Briggs Intek V Twin surging

[Avery4]

Hello everyone, I am currently working on a friend's riding mower with a 22HP 724CC Briggs Intek V Twin motor and it suddenly started surging. It starts fine, but it surges at all throttle positions. If I dribble some gas into the carb while it's running or I get the choke set just right, I can get it to run smoothly.

Sounds like a typical carburetor problem or bad gas, but the mower is barely 2 years old and my friend took great care of it. First thing I did after checking for vacuum leaks was pull the carburetor bowl to look for signs of water, corrosion, gunk, etc and to my surprise the carburetor looks like new inside! The fuel filter is clean and the pump seems to be working also since the carb bowl was full every time I took it off.

Does anyone have any suggestions of what else the problem could be? It sure seems like a carburetor problem but as clean as the old carb looked and with a new OEM carb costing $120+ I'm having trouble pulling the trigger and buying it a new carb. Every other time I needed to replace a carb there was pretty obvious signs of contamination.

So if anyone has any ideas of what else to check before replacing the carb I would greatly appreciate it, my friend needs his mower back ASAP and I would hate to replace the carb unnessisarily when I am overlooking something simple.

 

[MParr]

Has the fuel filter ever been changed?
Pull the filter off and drain some of the gas from the tank. Drain from the line running from the tank to the filter. Then, put one of these on.

Amazon.com

 

[Astro_Guy]

Hello everyone, I am currently working on a friend's riding mower with a 22HP 724CC Briggs Intek V Twin motor and it suddenly started surging. It starts fine, but it surges at all throttle positions. If I dribble some gas into the carb while it's running or I get the choke set just right, I can get it to run smoothly.

Sounds like a typical carburetor problem or bad gas, but the mower is barely 2 years old and my friend took great care of it. First thing I did after checking for vacuum leaks was pull the carburetor bowl to look for signs of water, corrosion, gunk, etc and to my surprise the carburetor looks like new inside! The fuel filter is clean and the pump seems to be working also since the carb bowl was full every time I took it off.

Does anyone have any suggestions of what else the problem could be? It sure seems like a carburetor problem but as clean as the old carb looked and with a new OEM carb costing $120+ I'm having trouble pulling the trigger and buying it a new carb. Every other time I needed to replace a carb there was pretty obvious signs of contamination.

So if anyone has any ideas of what else to check before replacing the carb I would greatly appreciate it, my friend needs his mower back ASAP and I would hate to replace the carb unnessisarily when I am overlooking something simple.

Have you tried a fuel treatment or fuel system cleaner? I've recently had some impressive results with Seafoam.

 

[Avery4]

Has the fuel filter ever been changed?

Yes, my friend takes great care of his mower. He did a tune up about a month ago and it just started acting up yesterday.

 

[jhs914]

Could be a small piece of trash clogging the jets. If you don't have a small enough piece of wire to dislodge it, blast it with carb cleaner/brake cleaner in both directions through the straw on the can. How did you check for vacuum leaks?

 

[MParr]

Yes, my friend takes great care of his mower. He did a tune up about a month ago and it just started acting up yesterday.

There still can be water or trash in the fuel. Also, a filter not made for a fuel pump system can cause problems.
A tune up recently? Are the plugs tight in the head? Are the plug wires pushed on all of the way?

 

[Avery4]

Could be a small piece of trash clogging the jets. If you don't have a small enough piece of wire to dislodge it, blast it with carb cleaner/brake cleaner in both directions through the straw on the can. How did you check for vacuum leaks?

That's what I'm thinking. I tried cleaning the carb and spraying brake cleaner through all the passages and the mower still surges. Sometimes for whatever reason cleaning carburetors doesn't always work though.

 

[Avery4]

There still can be water or trash in the fuel. Also, a filter not made for a fuel pump system can cause problems.
A tune up recently? Are the plugs tight in the head? Are the plug wires pushed on all of the way?

The fuel looked and smelled fresh, but just to make sure it wasn't a problem I drained the tank and put some known fresh fuel in it for testing. Good point about the fuel filter too.

 

[samven]

Check the governor spring, it sounds like its hunting. It might be weak or just got stretched. If the first time the bowl was off was after the problem started I doubt the float level is off but I would check the bolts on the carb to make sure nothing loosened up in use and caused an air leak.

 

[Mazomopar]

You can try running it with the gas cap off. Might be a little hungry for fuel and the cap vent might be plugged. Simple 2 min test that doesn't cost a thing.

 

[Avery4]

Check the governor spring, it sounds like its hunting. It might be weak or just got stretched. If the first time the bowl was off was after the problem started I doubt the float level is off but I would check the bolts on the carb to make sure nothing loosened up in use and caused an air leak.

