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Engine Power Loss


murray90's Avatar
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04-08-04, 02:56 PM   #1  
murray90
Lawnmower

I have a '90 42" Murray that loses power with deck down in #1 position when I ride into thicker grass (not enough to make the blades down, but they do). I can raise the deck and the blades resume proper RPMs. Installed new plug, air filter, belt and changed the oil. Any suggestions will be appreciated.

Thanks

 
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04-08-04, 03:08 PM   #2  
Hello and Welcome murray90 to the Do-It-Yourself Web Site and the Small Engine forum.

Question to you is, did this condition exist before the belt change? If not, problem may be with how the belt is currently installed. Creating some drag and or resistance some where.

Double check. Lower deck, engine not running and note the angles of the belt(s) in relationship to pulleys.

Another possibility may be a fuel starvation problem causing a loss of power. All depends on how engine and machine ran prior to any repairs or maintainance.

Use the reply button to update this post with more details. Doing so allows all us pros and to better help you.

Check back on your question several times over the next few days for additional replies.

Small engine repair parts, generic repair manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Regards. Sharp Advice.
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04-08-04, 03:49 PM   #3  
Sharp Advice brought up very good points. I would check that. But I would also like to ask you this. You said you installed new plug, air filter, belt and changed the oil.Did you do these properly? What I mean is. Did you use the proper oil in that engine and did you fill it up to the full level point shown on the dip stick? When you installed a new plug, was it the proper plug for that engine? And finnaly, correct air filter? I think the problem lies with your new belt too. But, I wanted to cover all of the posibilities. I would make sure your pullies are secure and tight too. Let us know how it goes.

 
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04-08-04, 03:50 PM   #4  
power loss

First let me say that I think you're cutting too low. Something to bear in mind: The engine pulley is in a fixed position, the deck pulleys move up and down with the deck. It is possible (by way of wear, since the machine is "older" < (don't want to suggest it's old ya know!)) that the deck is now dropping down further than it should. This will create an unusual angle on the belt and thereby cause an excessive parasitic load. Moral: Cut your lawn slightly higher. This may not be the exact trouble you have but is definitely possible. Try this. With your machine off, lower the deck all the way down. Take a look at the belt angle, between the engine pulley and the deck pulleys, and see if it looks excessive. If so, refer to the moral of the story. If not, let us know.

 
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04-08-04, 07:15 PM   #5  
murray90
Power loss

Thanks for the advice and suggestions............

I did experience the problem before changing the belt. As far as servicing the mower, I replaced all parts with identical parts as the years before and the oil is full on the dip stick. I will have to check the angle of the pulleys in the down position compared to the drive pulley. Also, it has been several years since any work has been done to the carburetor. I have confidence that I could overhaul the carb if needed with tips from you'll as to what i need to clean and adjustments if that is part of the problem. I hope I didn't leave anything out. The motor is a 12 HP B&S. Model 40604A.

Thanks again

 
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04-09-04, 12:06 AM   #6  
Hello murray90!

First...let me ask is it the engine losing power (running too slowly), or is the engine running just fine, but the blades are just not turning as fast as they should. This will narrow the problem down to just a couple of things.

The proper oil and oil level, etc.. shouldn't have any effect on engine power. Of course, it does have an effect on whether the engine will run longer than 30 seconds or not, lol .


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04-09-04, 06:01 AM   #7  
Hi: Murray90

So the problem did exist prior to the recent repairs or parts replacement. Important fact. Thanks for that update.

If the angle of the belts, blades and pulleys are correct, that load on the engine is not likely the cause of the power loss.

I agree with you. the carb may infact be the problem. But so can fuel flow to it. A carb starved for fuel will run fine in some cases until a load is placed on the engine.

Therefore, it must be first determined if a fuel restriction to the carb from the fuel tank exists. Pull fuel line off carb and allow fuel to flow. Watch the flow rate and volume. Should remain constant.

If not, fuel flow from the tank is likely. Looking inside tank may reveal a filter. If so, may be restricted. May also have a restricted vent hole in the fuel tanks cap.

Fuel flow decreases when line pulled off carb? Remove cap and note fuel flow. Refer to above. No change after several minutes, flow flow, with cap on, remains constant, not a fuel flow problem.

Next logical diagnostic step, check carb. May in fact be restricted and or plugged. Not allowing sufficient fuel to flow through it. Allows engine to run fine without the load but not with the load.

Carb thus needs internal cleaning and new OEM parts. Proper reassembly is also a must, including reattaching to engine and all it's associated parts.

Regards & Good Luck. Sharp Advice.
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04-10-04, 02:15 AM   #8  
murray90
power loss

Sorry I haven't been able to answer you, but my pc is locking up. I removed the air filter and adjusted on the carb which seems to run fine. Gas is obvious in the bottom of the carb. When I put it to idel, there is no adjustment about half way down from the throttle being wide open.

As far as the belts, it has a drive belt that runs from the drive to the front to turn the pulley that drives the deck. It's the drive pulley over the deck pulley. Looks fine to me.


Thanks

 
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04-10-04, 06:14 AM   #9  
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Hello: murray90

Hope you get the pc working correctly. I combined the above post into your prior post to keep the threads together. Doing so helps to follow along in the progress of attempting to resolve the engine problem. Kindly use the reply button to continue this thread. Doing so is a benefit to us all.

Another request, if you don't mind, is to focus on answering the questions asked by those in this forum whom are asking them. Reason being, helps us to determine the problem cause through the process of elimination of possible causes.

Your determination is the belt(s) and pulleys are okay. No visable signs of binding or dragging. We got that, thanks.

Carb has fuel in bowl. But did you run the fuel flow test? And the results where????

Another question regarding the blades was asked to which no answer was supplied:

Quote "First...let me ask is it the engine losing power (running too slowly), or is the engine running just fine, but the blades are just not turning as fast as they should. This will narrow the problem down to just a couple of things."

And the answer to that question is...????

You stated: "When I put it to idel, there is no adjustment about half way down from the throttle being wide open."

My assumption, (hate making assumptions... ) on that statement is the throttle linkage is not fully moving the carbs linkage on the carbs body? Yes or No?

Linkage binding? Yes or No?

Or is the linkage simply not adjusted or in place properly....????

The linkage has to be anchored correctly and held firmly in place. Half inch one way or the other out of adjustment at the anchoring points effects the adjustment of it's length and the throw of it.

Thus effecting engine speed and power via the carb. Cable may move fully at the lever you are pushing but only moving carb throttle half way. Thus half power.

Hope this description makes sense.
Based upon an ASS-umption... from what info you provided.

 
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04-15-04, 10:46 AM   #10  
Did you get this fixed?

 
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04-15-04, 01:01 PM   #11  
gmcfan
A friend of mine has this old International Harvester Riding lawnmower, and he was having the same problem: when He would try engaging the blades, the engine would bog down. It turned out, that the bearings that support the blade shafts were frozen, from lack of lube. You may want to check, and take the belts off, and spin the blades. They should turn easily. If they are very stiff, your blade bearings are the problem.

 
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04-21-04, 04:19 PM   #12  
Any resolve to your trouble? Let us know.

 
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