thill
Seaman Apprentice
- Joined
- Jun 17, 2008
- Messages
- 33
Have a 1987 Mercury 35 classic. Got it in partial trade. Nice little engine. Compression is 140 PSI both cylinders. Has lots of power, revs up normally to WOT. Starts easily, idles smoothly and runs great at almost any speed EXCEPT in gear at slowest idle. Out of gear she runs great, but the engine shakes violently and stalls in gear, and I can't figure it out.
But if I give it even a tiny bit of throttle, she picks up RPM and runs smoothly.
I'm familiar with carb work, but have not seen this particular Mercury side-bowl carb before. This one is very different than the ones I'm familiar with.
So far I have played with the idle mix, timing, throttle pickup setting, and no matter what I try, it won't run at idle in gear. A real head-scratcher!
Let me go back and give the history of this particular problem. Previously, she ran well, but the carb leaked gas when you squeezed the bulb. Stuck float - easy fix. So I pulled carb and cleaned it, but no change. Went back in and replaced the float, seat and valve. The old seat was pretty oxidized, and I figured that's why the float was sticking, and sure enough, no more fuel leak, and she ran great... except at idle in gear. Hmmm...
I adjusted the idle mix, but always end up at. 1-1/4 -1-1/2 turns out. Any less than 1-1/4, and she starts to pop. Any more than 1-1/2 and she starts to load up and get smokey. Anywhere between the two, and she starts easily and runs smoothly, so I'm guessing this is the right setting. Same thing with the timing and pickup point. I always end up right where it started. Idle mix and timing seem to all have been correct.
The only indication that I have that something is wrong is that running at idle out of gear I notice a tiny drip coming from the bottom of the throttle plate shaft. Changing the mixture screw doesn't seem to alter this. Give it any gas and that drip goes away.
So it seems that for some reason, the carb is loading up at idle. I ran her in gear and adjusted to get @900 RPM, But when I put her back in neutral, she ran at 1500 RPM. Way too fast. Ended up back at original settings.
So I'm back to where is this drip is coming from? Why is she loading up?
Well, what has changed? I swapped out the float, needle and seat. It has to be there somewhere, right?
Could it be that the double-lever float valve assembly is slightly out of adjustment, causing the fuel level to be only slightly high, but not enough to pour out of the front of the carb? Just enough to make it idle rough? Maybe the valve is dropping too much?
Thoughts?
Thanks for any feedback.
-TH
But if I give it even a tiny bit of throttle, she picks up RPM and runs smoothly.
I'm familiar with carb work, but have not seen this particular Mercury side-bowl carb before. This one is very different than the ones I'm familiar with.
So far I have played with the idle mix, timing, throttle pickup setting, and no matter what I try, it won't run at idle in gear. A real head-scratcher!
Let me go back and give the history of this particular problem. Previously, she ran well, but the carb leaked gas when you squeezed the bulb. Stuck float - easy fix. So I pulled carb and cleaned it, but no change. Went back in and replaced the float, seat and valve. The old seat was pretty oxidized, and I figured that's why the float was sticking, and sure enough, no more fuel leak, and she ran great... except at idle in gear. Hmmm...
I adjusted the idle mix, but always end up at. 1-1/4 -1-1/2 turns out. Any less than 1-1/4, and she starts to pop. Any more than 1-1/2 and she starts to load up and get smokey. Anywhere between the two, and she starts easily and runs smoothly, so I'm guessing this is the right setting. Same thing with the timing and pickup point. I always end up right where it started. Idle mix and timing seem to all have been correct.
The only indication that I have that something is wrong is that running at idle out of gear I notice a tiny drip coming from the bottom of the throttle plate shaft. Changing the mixture screw doesn't seem to alter this. Give it any gas and that drip goes away.
So it seems that for some reason, the carb is loading up at idle. I ran her in gear and adjusted to get @900 RPM, But when I put her back in neutral, she ran at 1500 RPM. Way too fast. Ended up back at original settings.
So I'm back to where is this drip is coming from? Why is she loading up?
Well, what has changed? I swapped out the float, needle and seat. It has to be there somewhere, right?
Could it be that the double-lever float valve assembly is slightly out of adjustment, causing the fuel level to be only slightly high, but not enough to pour out of the front of the carb? Just enough to make it idle rough? Maybe the valve is dropping too much?
Thoughts?
Thanks for any feedback.
-TH
Last edited:
