missing at low rpm

[antman993]

Mercury blackmax 200hp. Has a miss under 2000 rpm runs awesome above that. Stator or carb issues?

 

[WrenchHead]

I would guess carb. Probably low speed jets are plugged while high speed jets are clean. Try this -- when missing at about 1800 RPM put on a little choke with the linkage or with your hand. If engine stops missing then it's the carb because your test of partial choke has richened up the mixture.

 

[Dukedog]

Might be carbs. Those only have idle and mains for jetting. Idle drops out and goes ta mains soon as ya go "off idle" with tha throttle. Good cleanin' and "new" gaskets in 'em will eliminate those. Never hurts to do it anyway. Think gasket kits for those are pretty cheap. Take a peek at tha reeds while ya got 'em off. Still does it after that ya can start checkin' more expensive 'lectric stuff............jmo

 

[antman993]

I should have said I lost spark on one bank fixed that with a new sw box, ran good for one day then the next day had this miss goes away after 2k. Tested the stator reads 74 on red and 3700 on blue??? Looks like a 16amp stator

 

[Dukedog]

Not to shiny at all.....go here.

http://www.outboardignition.com/page39.asp

low side (blue and blue/white) 5800. high side (red and red/white) 7000. If either of these are off its gonna be bad and no reason to go to dva. If these read good then tha dva is needed to make sure its not tha problem............Good resistance readings may not indicate good stator.

 

[enginepower]

I have a similar issue on my 95 90hp. You need to check dva output of stator, ohms it just a check against shorts. I knocked out 2 switch boxes already but I think I found the problem. When measuring DVA on cyl 2 and 3, I get around 185V at idle to my ignition coils. When I check #1, I get about 185 as well but within a few seconds, my meter goes nuts and will even blank out. Tried another meter and it does same thing. My secondary coil resistance is open circuit. I think some of the spark is feeding back and knocking out the switch box. Haven't changed the coil yet, but I'm sure that is going to fix the situation.

 

[antman993]

I pulled the Stator off and a buddy has a good one guna try that, I think the stator going south causeed the cdi box failure. I just bought this boat so I don't no how long it has been having issues, it only
Misses under 2k and it feels like it's loosing 3 cylinders for a split second the under 2k rpm is why ibthink stator and a lot of them go out, trigger tested good on my ohms meter

 

[Dukedog]

Ya might wanna visit tha switch boxes again also. A bad bias circuit can make "both" boxes do strange things. One of which is makin' a good box seem bad but all tha while its actually tha one that's bad. That's why is recommended changin' both.....

 

[antman993]

Update.. today I did a coil ohm test 5 were 900's and one was 546, could this be my miss at low rpm should I replace it?

 

[Dukedog]

Could be but they usually show up at any rpm. Think minimum is 'bout 800 ohms. Ya might check plug wires. Easiest way is start motor in tha dark. Using a screwdriver move it around tha wire with it (screwdriver) grounded against tha block (head).......VERY CAREFULLY!

 

[enginepower]

Update.. today I did a coil ohm test 5 were 900's and one was 546, could this be my miss at low rpm should I replace it?

Definitely replace that one if the wire ohms good. The windings have an internal short and will make it produce weak spark, if any. Hope that fixes you up.

 

[antman993]

Update blew a hole out the side of the motor last weekend, pulled the motor apart and the piston and half gone and rusty and dry, what would cause this bad reeds? Bad carb? Rings being shot and not pulling fuel in? I no it's shot but I'd like to no what happened

 

[antman993]

Update blew a hole out the side of the motor last weekend, pulled the motor apart and the piston and half gone and rusty and dry, what would cause this bad reeds? Bad carb? Rings being shot and not pulling fuel in? I no it's shot but I'd like to no what happened

 

[quicktach]

Rust usually equals water in the cylinder - getting in somewhere. Dry sounds like not enough oil. Blow hole .... con rod OK ? I've heard of hydraulic lock up doing this too.