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Discussion Starter #1 (Edited)
Here we go. Since there are threads popping up almost daily asking about this problem on older (K7 and up) Burgman 400 scooters I decided to make a better guide.
What this mod does is essentially bypass the internal (hidden and irreplaceable) fuel filter/strainer with an inline one.
Cost is about $10-15 and you also get the gas line replaced in the price (which costs $40 normally from Suzuki).

This mod fixes the following symptoms:
- Bike will not go over some RPM value (typically around 5k or 6k, will drop off with time)
- Bike bogs down under throttle / when accelerating
- Fuel starvation

Time needed: 1-3 hours.

Items needed:
- Universal EFI fuel fiter for cars (8mm or 6mm, both will work):

- 6mm rubber gas hose, 0.5m in length (I'm not pasting a picture of this, you know what a hose looks like).
- 4 small screw clamps (the ones looking like a ring with a screw to tighten it)

Tools needed:
- Screwdrivers, allen keys
- Dremel
- Scalpel

Now for the steps:

REMOVING FUEL ASSEMBLY
- Remove the seat by unscrewing the 4 bolts that hold it to the bracket. Unclip the under seat light.
- Remove the engine cover plastic by popping the two clips.
- Remove the plastic just in front of the engine, also held by two clips. This is the plastic under the nose of the seat with small vents in the middle / front.
- Remove the rubber L piece connecting the intake and the air box. Might take a bit of 'massaging', don't be afraid to manhandle it a bit.
- Remove fuel from tank if tank is more than half full.
- Unscrew the two allen head screws attaching the fuel hose to the injector (at the top of the engine).
- Unscrew the two allen head screws attaching the fuel hose to the fuel assembly (down where the tank is).
- Remove 6 allen head screws that hold the fuel assembly attached to the tank, they are arranged in a circle, can't miss them if you tried.
- Disconnect the wire going from the fuel assembly to the harness. Might be a bit tricky but try using a thin screwdriver.
- Pull out the fuel assembly. You will need to rotate and wiggle it around. Think of it as a puzzle.

MODDING THE REGULATOR BOX
- You now have the culprit out. Put it on a desk somewhere and remove the two Phillips screws from the sides, down near the bottom of assembly.
- Pull everything apart. Do remember which wires go were. There are only two but still.
- You should now have the bottom cap, fuel pump, regulator box (white box with the float attached) and the 'metal part' with two rails on which everything was assembled. If you do not have those parts you have not pulled enough. Only O-rings hold things in place.
- Remove the metal relief valve from the regulator box, again held in by stubborn O-ring.
- You now have a regulator box with three holes and a float attached to it.
- Look through the holes and you will see a metal mesh inside the box. Might be black or orange or whatever color from the dirt / goo / etc. This is what is causing the problem and can not be replaced. Suzuki requires you to replace the whole assembly for $550 or so.
- Try blowing into the top hole while holding one of the bottom holes closed so that air must pass through the mesh. If it is normal there should be no resistance. Mine took some effort to get a breeze on the other side.
- Take a sharp and thin something. Such as a small screwdriver or sharpened bicycle spoke and poke holes into the metal mesh. It is pretty soft so not much effort needed.
- Blow again, should be nice and easy now.

MODDING THE GAS HOSE
- Since now we essentially do not have the strainer anymore we need to put another, better, filter in.
- To do this take the original hose and cut the metal clamps / rings around the ends of the original rubber hose, where rubber meets the L pieces that attach to injector / tank. Make sure to cut only to the rubber as not
to damage the metal L pieces.
- After cutting through pry the clamps open and remove them.
- Use scalpel or wherever method you have at hand to remove the original hose from the L pieces. It is glued on so will take some effort. Clean them up until there is no rubber left on the pieces themselves.
- The new fuel filter can be mounted just under the nose of the seat, behind that plastic that you removed earlier - with a grille on it, so place the filter there and measure how much hose you will need on the side that goes to
the tank and on the side that goes to the injector.
- Cut the hose to length and force it onto the filter. Some soap might help. Tighten (tightly) to the fuel filter with clamps.
- Do the same to the L pieces. Don't forget to put the clamps and the factory insulation onto the hose beforehand :D
- Now you should have a hose that resembles the original but with a fuel filter in the middle.
- Use large screw clamp / zip ties to secure the fuel filter to the frame in front of the frame as described above. Image in attachments.

