2000 Merc 125 Idles on #3 cyl also

[dragonslayer]

I've got a 2000 Merc 125 4 cyl in the shop that is picking up fuel and idling on the #3 cylinder. I'll be honest, I'm an old Johnny/Rude guy recently into Mercs. <br /><br />I've checked everything I can think of. There's no gas getting past the needle and seat. I put a clear line on the pulse hose to the fuel pump from the #3 cyl and no fuel there. I put a pressure gauge on the #3 accelerator pump check valve and it opens at 11psi and holds at 10. I clamped off the enrichener lines, no difference. I checked the bleed check valve from the #3 cyl and made sure the fitting from the block is open. I even put a pressure gauge on the fuel pump outlet and it's at 3.5 lbs. I can find no fault in the carb itself. Of course the first thing I did was a complete sync & lync. <br /><br />Any ideas?<br />Thanks in advance for any help.

 

[WillyBWright]

Re: 2000 Merc 125 Idles on #3 cyl also

Some possibilities...<br />1 Wrong jet size in the carb, (defective, mislabeled or modified). Try swapping them between #3 and #4 (not sure that's possible). <br />2 Casting flaw or freeze damage in the carb body that you can't see or do anything about.<br />3 It may be scavenging excess fuel from the cylinder that's at BDC when #3 is at TDC thru the bleed system. Maybe that cylinder's carb needs a looksee.<br />4 Crankcase sealing problem between #2 & #3. If those sparkplugs burn similar to eachother but different than #1 & #4, that could be a sign.<br />That's about in the order of likelyhood.

 

[2springers26]

Re: 2000 Merc 125 Idles on #3 cyl also

how hi a rpm is it idleing .. I've seen a couple start to kick in 3& 4 @ 1400 When it's normally 1800 rpm's

 

[dragonslayer]

Re: 2000 Merc 125 Idles on #3 cyl also

Thanks for responding guys, I thought about an internal problem also. Do you know if there is any kind of reflow passages in the intake area or is there just the external bleed system.<br /><br />As far as the idle speed it's at about 1000 in gear at idle timing of 1ATDC. Pull the plug lead on #3 and it drops to specs. It acts like #3 carb has a normal idle circuit.