Logo
FULL SITE MENU

1985 Mercury 115 stalling at midrange

F

fpunzo

New member
1985 Mercury 115. Starts and runs good at idle and (if I can get it there) will run well at WOT for as long as I leave it there. It will also run well at up to 1/3 throttle. However when I try to throttle up to WOT the engine will bog and stall. I've tested it in the water and noticed a few things that will hopefully help you help me figure out how to fix it. When I take the cover off and squirt gas in the carbs while throttling up from 1/3 to WOT I can get it to WOT without bogging and stalling. I've also noticed that pumping the priming ball hard while throttling up makes a difference and lets me get to WOT without stalling. Not sure if this is related but it also seems like the engine runs much better with the cover off. For example, when I'm idling or running at 1/3 throttle with the cover off, if I put the cover on the engine will immediately run rough and stall. I rebuilt the carbs over the winter and also rebuilt the fuel pump and replaced the check valves. I did this work because the engine didn't idle well. As my next step I'm going to replace all the fuel lines from the gas tank to the carbs. I'm hoping someone here can give me some pointers on what they think it might be and anything else to try other then replacing the fuel lines.
Thanks in advance for your help.
 
fpunzo said:
1985 Mercury 115. Starts and runs good at idle and (if I can get it there) will run well at WOT for as long as I leave it there. It will also run well at up to 1/3 throttle. However when I try to throttle up to WOT the engine will bog and stall. I've tested it in the water and noticed a few things that will hopefully help you help me figure out how to fix it. When I take the cover off and squirt gas in the carbs while throttling up from 1/3 to WOT I can get it to WOT without bogging and stalling. I've also noticed that pumping the priming ball hard while throttling up makes a difference and lets me get to WOT without stalling. Not sure if this is related but it also seems like the engine runs much better with the cover off. For example, when I'm idling or running at 1/3 throttle with the cover off, if I put the cover on the engine will immediately run rough and stall. I rebuilt the carbs over the winter and also rebuilt the fuel pump and replaced the check valves. I did this work because the engine didn't idle well. As my next step I'm going to replace all the fuel lines from the gas tank to the carbs. I'm hoping someone here can give me some pointers on what they think it might be and anything else to try other then replacing the fuel lines.
Thanks in advance for your help.
Click to expand...

You've clearly identified that it's fuel starved. Lines, filters, the fuel itself. Float level could be out or affected by fuel starvation except at WOT. Poor idle - partially clogged jet, fuel mixture lean. Just things I'd look at. Go over everything from the beginning.
 
Last edited:
Mid carb circuit clogged remove and clean carbs sounds like clogged jet as scamper said
Had same problem on 200 merc sprayed cleaner in air jets ran perfect for half a year now same thing I think there some debris floating around in my carbs jus temporarily moved it now going in for thorough cleaning
 
Thanks for the input guys. I'm going to replace all the lines from the tank to the carbs as step one. Pull and clean the carbs as step 2. I'll post back here with results. Maybe it'll help someone like me down the road. I've used this forum a lot and it's been very helpful.
 
Hey again guys. So here's where I am... replaced all gas lines from tank to carbs. Removed carbs and cleaned them. They were already clean but I noticed something on all three carbs. The long jet that goes down from underneath the idle screw to the bottom of the carb was gunked up on all 3 carbs. Only a little light was passing through this. I pushed a small wire down through it and it opened the hole up considerably. I also pushed a tiny wire down through the jet thats in the middle of the throat of the carb (the one you can see sticking up when your looking at the carb). This one seemed clean already. I had to re-adjust the idle screws after this cleaning and the motor idles better now. I can let it idle at 800-900 without it stalling. Before I had to keep it at 1100. Problem is I still have no midrange. As soon as I hammer down it stalls. What else could it be? What else can I check? Are there other jets in the carbs that I'm missing? The little screw jets are clean as a whistle too. Also, I set the float level to specs in the Sealoc book for that engine (3/16" spring hieght and 1/4" on the needle mechanism). Should I try and tweek the float hieght? If I can run it at WOT it's not likely the fuel pump right?

Thanks,
Frank
 
If it stalls on acceleration ( classic problem ) you need to open up the screw for lowspeed fuel mixture,-------1/8 turn at a time untill the problem goes away.
 
Ok as promised here's what fixed it. Thanks again for all your help. Your suggestions were invaluable. One thing that made a the biggest difference was removing an inline fuel filter I installed. There wasn't one on there. I put one in to be safe and it ended up causing me a problem. It was either letting air into the system or it was too big and had too much air in it to let the system prime itself. Other things I did that all made a big difference. Cleaning out the jets with wire. Backing out the idle screws 1/8 turn until the engine could get to WOT with no bog. Replaced the fuel lines from the tank to the carbs. Rebuilt the fuel pump. Long live the TOP :).

Thanks again,
Frank
 
You didn't mention that added filter or I would have jumped on it. Outboard fuel pumps have lousy suction and can't pull fuel through a filter palce BEFORE the pump. After the pump is fine.

Jeff
 
fastjeff said:
You didn't mention that added filter or I would have jumped on it. Outboard fuel pumps have lousy suction and can't pull fuel through a filter palce BEFORE the pump. After the pump is fine.

Jeff
Click to expand...

Thanks Jeff,

I'm going to let the fuel pump screen do it's job for a few trips (so we can get some boating in). Then I'll add the filter after the pump. Thanks for the suggestion.
 
Back
Top