# Riding Lawn Mower - Engine Sluggish when in gear or when the blade is engaged.



## s2kfan (May 5, 2007)

I've signed up to get some help on my riding lawn mower. It's an older Craftsman with a 4 year old Tecumseh engine (12.5hp).

It was blowing black smoke like a chimney so I had the carburetor rebuilt. I have re-installed it and the bowl is filled with gas. Now...

1. I started the engine and adjusted the carburetor such that the engine idled appropriately (no lope and not too fast). 
2. When I engage the transmission into any gear it bogs the engine down and if I engage the blades it caused further issues. The blades aren't even spinning fast enough to thoroughly cut the grass.
3. If I engage the blades while in neutral the engine still bogs.

I'm not as familiar with lawn tractors as I am with cars so I need some help getting this sorted out. I know I have 3 adjustment screws - 1 is for the bowl, 2 is for the gas flow into the carb venturi and 3 is for the stop on the butterfly (engine side). The last one adjust how far open the butterly is at idle. 

Anyone have any suggestions, they would be greatly appreciated.


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## 30yearTech (Sep 14, 2006)

Did you replace the air filter? A clogged filter will cause an engine to bog down under a load.

The screw on the bottom of the carburetor is the load or high speed adjustment and this may be set too rich and or too lean. If it's set too lean the engine will usually bog down and die when a load is applied, if too rich then the engine will usually continue to run albeit poorly with low power and usually some black smoke.

The screw on the side of the carburetor is the low speed adjustment and will affect the load somewhat but is not used for high speed or load adjustments. This adjustment is used to set the mixture for a smooth idle and good throttle response.

The screw on the top (butterfly stop) is simply used to set the idle speed and has no effect on the way the engine runs.


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## s2kfan (May 5, 2007)

Thanks for the input. I did not know that the bottom screw was for high speed. I believe my air filter is good to go, but I may replace it just for good measure. So...going forward I will try:

1. Re-check idle speed (it seems to be ok).
2. Adjust the high speed adjustment screw to see what effect that has. By the way, I'm assuming screwing it in causing less gas flow while backing it out causes more flow. Please correct me if I'm wrong. As I said, I'm pretty green with a mower engine.


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## s2kfan (May 5, 2007)

So, I've exhausted my carb options. When I adjusted the high speed adjustment, there was no difference in performance. I'm wondering now about compression? Can a small engine idle ok with a compression leak? That would explain the problems when put under a load. I may just give up and take it in for troubleshooting as I don't have the time to mess with it...

BTW, which part of Central Texas are you from? I grew up near Waco, I now live in Indiana, but Texas will always be home.


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## 21tgs (Oct 26, 2006)

Is there a chance that the governor is no longer properly attached to the carburetor linkage? If you pulled the carburetor you had to remove the governor linkage.

If the engine with no load runs at wide open throttle normally I think that you may now focus on proper governor settings. May be the governor can not open the throttle to compensate for the load. One way to verify this is to manually open the throttle for a second or two while the transmission is in gear or while the blades are engaged. Of course you need to be extremely careful when doing this. Not just because you can easily over speed the engine but more so because you will be trying to move a linkage while the tractor is in motion or may be worse the blades are engaged.

I suggest using a helper to engage the blades while you stand to the side and nudge the governor linkage to open the throttle plate.


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## mae27360 (May 15, 2007)

3.75 hp briggs, I have no spark. and no points that I can find, what gives, help???


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## oscaryu1 (Mar 25, 2007)

Mae27360: Make your own thread, we can help you there.


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## 30yearTech (Sep 14, 2006)

It could be a compression issue, or there could be an ignition problem. Do you have the Model an Spec number from the engine on your rider?

About a hundred miles south of Waco, in the Austin area....


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## s2kfan (May 5, 2007)

21tgs I tried what you stated and the engine revved up and the mower sped up. I've got long arms so this was fairly easy to do while on the mower. I was very careful when removing the linkage and replaced it just like it came off. I think I'm going to just take it in and have someone else look at it as my time is short on this. Thanks for all of your input though, it is much appreciated!


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