Logo
FULL SITE MENU

1986 35HP Mercury Surging

S

Shakoo

New member
My old motor is surging at all speeds, definatelly sounds like a fuel problem, I replaced the fuel lins and filter already and have a carb rebuild kit on order. My question is when I squeeze the fuel bulb should fuel come out of the Jet in the Carb? I'm trying to find out if this is normal, or if I have a problem with the pump.
 
The bulb is nothing but a manual pump.---------------Fuel leaking out of the carburetor means there is an issue with float / float valve.
 
Could be, but remember this: The fuel pump makes about 5 psi, where you can make about 15 psi squeezing the bulb.

Squaring away the carb is a good start.

Jeff
 
Jerryjerry05 said:
The tank vent. Open?
Do a compression test.
Rebuild the fuel pump.
Click to expand...

Vent is open, fuel pump was rebuilt 8 months ago, along with compression test (less than 10 difference between the 2)

Finally got the carb rebuilt kit in the mail, gonna work it this weekend. Any advice/tips, this will be my first carb rebuild..
 
Shakoo said:
Any advice/tips, this will be my first carb rebuild..
Click to expand...

Don't use carb cleaner. When you get the carb apart, ordinary dish soap and warm water works great, and use a small brush to scrub everything. Make sure all the little passages are clean. Best way to dry everything is with compressed air if you have access to it. If not just use a clean rag and dry everything as best as you can. You need not use every little piece and part that comes with the kit. Just the new gaskets, needle valve, and float valve is the important stuff. After you've got it all put back together, set the jet to 1.5 turns. Make sure you're running clean and fresh fuel to it before you go to start it. And most importantly, take care of your fuel.
 
LSXG8GT said:
Don't use carb cleaner. When you get the carb apart, ordinary dish soap and warm water works great, and use a small brush to scrub everything. Make sure all the little passages are clean. Best way to dry everything is with compressed air if you have access to it. If not just use a clean rag and dry everything as best as you can. You need not use every little piece and part that comes with the kit. Just the new gaskets, needle valve, and float valve is the important stuff. After you've got it all put back together, set the jet to 1.5 turns. Make sure you're running clean and fresh fuel to it before you go to start it. And most importantly, take care of your fuel.
Click to expand...

Thank you, the rebuild was actually really easy, even setting the float levers, only had to bend the primary lever a little bit to get the 13/32 and the seconday lever was already at 1/4in. However the motor still surges :(
I don't think it is the fuel pump because when it surges I can squeeze the bulb and it doesn't change anything. My next guess would be the fuel line from the pump to the carb, I do not see any leaks, however there are also no clamps at the pump or carb. I had the motor checked out when I bought it 8 months ago and there were no issues, this surging issue started 3 weeks ago, up until then it ran like a champ. I run 50:1 in the tank with about 1/4oz of fuel stabiliter (5 gal tank).
 
"When it ain't fuel, it's gotta be ignition," goes the old adage.

You might have an ignition coil going bad--seen a bunch of them lately. You can narrow down the possibilities with a plug test. To wit:

Run the hell out of it, making it surge (if it will co-operate) then QUICKLY shut her off. Do NOT let it idle. Next--and be careful for they will be hot--remove both plugs and see if they are different (being sure to note which plug came from where).

Note: If your engine has gapless plugs (most likely) you'll have to buy some "test" plugs. I recommend NGK BP8H-N10 for this purpose, as does Mercury.

Now, if one plug is darker than the other, that's a dead giveaway the coil for that cylinder is bad. You can find out for certain by switching the wires around (the greenish wires to the coil and the wires to the plugs). Make a diagram first so you won't get screwed up. If that's your problem, the darker plug will "move" to the other cylinder.

Good luck!

Jeff
 
Last edited:
fastjeff said:
"When it ain't fuel, it's gotta be ignition," goes the old adage.

You might have an ignition coil going bad--seen a bunch of them lately. You can narrow down the possibilities with a plug test. To wit:

Run the hell out of it, making it surge (if it will co-operate) then QUICKLY shut her off. Do NOT let it idle. Next--and be careful for they will be hot--remove both plugs and see if they are different (being sure to note which plug came from where).

Note: If your engine has gapless plugs (most likely) you'll have to buy some "test" plugs. I recommend NGK BP8H-N10 for this purpose, as does Mercury.

Now, if one plug is darker than the other, that's a dead giveaway the coil for that cylinder is bad. You can find out for certain by switching the wires around (the greenish wires to the coil and the wires to the plugs). Make a diagram first so you won't get screwed up. If that's your problem, the darker plug will "move" to the other cylinder.

Good luck!

Jeff
Click to expand...

I don't know if I want to purchase a tester plug, I have to sell the boat in 4 months when I move to Alaska
 
Back
Top