How to Adjust Engine Speed--Briggs

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  #1  
Old 05-19-09, 06:37 AM
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How to Adjust Engine Speed--Briggs

I inherited a 2 year old 6.5HP Craftsman lawn mower. It's in pretty good shape. It starts right up, etc. But the engine speed with no load on it is not high enough. It's basically idling and when you go to cut, the speed isn't high enough even though the governer seems to be working (although hard to tell because the engine speed is so low). There is no throttle adjustment and the engine does rev nicely when I manually move the linkage. I can carefully move the governer linkage and it seems like there are no obstructions, not sticking, etc although I haven't taken the top cover off the engine. There is a very slight scraping of the spring where it rests but it doesn't hang up. What is the proper or best way to increase the engine speed? According to the small amount of info I got from the previous owner, it used to have a good engine speed and cut right through tall grass.
Here is a picture (not the best) and you can see the type of linkage set-up.
Thanks.
http://img257.imageshack.us/img257/558/013f.jpg
 
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  #2  
Old 05-19-09, 10:05 AM
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Did it originally have a cable hooked to it to advance from slow rpm to fast? It looks like there may be a place in your picture for one to bolt on. Just thinking??? What is the Model number of the mower and engine?
hh
 
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Old 05-19-09, 10:23 AM
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The model# of the mower is 917.388851. It looks like I'll have to disassemble part of it to find the engine model#.

I seriously doubt it ever had a throttle cable but I will find out for sure. On other mowers I've had that have throttle cables, they attach to linkage on the engine which then moves the throttle blade. So without a cable (when they break and I take them off), you can just move the linkage piece by hand and it will stay there. This has no way to permanently change the engine speed by hand and have it stay there. Kind of strange it seems to me.
 
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Old 05-19-09, 10:54 AM
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I did confirm it never had a throttle cable when it was purchased new. They claim after hitting a rock with it, the engine speed was never high like it used to be. Everything seems fine with it though--no bent blade, no wobble or vibration, revs good, etc.
 
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Old 05-19-09, 01:25 PM
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Ok. The engine model# is 123K02-0541-E1.
Thanks.
 
  #6  
Old 05-19-09, 03:55 PM
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I found the Owner's manual online at Sears and was checking it out. It states "The engine speed was set at the factory for optimum performance. Speed is not adjustable". Well, that's nice. There has to be a way to adjust it. Very strange way to set up an engine.

It also states in another place in the manual that if you believe the engine speed is too high or too low to bring it to an authorized dealer to have it adjusted. So, apparently it is adjustable somehow.
 
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Old 05-19-09, 04:35 PM
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There never was any speed adjustment on this engine. EPA did away with mixture and speed adjustments back in the mid 90's for emission reasons and to protect ourselves from ourselves cuz we are stoopid idiots and the government knows everything!!
Engine RPM on your engine is 3100. You stated " They claim after hitting a rock with it, the engine speed was never high like it used to be. "
You need to replace the flywheel key. It hit a rock and sheared the flywheel key, throwing the timing off. I bet you also get some recoil "kick back" when starting it cold sometimes. The carb could also be clogged after sitting all winter. I would buy a can of "SeaFoam" carb cleaner and add it to your gas at 1 oz per gallon. This does a good job of cleaning the carb while running it. Since yours runs now, the SeaFoam should help it.
The flywheel key is your major problem.
 
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Old 05-19-09, 04:39 PM
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The spring connects to a metal tab with a hole in it near the front of the mower. This tab gets bent back sometimes when pushing the mower under bushes etc... Bend this tab out toward the front of the engine to increase spring tension, which in turn increases engine rpm. Get it to where it sounds right, or is running at around 3200 rpm.
 
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Old 05-19-09, 04:40 PM
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Hmm.. Well, wouldn't the engine run bad if the cam/valve timing was off? When I do rev it up manually, it revs nicely. I would think it wouldn't run good (or not at all) if the key was sheared.
 
