200 Mercury Carb WMV-18 Jets

[Peetee907]

Hello All,
I have a 200 hp mercury with the WMV-18 carbs and am loosing power at mid-range. Runs great up to 3200 RPM and above 4200 RPM. If set at 3800 will drop down slowly to 3200....bump the throttle slightly and it shoots up to 4000. I'm thinking the backdraft jets need to be changed. Currently have .086 stock jets. Anyone have any suggestions on what size jet to change to? Or if other settings on the carb need to be made?

[FORBESAUTO]

Try removing them and see if problem is resolved. Pretty sure merc has a bulletin to remove them for those type issues. If it does cure it, I personally would leave them out, or if you wish to keep them need to start increasing size until get it rich enough to prevent surging/loss of power

[Peetee907]

Thanks for the reply. I try that this AM and see what happens. By removing them, is there any other adjustment that would be needed?

[FORBESAUTO]

Nah, they only lean mixture at part throttle for emissions and economy. It’ll just richen mixture at cruising speed. Idle and wot won’t change enough to bother with

[Peetee907]

Thanks for the guidance Forbesauto. It ran perfect at mid-range. I do notice a little rougher at close to idle speed. Is that the trade-off and something I just need to live with?

[FORBESAUTO]

It’s a little richer off idle, which isn’t necessarily a bad thing. You will notice a difference, maybe not a problem, just different. If it’s annoyingly rough or stumbles when coming off idle, try leaning idle mixture by turning out air mixture screws. They will have a plastic cover over screws to prevent major adjustments, turn them to stops and see if helps, if going in right direction, but not 100% resolved, you can remove the caps and get more adjustment.

[Peetee907]

Thanks for the help. I'll need to play around with that to see if it makes a difference. At least my main issue seems to be fixed which was the loss of mid-range RPM.

[Peetee907]

Set the idle air adjustment 1 1/2 turns out. Factory setting is 1 1/4. Running much smoother but still has a slight shudder when accelerating. Probably not even noticeable to anyone but me. Thanks for the help!