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Craftsman 4.5 HP Mower Loses Power Under Load

8K views 17 replies 5 participants last post by  The_Geologist 
#1 ·
Hi All,

I have been having trouble with my 2004 Craftsman 4.5 hp push mower (model number 917.388630), with a Tecumseh engine. This summer, it has started well, but when I get into any amount of grass, it loses power and stalls. This is a new issue...hasn't happened before.

I went ahead and removed the carb and cleaned it out in the ultrasonic cleaner. The original carb looked quite clean inside even prior to cleaning, I noted. I also noted that the needle seat was not in great shape, so I replaced it. Upon reassembling the mower, the carb proceeded to overflow without mercy...and I did place the seat in the correct orientation. Even after pulling the carb apart again and rechecking the float, needle, and seat, it still flooded itself out.

So...I went and found a replacement carb on Amazon. I just installed it this afternoon, and while the carb no longer floods itself out, the lack of power still exists. It will idle fine, but proceeds to bog down under the load of cutting even the smallest amount of grass.

I am using fresh fuel, 93 octane, without ethanol in it. The air filter is new, the spark plug is new, and the carb is new.

I did notice it ran better without the old air filter installed, so that is what led me to replace it.

The mower in question is the green one on the left in the pic below.



Part of me is wondering if it is just getting worn out...it is 15 years old, after all! Though I realize folks on here are using much older mowers without issue. At this point, I just needed to step away and seek help, as it was getting too frustrating.

Thoughts, comments, and suggestions are greatly appreciated!
 
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#2 ·
My first thought is the governor isn't working correctly. Second would be the valve clearance is to tight and your loosing compression and power after the engine warms up. Third would be a plugged gas cap vent.

Look under the trouble shooting manual ( 7th down from top) for governor help.

https://www.mymowerparts.com/pdf/Tecumseh-Service-and-Repair-Manuals/
 
#3 ·
Thanks for the tips! I will look into them when I get the chance.

As a side note, is it possible that the return spring on the governor could be the issue? Mine seems to have lost tension, and looks a bit stretched out.
 
#5 ·
I'll take a look through the assortment of springs I have, and see if one will work there. Failing that, I will see about ordering a replacement online.

Thanks for all the help!
 
#6 ·
A small update...I did find a spring that had a similar length and, hopefully, a similar original tension. After installing it, the mower started up much easier than it had before, and blew out a huge cloud of white smoke before settling down into the normal RPM that I have heard its entire life (I've had this mower since it was new in 2004).

I did not have any tall grass to test the mower with (I had just finished mowing with the Snapper before tackling this task), so further testing will be when I mow the lawn again next time. I'll follow up further after that time.
 
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#7 ·
More Updates After Mowing the Lawn Today...

So, I accidentally let the lawn get a bit long over the past week, which I then realized would be a perfect test for my mower repair.

The mower performed well, considering the higher-than-average grass height it was cutting. I didn't do the entire lawn with it...just the edges. The rider took care of the rest.

It does seem to run at a slightly higher RPM than it used to (without a load on the motor), based upon the sound of the motor. However, I am not sure if I should do any adjustment(s), because it did respond well to load when it was being run through the high grass.

I do realize that too high an RPM is not good, so any further suggestions would be welcomed.
 
#8 ·
The End of an Era...and the Beginning of Another

Well, to follow up on this mower, I have discovered that the engine is officially on its way out. I may have killed it with running it at too high an RPM this last time...or it may have just been it's time.

It seems to have very low compression, followed by little power, and when I do finally get it started, there is a significant clattering noise from the head that has now become very evident. I have even had the engine seize on me while pulling on the pull start, though I was able to get it to release by moving the blade (with the plug wire taken off, of course...) The engine will not start with the air filter attached. So...I have decided not to screw around with it any longer...I need a reliable push mower! I am sure I could have done some more work to it, but I am over it now.

This Tecumseh engine has served me well since I bought it brand new in 2005, so I think it had a good life.

Now for the next chapter: I was checking out some things at Harbor Freight over the weekend, and they were having a manager's special: 50% off open box items. In the stack was a 5.5 hp Predator vertical shaft motor that someone had returned, so I snagged that for $49.99. I got it home and found it had never had fuel or oil put in it...so whomever bought it first found it didn't fit whatever they were trying to accomplish.

I have the new motor mounted on the old frame, and just have to finish attaching a throttle cable. I also need to get a new blade adapter as the old one is too large (apparently fairly common, from what I read online). I did confirm that the Predator starts and runs just fine while I controlled the throttle linkage by hand. I let it idle for about 15 minutes just to burn the coating off the muffler.

If there is any interest, I can take some pictures of the final result of this transformation and post them.
 
#10 ·
An Update!