PUTTING IT TOGETHER
- Retrace the steps above in reverse order.
- Massaging the fuel assembly back into the pump takes some patience. Just wiggle and rotate the assembly around and you should be good after a minute or so.
- Make sure to connect the gas tank side of the hose first and prime / remove the air from the filter and hose by turning the key one or two times until the gas flows out of the other (injector) end and then screw it onto the injector. Not
really needed but will save you a few seconds of cranking as gas needs to fill the hose and filter.


Take the bike for the test ride and your problem will almost certainly be gone.
One thing I can recommend is to clean the pouch / filter under the pump before reinstalling or if you want and have one, replace it. To me that thing did not make any difference but some users had a lot of gunk in it.

Have fun :D

WARNING Make sure that the hose, filter and L pieces are clamped down tight and will not come apart when the fuel hose is pressurized.
These are steps that I did to fix the problem and if you are going to replicate them you are doing it at your own risk as working around gas can be dangerous.
 

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I am doing the mod as I type this , do I have to trace the wiring harness forward to connectors or do the wires remove right at the pump ?
I don’t want to break anything .
Thanks
 

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Discussion Starter #3
I am doing the mod as I type this , do I have to trace the wiring harness forward to connectors or do the wires remove right at the pump ?
I don’t want to break anything .
Thanks
There is a plastic jack on the left side near the tube frame. Just follow the wiring from the top of the fuel assembly and you will find it. It is a bit in there but can be removed with a thin screwdriver and a bit of swearing :D
 

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There is a plastic jack on the left side near the tube frame. Just follow the wiring from the top of the fuel assembly and you will find it. It is a bit in there but can be removed with a thin screwdriver and a bit of swearing :D
Got it , ya you are right .
They didn’t leave any extra wire out of the harness :serious
 

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I had a similar issue, but it was caused by a bike sitting, the gas going bad and the strainer (part at the very bottom of the fuel pump assembly) disinigrating and clogging the internal screen. I replaced the strainer, which was $40 shipped OEM Suzuki part, then cleaned the internal filter, and reassembled.
 

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Discussion Starter #6
I had a similar issue, but it was caused by a bike sitting, the gas going bad and the strainer (part at the very bottom of the fuel pump assembly) disinigrating and clogging the internal screen. I replaced the strainer, which was $40 shipped OEM Suzuki part, then cleaned the internal filter, and reassembled.
Glad it worked. Of course, if you can you can always try and clean the screen inside. Maybe ultrasound cleaner would help. Mine was full of black gunk that didn't go with anything so had to resort to this. Actually cleaning it worked for about two weeks before gradually starting to show the symptoms again. Now I am at some 6000 miles post-mod and everything is running great, with about 75mpg (US).
 

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Glad it worked. Of course, if you can you can always try and clean the screen inside. Maybe ultrasound cleaner would help. Mine was full of black gunk that didn't go with anything so had to resort to this. Actually cleaning it worked for about two weeks before gradually starting to show the symptoms again. Now I am at some 6000 miles post-mod and everything is running great, with about 75mpg (US).

Just a quick update. I am at about 10k miles from when the mod was done and not a hiccup so far.
 

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What is the general consensus - are folks doing this modification proactively as a preventative measure or waiting until or if it becomes a problem?
 

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IF I had a 400, I think I'd do this proactively BEFORE it bites my butt 150 miles from home.

So stupid of Suzuki making the 400's tank of steel in this day and age. It is so easy to extrude one from polyethylene like the 650's.
 

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Discussion Starter #10
What is the general consensus - are folks doing this modification proactively as a preventative measure or waiting until or if it becomes a problem?
No need to do it proactively IMHO except if you are planning a really long trip of few k miles. Symptoms usually come slow and mine was loosing maybe 100 rpm per 100 miles until I did the fix when it would not go over 5k rpm. So it is not that sudden.
 

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I'm guessing this has only been a problem when the tank starts to corrode. Even though my tank is clean as a whistle I'm going to add this to my list of maintenance and mods to do together when I have all the Tupperware stripped off.
 

