mikuni tm 40 awesome...but?


28 replies to this topic
  • supermotodr

Posted 12 April 2008 - 01:59 PM

#1

just fitted the mikuni tm 40 and it is pretty awesome but i have a few small problems with it, hopefully you guys can help me out. i think it is running slightly rich but i dont know much about carbs so any help would be aqreciated.it wont start with the choke even when cold i have to wind the idle up to about 1500 rpm to get it to start but then runs fine also when warm it bogs slightly just off idle but doesnt do this when cold.i have been assured it is jetted correctly for this bike.so i am thinking its either the mixture screw or the ap.what is the routine for setting these two things up.cheers

  • brianwheelies

Posted 12 April 2008 - 03:06 PM

#2

1500 rpm is factory recommended idle for the DR650SE, other models of the DR that have the longer stroke engine, not sure what the idle is for those.

  • mxrob

Posted 12 April 2008 - 05:01 PM

#3

just fitted the mikuni tm 40 and it is pretty awesome but i have a few small problems with it, hopefully you guys can help me out. i think it is running slightly rich but i dont know much about carbs so any help would be aqreciated.it wont start with the choke even when cold i have to wind the idle up to about 1500 rpm to get it to start but then runs fine also when warm it bogs slightly just off idle but doesnt do this when cold.i have been assured it is jetted correctly for this bike.so i am thinking its either the mixture screw or the ap.what is the routine for setting these two things up.cheers


If it doesn't bog when cold but does once it's warmed up you are too rich on your pilot circuit. After completely warming up your engine let it idle and slowly turn the pilot screw inwards until the engine begins to idle erratic or sound like it is changing speed (surging) From this point back the pilot screw out until the engine just smoothes out. From this point I add about 1/8 turn extra out (richer). Check where your pilot screw ends up (how many turns out from lightly seated). If it's less than one turn out you may want to consider going to the next smaller pilot jet. If it's more than 2-1/2 turns out you may want to go to the next richer pilot jet. Hope this helps!

  • supermotodr

Posted 12 April 2008 - 10:49 PM

#4

thanx mx rob,i thought it might be you answering this one.just what i wanted to hear,i will make some adjustments today,didnt want to mess with anything until i knew the correct procedure.Anyone know the procedure for adjusting the ap,unfortunately the hessler carb didnt come with any info regarding this.The bike is a 1990 sp41a,top of airbox cut out,k+n filter,leo vince x3 exhaust(the 96db offroad one) holeshot stainless header.the bike is only used onroad(supermoto conversion).cheers.

  • ProCycle

Posted 13 April 2008 - 08:15 PM

#5

when warm it bogs slightly just off idle but doesnt do this when cold.


Sounds like the AP is starting it's squirt too soon. There should be 2mm-3mm gap between the AP rod and the white plastic arm. There is a screw in the plastic arm to adjust the gap. There is a small long allen set secrew coming down from the top that limits the AP arm travel. You want the screw set so the arm contacts the screw at about 3/4 throttle. Put a drop of silicone or something on that screw so it can't vibrate itself out of adjustment.

Here's a link to the tuning manual Mikuni supplies for this carb:
---> http://www.mikuni.co...hs40_manual.pdf

The Hessler setup is pretty far on the rich side. With those mods I'd expect you would need the needle in the 3rd (or possibly 2nd) position. A 22.5 pilot and 145 or 150 main jet.

  • supermotodr

Posted 14 April 2008 - 08:40 AM

#6

Thanks procycle,i was thinking the same thing,the ap is operating immediately on turning the throttle i will adjust it today.Dont know why hessler didnt supply any set up info just the carb and a few main jets maybe should have got it from yourselves but germany is alot closer.The jets are indeed a 22.5 pilot and 150 main.Apart from these small niggles the carb is awesome,only problem now is no more mods to do,guess i will just have to ride and enjoy.cheers

  • ProCycle

Posted 14 April 2008 - 01:53 PM

#7

Don't forget to check the needle clip position.

  • 396dave

Posted 14 April 2008 - 02:19 PM

#8

procycle is mosy likely right on with his diagnosis you have to have that accelerator pump gap set right or it will do exactly what you are describing if you have it set so it squirts right at the instant of throttle movement it will go momentarily over rich. i believe the squirter nozzle is a little oversized for this application (as they were really designed as a harley davidson replacment carb.) but i don't think smaller ones are available. follow all the other posts instructions and you'll hit the sweet spot. once you get it dialed in you'll really get a feel for just how vast an improvement it is over the bst. the low rpm throttle response and lugability makes it seem like a different motorcycle.

  • ProCycle

Posted 14 April 2008 - 02:41 PM

#9

procycle is mosy likely right on with his diagnosis you have to have that accelerator pump gap set right or it will do exactly what you are describing if you have it set so it squirts right at the instant of throttle movement it will go momentarily over rich. i believe the squirter nozzle is a little oversized for this application (as they were really designed as a harley davidson replacment carb.) but i don't think smaller ones are available. follow all the other posts instructions and you'll hit the sweet spot. once you get it dialed in you'll really get a feel for just how vast an improvement it is over the bst. the low rpm throttle response and lugability makes it seem like a different motorcycle.


The Hessler carb does ship with a smaller nozzle (hard to come by here in the US). If it starts to squirt too early the stream hits the slide which apparently isn't a problem on a Harley but does cause a little bog on the DR.

