1987 150hp yamaha ob will start missing at running speed and just go dead

[SHJ]

Starts missing and will just go dead when running at cruising speed. Checked compression runs about 115+- (within 10%), changed ignition coil wires-they are good, ran sea foam through it with ethanol free gas (bypassed gas tank), ran same way (has gas/water seperator). Could it be something in flywheel? I always put additive for ethanol gas when fill up. Does anyone have any suggestions?

 

[robert graham]

Re: 1987 150hp yamaha ob will start missing at running speed and just go dead

What is your "cruising speed" RPM? If it's say, 3500RPM, then does this also happen while cruising at 2500RPM? What I'm getting at is it sounds like a fuel/air vent restriction. The fuel/vent works up to but not beyond a certain RPM. Check your fuel system, tank, vent, pick-up, fittings, primer bulb, quick-disconnect, filter, fuel pump, etc. for restriction or air leak. When motor "goes dead" check primer bulb, if it's flat then you have a plugged air vent or fuel line. good Luck and let us know what you find!

 

[SHJ]

Re: 1987 150hp yamaha ob will start missing at running speed and just go dead

Actually the explanation was when problem began, was running 4000 rpm it went down to 2000 rpm, cleared and ran normal, but when I took it down to idle at wake area went dead, start idle again, goes dead again, trolled into launch. Now it misses at a high idle (at home)--can pull plug wire off can't even tell difference in missing. Misses at any speed even rev'd up. Have to keep giving a little gas to keep it running. Fittings, primer bulb, fittings, quick-disconnect, filter, fuel pump, system/tank seem fine.

 

[GrayBlue]

Re: 1987 150hp yamaha ob will start missing at running speed and just go dead

When's the last time you changed the water separator? How full is your tank when this happens? When is the last time you cleaned the carbs? Clean spark plugs and run again, if continues then remove spark plugs and take a look and let us know what they look like or better yet, take a picture and put it on here.

 

[99yam40]

Re: 1987 150hp yamaha ob will start missing at running speed and just go dead

You can test the voltages on ignition system,
check timing,
check alarm system to make sure it is functioning properly,
check fuel pressures and vacuum to make sure pumps and supply has a problem