QuestionQUESTION: I have a 16.5 hp riding lawn mower that just quit running while mowing. Through trouble shooting I determined that it wasn't getting fuel. After taking the Nikki carb apart and finding nothing apparent except the main jet being a little loose, I determined that the anti backfire solenoid would work out of the carb but not installed, so I removed it and put in a plug. Then the engine started but ran very erratic so I figured the the loose jet may be the culprit. Since I couldn't find any O' rings that small I ordered a new jet, bowel gasket and intake gasket from B&S. When I installed the new jet and gasket and reassembled the carb it wouldn't start at all. After much trouble shooting and trial and error I reinstalled the old jet minus the O' ring and held it in with a flat washer under the spring. She started right up and ran smoothly after adjusting the air mixture screw. The new and old jets mare the same number and the orifice seems to be the same size. So what's up with this carb? I don't really want to leave it this way and would like to reinstall the new jet and have it run.
ANSWER: Are you sure the solenoid was bad? Often times bad grounds or poor connections will cause the anti-afterfire carb solenoid not to function.
If the engine is running good I would leave it alone and just use the mower. If you suspect the engine is running lean or rich then I would change the jet. I would run the engine for a couple of hours and then read the spark plug to see how the carb is performing.
Eric
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QUESTION: Eric, yes I'm sure the solenoid was bad. I watched it work out of the carburetor, and I listened to it work with my stethoscope while I was screwing it in to the bottom of the float bowl. When I got it screwed all the way in it wouldn't work so I suspect that it is too weak to work with the small resistance of the spring it goes inside of. I did as you suggested and ran it for 2 hours and looked at the plug and it is burning just right so I can safely say it is not running rich nor lean. I can't put the new jet back in because it won't run with it in. As I stated before, it runs fine with the old jet without the O ring and using a flat washer to hold it in. I would like to get a new solenoid at some time but it wouldn't work to shut off the gas to the jet, when you turn off the ignition, because of the flat washer. That's why I need to know what's going on with this carburetor. I fear that whatever is causing it to starve for gas with the new jet may heal itself at some time and then it will run way to rich. I suppose that at that time I could just put the new jet back in and all will be fine. Is there anyone who is an expert on the Nikki carb. that could try to explain what is going on with this?
Thanks for your replies in this matter.
ANSWER: I as well as a couple of other techs at the shop have had some odd problems with carbs. Last weekend we had an engine that kept surging with the throttle rod spring installed. The spring became dis-connected while working on the engine and it stopped surging with the spring dis-connected. Connect the spring, it started surging again. We are still not exactly sure if the spring might have been defective, maybe the spring rate changed or a natural oscillation was occurring with the piece of equipment. Removed the spring and it ran great. The point is sometimes we can't always know exactly why the part caused the problem. I had another carb, similar to yours, which I just ran the old jet.
Are you absolutely sure there is not a weak ground or power issue and there are no intake leaks?
I am guessing there are no intake leaks if the plug is reading correctly. Will the engine die if you keep the choke closed? This will help tell you the intake system is sealing and sucking all the rich choke fuel into the intake system.
Did you verify no weak ground issues by make a jumper wire and connecting to the carb mounting bolt and an engine ground?
Eric
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QUESTION: Eric, I did replace the intake and bowl gaskets when I first installed the new jet. Yes I can fully choke it and it will sputter and even quit if I use my hand to choke it. Plus, as I said, the spark plug is running just right. I suppose that whatever is causing that carb to starve for fuel with the new jet in will eventually come loose and then she'll run very rich and probably stall. Then I'll try the new jet.
On the issue with the solenoid, I'm sure it's getting enough power. As I said, I can hear it activating with my stethoscope when it's partially screwed into the bottom of the float bowl but when I screw it all the way in it no longer works. However, the engine's running fine without it anyway and I just make sure it's idled all the way down before I shut her down.
I really appreciate you're taking the time to talk with me on this.
Ed
AnswerI had a one carb similar to yours. I ended up using the carb, once I had a used jet that worked, for several years. As my engine was old I eventually replaced the whole engine...more power.
If the carb is functioning I would just run the engine as is and not worry about. It may, like you said, come "clean" sometime but who knows.
I have had customers run without the solenoids for many years with no problem. Some will just cut the tip off the solenoid and put it back in...saves a few dollars.
Check the plug every couple of mows or so and it if looks good you will be fine.
Eric
