99 50 4 stroke choke issue

[OMC-boy5.5]

Hi everyone,

I have a 99 mercury 50 hp Bigfoot. This is the 4 cylinder carb model. I am having issues with the choke and high idle system upon startup.

I have narrowed it down to what they call the autostart actuator. It is not expanding far enough to lower the throttle advance. I can set the choke linkage to make up for its lack of travel and allow that to turn off properly, but it will not expand enough to allow the high idle linkage to move and allow the engine to idle down completely.

I took feed voltages to this actuator to be around 6.9-7.0V DC while running.

Battery shows 13.5V while running and 12.6 while off.

So do I have a bad voltage regulator not sending enough power for the actuator to work properly? Is 7V the proper voltage for this equipment? Should I source a new actuator?

 

[boscoe99]

Do you have the applicable service manual to assist you is adjusting those carburetors and associated linkage?

 

[OMC-boy5.5]

Yes. It is available in PDF format. It does explain how to test the regulator/ rectifier but I wasn’t sure that would tell me anything if it was designed to operate on some sort of variable or lower voltage source. I think I’ll just make a jumper wire straight to the battery and see if I get better results

 

[boscoe99]

If you are seeing 13.5 volts at the battery with the motor running then the rectifier/regulator is doing its job.

What is the complete engine ID?

 

[boscoe99]

Is this what you are seeing in your manual?

 

[boscoe99]

 

[boscoe99]

The choke solenoid and the electrothermal ram both share the same ground on the block. Don't forget to inspect/test the wiring. All the power in the world is no good if the ground is no good.

 

[OMC-boy5.5]

I completed the electrothermal ram test as illustrated. It extended about 1/8-3/16” and is bouncy at full extension. I think I needs to come out about 1/4” and be firm to work properly by my observation. It extended about the same distance as it does when running normally on regulator power
I had 7V at the green and white lead with the other lead grounded directly to the frame while running.
I did the rectifier tests as outlined and the results kinda stumped me. My meter read 530 for all the leads that are supposed to be 0.3-0.8. And 916 for the lead that is supposed to be 0.8-1.3. I’m assuming this is an error in scale?

Stator checked out fine.

I am leaning towards worn out electrothermal ram at this point. Just don’t really wanna spend the $2-300 on a new one.

 

[boscoe99]

There might be two electrical connectors between the R/R and the Ram. I would make sure there is nil voltage drop across those connectors.

 

[boscoe99]

Everything that I am seeing leads me to believe that motor was made by Yamaha for Mercury. Do you agree or disagree? I am basing my comments on what I see from Yamaha data.

 

[OMC-boy5.5]

Yes it is the Yamaha made engine.

I also had 7 volts directly from the regulator.

 

[boscoe99]

How many volts out of the red wire?

 

[OMC-boy5.5]

I believe it was 13 something. A normal voltage for sure or I would have remembered

 

[boscoe99]

If you have verified that the choke linkage is moving freely and clearly and is not part of the problem, and if you can push the linkage that the ram should be pushing on, and it comes out of a fast idle, then it might appear that the ram is unable to do its intended job.

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[OMC-boy5.5]

Yes and yes. It moves freely and operates correctly once you push out on the lever that the ram is supposed to be moving. Just wanted to isolate which is the more common problem mainly. Was worried that the 7 volts was holding it up but hooked straight to the battery it does the same exact thing

 

[OMC-boy5.5]

This brings me to the next question - being a Yamaha made engine - can I replace it with the comparable Yamaha variant or does it need to be the mercury one? Mercury wants $250+. Yamaha is around $160?

 

[boscoe99]

No reason at all for the Yam branded part to not work.