1997 Mercury 15hp two stroke - only runs on choke.

**cmb1998** · 09-06-2020, 06:32 PM

Hello, I picked up a old (1997) 2 stroke 15hp mercury that has been sitting for the last 20 years. It's still got the factory plugs in it. I cleaned it all up, changed all fluids, replaced impeller, plugs, and rebuilt the fuel pump and carb. I started it up and it fired the first time i hit the start button and ran great. However when I shut the choke off it sputters and dies.

I've checked the timing and it's right at 8 BTDC when running on the choke. It appears to stay the same when I shut the choke off. I checked the idle mixture screw - out 1-1/2 and doesn't make any difference. I tried adjusting it in and out and no difference. I played with the idle speed and no difference. Does the same thing.

Any ideas where to go next?

**XstreamVking** · 09-06-2020, 07:24 PM

Still has crap in carb? Restricted fuel line?

**SS Minnow** · 09-06-2020, 07:42 PM

Originally Posted by XstreamVking

Still has crap in carb? Restricted fuel line?

^^^^^^^^

What he said. If it will only run on the choke, the main jet, or some part of the fuel line is likely restricted.

Do you have a fuel filter?

Where is it located? (in relation to the fuel pump/fuel tank?)

**FMP** · 09-06-2020, 08:11 PM

First, no typical choke. Turn the knob for fast idle ign advance. If the linkage isn't moving moving back it's out of adjustment. If it's staying advanced enough the rpm will be up. The idle mix needs dead slow rpm in gear to set with motor warned up. From memory also a throttle pickup set screw for getting in range, works the throttle plate from the linkage.

You need to dial it in without advance when warm in gear then fine tune the idle mix. You'll see how much advance it needs which is less than on fast idle warn up.

Not sure but check the pull knob position, could be three steps ( 20-25hp had this), all in is dead slow, second step is cold start, third is a prime squirt.

Then the turn is a further troll speed adjustment, set the idle mix at the slowest adjust of the knob.

When starting from dead cold morning, prime the bulb , pull the knob to squirt two or three times and leave at second cold start position, or whichever step it has all out , when it fires on pull push the knob in one step . Motor should fire within 1-2 pulls every time even in very cold . If near freezing knob it to squirt 3-4 times, no more or its flooded. If flooded use the throttle pickup to wide open the plate and pull repeated times to start.

**Soporific** · 09-06-2020, 11:33 PM

As above, fuel issues could be only issue here. However, I would also check compression, even to have a base line. This engine could have been damaged running straight gas for example and would still start. Assume nothing.

**cmb1998** · 09-07-2020, 05:54 PM

Originally Posted by cmb1998

Hello, I picked up a old (1997) 2 stroke 15hp mercury that has been sitting for the last 20 years. It's still got the factory plugs in it. I cleaned it all up, changed all fluids, replaced impeller, plugs, and rebuilt the fuel pump and carb. I started it up and it fired the first time i hit the start button and ran great. However when I shut the choke off it sputters and dies.

I've checked the timing and it's right at 8 BTDC when running on the choke. It appears to stay the same when I shut the choke off. I checked the idle mixture screw - out 1-1/2 and doesn't make any difference. I tried adjusting it in and out and no difference. I played with the idle speed and no difference. Does the same thing.

Any ideas where to go next?

Thank you. Bought a new fuel tank and hose. No difference. I replaced the filter on the motor when I did the initial carb rebuild. I pulled it an it looks new. I tore the carb off again and have it all torn apart, then realized that my compressor is MIA.

Does anyone have a picture of the other end of the linkage that goes from the top of the carb (the one directly above the carb) to where it connects under the flywheel? I think that I may not have it back together correctly. My manual doesn't show that one, i've been through every page.

**FMP** · 09-07-2020, 06:00 PM

Check the parts catalog, marineengine etc
http://www.marineengine.com/parts/me...board-parts/15

**Soporific** · 09-07-2020, 06:04 PM

Compression numbers? When idling, try squirting in fuel through carbs with choke off to see change, open throttle if it bogs down, note change?

If motor responds to extra fuel/air then I agree that carb cleaning is not complete.

**FMP** · 09-07-2020, 06:24 PM

Without ign advance to lead the throttle good chance it falls on its face and stalls

Do a proper link sync and idle low speed mix adjust

**Soporific** · 09-07-2020, 06:32 PM

Maybe, but advancing that timing mechanism manually is probably a no go.

**FMP** · 09-07-2020, 06:41 PM

And do your final mix idle set motor warm, in gear and down position in the lake.

**FMP** · 09-07-2020, 07:29 PM

With your favorite prop, cannon ball down on the downrigger, dragging your biggest spoon, with the sun over your left shoulder.

**Capt.Insane-o** · 09-07-2020, 08:09 PM

there is no choke, it's a primer. they are a very simple motor.

**Soporific** · 09-07-2020, 08:27 PM

Originally Posted by Capt.Insane-o

there is no choke, it's a primer. they are a very simple motor.

Unless Mercury deleted the choke/primer/fast/slow idle as FMP describes by 1997 I think he might be correct. I have a 1992 15hp that is exactly as FMP describes.

cmb1998 can clear this up.

**Capt.Insane-o** · 09-07-2020, 08:46 PM

Merc never deleted any of that. On the the ones I own, pull the primer out twice, turn the knob full right and one or two pulls they start. Now if someone pulled the cowl off and started turning screws that is another thing, they have a very narrow happy synch range.