Hey y’all I’m hoping someone can help me out because im stuck at this point. Last spring I decided to start a landscaping business as a side hustle. I picked up a very used 2009 cub cadet 50” with a Briggs and Stratton VTwin. I did a full tune up and the engine worked great for the year. Over the winter I did a little bit of work to it but nothing too crazy. I did pull the engine off to replace the crankcase gasket but I’ve done that on other mowers in the past. I pulled the mower out of storage this year and put fresh gas in it but while at my first job for the year I noticed the mower is running like crap. What’s weird is it runs decent while the blades are engaged but as soon as you turn them off it runs very rough with a lot of backfiring. I had a new carb sitting on the shelf so I put that on it hoping it was a fuel issue but it didn’t change. I pulled spark plug wires to let it run on one cylinder and I’ve learned the problem is on my left cylinder. So I adjusted the valves hoping that was the problem but it did not help. The only thing I’ve found to help is if I add a little bit of choke it will clear up for a minute before running rough again. I just can’t figure out what could be the problem because so many parts have been replaced on this in the last year. If someone has any suggestions of what to try please let me know. Engine model is 44M777.
Briggs Vtwin backfiring constantly
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bertsmobile1
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Start by checking that all 4 valves are moving
Try swapping the spark plugs
Try removing both kill wires
Let us know what happens
Try swapping the spark plugs
Try removing both kill wires
Let us know what happens
mechanic mark
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Post Type xxxx, Trim xx & Code xxxxxxxx numbers for your engine manuals. Thanks, Mark
Add Star Tron Fuel Treatment per instructions on bottle to your tank.
www.ccpartsnmore.com
Add Star Tron Fuel Treatment per instructions on bottle to your tank.
Cub Cadet Service Manuals
Manuals and Diagrams for Cub Cadet Mowers and Tractors. Factory Direct from Cub Cadet. Buy Parts for Less.
www.ccpartsnmore.com
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Hammermechanicman
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Spray some starting fluid over the plastic intake manifold especially where it meets the heads. If the engine changes how it runs. Either a cracked manifold or bad gasket at the head. These need to be changed ANY TIME the the manifold is taken off the heads. They compress and don't reseal good qhen reused.
Sorry had a long day at work and just got around to replying to everyone. All 4 valves are definitely moving. I removed both kill wires and it still ran the same way. I just had to choke it out to turn it off lol. I have also switched the spark plugs and it’s still the left cylinder that is having issues. The engine is Model 44M777 Type 0729 B1 Code 090203YG. I can try a fuel treatment but I have also already drained the tank and bought fresh gas so I am not sure if there is anything wrong with the fuel. Lastly I used brake cleaner and sprayed all around the heads, all over and around the intake manifold, and all around the carburetor but did not find any leaks.
bertsmobile1
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OK,
Well assuming everything was done correctly the next easy step is to undo the flywheel bolt & check the timing key has not cracked so the engine is slightly out of time.
As it runs fine with the blades on when the main jet would be supplying the bulk of the fuel we can rule the fuel pump out
Now we are left with timing & carb
The important question is what carb did you fir & where did you get it from
If it was a cheapie off Scamazon or Evilpay then there is a 50% chance it is a defective carb that qa pulled from the recycling scrap stream to be sold to idiot cheapskate Americans.
If it came in a kit with a filter & plug then the odds of it being defective go up to 75 % .
Go to Out Door Power Equipment navigate to the repairs section, find your carb and clean it according to the photo instructions you will find there.
Good chance there is an obstruction in the idle circuits
And buy a genuine service kit for it from a real mower parts retailer not from an Amazon criminal .
Well assuming everything was done correctly the next easy step is to undo the flywheel bolt & check the timing key has not cracked so the engine is slightly out of time.
As it runs fine with the blades on when the main jet would be supplying the bulk of the fuel we can rule the fuel pump out
Now we are left with timing & carb
The important question is what carb did you fir & where did you get it from
If it was a cheapie off Scamazon or Evilpay then there is a 50% chance it is a defective carb that qa pulled from the recycling scrap stream to be sold to idiot cheapskate Americans.
If it came in a kit with a filter & plug then the odds of it being defective go up to 75 % .
Go to Out Door Power Equipment navigate to the repairs section, find your carb and clean it according to the photo instructions you will find there.
Good chance there is an obstruction in the idle circuits
And buy a genuine service kit for it from a real mower parts retailer not from an Amazon criminal .
Well it’s definitely an Amazon cheapie because I couldn’t spend $200 on a Briggs carb. But I used one of these carbs last year and it ran great. I can get a rebuild kit and tear it apart and hope that’s the problem. I will try to look at the fly wheel key but last time I tried taking the flywheel off it was so stuck it wasn’t budging. Do you think it could be something internal like a can lobe being worn down?
bertsmobile1
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No
You do not need to remove the flywheel to check the key , in fact it is often better if you don't
The flywheel has a rectangle shaped slot
The crankshaft has a rectangle shaped slot
So if the 2 of them line up PERFECTLY to make a square, the key is fine
The fact that it gets better when with a little choke means it has to be a slightly advanced spark or not quite enough fuel to run at those speeds
The fact you said it is missing points towards a fouled spark plug or the wrong grade of plug or the plug gap is too wide
You do not need to remove the flywheel to check the key , in fact it is often better if you don't
The flywheel has a rectangle shaped slot
The crankshaft has a rectangle shaped slot
So if the 2 of them line up PERFECTLY to make a square, the key is fine
The fact that it gets better when with a little choke means it has to be a slightly advanced spark or not quite enough fuel to run at those speeds
The fact you said it is missing points towards a fouled spark plug or the wrong grade of plug or the plug gap is too wide
mechanic mark
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OEM B&S Fuel Filter above
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Dreaded
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There is another possibility. A sticky valve, it may be opening and closing but may be slightly sticky and not closing fast enough. I had this on a Vtwin and it would backfire at certain RPMs especially lower RPMs or when decreasing PRM. Had to remove the head to clean valve stims (build up of carbon on stim) and lap the valves.