raw fuel was in there. Come to find out it had the WRONG small-hole throttle plate in it. Now it has the CORRECT throttle plate with a #68 drilled main and a stock "37.5" pilot and is now running near perfect / 100% better.

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