1999 yamaha 200 sws surging

[eddie m]

Compression good, all grounds clean and tight. Ignition connections intact. LP fuel pumps replaced, vapor tank cleaned and HP filter serviced, regulator and injector screens cleaned, fuel/ water filter serviced, no fuel restrictions, new o2 sensor. Last one had clogged tube and heater out of specification. Checked fuel pick up to LP pumps. New OMC primer bulb. Tps within reference points. Plugs replaced. Fuel new, non-ethnol. I have a shop manual and think the next step would be the Blink cable for sensor/ignition DX. This thing has me scratching my head. Start up is good but cold idle is at 1000-900 and then wavers between 600-800 rpms. Surges at all speeds and tops out at 5700. Runs strong except the surging and start up with too much negative trim. It will not warm up idle with the slightest negative trim. It will stall. I am all ears for anybody with experience with SWS engines.

[boats.net]

Make sure throttle body is synchronized correctly, check for air leaks on intake manifold and throttle body. Check fuel pressure and timing when engine is surging.

[eddie m]

Make sure throttle body is synchronized correctly, check for air leaks on intake manifold and throttle body. Check fuel pressure and timing when engine is surging.

Fuel pressure within specification at all speeds. I will check the throttle body and intake manifold Thank you for the help. I am stuck. I will post the results when i check this week. Great site!

[eddie m]

Checked and adjusted throttle valve plates to specification. No intake leaks noted during inspection. R&R injectors double checking my work ( I cleaned the screens) to see if I pinched an rubber o ring or sleeve. Will water test Thursday. Idle still wavers in the tank between 700-800 (not often). Water test will tell. Also takes two to three turns of the key to catch the high idle. R&R all fuel lines again and tested for leaks. Negative trim effects engine with poor initial start up. My carb. motors used to do this on start up. Could it be the needle in the VST? I question that because of the HP pump being submerged in fuel. This motor runs good after warm up and it is run at midrange. It seems run rough until it has cleared the cylinders. If this does not work I think I might have to get the signal light for system-sensor check?

[jb123]

thermosensor issue ?

[eddie m]

JB, I am trying to relate my manual to the word "thermosensor". Is that the engine cooling H20 tempature sensor. Do you have a motor like this SWS? It has a lot of sensors and, I might have to get the light harness if the water test does not pan out. I purchased the boat in October and the motor ran good but was not serviced regulary. It is a positive testment to this paticular Yamaha. Thank you for your response.

[jb123]

Yamaha Outboard Parts 1999 S200TXRX ELECTRICAL 2 Diagram

Boats.net is the tech here, mine is just a lightly educated guess

[eddie m]

Just came in from studing the manual and removal of sensors. I will test the thermo switches and coolant temp sender constants tonight with the help of my wifes pots and stove. This should be intresting. Will post results if the project does not interfere with cooking dinner. I want this motor running as it should. Thank you for the insight.

[bill5280]

Eddie, My buddy had a problem that sounds the same, he has a 2000 250 hp he said it was his anti knock sensor. all he did was use a higher octane fuel. Worth a try ?
Bill

[eddie m]

Thank you Bill for the information. I buy my fuel at the marina because of the non ethanol blend. I will research adding octane or finding an alternate blend. Maybe as the administrator suggested, check the timing which, I have not checked as of now. I did however check both thermosensors and, they failed the ohm. specification. The coolant temperature sensor did pass the test. Next is theromsensors, timing and octane. I will order the parts today, test A.S.A.P. and report. Thank you to all.

[eddie m]

Spun the propeller hub yesterday. Will post results of motor test when I get the propeller repaired. Thank you.

[eddie m]

Just got the prop back last weekend. While waiting for the prop hub, I removed the injectors. Made a harness with an on / off switch. Removed the battery from my prize vintage FLH, (OH BOY) and, connected the harness to the battery with spade connectors to the injector spades. Connected a 5/16 fuel hose to the inlet of the injector. Connected a pneumatic connector to attach my compressor. Applied 50lbs of pressure after filling the 6ft. long hose with carb. cleaner. Flipped the switch and found two injectors not functioning properly. One dripping and the other spraying an uneven pattern. All six were spraying nicely when I was finished. My motor has about 1000 hours on it and was minimally serviced. Now it runs like it should. Starts up quick. All the sensors are working in a closed loop. I water tested it today. It runs perfect. I have to say it was the injectors that caused my surging combined with an open loop. The motor runs better than ever. Thanks for the suggestions with my repairs. All posts helped me get this motor fixed and, I think it will run well for a while since I plan on servicing it regularly. Thank you again to all.