95 Mercury 125hp 4 cyl Help

[skatermike24]

I have a 4cyl 125hp, motor is popping when idling, like a small backfire, all electrical checks out fine, when I cover no#3 carb and block off air motor smooths out and runs fine, checked reeds and cage, looks good, any ideas???? I'm stumped now!

[cali kid]

I have a 4cyl 125hp, motor is popping when idling, like a small backfire, all electrical checks out fine, when I cover no#3 carb and block off air motor smooths out and runs fine, checked reeds and cage, looks good, any ideas???? I'm stumped now!

Motor only idles on top 2 cylinders. the bottom 2 come in around 1800 rpm. I bet the throttle plate is open on #3. Make sure all throttle plates are closed at idle.

[skatermike24]

Dam why didn't I think of that!!!!!! I'll check tonight.

[skatermike24]

looks like all butterflies are closed

[mn808gade]

had one w/#3 needle/seat for accelerator pump stuck open.pinch off hoses going to #3-#4 cylinders.run at nite/under cover to locate cyl with coughing problem-have to remove electrical plate to get to n/seat valves-th

[cali kid]

looks like all butterflies are closed

There are soft plastic check valve-restrictors in the bleed system that could also cause it, as well as leaky needle and seat in the carb.

[skatermike24]

I will check valves and take carb apart , thanks guys stay tuned.

[DanUmbarger]

Many years ago my Merc 115 ad the same issue and I eventually found that the 2 brass check valves in the recirc system were dirty. Took them apart, cleaned them and stretched the spring just a whisker, put them back together and made all the difference in the world. Had another motor come into the shop doing the same thing and doing this cleared up that motor too. I believe the later models did away with the cleanable brass check valves.

[DanUmbarger]

Just to clarify...the check valves I'm talking about thread into the block and the electrical plate needs to be unbolted and moved out of the way enough to get at them.

[skatermike24]

Ill check them on Wednesday so they should only blow one way I'm guessing, are they cleanable with some brake clean or should I just order new ones.

[DanUmbarger]

If I remember correctly it's a needle/seat assy...don't remember if it was a brass seat and a rubber tipped needle or stainless needle. I just removed the whole assy, disassembled, cleaned with carb and choke cleaner, stretched the spring just a little, blew dry with compressed air, reassembled and reinstalled. Pretty straight forward. After you clean them put a little sealant on the threads before reinstalling.

[skatermike24]

Yep little brass fitting, it actually has a carb needle and spring in it, I didn't get a chance to fire it up , ill do that Thursday. Hope this does it. Tiny little hole spraying in the cylinder??????

[DanUmbarger]

You cleaned them both right? One about mid block and the other a little lower. Not sure what the reasoning is...all I know is that crap must be holding the needle open causing some sort of a lean condition in the recirc system. Also...like the others have said do a good link and sync,all carb butterflies closed at dead idle and low speed needles adjusted correctly.

[skatermike24]

Well after cleaning both needles and replacing the tiny fuel line, motors running awesome no popping, thank you all for you help, much appreciated!!!!!!!
my manual says start with idle screws at 1 1/2 turns out, seems to be ok there , I need to put it in the water and check timing hard to do it on a hose, thanks again