I received the correct blade adapter in the mail last weekend, and was able to install it last night. It fit the Predator crankshaft perfectly, and the blade fit the adapter perfectly as well.

As a point of reference for anyone who might read this thread in the future, I purchased the following blade adapter:


Craftsman 581547901 Blade Adapter

I also installed the throttle control on the handlebar. Had to place the control on the outside of the handlebar so it wouldn't interfere with the engine brake lever. As the control is entirely made of plastic, I have concerns as to how long it will last.

The Predator starts easily and runs just fine. I have been running it at 3/4 throttle for 10 - 15 minutes at a time for now. Haven't mowed with it yet.

The only issues I see are as follows:

  1. Where the old motor was essentially sealed to the deck, the Predator has a decent-sized gap between it and the deck. Not sure how much debris will find its way through.
  2. The Predator crankshaft is a good 1/2 inch longer than the old one. I need to see what setting I can put the mower wheels at in order to avoid cutting to short. Or I have to figure out a non-******* way of raising the engine off the deck.

Questions and comments are welcomed. Thanks for all the help!
 

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#11 ·
Nice work getting the Predator to fit. Could you cut the crankshaft to the correct length to make the motor sit flush to the deck? If no, maybe buy some thick black rubber weather stripping ( not sure how long it would last) and let the engine compress it to the mower. The space will have an effect on suction and clipping ejection.
 
#12 ·
Hmmm...cutting the crankshaft might be an idea. I'll have to look at how deep the hole goes for the blade bolt. Any tips/tricks for cutting the crankshaft squarely (so the angle of the blade is minimally affected? Or does the blade adapter allow for some wiggle room that way (if that makes sense)?

The gap between the deck and the motor is odd to me. Wasn't expecting that. I can use weatherstripping, or I might see if I can find something else I have lying around.
 
#13 ·
I went ahead and did some test mowing on Sunday. I can say that this Predator sure is quiet compared to the old Tecumseh, and it has more power (5.5 hp vs 4.5 hp, for whatever those numbers really are worth). It's also a lot easier to start, and I like having the ability to adjust the throttle speed on the new motor.

It cut cleanly and evenly in what grass was there, and didn't even slow down the motor at all. I'm trying to not overtax the motor with a heavy load during the break-in stage. I think I've run the new motor at least an hour by now, over the course of several days.

The cutting height is lower than I am used to (about 1/2 inch or so). I didn't hit any of the tree roots that I am used to avoiding, so that is something. I think I still have enough wiggle room on the wheel height that I may be able to get by without cutting the crankshaft. It's not something that I have done before, so I am less confident in my ability to do so and still have a decently level blade. I'll look more into cutting through a crankshaft and see what I feel like by spring. It's getting late enough in our mowing season here that I may not worry too much about it until next year.
 
#15 ·
Have to say, that looks seriously boss!!

When I need to fill a gap like that, I cut up old inner tubes -- they work well as seals, and are extremely durable. If you need a thicker piece, just fold it over a time or two. (My first car had a couple layers of inner tube sealing the fuel pump bowl -- the 'correct' seal always began leaking after just a few months, but my homemade inner tube seal fixed it permanently.)

Could also use a piece of corkboard, cut to fit and glued down.

Instead of cutting the crankshaft -- how about putting bigger wheels on it, to hoist the whole affair up by an inch or so? I did that with a mower that came with punywheels and not enough clearance -- filched bigger ones from a dead mower, worked great.
 
#16 ·
These wheels aren't the original ones (which were a bit smaller), as one of the originals finally broke a couple years ago. Larger wheels shouldn't be difficult to find at the mower repair shop (if he hasn't purged his salvage yard yet for the fall). Or else, there's Amazon... I might still have some old motorcycle tire inner tubes lying around, too.

I forgot to mention in the last post that I noticed just how much heavier the Predator is than the old Tecumseh. It kind of throws off the balance I have been used to all these years, but I'll adjust to it.

I really like your ideas. Thanks for the input!
 
#18 ·
I went ahead and measured the wheels I put on a couple of years ago, only to find they were 6.5" wheels. The originals were 7"! I was looking at some 8" wheels at Harbor Freight, but when each wheel weighs 3 pounds, that adds a significant amount of weight to the mower that I didn't need.

To make a long story short, I reinstalled the original wheels (the cracked wheel isn't as bad as I remembered, so I went with it). This raised the blade enough to make it a good mowing height for what grass I still had growing the past week.

I went ahead and mowed and was happy with what I saw this past weekend. It has a good hour and a half of run time on the engine now, and I'll keep running it here and there over the next couple months for break-in. When the one cracked wheel finally gives out, I might just use one from Harbor Freight.

So, I think this project is done! I thank everyone for their help!
 
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