Craftsman LT1000 running slow

kclawnNovember 28, 2010

I have a Craftsman LT1000

Model 917.272681

Nikki Carb

Ok here is the problem... the motor will run but not at full throttle. The motor will not run at full speed.

Ok here is what I have done to correct the problem:

Rebuilt Card and I soaked card in Seafoam to remove any varnish.

Checked fuel lines. Good

Checked gas cap. Good

Replaced fuel filter. New

Adjusted valves: .004 of an inch.

Checked fuel pump: Good. When I connect to 12v the plunger comes down till I disconnect from 12v.

Here is what is happening:

The motor will start fine but will not run at full speed.

When I was adjusting the valves I noticed the exhaust value was not moving/opening as much as the intake valve. I am not sure if this is normal, I am thinking not. Both rods are in great shape along with springs.

The motor acts as if there is a restriction; Maybe fuel or exhaust but I am not sure. If I had to guess at this point I am thinking it is the exhaust valve but I am not 100% positive this is the problem. I believe the muffler is in good shape and has no restrictions. I do get a backfire every now and then and am not sure if this is a problem. The motor may backfire once every 50 starts.

When I disconnect the fuel pump the motor will run at full speed for about five seconds and then shut down unless I reconnect the fuel pump. Maybe the pump is bad but I do not think so.

I have done a lot of research on this problem including this forum and it seems this is a common problem with this motor. I am hoping someone can lead me to the correct solution.

Any Ideas?

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Engine is 31C707
"Exhaust valve does not moving/opening as much as the intake valve."
That is indicative of a worn out camshaft.
And yes, that will make the engine run poorly as it is barely breathing.
There are a few threads in this forum where this has occurred with 28 & 31 series Briggs.

    Bookmark   November 28, 2010 at 6:12PM
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Oh man, that does not sound good. So I take it the engine is basically going to need to be rebuilt or try and find a replacement engine. Any advice oh how to fix this or at this point is the cost of fixing it not worth the money?

    Bookmark   November 28, 2010 at 7:45PM
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How much difference is there in between the lift of the two valves? Certainly could be an issue. If that is your issue, the engine gets split at the sump and a new cam installed + gaskets. I seem to think that the cam kit and gaskets will be ~$80- 100. One other item that can happen from time to time is a badly worn throttle shaft. If you remove the air filter base, you can get a good look. the shaft will actually wear considerably oblong.

    Bookmark   November 29, 2010 at 12:04AM
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I don't think it is the throttle shaft as it looks good. The exhaust valve is moving about a 1/4 as much as the intake valve. before this problem became serious the motor would act as if it was running out of fuel. It would run just fine and then just slow down. It would restart and run rough or it may run great again for a few minutes and then shut down again. Sometimes it would run great all day and the next day it would run bad again. I thought maybe it was the carb and so rebuilt the carb. The cam shaft seems like the next logical step so I will pull it apart and take a look at it this week sometime.

    Bookmark   November 29, 2010 at 9:22AM
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I don't know if they are still doing it but for some time B&S was furnishing a free camshaft and gasket even though the warranty was expired because there was a flaw in manufacturing of the camshafts. An authorized tech had to verify the bad camshaft. Any labor was on you. You had to call B&S Customer Service as dealers will deny there is such a thing.

By the way, you'd better get some better instructions on valve setting. Since you did not set the exhaust valve at the correct setting, did you set them at 1/4" down past TDC?

Walt Conner

    Bookmark   November 29, 2010 at 12:05PM
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I adjusted the valves by turning the motor till the exhaust valve was in the complete open position then I used the feeler gauge on the intake valve and adjusted the intake to .004. Then I rotated the engine till the intake valve was at the full open position and adjusted the exhaust valve to .004. From what I have read this is the correct procedure for adjusting the valves. Are you saying the adjustment needs to be made from TDC?

    Bookmark   November 29, 2010 at 12:59PM
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unless you typed what you didn't mean to say? I Never heard of adjusting valves in the open position and not TDC. I would think pressure or Lift from the cam shaft would be present??? IMO the idea is to take all the slack or pressure off the cam shaft to push rod and adjust a few thousands for heat variations as the engine warms up and the parts grow due to getting hot (expanding)?

I would make sure the valves are adjusted right and are closing (compression check) before I would tear it apart. But that's me.

Evidently walts thinks your model engine has compression release system and that would require the 1/4 beyond TDC. he has helped amany on this forum with valve train problems. If it was me I would Seek his advice on how to adjust the valves on your model. If they are adjusted right then look elsewhere?

    Bookmark   November 29, 2010 at 2:33PM
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Yes, if the proper Briggs procedure was not used to position the engine for checking/adjusting the valves you may in fact be misinterpreting what you think you see (regarding the unequal valve movement).
Yep, you need to go back to "square one" and get the correct procedure on setting the valves before you commit to more work.
You can e-mail me for my procedure or get Walt's.

    Bookmark   November 29, 2010 at 3:14PM
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Mownie, PM sent.

Ok it sounds as if the valve adjustment I made is not correct so I will wait for the proper procedure before I tear this engine down any more than I need too. It would be great if the proper valve adjustments would fix this problem. I will let yall know what happens.

By the way. I read a lot of the forum threads here and you guys are a big help to the novice wrench turner like myself. Thanks for the advice and help.

    Bookmark   November 29, 2010 at 4:41PM
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