part no./ new LB duraforce carb.

quintusDecember 6, 2006

A while back I posted a message on duraforce carbs. ( see my post 'new info./LB duraforce carbs.'. The new no. is 98-7042 and the carb does come as a kit. The parts guy could not give me the old no.. What is even more disconcerting, not one person in the shop could tell me what the difference was between the new carb. and old carb., except for the fact that the new carb was in kit form. The tech. said that most of the time changes to fix a particular problem came with no explanation except replace old part with new part. Is the surging problem fixed? YES!!, most definitely! The engine runs steadily with no load, occasionally popping up 10 RPM, from 3150 to 3160 and then down as measured with a Stihl inductive tachometer. My four cycles do the same thing, so this must be within the tolerance of the measuring device, and it is not enough to be detectable by ear. Conclusion? I have no idea, since I am not any kind of expert on engine design. But I wonder, perhaps there was some design flaw in the carburator that Toro/LB fixed. That flaw may be masked by increasing the size of the jets as many have done. If any one has an LB duraforce under warranty you might try letting the shop fix the problem before going the route of increasing jet size.

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1saxman

'But I wonder, perhaps there was some design flaw in the carburator that Toro/LB fixed. That flaw may be masked by increasing the size of the jets as many have done.'

Probably an air leak leaning out the mixture, because not all of them surge.

    Bookmark   December 6, 2006 at 8:18PM
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fordtech

98-7042 has been out for a long time. As long as I have had Duraforces anyway, which has been several years.

    Bookmark   December 8, 2006 at 4:30PM
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quintus

98-7042 has been out for a long time. As long as I have had Duraforces anyway, which has been several years

Well 'fordtech', the shop did seem confused about the whole issue. I guess its a wonder they got the engine fixed. Even though the problem was rectified, it really does bother me when the essentials surrounding a problem are so nebulous and unclear. If any one has the straight story about a carburator fix instituted by Toro/LB for the duraforce engine I sure would like to hear it.

    Bookmark   December 8, 2006 at 6:47PM
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fordtech

Well that is simply a mystery that no one will likely know I guess. We have a number of lawn mower technicians here and none of them seem to know the final answer. The original carb number was 98-7000 and many of us have that carburetor. The number was updated to the 98-7042 several years ago. I guess one could assume that the techs will say the "new number" rather than updated part number. One has to realize that Duraforces stopped production in around 2002 and the last retail sales in 2004. All others after that were just NOS left over mowers. So a NEW number may be several years old. I have never seen a 98-7048 number on a carburetor though. One can hope if you get a carb with that number on it that it is improved. But many I have seen are the old number being sold as the new part number. SO how the heck do we know what we are getting?
I guess some courageous soul will have to get one that has that number on the side of it and take it apart and let us all know what the difference is. Until then we will all speculate till the cows come home.

Are you volunteering? :-)

    Bookmark   December 10, 2006 at 11:57AM
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dave101

Just wanted to ask a few questions on this subject matter. I purchased a Duraforce 10550 a few years back and I am thinking about breaking it out this year. I believe I want to do the carburetor modifications before It is ever fired up. I want to install the the Toro pilot jet and drill out the main starting at #67 then drill to #66. I know there is lots of discussion out there on the subject matter. To me it just seems to make sense to break it in with the increased jet sizes. Eventually it seems everybody experiences surging problems and why not get into the carburetor while its clean. Please add your input folks. Thanks

    Bookmark   January 28, 2008 at 6:24PM
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rdaystrom

That makes sense to me. They are jetted incorrectly from the factory just to meet EPA regs as you already know. I have a new one that I may do that way too. One thing that hasn't been discussed yet to my knowledge is switching to a hotter heat range plug if the jetting causes it to burn black. Good luck with it.

    Bookmark   January 28, 2008 at 8:15PM
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dave101

Thanks for the reply. The question I now have would be what would one look at if the machine is burning black. Would running richer cause excessive(harmful)deposits? It would make sense to run a hotter plug. I guess if the ports become dirtier than before jetting you may have completed the master plan for Duraforce reincarnation. Thanks for the input.

    Bookmark   February 1, 2008 at 10:01PM
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