Question for the small engine gurus

[DGXSER]

I have a craftsman lawn tractor with a B&S 17.5 HP engine. Has the over head valves. Ran great all summer till about three weeks ago. Sounded liek running out of gas but tank had plenty so I switched out the fuel filter and it ran great again. That is untill this weekend, now it surges badly.

Symtoms, runs well with choke on but after a bit it starts to bog down, pull the choke off and it runs ok but starts surging till it almost dies then put choke on and repeat cycle.

What I have done, checked the solenoid is gettign twelve volts, pulled the carb apart and cleaned the jets and every passage I could see. added seafoam to the gas and let is sit overnight after getting it into the carb. Checked compression and it is running 120 psi. Checked valve clearances and they are about .007 on intake and .009 on exhaust. Cleaned up the spark plug, cleaned the carb again.

First time, after I cleaned the plug and the carb it ran good for about 10-15 minutes then back to surging. Ever since it just continues to surge unless I choke it.

Any suggestions appreciated. I can turn a wrench ok and diagnose decent but surgin liek this on a one cylinder engine is wierd to me.

[XSokieSPECIAL]

Air filter clogged? I believe there is also a vacuum diaphragm in the carb that acts as a fuel pump. Pull the carb apart, it is a lot simpler than your XS's.

Greg

[DGXSER]

Thanks for the suggestion Greg. The air filters have been blown out with compressed air and are fairly clean.

I pulled the carb as far apart as it goes I belive. There is a solenoid valve on the bottom of the float bowl that blocks fuel from going up the main until it is powered. It is getting voltage and I tested it out of the carb and it worked fine. Then there is a float with valve very similar to the XS carb, it is clean and appears to be working. There is a small jet screwed into the side of the fuel tower, and then what I would call the main/emulsion tube that screws out and all of its passages are clena and open. In the inlet side of the carb behind the choke valve is three holes. two look to have pressed in jets in them and one is just open. All of them free flow compressed air to the bowl of the carb.

If I am missing a passage to clean or open up, please let me know.

[Ken Talbot]

Maybe time for a new plug! My BIL the mechanic taught me years ago that the first thing to do with a small motor is replace the plug. Then you can start looking for other problems. 90% of the time, the fresh plug will solve the problem.

YMMV..

[mro]

If no problem with the fuel system...
Can you hold the rpm steady by holding the throttle at the carb?
Could be the governor needs some attention.

mro

[DGXSER]

You know Ken, I had the same thought and admittedly I believe it is the same plug it came with more than a few years ago. In my defense I do clean it up every year and regap it. I'll get a new one today.

MRO, I had not thought of that, I will watch the throttle and try to manually manipulate it.

[xswilly]

had the same problem with a snowblower
rebuild the carb and put an inline filter in the gas line
crap keeps going from the tank to the carb
especilly with the ethenol in the gas,
it removes the build up of sludge in the tank,
guess where it goes from there

[red bandit]

I've got a 2000 B&S 14.5. Had same symptoms. There is a 2 wire plug on the right side of motor. One wire goes to solenoid valve on the bottom of the float bowl. When the motor would start to act up I would touch/hold that plug and everthing would be ok. I used a bread tie to fold the wires over. No problem all summer.

[rpgoerlich]

The old Craftsman mower I have, has gravity fuel feed to a mechanical fuel pump. It also had a filter before the fuel pump. It has a plastic fuel tank.

If a new spark plug doesn't fix it, might check your fuel(gotta luv ehtanol...) and all the grounds on the wiring. I had to re-solder the wire onto the solenoid as the spade was broke off.

[DGXSER]

Doooooo

Well, I got it figured out. Turns out the vent hole in the gas cap was plugged. I had noticed when it surged I could watch the gas in the fuel line bubble and surge as well.

Thanks for all the great advice! At least now my carb is REALLY clean and I am going to replace the plug anyway!

[XS1100 Newbie]

Hey DG
Will it outrun the XS now? LOL

[DGXSER]

Hey DG
Will it outrun the XS now? LOL

Actually, the way the XS is rinning as of noon today, maybe. I think it got jealous of me spending so much wrench time on the mower.