Yamaha EF2400iS Generator Surging Idle Fix

Finally, a real solution!

UPDATED 01/31/22

Did you know your generator has NO fuel filter?  That screen inside the fuel fill port is too course to stop fine enough particulate to clog a jet on your carburetor.  A fuel filter is very cheap, and takes only a couple of minutes to install.  I'm amazed Yamaha didn't add one.  If your generator is running good now, go get a filter this weekend and install it.  It's a lot easier to keep it running good than to tear it apart and fix it!


In the following pictures, you'll see which part clogged that caused the engine to surge at idle.  The usual disclaimers apply.  If you're not comfortable working on small engines, don't.  If you break yours, hurt yourself, burn down your house, don't call me.  This is NOT a difficult fix once you know how.  I'm not going to give you specific details, but here's the basic overview.

I recommend running the generator, shutting off the fuel, and wait about 2 minutes for the engine to quit.  Less mess that way.  Remove the back and side covers so you can see the carburetor and air filter.  Remove the air filter.  Remove the three bolts inside the air filter housing that hold the carb to the engine.  Disconnect the throttle linkage, fuel line, and remove the plastic cover over the throttle servo - this will expose the servo connector, unplug the cable.  You should have the carb free at that point.  Move onto the pics.


IMPORTANT UPDATE:  As it turns out, Yamaha used two DIFFERENT versions of carburetors on this generator.  There's no visible P/N on the carb body itself.  The main difference is the jet looks completely different.  They are not interchangeable.  In the later model EF2400iS generators, Yamaha started using carburetors from the newer EF2400ISHC.  No difference to the owner unless you're looking for replacement parts.  Many thanks to Marty for helping solve this mystery!


Click on the image to enlarge it.  That's the magic screw.  It's a booger to remove as it has a Loctite type adhesive on it.  It was easier to remove by taking off the servo mounting plate first.  This allowed the screwdriver to get a straight shot at the screw.  Once the screw is removed, the washer with a tang on it can be removed.  That holds this little brass jet in place.  A small pair of needle nose pliers can gently pull it out of the hole.  It's not screwed in, the o-ring is a tight fit.  Those little holes in the sides can get crud in them, along with the very tiny hole in the end of the jet.  A #78 drill bit (0.060") was gently pressed into the hole, and turned with finger pressure to auger out the crud.  It was then flushed with a little solvent.  Be careful not to damage the o-ring with anything used to flush the jet.


If your jet looks like this, then you have a carburetor from an EF2400ISHC. They are items number 9 and 10 on the Yamaha parts drawing.  The o-ring is P/N 2H0-14147-00-00.  The jet is P/N 7CU-E414J-16-A0.  I know two people with this type of jet in their carbs, even though they have EF-2400-iS generators.

If you have the standard EF2400iS, as most of apparently do, it's item number 6 on Yamaha's drawing.  This one has no o-ring.  The jet is P/N 620-14142-35-A0.  Note the lack of an o-ring and the body of the jet is threaded.

Another view of the EF2400ISHC jet, this time upside down.  You can get a better view of what needed to be cleaned.  The EF2400iS jet is cleaned in the same fashion.

This is the fix for the idle surge.  Clean it up, put it back together, you're done.  The rest of the images show another jet cleaned first, but that didn't fix the issue.  We tried one fix at a time to verify the actual cause/fix for the idle surge issue.  You might want to clean next one too as we DID find crud on the needle seat.


To the right of the screw that was removed in the previous pics is a black plastic cap.  This can be gently pried off with curved needle nose pliers.  It's pressed into place.  Be careful not to lift up on the brass piece it's attached to.

With the plastic cap removed, you can see how the cap will fit back into place when you're done.  I HIGHLY recommend marking the needle valve BEFORE you back it out.  See the line scribed onto the bottom lip?  This one made a full SEVEN turns before coming out. 

I put a flashlight into the body of the carb.  If you look into the needle jet hole, you should see a light.  If it's occluded at all, it will need to be cleaned.  A little piece of debris was found at the top left edge of the seat.

The needle was cleaned with a little solvent, wiped off, then re-installed seven turns.


My coworker has the same generator, and had the same idle issue.  He tried using SeaFoam, and a carburetor cleaner spray, neither helped.  We took his carb apart at work during lunch, and found the debris in the needle valve.  The pictures above were from his generator.  My coworker Barry said "the huddenn-huddenn" is gone!  I later performed the same fix, and mine has been trouble free for many years.

Add A Fuel Filter - Prevent The Problem!

Most small engines use 1/4" fuel line.  This generator uses ~3/16" (or metric equivalent).  There's an outer tube that helps protect the line.

I bought the cutters at Sears many years ago.  Can find them most anywhere now, such as Harbor Freight, Ace Hardware, etc.  These are ideal for cleanly cutting the fuel line.  I removed about an inch of line, the removed the outer tube, and cut a couple of inches off it.

I wanted a clear filter housing so I could visibly see if any particulate is trapped.  Some filters are too restrictive, and this motor doesn't have a fuel pump, it's gravity fed.  So I bought a filter intended for a lawn tractor at Home Depot.  Under $10.

I couldn't find a fuel filter with 3/16" barbs, so I went with one with 1/4" instead.  To get the fuel lines to fit, I had to soften them with a heatgun.

A couple of small hose clamps sealed the fuel lines onto the filter.

The fuel valve was opened and fuel flowed into the carburetor.  I ran the generator both at idle, and with a 1500 watt load to verify the filter flowed freely.  Work great.  Hopefully the filter will prevent any further problems.


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Last updated 01/31/22   All rights reserved.