Tecumseh 15.5 Model OV490EA Engine

[FDenny]

Question on this engine
Model OV490EA
Spec 208029C
DOM 06009LB0261
Eng Fam 6TPXS
Disp 490cc

Given this mower by a fellow who could not get it running this spring. Would not fire on its own. It would start and run a few seconds if you poured gas into the carb. Took carb off cleaned it out good with air. Put back together and naturally had blown out the needle valve seat and lost it . Ordered and replaced and same result trying to start.
When initially took carb off remembered how the 2 wires went to the solenoid at the bottom of the float bowl and always replaced in same location.
Just for a try left the wires off. Motor started and ran fine. Put wires back on and would not start. Reversed the wires and now starts and runs like a charm.
What does this solenoid do ? Why would reversing the wires make a difference?

[bgsengine]

Its an anti-afterfire solenoid - what it does is shut off fuel flow through the main nozzle while engine is shutting down - prevents fuel from being sucked in and not being burned due to no spark, which results in backfires (and flames out muffler or carb) which can start fires and cause other damage.

Reversing the wires, 2 possibilities - one is the solenoid has a diode in it that delays the solenoid from closing when , for example, starting the electric clutch or battery voltage drops too low - that diode is a one way valve , or two, wires were not making a good connection and switching them around resulted in having a complete connection.

Side Note:
If the solenoid fails , sticks closed, or no current to operate solenoid due to wiring issues, the solenoid prevents fuel from flowing in the main nozzle, which also feeds High idle circuit so it acts like it isn't getting gas.
Many engines like this are set up a little more sensitive on the governor so even if shutting down after idle, the throttle plate may still open up , pulling fuel from the main nozzle while engine winds down and governor opens throttle.. so even removing or bypassing the solenoid and "shut down at idle" advice that some people give, is not always effective or safe - only if you can ensure the throttle plate stays closed at idle even when engine is not running , would it be safe enough to bypass that solenoid - Of course if you don't mind the backfire (damaging expensive exhaust systems or blowing a hole in air filter) and risking a fire, then by all means it can be bypassed, but don't say you were not warned.

[Deere2me]

Question on this engine
Model OV490EA
Spec 208029C
DOM 06009LB0261
Eng Fam 6TPXS
Disp 490cc

Given this mower by a fellow who could not get it running this spring. Would not fire on its own. It would start and run a few seconds if you poured gas into the carb. Took carb off cleaned it out good with air. Put back together and naturally had blown out the needle valve seat and lost it . Ordered and replaced and same result trying to start.
When initially took carb off remembered how the 2 wires went to the solenoid at the bottom of the float bowl and always replaced in same location.
Just for a try left the wires off. Motor started and ran fine. Put wires back on and would not start. Reversed the wires and now starts and runs like a charm.
What does this solenoid do ? Why would reversing the wires make a difference?

Without lookin' up yer unit, I'm gonna say the solenoid is what most people call the " fuel solenoid". What it actually is called is the " anti-afterfire solenoid". When energized, the plunger retracts and allows fuel to enter the main jet/nozzle from the filled bowl. When ya shut the engine off, the plunger extends by spring and stops the fuel from being sucked in by the coasting engine and then hitting the hot muffler with a BANG!
Reversing the polarity MIGHT have caused it to work bas ackward, but prolly just had a bad connection/ground.

[bobodu]

Coils don't care about polarity .

[FDenny]

Thank you all for your info.