1998 Yamaha T9.9ELRX Won't rev past idle

[JimEdBrown]

Afternoon,

Just picked up a new to me 1998 Yamaha T9.9ELRX outboard (along with the rest of the boat.) Looks to have had very gentle use.

Engine ran great when I bought the boat last month. Its been sitting since then, as I've been sorting out the Merc outdrive (yikes!). Big motor runs and shifts, so was hoping to do a quick service on the yamaha and hit the water.

No dice. On the muffs, the thing starts easy as pie. Idles real well, pees like it should, etc.

But any attempt to throttle up, including but not limited to "fast idle," and the thing just starts chugging hard. It doesn't die, it just bogs down, and sounds bit like its maybe misfiring? The little engine that couldn't. Engine sort of twitches a bit, and its really chugging low and slow. RPMs sound like they decrease and become inconsistent when you give it any throttle at all.

I went through the likely suspects. Fuel is flowing, ran it off the bottle on some crystal clear ethanol free. I cleaned the carb and plugs as PO's fuel looked like half brewed sweet tea.

It has spark, as it idles like a top. Plugs are heat range 4 and should be a 6, so will get those swapped out, but those are the plugs that were in it when I ran it before buying the thing and it revved up fine then.

Anyway, been looking around, and can't find much on this particular issue. Figured I'd ask around on here and see if this is a common condition, and if anyone has any other components to check?

I'd rather not just throw parts at the thing until something works.Thinking maybe something with that electric wax needle valve job bolted to the carb? Not really sure how to test that thing.

What y'all got? Heard it before? Halibut season opens tomorrow and I'm landlocked..... bummer.

Thanks,

-hj

[99yam40]

Timing light hooked to the plug wires should tell you if there is a spark problem and you can see if the timing is in spec and advancing as it should.
lack of fuel( main jets), or too much fuel, spark not keeping up, and timing not advancing is all I got.

Need to figure out what is happening or not happening as you advance the throttle.

as far as the prime start system on that 4 stroke, someone with a service manual for that motor will have to chime in on testing, but on most 2 stroke models they have a lever to turn them to auto, open ,and closed to help eliminate/troubleshoot the system. or at least get you back to the dock when something goes bad on it.
maybe just like 2 stroke models you pull it off the heater unit ,measure, put 12 volts DC on it to see if the needle extends as it heats up would tell if it works as long as it gets 12 volts while running

[JimEdBrown]

Update:

Got it idling, and realized that there is no power to the Prime Start unit.

Neutral terminal has continuity to negative post on starter. Jumped power from positive post on starter to the PrimeStart positive side, full 12 volts coming out the negative side. Device definitely had power, and felt like it warmed up a bit, but no effect on the way the engine would run.

I also checked to see if the motor was sending power back to the battery, which it does not appear to be doing. Do these engines send a charge back to the batter?

Wondering if this is potentially an electrical issue more than a fuel issue. It has spark, and fuel, and air. So something is out of proportion somewhere.

I see that the power and neutral both go straight up to the coils under the flywheel, but I didn't have time today to get the flywheel off and see what lives up there.

I'm just learning these engines as I go here, so forgive me.

Any thoughts?

Also, I can't find a manual for this model listed on the manuals sticky. Anyone know where I might find that? Would love to get my hands of a factory service manual if one exists.

Thanks,

[pstephens46]

You can buy the manual from Yamaha