Motor Issues
- Thread starter Carl
- Start date
Carl said:
First do a compression check. No sense chasing a bad component if the engine block has issues. Many times an engine will start and idle seemingly fine on one cylinder. Check the plugs, check the coils.
Another thing may be a plugged high speed jet.
When my old 15 hp Yamaha did this, it was a bad pick up tube in the fuel tank. A new fuel tank fixed the problem.
What I found was that if I kept pumping the bulb, the motor would keep running at mid-throttle. Quit pumping, and it would stop pulling fuel and the motor would stall out.
What I found was that if I kept pumping the bulb, the motor would keep running at mid-throttle. Quit pumping, and it would stop pulling fuel and the motor would stall out.
Josh Schwenger
Active member
If you have spark in both cylinders and compression I would move to fuel. You can mix gas oil 50/1 in a squirt bottle feed it fuel as you try to rev it up. Sound like you have a clogged high speed jet in the carb but I'm not that familiar with mercury.
Paul Taylor
Active member
Sounds like carb related issue but consider checking (or replacing) fuel pump (and replace fuel filter) too. If pumping the priming bulb under load causes engine to run properly I'd start with a good carb soak and cleaning and then move to fuel pump.
David Clites
Active member
I always try to do the cheapest/easiest things first. If possible borrow another fuel tank complete with hose and bulb. Also check Compression--both AutoZone and O'REilly's are loaning tools for free now (O'Reilly's never even stopped due to Covid). In past year I had a 4hp Evinrude with blown Cylinder Head (one cylinder only), it started , ran a bit then quit. Eventually would not restart. If squeezing the Bulb keeps it running then yes it is likely Fuel Pump--easy and relatively inexpensive to replace or use Rebuild Kit. Clogged Jet is also a possibility, a bit longer process to remove/teardown/clean/reassemble, squeezing the bulb is not likely to offset a clogged jet. Good news it is very likely to be one of these 4 root causes.
Paul Taylor
Active member
Will it run while pumping the primer bulb?
Bob Holzworth
Member
Had same problem on mercury 25. Coil would go open in the circuit , due to being warm on one side and cold on far side of engine. Happened on two coils, so traded on New engine.
Paul Taylor
Active member
Before removing carbs pump primer bulb will running at higher throttle. If motor stays running I'd be eyeballing the fuel pump.
Bill Ferrar
Well-known member
I had a 25 mercery in the 80's - 2000 that needed the carb cleaned every year or so to run well.
It is a simple carb.
I would clean the carb first, you can't hurt anything by cleaning the carb.
It is a simple carb.
I would clean the carb first, you can't hurt anything by cleaning the carb.
Josh Schwenger
Active member
If you have a foreign object "dirt" in that carb and your not running a filter it's a good investment. My friend bought a different motor to resolve a issue with a carb. My friend being a bit on the thrifty side put the same fuel hose on new motor and week later same issue on different motor. Fuel line was failing on the inside putting garbage in the carb tiny rubber bits. He dropped it off to my buddy who is a marine mechanic. Long story short 200 bucks for carb clean a fuel line and filter.
Carl said:
Carl,
Need more info, Mercury does not reference model year when looking up parts. Under 25hp as an example, they show 12 versions, distinguished by letter and or serial number sequence. My suggestion would be go the the link below, "launch parts catalog" and scroll down until you match your motor. Then you should be able to view the proper diagram and part number for your motor.
Mercury Parts Catalog | Mercury Marine
Carl said:
Do know where the tag is located? For Mercury outboards, the serial number label is located on the transom bracket.