200 Merc Running pig rich on #2 and #4

[frogstomper1]

I've got a 94 200 2.5 Mercury. Always ran great for me no issues. A few weeks ago I noticed it to be a little sluggish while getting on plane, and would smooth right out once I was on top. It almost sounded like it dropped a cylinder or two while trying to get out of the hole. After getting back that night, I dug in... Plugs 2 and 4 very wet and black, all others ok. Compression is at 125 all around. Spark on every cylinder, got 198 volts with my DVA on all cylinders. Opened carbs up looking for some debris---nothing. Rebuilt fuel pump as diaphragms were original. All filters replaced after carb job. Visual inspection of reeds for damage or one hanging open---nothing. Statically checked base timing and W.O.T. timing---both right on the mark. Checked all recirculation lines---no kinks or breaks found. Thermal valve is operating correctly, as is enrichner valve. Took it out the next day, still a bit puzzled, same thing. Almost like it's loading up #2 and #4 at lower speeds, and then smoothes out once at high RPM. Am I missing something? What else can I be looking for? Thanks in advance.

 

[frogstomper1]

Re: 200 Merc Running pig rich on #2 and #4

Bump

 

[sxmerc]

Re: 200 Merc Running pig rich on #2 and #4

How was the float heights on the carbs?

 

[Superjetjim]

Re: 200 Merc Running pig rich on #2 and #4

Floats are sticking open on those carbs (2 & 4) is my bet.. Does it **** gas out of the effected carbs when you pump the bulb with motor trimmed up?

 

[Dukedog]

Re: 200 Merc Running pig rich on #2 and #4

ya got a switch box actin' stupid............

 

[frogstomper1]

Re: 200 Merc Running pig rich on #2 and #4

No fuel at all from those carbs up, down, primed or other wise. I was kinda' leaning towards the switchbox but I was looking for some input before I spend the money on one. Thanks guys.

 

[Dukedog]

Re: 200 Merc Running pig rich on #2 and #4

swap tha boxes, see if tha problem follows if ya don't have tha stuff ta check 'em...........

 

[sschefer]

Re: 200 Merc Running pig rich on #2 and #4

ya got a switch box actin' stupid............

Yup.

 

[frogstomper1]

Re: 200 Merc Running pig rich on #2 and #4

Thanks for the input fellas. Took the old girl out today, and noticed I'm missing about 500 RPM at WOT. I'm not sure if this was the case last time, but I would imagine it was. Very hard starting this morning also. Gonna' swap out a swithchbox this week from another motor, and see if this nails it.

 

[Faztbullet]

Re: 200 Merc Running pig rich on #2 and #4

Could be a weak stator(low speed coil) on that side not charging pack capacitor fully. This would not let plugs fire correctly under compression thus your "rich" symptoms or it could be in pack as suggested. I have seen a problem like this before on a 150 and it was stator and a old 225 ended up bia's problem(no fire).

 

[sschefer]

Re: 200 Merc Running pig rich on #2 and #4

Could be a weak stator(low speed coil) on that side not charging pack capacitor fully. This would not let plugs fire correctly under compression thus your "rich" symptoms or it could be in pack as suggested. I have seen a problem like this before on a 150 and it was stator and a old 225 ended up bia's problem(no fire).

From original post:

Spark on every cylinder, got 198 volts with my DVA on all cylinders.

More typical of a timing issue on 2 and 4 rather than stator. Most likely it's the bias cirucuit going bad on the switch box. #6 likes to run rich and I suspect that's why it's not showing up there yet.

 

[Faztbullet]

Re: 200 Merc Running pig rich on #2 and #4

The Bias can be tested by the followingisconnect the White/Black jumper between the switch boxes and check the resistance from the White/Black terminal on each switch box to engine ground. You should read 14-15,000 ohms on stock switch boxes MAKE SURE THE READING IS THE SAME
ON BOTH SWITCH BOXES! Any problem on the bias circuit and BOTH switch boxes must be replaced as a set. You can test the bia's voltage and it should increase with rpms @ 1000rpm should be 5-7 volts and @ 2500 should be 12-13volts and at WOT it will be around22-27 volts and this is a negitive voltage.You can also check the primary(coil) clamping diodes with meter and the HS imput diode. To check primarys set meter to diode check and from case ground to grn/grn-wht/grn-red terminals and reverse leads and retest and can do also for trigger clamp diodes and them must all read the same on trigger test !!! For HS check set meter to diode test and check between the HS and LS terminals,should read from HS to LS only. To test kill diode test between LS and blk/yel terminal, should only read from LS to KILL

 

[frogstomper1]

Re: 200 Merc Running pig rich on #2 and #4

Could be a weak stator(low speed coil) on that side not charging pack capacitor fully. This would not let plugs fire correctly under compression thus your "rich" symptoms or it could be in pack as suggested. I have seen a problem like this before on a 150 and it was stator and a old 225 ended up bia's problem(no fire).

I know it's not the stator as it was replaced a few weeks ago as I had lost spark to all cylinders. Engine ran fine for awhile and now this. I will swap in a pair of switchboxes as I've heard you should replace in pairs. Somewhere along the way I remember hearing or reading that replacing one box only could end up developing issues with the older box. Is this a correct statement? What are your thoughts on this? Thanks again for your input!!

 

[sxmerc]

Re: 200 Merc Running pig rich on #2 and #4

If you don't mind spending the money, why not? BTW... I just realized I know who you are. This story sounded waaaay to familiar to be "someone else" Once you figure out what you want to do, I'll be more than happy to sell you the parts you want. It's funny how someone can have no problem bending your ear for an hour everytime their motor hiccups, but end up trying to fix it themselves once someone has done the troubleshooting for them. I'll remember this next time you come in to "say hi."

 

[1992gradywith200merc]

Re: 200 Merc Running pig rich on #2 and #4

hope you dont mind me jumping in, I have a 93 200hp merc ob, and when at idle it coughs and revs up and then back to idle where itll stay a bit and then dies. i checked floats and gaskets and theyre ok, any ideas please? reading this thread it would seem a switch box issue?