  • supermotodr

Posted 21 April 2008 - 12:37 PM

#10

Hi everyone sorry it took so long to reply,weather hasnt been playing ball.
Firstly adjusted the ap it now has 2-3mm clearance and cured the off idle bog completely.Cracked the carb open and found it only had a 135 main jet,swapped it out for a 145 the biggest supplied with the carb,I thought it was set up for my bike???should i go bigger again?needle is on the third position.Pilot jet is a 25 with the mixture screw only just over half aturn out,even fully seated i cant get lean condition.Ordered a 22.5 today.Bike runs great apart from difficulty to start,kick start only,its times like this i envy you guys with e start.Takes 5 or more kicks to start and refuses to start at all with the choke,i am hoping this is a symptom of the too large pilot jet in conjunction with the choke is bogging it down with too much fuel,time will tell when the smaller pilot arrives,bike started first or second kick with the bst.Thanks guys for all your help couldnt have done it without you.PS anyone know how to post pics bike is 98%finished so pics coming soon,cheers.

  • Bogieknight

Posted 24 April 2008 - 09:28 AM

#11

Well I've got a TM40 kit on order from Allens Performance in England (sorry ProCycle, I was going to get it from you, but I would've taken a hit on the package at customs which would've made it expensive).

Once I've got it on the bike, I'll let you know how I'm getting on with it. I'll be fitting it to the stock exhaust until I can sort out a Gixxer pipe.

It should arrive tomorrow. Can't wait:thumbsup:

  • supermotodr

Posted 25 April 2008 - 05:24 AM

#12

Well I've got a TM40 kit on order from Allens Performance in England (sorry ProCycle, I was going to get it from you, but I would've taken a hit on the package at customs which would've made it expensive).

Once I've got it on the bike, I'll let you know how I'm getting on with it. I'll be fitting it to the stock exhaust until I can sort out a Gixxer pipe.

It should arrive tomorrow. Can't wait:thumbsup:


you will love it, ive had mine a week and still grinning .Allens are pretty good too ,ordered some jets from them,very helpfull and they arrived the next day.Check the jetting is correct before you fit it although it is easy to work on,just slacken both boots and twist the carb until you can reach the screws on the float bowl.enjoy.

  • Bogieknight

Posted 25 April 2008 - 06:49 AM

#13

Cheers SuperM,

I wondered if you could tell me which pipes fit where? What jets and settings are you running with your carb? At the moment I'm running a stock exhaust but I will have the airbox mod done when I install the carb.

  • supermotodr

Posted 26 April 2008 - 07:44 PM

#14

Hi mine is a 1990 model so is probably slightly different to yours.the small diameter hoses are just breathers and are run behind the engine and beside the swing arm where the breather from the original carb ran.the only other hose i have is the fuel line it runs to the swivel type fitting on the body of the carb.your bike might also have a vaccum hose on the fuel tank this would connect to the only other connector on the carb just above the bore,mine is capped off with a rubber plug as i dont need it i have a ktm tank on mine it only has one line no vaccum .as for jetting i am running a 20 pilot and a 145 main.yours should run straight from the box just adjust the idle to get her running and go from there you will only dial it in correctly through trial and error and if you dont have the tuning manual there is a link to it in one of the posts on this thread it is invaluable and explains how everything works,.hope this helps.

  • Bogieknight

Posted 27 April 2008 - 04:51 AM

#15

Thanks for that. I've got the TM40 fitted now. Wasn't too bad actually. I just looked like a bit of jumble as it was sat in the box. The only problem I had was fitting the intake boot from the airbox to the carb. It was a v. tight fit. I heated it up and applied a dab of silicone grease and just persevered.

I took it for a quick blast to see what it like, and wow:eek: it's like a different bike. I've got to do some tweaking now. I've modded the airbox, and once my new armature comes for my Dremel, I'll grind the downpipe joint. I'm using the stock exhaust at the moment. The carb has a 140 main jet, 25 pilot jet and the needle clip is on the third clip (middle posn).

Have the forum sages :thumbsup: got any advice on what should be in it, I wonder?

Any help would be much appreciated.

  • ProCycle

Posted 27 April 2008 - 06:24 AM

#16

Stock exhaust, modded airbox, uni filter:

135 main, 22.5 pilot, needle clip 2nd position.

  • Bogieknight

Posted 27 April 2008 - 06:45 AM

#17

Stock exhaust, modded airbox, uni filter:

135 main, 22.5 pilot, needle clip 2nd position.


Thanks ProCycle, much appreciated. I figured the 25 pilot was a little too big, as I'm struggling to set up the idle. With it wound in all but .25 turns it doesn't slow/become irregular.

I'll get some more jets this week.

  • Bogieknight

Posted 27 April 2008 - 06:46 AM

#18

Stock exhaust, modded airbox, uni filter:

135 main, 22.5 pilot, needle clip 2nd position.


Thanks ProCycle, much appreciated:worthy: :thumbsup: . I figured the 25 pilot was a little too big, as I'm struggling to set up the idle. With it wound in all but .25 turns it doesn't slow/become irregular.

I'll get some more jets this week.

  • supermotodr

Posted 27 April 2008 - 11:37 AM

#19

had the same problem with a 25 pilot even with the mixture screw fully seated no lean condition.allens only do the pilots in increments of 5 eg 20 25 etc no 22.5 so i went with the 20.much better, mixture screw 1and 3quarters out,really is like a different bike,and you still have the exhaust to go yet that will improve things further.

  • Bogieknight

Posted 27 April 2008 - 01:26 PM

#20

I adjusted the AP lever gap as mine was bogging down a little on accel from throttle closed. That's now sorted.

So I'll get the jets this week. How much did Allen's charge you for the jets?

It's running fine at the moment with the 140 in, but I'll do as ProCycle suggests and hopefully get it running even better.

It's impossible to appreciate how much difference the carb change makes by just reading about it from these threads. It really is a huge improvement. The bike really flies now :ride:

And hopefully I may be able to squeeze a bit more out of it with the header grind and an exhaust change. My Blackbird hasn't been out of the garage for 3 weeks; I'm having too much fun with the DR!:thumbsup:




 
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