130Hp 2 stroke running rough & low WOT

[lloydj601985]

Have twin 130hp 2str saltwater series V4s on a 25ft Hydrocat. Stbd motor is fine (WOT 5700rpm) & idles good @750rpm. Port motor stalls @ idle after a couple of minutes, runs rough & has low WOT (4700rpm). Carbs were professionally cleaned 6months ago & I have checked mixture settings & changed spark plugs. Oil pump setting is correct (as per manual). Port & Stbd water seperator fuel filters changed and motor filters cleaned. I have a new fuel pump in the mail for this weekend however would like to know if there are any bases I'm not covering. Living remote NW coast Australia so can't run down to the mechanics for advice or parts. Can inter change parts between motors to isolate issues if required.

[Sequoiha]

I would start with a compression test. need to make sure what you are trying to fix is fixable...

[99yam40]

Cleaned carbs months ago means nothing.
You can get water or trash into a clean carb as soon as you fill it up with fuel

But compression,spark,timing , and fuel pressure/vacuum are all easy to check to make sure they are good. then deal with the fuel/carb issues

[lloydj601985]

Between work and cyclones it has taken some time to get the opportunity to do a compression check as suggested.
All cyclinders test at 145 to 150psi.
Initial step when trying to sort out this problem was to change spark plugs. When doing compression test, noticed lower Stbd plug is very black & oily, all others are brown/tan & clean. Engine only run for half an hour since new plugs installed & problems persisted.
Checked spark strength & when disconnecting leads to individual cyclinders, all exhibit change to engine RPM except lower Stbd. Swapped lead and coil from good engine with no change to RPM when disconnected whilst running.
Very much appreciate your help with this guys. Limited resources where wee are so hope you can advise a solution.

[rodbolt17]

did you yest the fuel pump per manual?
and its still possible that you have a fouled carb.
if the diaphram leaks in the pump it can flood a lower cyl.

[lloydj601985]

Don't have equipment to test fuel pump so changing for new tomorrow. Will put carb cleaner through as well to see if this is an issue. Can you advise anything else I should be looking at?

[99yam40]

Don't have equipment to test fuel pump so changing for new tomorrow. Will put carb cleaner through as well to see if this is an issue. Can you advise anything else I should be looking at?

Test equipment is not that hard to find, even auto part stores carry some of it that would work for testing pressure/vacuum, even spark testers.

Hope you are not speaking of just running snake oil through to see if it cleans the carbs and hopefully that is not the way you cleaned the carbs before