MTD Power Shredder Help

[MAYOR28]

I just picked up a MTD Power Shredder (model 249-650) with a briggs and stratton 5 HP engine. Like this:

http://www.ereplacementparts.com/mtd-249650000-1989-chipper-parts-c-20039_21605_133188_21924.html

I have been trying to get it to run, I changed out the fuel and oil for fresh new and cleaned the spark plug, but it will not start. I can get the engine to catch and run for awhile with starting ether sprayed into the carburetor.....The engine is generating spark (tested with multimeter & father's finger....). Which leads me to believe that there isnt gas getting to the engine. After a few (hundred) pulls on the cord, we took the spark plug out and it did not smell of gas.....

I think that the issue may lie in the gas line inside the tank or with what appears to be a vacuum line from the cylinder back to the carburetor....

Anyone have a quick diagnosis?

Thanks,
Matt

 

[richashley]

Take off the float bowl and see if gas is getting to the carb. If it is, the passages in the carb may be clogged, especially if it's been sitting for a while. Try getting a rebuild kit for the carb and clean it very carefully. Run something through all of the jets and passages. Welding tip cleaners work real well for that.

 

[Greatbear]

If the fuel tank is below the carb, most likely the fuel pump diaphragm or flap valves are shot. This is a simple fix, remove the tank and carb assembly from the engine, then remove the carburetor from the tank. The "gasket" between the two is also the pump diaphragm, the small cup inside the tank is the carb "bowl". Vacuum impulses actuate the pump diaphragm, which pulls fuel through the long pickup tube and pumps it into the bowl. There is a hole in the bowl near the top, so the constant pumping will fill the bowl to a certain point until excess fuel spills back into the tank. If the rubber is stiff or cracked, or the little flap valves that control the fuel flow are stuck, fuel will not make it from the tank as a whole and into the internal bowl (then into the carb, then the engine).

A quick test is to remove the air filter and dribble some fuel into the carb air inlet. Pull the starter. If it fires, you have carb trouble. Some cleaning and new (cheap) parts are in order.

 

[MAYOR28]

Awesome advice so far. The fuel tank is below the carb, and I did see that there was something in the tank below the carb.

Greatbear & Richashley - Does the vacuum connection need to be completely airtight from the engine to the carb? It looks like the metal vac tube has been dented and moved, so the little rubber connections on the end seem a little loose......Is this okay?

Thanks so far! I will give this a try today!

 

[theoldwizard1]

Greatbear is right on, with one possible exception. IIRC, the fuel pump diaphragm is mounted on the side of the carb, under 4 small screws.

If replacing the diaphragm doesn't solve your problem, carefully, gently, turn the adjusting screws in until they just seat, counting the turns (usually between 1 and 3 turns, down to 1/4 turn). Then back them out and using a carb cleaner spray try to shoot into these holes. Replace screws. Gently seat and back out the number of turns you counted before.

If this does not work, you will need to remove the carb and soak it something like ChemDip.

Last tip, B&S makes an electronic ignition upgrade for old engines. Magnetron Upgrade Kit. Best $20 you will spend, because that engine will start in 2 or 3 pulls every time and at any temperature !

 

[cashishift]

This would be a great post for the Small Engine forum that I have requested!!

 

[kbs2244]

Something I learned from my Dad (who was an airplane mechanic on board a carrier in the Pacific during WW II) was:

“Everyone wants to play with the carburetor.
It is never the carb. It is always the ignition.”

This is very true with B&S engines used in any application where there may be a strong impact. Rotary lawn mowers and chippers are classic such applications.

Ignition timing on a B&S engine is controlled by magnets on the flywheel.
The flywheel is keyed to the crankshaft with a soft aluminum key.
It is a sacrificial key designed to deform and save the crank from cracking under the stress of an impact.
Much like a shear pin on an outboard motor.
The problem is the engine ignition is now out of time.

You need to remove the starter rope housing and then the fly wheel.
You will need an impact driver to get the fly wheel nut off and a gear puller to get the fly wheel off. (It is a tapered shaft.)
Do some research on your engine model number.
It is rare but some flywheel nuts were left hand threads.

