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Mercruiser 37 4cyl running problem

H

hammeresq

Member
"I have the infamous Mercruise

"I have the infamous Mercruiser 3.7 165 in my starter boat. The engine has been great for the most part over the last 2 seasons.

At the end of the last season the boat developed a strange problem. The tachometer would bounce around, typically above where the engine was running, and at certain RPM's the engine would sputter and seem to make a popping noise out the carb.

The only thing I have done to the boat in the year that I have owned it is have the carb rebuilt, changed fuel filter, and change the oil. I am going to be replacing the coil, wires, cap, rotor, etc at the start of this season, but I was curious if anyone has heard of a problem like this.

Thanks,
Eric"
 
"I recommend that you DO NOT r

"I recommend that you DO NOT replace all of the ignition components at once so that you can find the problem. First, what type of distributor, points or electronic module? Did you you have the carbuerator rebuilt because of the problem?"
 
"No, I had the carb rebuilt be

"No, I had the carb rebuilt because the lets were clogged, and I wanted to solve some other running problems with the engine. After the rebuild I got an entire season out of it before this problem started.

The distributor uses points, which I am also planning to replace. This boat was used once per year before I picked it up. Even looking at the plug wires, I can see the orange boots are cracked and starting to fall apart. But I do like the idea of replacing ignition components one by one. Where do you think I should start?"
 
"If the wires have cracked boo

"If the wires have cracked boots, start with those!
One at a time to preclude miswiring them."
 
"dudes... if this thing has po

"dudes... if this thing has points, that's the first place i would go.

Check the poing gap and the contact surfaces. Replace plugs. Put points, condenser in it, set the gap to specs (0.020 will probably get you there), start it, set the timing advance, then put a cap and rotor on it. If the points are three seasons old, they need to go any way. These are inexpensive parts that need to go on a regular basis.

Moisture under the cap will also cause cross fire which will make it run just so... misfiring, sputtering, back firing.

This assumes we have an ignition problem and not a carb issue.

Last thing is to replace plug wires. Stick to a good brand as I've had too many come backs on cars where i was attracted to the margin i made on junk wires. NGK, Taylor, OEM brands like AC DELCO, Autocraft, Mercruiser... I'm sure there are plenty of other good marine brands as well."
 
"if Your tach is acting up, di

"if Your tach is acting up, disconnect it at the coil and proceed with Your diags. bad tach can cause problems."
 
"David,
My hope is the carb

"David,
My hope is the carb ran well for most of last season after the rebuild, and the ignition system is so shot on there anyway, that the issue lies there. I have a new set of points, I just need to get a good dwell meter to get them installed.

I also noticed you were local. Where do you drop in? I am at Tyme 'n Tyde in woodbridge. If it's the points first round of beers at Tim's is on me :)

Scott~ You wouldn't happen to know what the tach signal wire is on the 3.7?"
 
Eric D: Points? Do yourself a

Eric D: Points? Do yourself a big favor and get rid of the points with an electronic conversion kit for about $100. Anyone can put in the kit and never fool with points again. The wires definitely have to go as previously suggested. The backfiring you are experiencing is probably caused by plug wire cross over firing due to their condition. Points wear and change the timing somewhat. You'll be elated when you change to elec. ign. Guy
 
"Eric D,
In your frist post

"Eric D,
In your frist post you said "at certain RPM's the engine would sputter" was that certain RPM about 2000 - 2200?

Electronic conversion kits are the best. Ill never buy points again.
Greenly"
 
"Yeah, it def. in the lower RP

"Yeah, it def. in the lower RPM band. Do you guys recommend a specific electronic conversion kit? I've been looking at these. www.sterndrive.info/sterndriveparts/id42.html"
 
Before you go too far trace th

Before you go too far trace the engine loom back to the connector pull it apart and make sure the pins arent corroded. I had a Bertram with twin 165's that had a similar problem and that was it.
 
"Eric,

A conversion to elec

"Eric,

A conversion to electronic ignition is probably the way to go. Good suggestion, Guy. I live in Arlington and have my boat at Columbia Island up in DC. Give me a holla and I'll help you if you are in the area. 703 856 3588. Will take you up on those beers.

If you are just going to replace points, et al... you can do so without a dwell meter if you have a timing light."
 
"Andrew, Thanks for the link.

"Andrew, Thanks for the link. I'm going to be sending a big parts order your way, as soon I can get back in my boatel and start getting ready for summer!

David, I live in Arlington too (Ballston area) and the boat is in Woodbridge, when the weather gets a little better we'll work something out! Thanks again for all the help!

Eric"
 
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