Switchbox issue?

[talbee]

When I purchased my boat it came with a '78 Mercury 900 90hp. The guy said I may need to take a hairdryer and heat up the switchbox for about 5-10 minutes to get it started. It does fix the starting issue. I would like to know if it could be something else causing this to happen?

 

[Texasmark]

Chris1956 is pretty good on these engines, as is Steelspike. Give them a yell. I have had temp problems in electronic circuits on later models. Probably similar components used on early models. Long story but electronic components are sensitive and do age. Question is which one is your smoking gun. On later models with the CDI modules troubleshooting is pretty easy. But these guys ought to be able to guide you through it.

 

[Chris1956]

OK, heating the switchbox is crap. If that is the cure, you have a switchbox issue. But hold off replacing it, until we test further.

Let's start with the basics. The starting procedure is as follows. Pump primer to fill carbs. Stop when primer is hard. Lift cold start lever all the way. Hold choke button and crank motor until she starts. Feather choke and cold start lever until she is warm.

If that doesn't work, check to make sure the two carb choke shutters are closing when choke button is pushed. Put a timing light and the cold motor and crank it to see if you have spark.

Post back.

 

[gm280]

Okay this is the opposite to heat issues experienced by so many. I have never heard of heating circuits to make them work. I have seen tons of circuit that quit after heating up though... Used a lot of cool spray in my repair days to locate those defective parts. Interesting...

 

[talbee]

It is VERY interesting. The motor will NOT start unless I warm up that part.

I thought it could be the starter, so my mechanic and I took it apart and he said it's fine after testing. We didn't have time to test other things since he was at work. Any other thoughts?

 

[Texasmark]

Okay this is the opposite to heat issues experienced by so many. I have never heard of heating circuits to make them work. I have seen tons of circuit that quit after heating up though... Used a lot of cool spray in my repair days to locate those defective parts. Interesting...

Well sir you are "fixin" to hear it. I had an intermittent problem with my 2002 90 hp triple Merc with individual CDI modules. One had a thermal problem and had to warm up to work. I verified it with a heat gun and timing light on muffs in my driveway. 100 bucks later, new CDI and problem gone!

In industry thermal problems were constant problems. Same sort of components used there as are hanging off your transom.

 

[Faztbullet]

Uh CDI modules are a little different internally than a switchbox....

 

[gm280]

Well sir you are "fixin" to hear it. I had an intermittent problem with my 2002 90 hp triple Merc with individual CDI modules. One had a thermal problem and had to warm up to work. I verified it with a heat gun and timing light on muffs in my driveway. 100 bucks later, new CDI and problem gone!

In industry thermal problems were constant problems. Same sort of components used there as are hanging off your transom.

Texas, don't take my comment as saying you're wrong That is not what I was implying in the least. I just stated that I have never seen such a problem exist. I know all too well how finicky electronic components are and therefore anything can happen... When I was younger and stupider (if you can imagine that), I wanted to be an astronaut. And after understanding electronic circuits and component failures, I never wanted to be a space astronaut anymore! Not me....

 

[Texasmark]

Texas, don't take my comment as saying you're wrong That is not what I was implying in the least. I just stated that I have never seen such a problem exist. I know all too well how finicky electronic components are and therefore anything can happen... When I was younger and stupider (if you can imagine that), I wanted to be an astronaut. And after understanding electronic circuits and component failures, I never wanted to be a space astronaut anymore! Not me....

Well I started out playing with trucks in a sand pile......made me want to be a dump truck driver. Then I had to keep mom's car running so that I had transportation and developed a taste for mechanics. Then the draft was upon me and I chose the USAF and wanted to be a jet engine mechanic....I thought because I liked airplanes and engines. The recruiter gave me an aptitude test and I peaked in electronics so that's where I went.....one of the better things I had happen.....much cleaner, air conditioned job. I've been at it since 1959 and still learn something every day. I'll tell you this. I retired in 2005 which was the right time for me. With all this swipe your finger across the face of a widget that most everyone is addicted to electronics digital madness, I would have preferred jet engine mechanics to this had I been cycled through this time period.