It depends on the application of the engine. You can determine if you have a fuel pump by following the gas line backwards from the carb. I would expect if you find anything other than a filter and shutoff valve you have a fuel pump. A cheap and dirty test for a fuel pump is to place a gas line from the output of the pump in to a cup or other container and turn the engine over. You should see gasoline pulsing out of the hose. It won't seem like much but it doesn't take much to keep a small engine running.

If this is the first time you are trying to start this engine after being in storage I would look to old gas in the float bowl or a gummed up carb before suspecting the fuel pump.

Hope this help you.

"Running roughly" when...? Will the engine idle or does it simply "quit" when the RPM gets low? Are you just now trying to return the machine to service after storing over winter? When you are spraying the carb cleaner and the engine "smooths out" (with just the right amount of spray), that indicates that the engine was trying to run with too little fuel (lean condition). It is beginning to sound like you might have some blockage of the jets in the carb. If the engine will not idle at all, but runs at higher RPM, the small "pilot jet" may be completely clogged up. If the engine seems to run worse as you attempt to increase the RPM (you open the throttle), the main jet may be partially blocked. Typically, the blockage is due to varnish/gum that has formed during storage. A big factor with some Kohler engines is using the proper fuel filter. Some Kohlers are very picky about fuel filter characteristics and will only perform properly with a Kohler brand fuel filter in place. As to answering the question of whether this machine uses a fuel pump........follow the fuel hose from the filter toward the carburetor. If this machine uses a fuel pumo, it will be between the filter and the carb. Another telling factor is the location of the fuel tank. If the fuel tank is mounted "higher than the carb", it might not use a fuel pump. If the fuel tank is located "lower than the carb" (like under the seat), it most certainly requires a fuel pump to bring the fuel to the carb. Fuel pumps hardly ever get "weak" (though not unheard of). Usually they work one minute and don't work the next time. You can check the flow of the pump by disconnecting the hose from the carb inlet fitting and holding the hose end in a "catch bottle" while someone cranks the engine. With the hose loose from the carb. you should observe "pulses" of fuel flow into the bottle. Each pulse should be about 1/4 to 1/2 teaspoon of fuel. That is not a great amount of liquid but it is sufficient for this size engine.

atschirner, I wasn't "copying" your post. I had a few "interruptions" while I was typing (plus, I'm long winded) and so our posts appear similar. If this occurred on a test.....we might be accused of "cheating". :^)

No problem mownie. I'm happy to have the confirmation that my advice was on track.

Thanks for the advice -- you gentlemen are amazing. Answers to your questions. Problem actually started in the fall just before it was put away for the winter. (I know, I know.) I took off the gas tank blew out the gas line back to the tank. Nothing. Replaced the plug. Put on a new filter -- 1st one was not a Kohler but this spring I put on a Kohler filter. Gas is fresh this year. The tractor does not have a fuel pump. I ran it several times and squirted Gum out carb cleaner to see if I'd eventually get rid of whatever.
Drove it around-- it's rough at any RPM but will go up a hill -- won't run on lowest idle setting -- It has a slight surge and yesterday while "exercising" it, it popped a couple of times. My sense was that this was through the exhaust -- but not sure. It will occasionally "Pop" when starting it. At the beginning of this, it would vigorously "backfire" when starting it. It hasn't done so lately. Does this help?

Beginning to lean toward a clogged pilot jet (slow speed and idle RPM range controlled by this jet). It might also be caused by too low of a fuel level in the float bowl. At any rate, the "popping" and "backfiring" point toward a very lean mixture (especially when attempting to "open up" the throttle). It would be a good idea to take this carb apart for a thorough cleaning and "probing" (with fine diameter wire through all the jets and passages) followed by blowing out with compressed air. Follow the instructions in the service manual (or the kit) on any adjustment available for setting the float height (this sets the fuel level of the float bowl). I have seen engines act like yours due to the float being set too low, though, (admittedly) very rarely.

Carb. still dirty IMO as suggested above. keep dumping the carb. cleaner in the gas tank or take the carb. off and clean it using a can of spary carb. cleaner, tooth brush, fine piece of wire and compressed air.

Thanks yet again. Will work on this, but have to leave for a several days so will let you know when I get back. I'll post a followup to this or is it easier for you guys for me to do a new post after that amount of time? (probably about April 30) I never really know what the best way is to keep in touch.

malamute5, you can keep this thread going. It has all your opening remarks and stuff. You are the OP. Good luck with whatever you will be doing in the mean time. :^)

Just to let you fellas know.... Have mowed twice --- before I left and once since my return. Some pretty thick grass. It isn't running just right, but is a whole lot better than before. Just have been using the carb cleaner with each fill up. Am still trying to avoid taking the carb off. Start up still gives a pop and isn't immediate, but I'm still hoping that it will finally clear itself up. (Probably not too realistic -- but hope springs eternal.) If more happens, I'll let you know. Thanks for everything.

Thanks for the update sir. We don't get nearly enough folks to offer continuing updates. Updates and replies are very welcome here. It's another way to share info.