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Thank you So Much, I just got mine back together after doing this, it is like a NEW Bike! It had been nothing but a paperweight for the last 3 months, as it didn't have enough power to get out of its own way...

It took more than 3 hours, but, I am a Slow Old Man, no prob.
 

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...you're slow?...

Thank you So Much, I just got mine back together after doing this, it is like a NEW Bike! It had been nothing but a paperweight for the last 3 months, as it didn't have enough power to get out of its own way...

It took more than 3 hours, but, I am a Slow Old Man, no prob.
So funny. I started this process two weeks ago... basically tried to follow the directions here - which are excellent !! - until I realized that my 2003 K3 series isn't what this was for. So my garage has several areas of tupperware in it now. It's all good, in a way... evicting former furry tenants and their belongings, etc.
I got far enough along to move the radiator the 1.2439" I needed to get the fuel pump assembly out. I'm also going to replace the seat latch and parking brake cables... they are both very accessible now! I'd really like to ride this someday. "Soon", he said, "...soon."
Ha!
 

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I did complete this job; got it back together last weekend; not hard, just needed time. This tank is suprisingly clean! It fired right up for about a minute, then died. Can't get it going now. Cranks over fine, but acts like no spark. There is spark, but the plug I pulled out was dirty (black & gas fowled), and I'll get a new one before I try to start it again. The more I read, the more I get the impression that these scoots are very finicky, and when something goes wrong, there's no grace. I'm still looking forward to getting this thing running! It did sit dormant for several years before I got it. -Thank you all!
 

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Update: I did two things:
1) replaced the spark plug. Tried to clean it first, but no change after cleaning.
2) took the injector out and cleaned it with carb cleaner and a 9v battery. A little messy, but evidently effective!
I did not notice any 'gunk' or dirt in a chunky or colored way, but after I put it all back together it fired up and I ran it for about 20 minutes or so, giving it some revs along the way. It sounds great and idles well.
My full put change was probably not needed, but knowing that the tank is solid is a comfort.
 

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Update: I did two things:
1) replaced the spark plug. Tried to clean it first, but no change after cleaning.
2) took the injector out and cleaned it with carb cleaner and a 9v battery. A little messy, but evidently effective!
I did not notice any 'gunk' or dirt in a chunky or colored way, but after I put it all back together it fired up and I ran it for about 20 minutes or so, giving it some revs along the way. It sounds great and idles well.
My full put change was probably not needed, but knowing that the tank is solid is a comfort.
After did the mode reset little improvement. Starts ok but will not accept throttle input...can get it to 4000rpm with sputtering,coughing,backfiring. It acts like it is starving for fuel. I did the resistance check on the injector and it is good. Do you guys think I should go ahead and clean it since it’s easily accessible now?
The dealer installed a new fuel pump but I removed it since the scoot was still running poorly. I think I will remove it and make sure I didn’t install something wrong. Can you recommend a check of the pump unit before I take it out?
Looking for new things to try🤐😄
Wick
 

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Possibly the lining in the tank is disintegrating with debris at the bottom of the tank? This is a common problem with older models and even if you change the pump the debris is still there. Take a flashlight and look in the tank. That is what this thread is all about. Installing a inline fuel filter.
 

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Possibly the lining in the tank is disintegrating with debris at the bottom of the tank? This is a common problem with older models and even if you change the pump the debris is still there. Take a flashlight and look in the tank. That is what this thread is all about. Installing a inline fuel filter.
Unc. The dealer "flushed" the tank about 40 miles ago and I installed the inline filter ..have run about 30 mins since. Fuel in the new filter is clear, but I will do what you suggest and see if I see anything. How do you suggest I test the pump while I have it out?
Wick
 

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Unc. The dealer "flushed" the tank about 40 miles ago and I installed the inline filter ..have run about 30 mins since. Fuel in the new filter is clear, but I will do what you suggest and see if I see anything. How do you suggest I test the pump while I have it out?
Wick
Just looked in tank ...looks clear as best as I can see. Disconnected the fuel line from the throttle body and turned on the key...it only pumped about 1-3 ozs. Clear.
Then shut off. Should it keep pumping while disconnected?
Wick
 
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