PTC Heater

I was reading something about these the other day. It is interesting, because when I went to sync my carbs a few months ago, I remember having a hell of a time getting the top carb to cooperate. And to this day, it takes some finagling to get it to start. Once it's been running, it fires up easily every time, even after sitting for hours. BUT, the first start of the day has always been difficult.

It's my understanding that this thing should be extended on start up and then slowly retract as the engine warms up? At what point should it be fully retracted and is there a simple way to bench test it by applying 12 volts? It appears to be just a solenoid.

Assuming we're discussing your MFS25A. Yes, the upper carb does have an ABS solenoid. They don't fail often, but if it does not activate, you will definitely have cold starting issues.

You have the operation backwards. The needle is retracted when cold, and the ABS heater causes a wax pellet to expand, and push the needle deeper into the carb, restricting fuel for normal warm operation. You can check for proper operation by starting with a cold solenoid, and then applying 12v to it. The needle should slowly extend over a few minutes. You can also check for power coming from the alternator; that pair of wires should be live any time the motor is running.

Oops... Yes. Sorry about that. MFS25A is correct. Thanks for the input on the test. I have been running it often without issue. The start up problem is annoying. I'm running some wiring on the boat today. I'll perform the test you mentioned and report back with the results! Thanks again! You are VERY helpful.

OK... I removed this thing. It is fully extended when cold. I hooked it up to the battery for several minutes and nothing happened. Black to ground and yellow to Positive. The top part got warm, but no movement at all? So, I assume it's toast. Not sure how? It looks like such a simple device and it's not cheap either!

You have diagnosed a bad ABS solenoid. The heater is clearly working, but the wax expansion cell seems to have failed.