Logo
FULL SITE MENU

3.5hp 4-stroke bogged then died

G

GregJ

New member
Hi everyone. Lots of great advice here. Hoping to get some feedback on my current problem. I have a 2007 merc 3.5 4-stroke F3.5M that has been running like a champ for the two years I've had it. I always run rec90 and run it dry at the end of the day. And I always get my gas from a local marina straight from a dedicated pump. Except one time last month. I'm almost positive this is what led to my current problem.

First sign of trouble was about a half a tank later when the motor started bogging down when over 1/2 throttle. Backing off and it ran great, idled great, hitting WOT it would bog and it would even die. Bad gas I'm thinking right away. Cut the day short and poured the rest of that gas into the truck. Got some known good gas from my regular place and topped off the tank. Ran it out in a barrel. Well I thought I ran it all out cause it died and wouldn't startup. But there was gas still. Drained all that, pulled the carb, found some gunk in the bowl. Cleaned it all out and blew it out. Still can't get it to crank. There's gas on the plug but it seems to be a weak spark. The coil Ohms out to spec at 2.2ohms, inspected it and the magnets seem okay so I'm not sure if its the problem.

Going today to get a new plug and some carb cleaner to give it a good soak. But I'm not sure of the coil pack (ignitor) Is there another way to test it?
 
Yeah I'll be rigging an air gap tester just to have it but I'm just not sure of what the gap should be or what I'm supposed to see. I'm thinking I should be able to get a reading on my meter but I have the service manual and all it mentions is the resistance test. I see a weak spark with the plug leaned up against the ground bolt for the kill switch. I hear this is variable according to rpm so maybe its nothing. This motor doesn't cough or anything so I'm really scratching my head. Even though the spark plus is clean I did get a new plug today but got back too late to try it. I'm back at it tomorrow if time permits.
 
Ohm test and spark gap tests are the way to check your ignition. Since it was working OK until you increased throttle (more air), you are probably not getting enough fuel for a proper mix; might have had some water, etc in the mix somewhere. Since you did find junk in the carb bowl, the carb is definitely in need of a Proper cleaning.
 
Thanks for all the input. It turned out to be a little of everything. A new plug made all the difference. Even though I cleaned, sanded, and gapped the old one it just wouldn't give up enough spark. Still a little puzzled over it but its running as good as ever.
 
GregJ said:
Thanks for all the input. It turned out to be a little of everything. A new plug made all the difference. Even though I cleaned, sanded, and gapped the old one it just wouldn't give up enough spark. Still a little puzzled over it but its running as good as ever.
Click to expand...

Defective ceramic insulation can "leak" to ground, and the core can break down some, or both. Sometimes, they come out of the box that way.
 
Back
Top