[jeuto]

I have a 1996 Saltwater series Yamaha 225, 76deg, 3.1L, carburated outboard (with 750hrs)that seems to have a problem at low RPMs. It does not like to stay running (occasionally stalls)and it has a hesitation (maybe 2 secs) when you push the throttle forward. My brother seems to think it is jets but could it be something else that is not obvious? It runs fine at higher RPMs.

[rodbolt]

could be weak fuel pumps or it could be the TPS is failing or it could be the enrichment pump is not woking or the prssure regulator is bad or the engine is not warming up and staying rich, this can also lead to loss of fuel in #6 fuel bowl at high speeds. first thing ya need is the diagnostic test lamp to look for any codes the ECU may be setting, if all is well then look for anything the ECU does not monitor. like a compression and spark test. if you dont have the various test harnesses and a DVM as well as the service manual its a tough motor.it can also be the stator charge coils are heading out. lots of stuff to check on that motor but its actually a fairly simple setup once you understand how and why it all works together.

[jeuto]

I appreciate your response. We have no diagnostic tools, but we have a manual and we do own a mechanics truck shop so we are pretty good with motors. The TPS has been changed, we tried to start it while looking into each carb chamber to see if fuel was leaking into the carb (bad jet seat), no luck. We are now ordering 3 new fuel pumps at 30 bucks each (those things are cool, how they work) and new plug wires. We thought about the enrichment pump but will wait on it for the last item to replace. The pressure regulator is a good thought...we will look into that.What hour time would you think the motor needs to be gone through? It runs great (except for the idle)now with good compression in the cylinders. Just wait or do some preplanned parts replacement?

[rodbolt]

if ya replace enough you may find it, however its so much easier to troubleshoot it, cheaper too. how did ya set the voltage on the new TPS ?at starting the enrichment jets will dribble fuel into the carbs, thats how it cold starts,accelerates, power enrichment for knock detected and decell. there is a lot of things going on in that motor, never heard of replacing the plug wires on one as they are or were sealed to the coil, the caps are replacable but if they test good why replace them ?this aint a truck, it will pop a piston in a heartbeat if all subsytems are not perfect, close may work on detroits and cummins but not on a V76. its a very high performance machine that is very durable as long as everything is inside its desighn paremeters, does not take much degradation of fuel,ign or cooling and a piston smokes.a stuck open T-stat can lean out #6 and smoke it. study your service manual.

[jeuto]

Not sure how the voltage was set, my brother did it. Is there a standard that perhaps we missed?How do we test the enrichment pump and coils? We put it in the water last weekend and it ran real rough at idle, it was missing. After we shut it off for 30 minutes it would not start again with just a turn of the key. We flooded it trying to get it to start. A hour later we turned the key and it fired right up. 2 hours later it would not start again unless you put the throttle all the way forward and tap the ignition. It has a shudder when you put it in gear and idle out. It makes you want to give it more throttle to smooth it out. It runs great at 1200rpm and above right up to 5100rpm. Thanks

[rodbolt]

it shudders cause its desined to run on 5 cylinders below 800,4 cylinders from 800 to about 2000. your going to have to buy a manual and some test equipment. then your going to have to read the manual and figgure out why yamaha stuck all that stuff on it and why it works with the other stuff. if your going to do your own testing and maint a good DVM,TPS test harness,service manual and diagnostic lamp is mandatory. a spark Kv tester is very handy. that motor is very touchy on the carb shutter sync and the TPS voltage. if not done correctly it suffers.it also does not like it when a plug cap fails.

[jeuto]

I tried to buy a manual from Yamaha but they are sold out for our model. How would we know if it is a plug cap?.Thanks.