How does the Prime Start system work?

[Bazooka Joe]

Maybe this a silly question, and you'll have to excuse my almost 20 yrs of OMC & Merc operation. Exactly how does the Prime Start system work on my 04 90hp?

I was reading the manual (after almost a year of owning the motor), and to my surprise, there is NO mention of pushing the key inwards to activate a choke system. The manual does give info on how to manually override the Prime Start for a dead battery & pull starting.

I asked a buddy who is usually pretty outboard knowledgeable, but he said "Huh-what..??!!", so I thought I better ask some Yamaha smart-guys.

So to get to the point, is the Prime Start an automatic enrichment device and pushing the key effectively does nothing?

Thanks in advance for the replies!

[Bobbyr]

Joe , your right pushing the key does nothing if your motor has prime start.It was a thermosensor to determine how warm are cold your motor is to adjust the amount of fuel it shoots into the area behind your carbs. If you have a choke , pushing key down activates the choke.

[Bazooka Joe]

Bobby,

Thanks for the info. It's impressive that Yamaha has developed such a feature AND have it work so well.

[SteveE]

Bobby: I have an '04 90TLRC and along the line of Joe's question....how can I tell if my motor has the Prime Start system or a choke? Like Joe I've always wondered if pushing the key in was doing anything but because it could be pushed in, I did.

[tripleb]

Hey All,

I have a 2005 90 TLRD and have wondered the same thing. I suppose one could remove the cover from the carburators and check to see what happens when the key is depressed.

If you see a mist of fuel, then it could be this infamous "Prime Start", or if you see some butterflies close then it would be a mechnaical choke system.

[Bobbyr]

Well if you know what to look for when you remove engine cover you can see the prime start system.It is in the fuel line ,past fuel pump or pumps, It gets fuel from one of the carbs and sends it into the intake manifold behind the carb(s) if needed. You can also see your choke(if you have one), you may have to remove cover from carb.If you have a choke you can push in key and hear solenoid clicking ,this is closeing the butterfly on the carb if you have a choke. I know this is just very basic ,but I hope this helps.

[Bazooka Joe]

I was doing a little checking on the parts list system. It appears that the Yam 90s have had the Prime Start since 1992 or 93.

Whether you have it.. Probably. My 04 90TRLD's manual only shows the instructions on how to override the Prime Start by turning the little red lever gizmo on the front/center the of the carbs. No mention of a choke whatsoever.

To be sure... Take a close look at your middle carb. The Prime Start is a cylinder-shaped device (approx 5/8" dia) directed mounted on the left side (oil tank) of the carb, and has some hoses coming in and heading out. Also, it has one black wire and one single blue wire. The blue wire routes under the carbs and up into the main wiring center on the back of the powerhead.

Also, if you look from the right side of the powerhead (shift linkage side), look closely for some small fuel supply hoses which head into the manifold between the carbs and the engine cases. These are the hoses which the prime start delivers the fuel.

Hope this helps.

Bz Joe