Great suggestion. I think there is more to the problem than the governor though because I tried manually holding the throttle at a steady position and although the RPM stabilized, the engine still didn't run smoothly. The only thing that smooths it out is dribbling fuel into the carb or setting the choke just right. There are no air leaks, I sprayed brake cleaner around the carb and intake manifold to check for vacuum leaks and nothing changed.

 

[Avery4]

You can try running it with the gas cap off. Might be a little hungry for fuel and the cap vent might be plugged. Simple 2 min test that doesn't cost a thing.

Great suggestion, I have seen that happen too. That isn't the case on this mower though, it surges whether the cap is on or off.

 

[oggb]

Almost any small engine that runs better with the choke on has carburetor issues. Take a fine wire and poke it through all of the jets/orifices (find a diagram that shows all of the jets if you can) and spray with carb cleaner a few times.

If it doesn't surge while the engine is under load (mowing) it's almost 100% a low speed/idle jet.

 

[Avery4]

Almost any small engine that runs better with the choke on has carburetor issues. Take a fine wire and poke it through all of the jets/orifices (find a diagram that shows all of the jets if you can) and spray with carb cleaner a few times.

If it doesn't surge while the engine is under load (mowing) it's almost 100% a low speed/idle jet.

Thanks. That's what I was thinking too, I can't think of any other issues that would be improved by running the choke. It just seems odd that such a new and well maintained mower would have carb issues even though it looked so clean inside.

I'm not totally sure if the engine surges while under load. My friend said it did, but I can't verify that at the moment because I just cut my grass the day before he dropped it off.

 

[danez_yoda]

Check you-tube for that engine and surging problems. Most are carb issues. A small jet that is clogged. Some videos actually take small 0.01" drill bits to clean out something lodged in there really good. You should see light through the hole.

He did a tune up, make sure he used the correct plugs. Same ones that came out not some "upgrades". Usually a champion plug. To cold of a plug can cause poor running but generally not surging.

What was done on the tune-up? Check those and everything you had to do to get to those things in the tune-up. The engines don't really need much "tuning up". Air filter, oil changes are the big ones. new plugs every season..... maybe... Fuel filter every 100 hours or so.

Is the fuel-filter the same as the one that came with the mower. Some might be more restrictive than the original requiring a little choking.

Is he running 87 octane? that is works best for these engines. No advantage to high octane and its harder to burn.

 

[Mazomopar]

The other thing I've found on my similar engines is the choke/throttle cable gets out of whack..if you push the throttle lever all the way forward into choke position, the choke linkage shouldn't have any play in it. if you can take your finger and move the linkage arm up towards the carb,you need to take slack out of the cable. Loosen the T25 cable clamp and tug the cable back till the linkage is maxed out. Another no cost, keep it simple test.

 

[Avery4]

Check you-tube for that engine and surging problems. Most are carb issues. A small jet that is clogged. Some videos actually take small 0.01" drill bits to clean out something lodged in there really good. You should see light through the hole.

He did a tune up, make sure he used the correct plugs. Same ones that came out not some "upgrades". Usually a champion plug. To cold of a plug can cause poor running but generally not surging.

What was done on the tune-up? Check those and everything you had to do to get to those things in the tune-up. The engines don't really need much "tuning up". Air filter, oil changes are the big ones. new plugs every season..... maybe... Fuel filter every 100 hours or so.

Is the fuel-filter the same as the one that came with the mower. Some might be more restrictive than the original requiring a little choking.

Is he running 87 octane? that is works best for these engines. No advantage to high octane and its harder to burn.

Great info. I checked Youtube but most of the videos I could find were of a different carburetor. This one is quite odd, the float is actually below a plastic plate in the bowl and the plastic plate is sealed to the carburetor body with a gasket. Never seen anything like it before and I do quite a bit of small engine repairs.

He didn't do anything major to it, he just changed the oil, oil and air filter, and fuel filter. He didn't have the carburetor apart or anything like that. Everything seems to be done correctly.

 

[danez_yoda]

if he changed the fuel filter it is possible the new filter had something in it on the carb side that worked its way into the carb. just a sliver is all it takes with ports that small.

 

[spasm3]

With the mower only 2 years old , the fuel line is probably not the problem. But on older mowers i've had the fuel line look good on the outside and was degrading internally and sending junk into the jets.

 

[Dinoburner]

Most surging problems here have been fuel starvation. Most likely in the carb but the fuel line or in tank filter if there is one. If its gravity feed pull the hose off the carb inlet and observe how fast the fuel flows. Do this outside carefully of course. If there is no fuel shut off then needle nose vice grippes with pieces of hose over the jaws can be used to pinch off the fuel hose works well to control unnecessary loss of fuel. Loosening the carb bowl to see if the float is dropping and allowing fuel past the needle is another part of elimination. If all is well after these checks then a very thorough carb cleaning is needed.


















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