Acerbis 4.1 Tank // KTM 3-Fiddy

Acerbis 4.1 Tank // KTM 3-Fiddy

UPDATE 8/1/17 – IMS Gas Tank Version 2 is OUT!

Check out the new IMS Gas Tank Version 2 review I’ve done, which does fit the 2017 KTM 350 EXC-F without the need to remove the thermostat.


You may have seen my previous IMS tank woes post that has led me to return the IMS tank and try out the Acerbis 4.1 tank on my 2017 KTM 350 EXC-F. I also spoke with Jeff Slavens over at to make sure the Acerbis would fit on the 17′ 350’s, no need to remove the thermostat and no other parts are needed to be ordered separately like I experienced with the IMS. (Acerbis does require hose clamps if using their fitting) He confirmed none of that is an issue. So I ordered one up from Slavens right here.

UPS delivers a nice brown box.. after opening it I was surprised to see it in very cool & professional packaging.. unlike the IMS tanks. The next thing I notice is all the OEM parts that you must order separately with the IMS tank are INCLUDED with the tank! Score!

ACERBIS Packaging


More Photos. Click to enarge…


First impression.. it’s larger BUT SUPER LIGHT!

That’s right… now I did not put these on a scale but if feels like the Acerbis tank WITH the fuel pump installed is lighter than the stock tank without the pump! That’s always a huge plus!

A few more differences…

Stock has the quarter-turn gas cap, which mine, probably cuz it was new, was a pain getting on and off. Acerbis has standard screw-on gas cap. Stock tank has brass threaded fittings on all of the mounting points, unlike the Acerbis where all are plastic threading except where the side panels bolt on the top of the tank. (more on that later!)

The stock tank is much thicker walled than the Acerbis… saftey precautions? EPA? This definitely adds to the weight of the tank.

The stock uses a 90 degree elbow at the fuel pump to the engine, whereas the Acerbis uses a straight fitting, which is included. Jeff Slavens retro fit the stock 90 degree fitting with the Acerbis tank by cutting down the mounting bolt. See the photo on right as it’s too long for the Acerbis install. I did cut mine down but for some reason it still would not secure the fitting, the bolt would just stop as if the threads stopped. Maybe it’s a 350 thing compared to his 500… or I just need to revisit it. I installed the fitting that came with the tank because I had to go riding! I’ll revisit it out probably this hot summer or in winter..

Stock 90 Elbow

Acerbis Straight


The install is pretty straight forward, but I will share a few things from my install.. including an issue I had with the tank mold that required a TIME-SERT!

First, you’ll need to remove your seat, side panels, unplug the fuel pump connector, unscrew the tank mounting bolt, then disconnect the fuel line. Next, remove the tank and flip it on it’s face to remove the two fittings shown in Photo 1 below.

Now you can unscrew the mounting plate on the back of the tank, this will allow you to feed the pump up through this opening. See Photo 2 below.

NOTE: For easiest removal, once the four mounting bolts are removed, push the threads of the pump inside the tank, then slightly tap the tank on the table or ground to allow the pump to fall into the forward pocket of the tank molding.. see Photo 3 below.

Photo 1 - Remove Pump Bolt & Fitting
Photo 2 - Mounting plate
Photo 3 - Pump forward in tank

Now you can fish the pump up through the hole, be very very careful!

Fish the pump up carefully
Inline filter & pump surface...
Fuel pump assembly

Time to install the fuel pump in the Acerbis tank… it’s much easier installing than with the stock tank. Here you can see the difference in the stock tank wall vs the Acerbis tank wall.. Acerbis fitting is on the right.

O-rings from your stock fittings will need to be used on the fittings that came with the Acerbis. One on the mounting nut and one on the straight fitting respectively.

Pump mounting nut


Notice how large the top left hole is compared to the other three.

After I installed the fuel pump and started to use the screws for the mounting plate, I noticed the top left screw never caught and I could push the screw all the way down touching the plate. The others caught and I was able to tighten them down. So that’s when I noticed the issue shown in the above photo!

This is one concern with the Acerbis tank.. but I read a post from them stating they believe the brass inserts can seize bolts and cause more issues… I don’t buy it personally. I think it’s a manufacturing cost thing.. anyway.. it is what it is. Return to Slavens… or fix it. I determined that ultimately I’d like inserts on all of these holes so I decided to fix it myself.

Using a 6mm Time-Sert insert I was able to fix it. I installed the insert and used some JB WaterWeld to help secure the insert to the plastic.

Place tape over the hole to keep debris out
Time-Sert installed.

So far I’ve had no issues with the Time-Sert or other with this tank. It has performed very well and is slim and light. Looks very cool too… here’s some finished photos..

Top View

Side View


I’m very happy with this tank over the IMS. You shouldn’t be forced to remove the thermostat to use the IMS tank.. and the very POOR customer support they gave me after contacting them directly and speaking to them on the phone. Emailing them and never getting a response, you can read all those details in my IMS post. That sure lost me as a customer and supporter of them from here on out. Shame on IMS.

Glad Acerbis has stepped up to the plate and delivered a quality tank. Yes, the plastic molded threads I’m not a fan of but there is a resolution for that.. two thumbs up!


Here’s Jeff Slaven’s review video on the 2017 KTM EXC-F Acerbis tank:

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