Briggs 15.5 HP Engine Problem

16 years ago

I have Sears riding lawnmower with a B&S 15.5 HP Engine Mode 28U700 with the Nikki Carb

The engine starts normally and sometime runs OK for a few minutes.

After this time, it will not run unless the engine is in the choke or near full choke position. With the air filter off, I can see that the choke butterfly is closed in choke position and opens wide in the operate position.

When the engine is fully loaded (deck engaged), the engine seems to run better. I'm not sure but I think it ran better when I used some gas with a small amount of oil (64:1). This was last spring. The problem is getting worse, it has been going on for several years.

After a few minutes in the normal operate position, the governor starts moving back and forth quickly and then the engine dies.

Here is what I have checked:

1. The gas cap is not clogged. I also get the same problem with the gas cap removed.

2. The fuel filter is not clogged.

3. The gas line to the carb is good.

4. I sprayed ether at the intake to the engine (just after the carb) to check for a vacuum leak. No change.

5. I planned on rebuilding the carb and found out after I started that I had the wrong rebuild kit. The carb did look clean and I sprayed everything with carb cleaner and put back together. No change.

6. The fuel solenoid appears to work correctly.

Any theories?

Thanks

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Comments (6)

rcbe
16 years ago
a carb can "look" clean and still be stopped up. Tear it down, soak it in the appropriate cleaner, run a small dia copper wire thru all passageways/jets/orifices and then blow everything out with clean compressed air. Rebuild the carb with a new kit (the correct one).Have a magnifying glass on hand to see those small holes.
If you have a gravity fuel setup (tank above engine), remove fuel line at card to verify you are getting a good steady flow of fuel.
If the engine still stalls, check for good spark at that time - you may have a coil breaking down or a cooling engine shroud full of trash.
mownie
16 years ago
I concur with rcbe. Whenever you have to apply choke to get an engine to run, it usually means there is something preventing enough fuel being fed to the engine. Applying choke reduces the amount of air entering the carb, if it runs better with choke, it is probably starving for fuel.
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alclark
Original Author
16 years ago
Good News!

Thank you rcbe & mownie!

I took the carb apart again. I inspected closely, looked at all the orifices, etc and blew out with clean air.

I don't think this mattered.

I thought more about the starving comment from mownie. I think the problem was that the fuel solenoid was partially sticking and therefore restricting the fuel intact.

I had checked the fuel solenoid some time ago and it seemed to work. The engine performance has been a problem for a long time and it has been getting progressively worse.

With the bowl removed, I could see exactly how everything was supposed to work. Two years ago, I tried replacing the fuel solenoid with a bolt and this didn't help. Maybe the bolt went in too deep and acted like the solenoid being engaged.

The solenoid has a plastic cap that is easily removed from the shaft. Removing this cap keeps the solenoid from doing anything except plugging its own hole. Now fuel is never restricted by the solenoid and the engine is running well in its normal operate position.

I'm not really sure the that the fuel solenoid adds much value. The replacement cost is about $45.
mownie
16 years ago
Uh huh! Those much cussed fuel solenoids can be troublesome. I think the fact that most often the solenoids are oriented right in the lowest region of the float bowl, where water will sink to. To add to that, by design, the plunger barrel must be an open tube for the plunger to retract into. So any water and/or fine solid debris will end up inside the plunger tube. The water corrodes the plunger return spring and rust flakes from that add to the collection. Over a period of time, the plunger movement can be restricted or even halted.
Gaston Diotte
5 years ago
can somebody hepl keep breaking keyway under flywheel 15.5 h.p briggs single had valve chek compression good
tomplum
5 years ago
UPDATED FLYWHEEL INSTALLATION SPECIFICATIONS MODELS: 210000, 280000, 310000, 330000 OHV VERTICAL SHAFT ENGINES ADVANCED PRODUCT SERVICE INFORMATION DISTRIBUTION SALES AND CUSTOMER SUPPORT POST OFFICE BOX 702, MILWAUKEE, WI 53201-0702 USA ® We have recently updated the flywheel installation procedures for the subject vertical shaft engines. Please retain this APSI for service reference until the repair manual is revised and re-issued. • NEW Flywheel Torque Specification - We have increased the torque specification for the flywheel bolt or nut to 110 lb-ft (149 Nm). • Flywheel Key - Use only steel key P/N 796335 for subject engine models. The IPLs will be revised accordingly in the near future. NOTE: For all other engines, ALWAYS refer to the appropriate Illustrated Parts List for the correct flywheel key part number. Following are steps to perform when preparing to install a flywheel on any Briggs & Stratton engine: 1. Thoroughly clean all surfaces of the flywheel and crankshaft tapers, including the keyways. NOTE: DO NOT use lapping compound or any type of lubricant or anti-seize on the tapers. Both surfaces must be clean and dry. 2. Use only the specified tools to hold the flywheel when the flywheel nut or bolt is torqued to specification. 3. Ensure the torque wrench is properly calibrated. Double-check for proper torque at the flywheel nut or bolt before reinstalling the blower housing. BRIGGS & STRATTON CORPORATION DR