150 SWS - Missing / Surging

[Parthery]

So....out today....and at varying rpms between 2800 and 4500 I have an intermittent miss or surge...engine clearly losing RPMS....and then it goes away.

I checked the usual suspects...plugs/wires all tight...replaced fuel filter with new 10 micron Yamaha.

Any thoughts on where to look next before I start tearing down the carbs?

 

[jaamm1]

Parhtery,
I had a 99 232 with a 250 OX66 with a surging problem. I did all the filters, VST screen, O2 sensor and finally changed the low pressure pumps (3) the problem was soved. The pumps are easy to change and about $40 apiece. Good Luck.
Also I took the old pumps apart to see what the failure was and could not determine what had failed.

 

[luvsno]

150 sws

Hi, last summer I had a similar situation. Was there anything in the old fuel filter, I had some black liquid that would flow like water and got through the filter and into the carbs. Drained the tank, cleaned out and dried out, blew out the lines and installed new filter. Thie summer start it up full of new fuel, dry gas, methyl hydrate and run it up to the cabin, same thing, surges, loses power, max rpm 2000, misfire. Get to cabin wait for rain to stop and find which cylinder is bad. I pulled the carb and there is the black liquid now hard blocking main jet passage. Cleaned carb and run down the river ok, has been good since. I still have no idea what the black liquid was but it seemed like a mould growing in the water that had accumulated in the tank from and faulty gas cap. Hope this helps. I have a non-fuel injected 150hp sws.