My Kohler CV15S lawn tractor engine will start if I put some gas into the air intake but it quits after blowing some smoke and running clean for about 4 seconds.

I have a gas pump between the filter and carb. It is about 3 inches in diameter, 1 inch deep, with a gas line in, a gas line out, and a vacuum (?) line attachment. It is not shown on my fuel system diagram or in the parts list. Can anyone confirm that this is the gas pump and/or have a part number?

When I disconnect the output gas line from the pump while cranking the engine some gas sputters out, but not as in the clean 1/2 teaspoon pulses suggested here.

Any suggestions as to why the engine quits before I continue on my own bumbling way?

Mister_Bob:

1) start your own thread on this forum's opening page. You'll get more responses/attention.
2) Find and post the tractor's model number to help in finding info/answers. We don't know how to mindread.
3) Sounds if either your fuel pump is crapping out; your fuel lines are pinched/clogged; your fuel filter is dirty/clogged; your fuel tank is dirty/inlet screen clogged or fuel cap vent is clogged.
By systematic elimination, chk 'em each out. Then - if prob still there - post back with details of yer troubleshooting and current symptoms along with model number..

I followed the advice from rcbe6 and found a hairline crack in the rubber fuel line between the filter and the fuel pump - in a severe bend at the entrance to the pump. The pump was sucking air instead of fuel at its intake, I guess. I replaced that line with a new one, also replaced the line from the pump to the carburator and replaced the fuel filter. A little gas in the air intake and the engine (Kohler CV15S PS 41526) started right up and kept running. Thanks rcbe6.

But a new problem has emerged. After I got the engine running smoothly, the engine died when I tried to move the tractor. It died even if I let the clutch pedal out with the gear shift in neutral!

Before my fuel problem, the tractor (CRAFTSMAN Model# 917271010) rode just fine, with the engine laboring only slightly if the grass was wet and high. So it seems strange that the engine can now deliver no horsepower.

Hoping the carburator was gummed up with all my fuel tinkering, I put some carburator cleaner in the gas and ran the engine 20 minutes or so. But the engine still quit (with a sputter and a bang) as soon as I let the clutch out.

It seems strange that my fuel problem is fixed but now I have a complete loss of power. Any advice on how to diagnose and fix this power problem?

Does the engine "die" instantly, as if you had cut off the ignition switch? or does the engine begin to act as though it is running out of fuel? If the engine is just suddenly changing from running great at good RPM, to just completely dying I would suspect the safety interlock switch on the seat. It sounds like you are describing that the engine runs good so long as the clutch/brake pedal is held down, or "locked down" (park brake). That scenario is ok AND.....is "permitted by" the safety interlock circuitry. What happens when you let up on the brake/clutch pedal to begin moving, invokes the function of the seat switch (to confirm or deny, the "presence of an operator"). It's as if the switch on the brake/clutch announces "Hey, the brake is being released and I think we're about to begin moving." But then the seat switch responds by saying, "Oh no we ain't gonna move! There ain't no operator occupying this here seat! Shut 'er down right now!" The seat switch already "knew" the seat was not occupied (before the brake/clutch pedal moved), but it allowed the engine to stay running so long as the park brake was on (that's a "safe and permitted" mode). But when the seat switch thinks the seat is empty and the park brake is not on....that is an "unsafe and forbidden" mode, so the seat switch kills the engine. The sputter and bang sort of says the engine is being deprived of "spark ignition", fuel still present in exhaust ignites when engine reaches zero RPM.

Mownie: Bang on! I reconnected the seat switch and the tractor now moves perfectly. Many thanks.

Why was the switch disconnected? In my attempts to diagnose the fuel problem I tested the seat switch by disconnecting it from the electrical input. To my surprise the switch showed a closed circuit. Ah ah, I thought. The seat must break the circuit when I am sitting on it. So I reasoned that keeping the switch disconnected would keep the circuit open. Sure enough, with the switch disconnected I could turn the engine over, watch fuel flow or not flow, et cetera. After I found the hairline split (which never leaked fuel, by the way) the engine started and kept running. But the tractor would not move for the reason Mownie deduced. Reconnecting the switch solved the power problem.

I was wrong (no surprise there!) about the switch; but I'm still curious how it works, if anyone knows .... I fix this and that just for the fun of it: at home, for my kids, for the neighbors, for our grandkids, and at a senior center with distraught and frugal citizens. So I love to learn and share how things work.

Thanks again and I hope I can reciprocate in some way.

***"about the switch; but I'm still curious how it works, if anyone knows"***
Most of the safety interlock circuitry now feature a "shorting connector" at the seat switch. There are 2 reasons it has been configured this way. (1) To prevent someone from defeating the OPS switch by simply unplugging it. (2) The shorting connector means that if the connector were to ever come loose from the switch body, there is no way someone could "unknowingly" operate the machine with the OPS system inoperative.

I have a kohler motor on my lawn tractor, my fuel bowl is full but won't get fuel to the throat unless I partially cover the throat than plenty of fuel but when I take my finger away, fuel is used and no more gets into throat. Any ideas?

prolly time for a complete carb disassy, cleaning and rebuild with a new kit....