accelerator pump install/spark arrestor out

I installed my new diaphragm in my 39mm FCR mx. The new one was slightly different than the old. The old one had a larger button portion; about 1/8". The new one was just about flat.

I installed it with the part number facing out. The smaller button on the inside and spring on the outside. My throttle response is really suffering. Just to note, I did remove my spark arrestor. I plan to put this back in to see if it is the spark arrestor removal changing the throttle response. The bike no longer wants to wheelie!!!! I also put my smaller sprocket on the front, the bike should be flipping me off!

Did I do something wrong when I put the diaphragm on? I re-lockwired the linkage as well. The only three changes are:

  • new accelerator pump diaphragm
  • spark arrestor removal
  • one tooth smaller gear in front

I do not want to go for a test ride right now, severe wobble from somewhere. Fix that, then install spark arrestor, and see what happens.

So you are saying the rivet is shorter? Confirm the linkage is correct (you did not turn the screw, right?).

Spring goes between the AP pump cover and the diaphragm. If that is not how it is, there is your issue.

Put the spring on the cover side, did not adjust the linkage, re installed the spark arrestor. (test rode, and it is the same). May try the other side of the diaphragm. I am not sure if this is a new style diaphragm or did I get the incorrect one and maybe installed it the other way around.

Really hoping to find out from someone who knows more than I.

hmmm, Maybe adjust the screw on the AP linkage? Try the diaphragm the other way round?


Confirm the chamber is getting fuel

Confirm the AP nozzle is not clogged

OK, thanks William, I will NOT adjust the screw.

You do not sound concerned the new diaphragm does not have the same size button. Can I guess this is the new style diaphragm? Or it does not matter. I read up on the slant style FCR, to file off the button for more volume. (I do not have a slant style FCR)

The rivet length affects the total amount of the squirt as well as the duration. A longer rivet means less fuel.

Who sold you the diaphram? It should of been the same.

AFAIK, all FCR-MX use the same one, only the slat style had various ones to use as an adjustment.

I got it from Winners Circle in Markham Ontario.

It makes sense I should actually have more power now, with the higher volume of fuel (no button). I cannot say the diaphragm I removed was the correct one; I purchased the carb used.

I am going to flip the diaphragm to see if there is a difference.

We are having torrential rains for the next few days, it may have to wait!

Ah, a used carb, are you sure it is actually a FCR-MX and not a slant version?

It sounds to me like the gave you a diaphragm for a slant.

Did you check to see if you even get a squirt at all?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By BikeChimp
      I'd like to turn my UK 2004 DRZ400S back to stock airbox (snorkel) and jets, needle shim position etc
      When I bought it the PO had fitted a Sigma6 kit and done the 3x3 mod but is doesn't have a tapered needle like the JD and other kits. Took me ages to get it running right, however it still runs rich and I'm fed up of arsing around with it. 
      So I've bought a standard airbox without 3x3 hole, stock exhaust.
      Q1 The Suzuki manual says this Mukuni BSR36 (29FA) carb should have a 142.5 Main Jet but the Clymer manual say its a 135.  In UK everything's from sea level to 1000m. I'm in Sheffield so nothing gets above 500m even in the Peaks (Hills). Any UK owners or anyone else know what the correct jet should be?
      Q2 Says the original needle is a '5DH36-2nd'. The needle has 5 notches on it. Currently set at 2 clip from bottom. The Suzuki reference says needle is 5DH36-2nd, Does the 2nd bit mean 2nd from top or bottom?
      Q3 - Does anyone have a detailed photo of the shim order just in case it was assembled wrong. (mine is attached)
      I know most people on here are going to be horrified I'm taking back to stock but any help on above would be really appreciated.

    • By Bgringo
      I've read a lot of threads about this but still haven't found exactly what I'm looking for.  I'm pulling my 2004 DRZ400S out of storage sometime this week and getting it ready for the season.  I live at 9,000 ft, but my first ride of the year is probably going to be at around 5,000 ft.  I was going to pull the 145 main jet I'm running and put in the 150 adjusting the needle from the 2 clip to the 3rd, then re-jet once I got home.  I already have the extended fuel mixture screw in place so I started thinking that I should just run the 150 jet set up and adjust the fuel screw to compensate for the higher elevation where I'll be doing most of my riding.  I will be going down in elevation for rides until late May or June depending on snowfall, but riding on the street when I'm able.  Are there any disadvantages with this?
      I'm new to posting on this forum, so please forgive me if I didn't get the right search words in and there is already a post about this.
    • By Markl5557
      I am currently running 10w 40 Belray non synthetic and I want to switch to full synthetic amsoil .... is it ok to switch from regular to synthetic? I have read it’s not safe to go from synthetic to regular can someone explain if it’s safe to go from regular to synthetic!? Thanks !
    • By RockyMtnMark
      Good Morning,
        Last night I measured my valve clearances for the very first time (I know...) on my DRZ400S.  It's a 2002 and I've owned is since 2011.  I bought it with t's got about 15,000 miles on it and most of it's miles these days are on dirt.
      Intake specs are 0.10-0.20 mm.  Exhaust specs are 0.20-0.30
      My intake valve clearances are in spec, forgot to write them down.  My exhaust valve clearances are between 0.1778 and 0.2032 which is slightly out of spec.  They are no more than 25 microns out of spec.  My question is, do I really need to shim these?  Will this kind of out-of-spec cause performance, mechanical, or other losses?  As far as I can tell, I'd have to buy a whole shim kit which is like $80.  Thanks!
    • By Zach440
      Selling my 2009 Drz400sm. Been a great bike but it’s time to let go . Not looking for any trades - spring is just around the corner ! Located in northern Virginia . Cash only $4200- willing to negotiate I have some wolfman luggage options available as well. Love to make a package deal for someone 

      -11640 miles . Mild off-road never wrecked.
      -Oil / filter changed every 1500 miles
      -New did chain , brake pads , front sprocket at 10400 miles .
      - valves checked and within spec at 10,000
      - jetted with JD kit and 3x3 mod
      -doubletake mirrors
      -waterproof usb wired and located next to Speedo
      - drc large foot pegs , barkbusters with integrated turn signals . 12oclocklabs tall delete with upgraded circuit board
      -thumpertalk case savers
      -sergeant seat (amazing) and Clarke 3.9 tank (190mile range )
      - fog lights wired in so they shut off with high beams
      -Shorai lithium battery
      -led headlight

      - stock gas tank and seat will be included

      The bike is dirty in photos and I apologize my water is currently disabled outside due to freezing temps . Radiator guards and skid plate NOT included but can be for some extra $$. Rear tire could be replaced but front is fine .