Mercruiser 3.7 Starting Problems

[Old Yeller Boater]

Thought I'd start my own thread to document a few thing in the hopes of someone else being able to find it in a search in the future.

Now that I have my head gasket problem solved, I'm moving on to my carb issues. I'm having two problems. First, starts either warm or cold take a great deal of throttle and playing to get the motor to catch and run. Lots of cranking on the starter before it catches. The second problem is significant backfiring through the carb when I give it too much throttle.

I've got a new starter and will be installing it tonight. Someone else reminded me to have the battery checked, so I'll take it to the local auto parts store for load testing. That way I'll be sure that part of the system is a-ok.

I'm also going to check the timing tonight to be sure it's at 4 degrees BTDC. After that, I plan to take it to a carb guy for a rebuild and proper setup. I know this could be overkill and not my problem, but as this boat is new to me, for a relatively small amount of money I'll have some piece of mind and know for sure that it's good.

Next step will be to wrap insulation around the fuel line to help prevent vapor lock.

So, some work and testing are in the works. I'll report back my results along the way. If anyone has any thoughts/input, as always it's appreciated!!!!

 

[wrestling coach]

Re: Mercruiser 3.7 Starting Problems

Upgrade to a series 27 marine cranking battery if you haven't already done so.

Dennis

 

[Old Yeller Boater]

Re: Mercruiser 3.7 Starting Problems

starter installed. Checked battery. Noted it was from2007, so decided just to replace it with a series 27 one.. It started up very well with only a small amount of throttle after priming two pumps. I also checked the timing while I had if running. It was at about 8 degrees AFTER TDC. Rolled it back to 4 degrees BTDC. Idle came up, so adjusted that back to about 800 rpm. When giving it gas, it didn't seem to backfire. Will need to lake test, but between the starter and timing, it seems to be running well.

 

[zlman1970]

Re: Mercruiser 3.7 Starting Problems

I think you'll find wrapping up the fuel line does a world of good. I used a self adhesive foil backed foam, probably a 1/4" thick, worked pretty well but I don't think it'll hold up for more than a season before the adhesive gives out. I wrapped the last 8-10" of line just before the carb.
Looked at a foam wrap but it was about 2" thick and I didn't think it would do the bends very well. Let us know what you find to insulate with.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 Starting Problems

I used some insulated adhesive wrap on my water lines at the camper, wrapping up a heat tape inside it. it's held up to weather for about 2 years now. I'm thinking of giving that a try. Got it from Lowe's.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 Starting Problems

got back from the beach today and decided to work on the boat some. In the process, I decided to start it. Didn't prime or anything prior to turning it over. Cranked just a second or two, but started right up. Excellent! Can't wait to get it to the lake next weekend to test!

 

[AMD Rules]

Re: Mercruiser 3.7 Starting Problems

Sounds like you have it fixed. I chased a starting problem earlier this year as well. I will say that upgrading to Pertronix ignition is highly recommended and really easy to install. Timing makes a huge difference in starting, and the electronic conversion kit keep it from meandering like you may see with conventional points. The coil I installed doesn't need the resistor wire either, so I believe that makes the cranking spark a bit stronger than normal (my opinion).

I burnt out two starters last season messing with a malfunctioning engine. This year, it starts when I just touch the key. Huge difference, and I bet the starter motor is much happier.

Happy boating.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 Starting Problems

tested at the lake this weekend. cold starts work perfect. Don't even have to give it throttle. warm starts are sluggish. I am thinking it's just the nature of these motors. I'm satisfied with it for now though. Perhaps over the winter I'll have the carb re-built just cause it's old and wouldn't hurt.