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I have a 5-year old DR Power Field and Brush mower, that is equipped with a 656cc, 20 HP, B&S motor. The motor model # is 40S877. The machine is only used around my own property, no commercial use. I may have 150 hours on it.

I was having issues with it running rough, surging and backfiring, but more on an intermittent basis rather than all the time. I added new gas and Seafoam additive, without much difference being realized. I decided to change the plugs, fuel filter and air filter, but it was still running rough. I figured it was probably a carburetor problem, so I researched a rebuild kit for it. I found out that for less than $20.00 more than the cost of a rebuild kit, I could buy a new carburetor. I bought the carburetor, installed it, and it runs much better. However, another problem arose with starting the motor. It would only start if I gave it a shot of starting fluid!! I thought that maybe the fuel pump was bad, so I just got through installing a new one of those. And....it still won't start unless I use starting fluid, even if it's been run a while. Any suggestions? Thanks!!

Now you know why the replacement carburetor was so inexpensive. If you still have the old one, rebuild it.

Okay....I get that I may have opted to go the economical route at first, but how do you reconcile the fact that it runs pretty well when you use starting fluid, but won't start otherwise. There must be some sort of technical explanation for it, and I'm all ears. Thanks for you reply!!

Is the choke closing all the way. Doesn't take much gap to cause big cold start issues.

Any carb gasket leaks? Like ILENGINE said, choke working proper? Is there a pilot jet to adjust? Do you have good fuel flow from the tank? Remove the fuel line AT the carb fuel inlet and check fuel flow from tank. Gas cap not venting starving carb for fuel? Valve clearance per manufacturers spec? Good spark?

slomo

slomo

Just so you know.
Most carbs have an idle circuit and a running circuit
On most all of the fuel at cranking speeds comes from the idle circuit
Once the engine fires and goes from ≈ 400 rpm to ≈ 1300 rpm most are running on both the idle & main jets
So if the idle jet is not supplying fuel, the engine will not start but will run .
How well it runs depends upon the balance between the idle & main jets at high idle.

If it has the 2 barrel Niki carb most likely the choke is not closing all the way or not at all. You can't see the choke butterflies so you have to check the linkage is raising the choke linkage up with no play when the choke is engaged. I have rebuilt dozens of those carbs. All you usually need is a few orings to fix the carb. The jets have very small o rings that shrink and cause poor running. There are a couple other gaskets that shrink and cause issues.

Thanks for all the suggestions. I have come to realize that even 71 year old guys can still make rookie mistakes. I took note of the responses regarding the choke, so I checked that out first. Lo and behold, I had put the choke rod linkage in the whole hole of the crank on the side of the carburetor. I probably should have taken a picture of it when I removed it from the old carburetor......live and learn. Runs like a new one now!!

Thanks, again!!