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Old 05-19-09, 04:42 PM
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Unless when the rock was hit it partially sheared the flywheel key the engine speed is adjustable, someone probably ran under a bush or something on this mower and bent the linkage, OK, the fat end of the spring hooks into a tang(I think that is what they are called), part of the linkage with a hole in it about the size of a pencil, to increase the speed just bend that tang forward until it is to your liking, just don't go too fast. I use a tach and set them to about 2800-3200 rpm, which ever sounds best. Have a good one. Geo
 
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Old 05-19-09, 04:46 PM
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Cheese and Indypower;
looks like we were all typing at the same time. Have a good one. Geo
 
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Old 05-19-09, 04:47 PM
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Originally Posted by cheese View Post
The spring connects to a metal tab with a hole in it near the front of the mower. This tab gets bent back sometimes when pushing the mower under bushes etc... Bend this tab out toward the front of the engine to increase spring tension, which in turn increases engine rpm. Get it to where it sounds right, or is running at around 3200 rpm.
Well, I see where the spring attaches to that tab you're talking about. If you look in the picture, you can kind of see it. The tab is horizontal so it could only be bent up or down--not forward or backwards towards the front or back of the engine. And, it is a thick chunk of metal. Can you tell from the picture?

Also, it appears to me that stretching the spring could work which would move the throttle linkage to the correct way to cause it to run higher. But, I really didn't think stretching the spring should be a good option.
 
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Old 05-19-09, 05:10 PM
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Originally Posted by Turbo98 View Post
Hmm.. Well, wouldn't the engine run bad if the cam/valve timing was off? When I do rev it up manually, it revs nicely. I would think it wouldn't run good (or not at all) if the key was sheared.
The flywheel key has nothing to do with valve timing.
 
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Old 05-19-09, 05:10 PM
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I can't see it in the pic, but it's not thick, it's easy to bend, and it is the manufacturer recommended adjustment for static governor spring tension adjustment. I'm thinking you're looking at the wrong thing, or your spring is connected wrong? Don't stretch or modify the spring.

You see the metal thing at the front right corner of the engine that has a pencil sized hole stamped out of it? That's what the end of the spring should be connected to, and that is what you want to bend away from the engine to increase engine speed. Do you have a macro setting on the camera (usually a little flower icon)?
 
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Old 05-19-09, 05:13 PM
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Originally Posted by Turbo98 View Post
Well, I see where the spring attaches to that tab you're talking about. If you look in the picture, you can kind of see it. The tab is horizontal so it could only be bent up or down--not forward or backwards towards the front or back of the engine. And, it is a thick chunk of metal. Can you tell from the picture?

Also, it appears to me that stretching the spring could work which would move the throttle linkage to the correct way to cause it to run higher. But, I really didn't think stretching the spring should be a good option.
No one suggested "stretching" the spring, simply bend the tap so that more tension is placed on the spring pulling the throttle valve further open increasing engine RPM.

The horizontal part of the tab continues on to a 90 degree bend that runs vertical and can easily be bent increasing or decreasing spring tension....look on your mower not the picture
 
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Old 05-19-09, 05:55 PM
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Ok. I'll try slighly bending the tab. Yes, it does run vertical and I will try and bend it away from the engine. Regarding the flywheel key, I guess the ignition timing is what would be thrown off? I would think it could affect RPM but not as drastically as this thing is.

Thanks for the help. I'll let you know what I come up with.
 
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Old 05-19-09, 06:36 PM
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Old 05-19-09, 06:53 PM
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On another note, check this out. Same mower, same brother in-law. He said he was cutting along and somehow the flap on the back got into the blade and busted the one side loose. It swung around and kicked up against the left back wheel knocking the rubber off the hub. He said the rubber part went flying past his head. The funny thing is that the hub and rubber part are completely un-damaged. But it is near impossible to get them back together. I must say, I've never seen this before!
http://img196.imageshack.us/img196/636/008k.jpg
 
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Old 05-19-09, 08:46 PM
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In the pic below you can see the where the spring is connected to the right, you do not bend where the spring is connected, you bend the linkage under the loop so the loop remains flat, it's hard to explain, however the object is to bend the linkage to put more pressure on the spring. The engine in the picture has a throttle cable but the hookup is the same. Have a good one. Geo
 
  #20  
Old 05-20-09, 04:42 AM
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Ok. Thanks. That's kind of what i figured. I'll mess with it a bit and see if I can bring the speed up. I just wanted to know the normal way to do it so I appreciate it.
 
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