Then just replace the damaged key and reassemble.

 

[Worsedog]

This:

I can get the engine to catch and run for awhile with starting ether sprayed into the carburetor.....The engine is generating spark (tested with multimeter & father's finger....).
Thanks,
Matt

Shoots this theory:

Something I learned from my Dad (who was an airplane mechanic on board a carrier in the Pacific during WW II) was:

“Everyone wants to play with the carburetor.
It is never the carb. It is always the ignition.”

This is very true with B&S engines used in any application where there may be a strong impact. Rotary lawn mowers and chippers are classic such applications.

Ignition timing on a B&S engine is controlled by magnets on the flywheel.
The flywheel is keyed to the crankshaft with a soft aluminum key.
It is a sacrificial key designed to deform and save the crank from cracking under the stress of an impact.
Much like a shear pin on an outboard motor.
The problem is the engine ignition is now out of time.

You need to remove the starter rope housing and then the fly wheel.
You will need an impact driver to get the fly wheel nut off and a gear puller to get the fly wheel off. (It is a tapered shaft.)
Do some research on your engine model number.
It is rare but some flywheel nuts were left hand threads.

Then just replace the damaged key and reassemble.

 

[kbs2244]

Not at all.
They will run on ether when mis timed.
The intake valve is not fully closed, but it is enough the give somthing of a power stroke on ether, but gas alone will not be enough power.

He didn't say, but if he is getting a back fire through the carb, it is a dead giveaway.

I would put a dollar on the tabel that he will find a bad fly wheel key if he digs that far.

 

[ksdaoski]

I had one sold it today. Had a safety switch under the bag catch. Make sure it's being triggered

 

[Greatbear]

Greatbear is right on, with one possible exception. IIRC, the fuel pump diaphragm is mounted on the side of the carb, under 4 small screws.

The Wizard is right. The horizontal shaft engines have a side-mounted fuel pump. I had recently repaired an old 3.5HP lawnmower for a friend where the diaphragm was shot, and I had that on my brain.

 

[treasureseeker]

Pull the float bowl off the carb and if you have a decent amount of fuel you are down to the carb. Take out the needle from the seat and clean up the main jet with carb cleaner and put it back together.

 

[metal1313]

more than likely it is the carb. every 5hp briggs ive worked on has had issues with some varnish or **** in the carb after sitting. this also makes sense since small chippers tend to throw a good deal of dust around, and most do not clean the machine off when refilling the gas tank. i bet if the op removes the tank, cleans it out and cleans the carb it will start right up.

 

[RonM3]

Most of the briggs I have worked on have had either a bad fuel pump diaphram or the jets are clogged. If you have fuel in the bowl chances are its clogged jets. If the bowl is empty then replace the diaphram. The fact that it will start and run for a bit using starter fluid tells you that the ignition is fine.

BTW: If you have an old wire brush you can cut one of the wires and use this to clean the jets.

 

[mdbeck1]

I finally got tired of paying someone every time my mower would do this. The bolt that holds the bowl on is a fuel jet and has a hole through it (Look from the thread end down and then on the side just above the head of the bolt). That hole gets plugged a lot. Take the bolt out, clean the hole out with a toothpick or paperclip, spray some carb cleaner through the hole, and replace it.

My motor started working just fine on the next pull.

 

[MAYOR28]

SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!!
I cleaned everything, pulled of the carb, all the linkages, fuel bowl, fuel line, jets, and magneto. Bottom line is, it runs, but I am unsure of what the fatal issue was, there seemed to be a combination of things.....

1. Fuel line had leaves stuck to the bottom of it.
2. Vacuum line from cylinder was not sealed/assembled well.
3. Stuck diaphragm valve/gasket.
4. Screw inside of the carb

The screw turned out to be missing from the side of the carb just above the choke butterfly. I think it may have been some other type of metering device or it was used to connect some other component on other engine models. Either way, it looks like someone accidentally dropped it in the carb..... I took it out and put it where it was supposed to go....

