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I have the following engine in my ride on mower https://www.engine-specs.net/briggs-and-stratton/40h777.html a 40H777 22HP V-twin and I can't get it running smooth. I have replaced the following with no success in fixing the problem. What am I missing?

1. carburetor
2. fuel pump
3. fuel filter
4. air filter
5. spark plugs
6. ignition coils
7. added new fuel

I confirmed vapor lock is not the problem by taking fuel cap off as the mower was stalling after running it for 30 mins before replacing all of the parts above.

I did find that when I run the mower and disconnect either one of the spark plug cables from the spark plug the sputtering stops. Does this mean anything?

Here is video of the mower running:
Any ideas? Thanks in advance.

I would try adjusting the valves.

Craftsman Garage said:

I would try adjusting the valves.

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Thank you! That is a bit over my knowledge so I will have to send it to a repair shop for that.

Or just look up a YouTube video-

camshaft time?

Hmm, I would say that's unlikely. It doesn't sound like they've had the case opened up.

rch316 said:

I have the following engine in my ride on mower https://www.engine-specs.net/briggs-and-stratton/40h777.html a 40H777 22HP V-twin and I can't get it running smooth. I have replaced the following with no success in fixing the problem. What am I missing?

1. carburetor
2. fuel pump
3. fuel filter
4. air filter
5. spark plugs
6. ignition coils
7. added new fuel

I confirmed vapor lock is not the problem by taking fuel cap off as the mower was stalling after running it for 30 mins before replacing all of the parts above.

I did find that when I run the mower and disconnect either one of the spark plug cables from the spark plug the sputtering stops. Does this mean anything?

Here is video of the mower running:

Any ideas? Thanks in advance.

Click to expand...

I have a great idea. Clean the OEM (probably Nikki double barrel) carburetor that you hopefully didn’t not throw away. Install on mower and see how it runs. If you don’t know how to properly and thoroughly clean a carburetor, take it to a shop that can. These carburetors have to be dead on to run right.

Craftsman Garage said:

I would try adjusting the valves.

Click to expand...

I adjusted the valves, much easier than I anticipated. They were not far off from spec. Engine still spits and sputters.

I do not see anywhere to adjust the air to fuel ratio on this carb, is there supposed to be a place to do it?

No, you cannot adjust the mixture on most carburetors due to emissions regulations. They are set from the factory. I suggest taking the old carb apart and thoroughly cleaning it.

I would pull the valve covers. Watch the valves go up and down. They should all move roughly the same in travel distance. Put a straight edge on a rocker, watch the valves move. Look for a valve that doesn't move at all. While you are there check lash.

I would check flywheel key, valves and fire on both coils jumping a 1/4"+ gap in free air.

Vapor lock doesn't happen on mower engines. That is an old school 1968 Olds-Mo-Dodge trick back in the day.

Head gasket/s blown externally. Put your fingers around the head to block area and also look for black carbon exhaust leaking out.

Smoke can find leaks too. Get out your evap smoke machine and smoke the oil sump. Should pour out all the leaking areas.

You can also pressurize the oil sump with shop air at about 10psi. Listen and feel for air leakage again.

Flush out your mower fuel can. Make sure you don't have a pile of grass and dirt in the bottom. If you do, every time you gas up the mower, all that trash passes to the mower carb.

Get a new style mower fuel can. If you have an old can with an open top, you are making trouble for yourself. New cans are sealed better than the old ones. Fuel cans are highly over looked items.

Most likely your carb is polluted.

Craftsman Garage said:

No, you cannot adjust the mixture on most carburetors due to emissions regulations. They are set from the factory. I suggest taking the old carb apart and thoroughly cleaning it.

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That is the only thing left that it can be. I don't know what else it can possibly be, I'm running out of things to replace. I plan to take original carb apart tomorrow and clean it out and throw it back on engine to see how it runs.

rch316 said:

I don't know what else it can possibly be, I'm running out of things to replace

Click to expand...

It's not about replacing anything. You must TEST what you have.