Eco switch not ramping up rpm on eu 3000is only 84 vac adj switch and get 125 vac and hardly any change in rpm.thinking it has bad carb throttle motor or harness

Hoping this is echo? If so screw L and H all way clockwise till stop then back each out 1 1/2 turn. Start and let warm up hold throttle to max rpm and adj. The H to max rpm then let idle and adj. L until it idles good and has very little hesitation when throttle is squeezed fast. Then adj H again to max rpm and then back off until it sort of growls not squeel.

Set both the H and L for 1 1/2 turn out from bottom, start and adj. The H for max rpm for full throttle, now set the low for good idle and very little or no hesitation when opening throttle. Now set H for max rpm again and then back off until you get more of rumble at full throttle.

Sounds like the throttle control motor is not adjusting the engine speed to compensate for the load. Does the generator rev up to full speed if you turn OFF eco with NO load?
Funny thing, I have one on my workbench that is doing pretty much the same thing. Runs on eco, revs up with eco off with no load, coughs, sputters and dies with a load in either mode. I will update with what I find when I figure it out in the next week or so. Have a new carb on order.

I swapped the carb and it made no difference. Still backfiring (rather dramatically) and won't stay running. I see on some other posts that Valve lash will cause this. It makes total sense as the exhaust valve gap actually tightens as the engine wears which would keep the exhaust valve slightly open when it ain't supposed to be allowing raw fuel to enter the muffler.
With this one I can believe it as it has a ton of hours on it and I know they have never been adjusted.
I will try to get a chance to do it over the weekend and update this post when I do.

Overhaul the carb. When you have to choke it to run, there is not enough fuel getting in

Here is how to do it. First disconnect the throttle cable to the carb and let it hang loose. Make sure the outdrive is in neutral and the boat is secured to the dock or on a trailer with a water ****.

Pull back on the throttle by hand directly on the carb throttle shaft. Observe the Choke cam on the opposite side of the Carb. Let go of the Carb throttle shaft and see where the Stepup Cam is set. The Choke plate should be closed most of the way. You will not have very much time to make an adjustment.

Start the engine and let the Choke work and observe the RPM. There are usually adjustments you can make to put the Stepup Cam on a lower step by bending the Link Rod if it is running too high in Choke. Sometimes the Cam is left alone and a screw similar to the Curb Idle screw on the Throttle side just needs reduction to ride lower on the Choke Cam.

After the Choke is warm, it disengages with a pull on the Throttle. Now you are using the Throttle side of the Carb to operate the engine RPM. You want a low RPM for sake of the outdrive gears and NO WAKE zone. The adjustment screw opens the Throttle shaft, You set it for the Manufacturers Spec. probably 550 RPM.

The Throttle cable is now adjusted so it pushes slightly against the Carb. This forces the throttle closed. The Throttle cable has threads and a sort of Knurled knob which runs on these threads. This device is used to lengthen or shorten the cable so that pressure is applied against the Throttle.

When the outdrive is in water you will has resistence on the Exhaust. This will slow the RPM. If the motor stalls you will need to adjust the motor to idle Specs while in the water.

For best economy, find a Vacuum port and attach a Vacuum guage to it and adjust the air mix to the highest Vacuum reading then turn in the Mixture screws slightly until the vacuum starts to drop.

I didn't think there was an adjustment in there, the air fuel screw?? Is it outside? Are there 2 screws outside? Is it Mikuni? If it has 2 adj screws outside, turn both in all the way, then back them out 1 1/4 turns each, this should get you running, some minor adj from there should make it right. But I could have sworn there was no adj on those, and the only way to adjust it is to change the jet. Check it out.

The air intake system on this unit is highly fine tuned. Make sure all covers including front battery cover, plenums, air intake system is properly installed and that any and all gaskets on doors and covers are not damaged.

and I'm out of ideas. I have a RR 125 Motard with about 12000 miles on the clock. It's been trouble free for the years that I've owned it. Recently I noticed a slight miss when running at part throttle. RPM doesn't matter it misses from idle to almost redline but only when the throttle is in the first 5% of it's range. I did the full routine, carb cleaning, valve adjustment (ugh...shims), air/fuel/oil filters. No change. At more than 5% throttle, there's no miss, and it pulls very strong. At full throttle, I don't have the guts to see the end of 4th gear. Tempurature doesn't make a difference, hot or cold, it runs the same, although when the choke is on (cold) there's no miss (but a high idle). Turning on the choke after it's wamed up it will bog and die (like it should). I suppose I could have missed something when cleaning the carbs, but usually, a little bit of choke will fix that. Not in this case. There's no hesitation when opening the throttle, and under high loads, any RPM, any gear, it runs fine. So, I'm at a loss. I'm open to suggestions. ,Check for vacuum leaks first - carb boots, vacuum lines, etc. Also check the CV diaphragms for cracks, splits and pinholes. Then, I think I'd re-check/clean the pilot jets. Then, if that doesn't help, I'd open the idle mixture screws a bit - maybe 1/8 to 1/4 turn to get a little richer mix.,,,

On the R.H side of the carb behind the automatic choke down on the rear throttle shaft there is a pin running thru the shaft with a lever that will lock it out. If the choke is not fully open or the weight behind the auto choke is not dropping the lever will not relase the secondaries to open.