I reassembled everything, took it outside, pulled the rope and I heard it catch on the first pull (something it didn't do before!). It sputtered a little and died, but on the second pull it caught and ran, I left it running on idle for 5 minutes, and then used it for the rest of the afternoon to take care some of our heaping pile of sticks and leaves .

He didn't say, but if he is getting a back fire through the carb, it is a dead giveaway.

I would put a dollar on the tabel that he will find a bad fly wheel key if he digs that far.

No back fire, and you owe someone a dollar.

Greatbear is right on, with one possible exception. IIRC, the fuel pump diaphragm is mounted on the side of the carb, under 4 small screws.

If replacing the diaphragm doesn't solve your problem, carefully, gently, turn the adjusting screws in until they just seat, counting the turns (usually between 1 and 3 turns, down to 1/4 turn). Then back them out and using a carb cleaner spray try to shoot into these holes. Replace screws. Gently seat and back out the number of turns you counted before.

You are correct that the diaphragm is on the side. Pretty neat design with the gasket and flapper valves. I might have messed the adjusting screw; the first time I was trying to get it started I turned this screw thinking it was the idle speed screw....
Any suggestions as to what the adjustment should be, or is it good if it is running?

If the fuel tank is below the carb, most likely the fuel pump diaphragm or flap valves are shot. This is a simple fix, remove the tank and carb assembly from the engine, then remove the carburetor from the tank. The "gasket" between the two is also the pump diaphragm, the small cup inside the tank is the carb "bowl". Vacuum impulses actuate the pump diaphragm, which pulls fuel through the long pickup tube and pumps it into the bowl. There is a hole in the bowl near the top, so the constant pumping will fill the bowl to a certain point until excess fuel spills back into the tank. If the rubber is stiff or cracked, or the little flap valves that control the fuel flow are stuck, fuel will not make it from the tank as a whole and into the internal bowl (then into the carb, then the engine).

Exactly right, one of the 'valves' was stuck in the diaphragm.......took apart, cleaned, and put it back together..

I had one sold it today. Had a safety switch under the bag catch. Make sure it's being triggered

I do not see anything like this. I am not going to worry too much about it (don't have a bag anyways), and its running now, so.......

Bottom line: I got a shredder for less than it would have cost me to rent one for half a day. And it only took about 5 hours of frustration to get it in running shape.

 

[MAYOR28]

Thanks for everyone's help. I knew that you guys would know what to do. You never fail to disappoint! I truly couldn't have done it without your help! Definitely saved me some time and money
It is such a great feeling to work on something and have what you did actually fix the original problem (it feel awful when you 'fix' something and it doesn't fix the real issue.....)!

This would be a great post for the Small Engine forum that I have requested!!

I agree. This would be a good addition.

 

[theoldwizard1]

Something I learned from my Dad (who was an airplane mechanic on board a carrier in the Pacific during WW II) was:

“Everyone wants to play with the carburetor.
It is never the carb. It is always the ignition.”

This is very true with B&S engines used in any application where there may be a strong impact. Rotary lawn mowers and chippers are classic such applications.

15-20 years ago, your Dad was right on. Not true with any small engine with electronic ignition. They will fire an old plug like a brand new one.

Mayor28 - Did you order that B&S electronic ignition retro fit kit yet ?

Ignition timing on a B&S engine is controlled by magnets on the flywheel. The flywheel is keyed to the crankshaft with a soft aluminum key. It is a sacrificial key designed to deform and save the crank from cracking under the stress of an impact.

Yep. Seen it happen. Typically only happens when you hit something hard with a rototiller or lawn mower.

 

[kbs2244]

I isn't a matter of spark strength, it is a mater of timeing.

But where do I send the dollar?

 

[MAYOR28]

I isn't a matter of spark strength, it is a mater of timeing.

But where do I send the dollar?

Do you think that the timing could still be off?

Worsedog doubted you, but I say keep the dollar and buy a soda on me.....

Thanks for all of your help.