XR650R carb mods: posted here.XR650R Carburetor Fix' Go

From borynack.com/XR650R/xr650r_caruretor.htm


XR650R Carburetor Fix' Go Back To XR650R Page


Remove the Choke flap with the spring off the choke plate!

Loosen both screws, then remove one. They have crimps on the end of them to make sure they never fall out so, they are a little hard to turn at the end. Push the flap down out of the way and put the screw you just took out back in with locktite on it to make sure it never comes loose again. Now take the other screw out and remove the flap. Put that screw with locktite back in and you are done. The reason for this that some have had this flap plate break apart and the small pieces go into the engine making a mess. With the carb jetted with a 68s or better yet a 70s the bike starts better for most and the choke still works great (maybe better) full on.


Rubber Plug (magnified)

Knowing what the AJCV (Air Jet Cut Off Valve) does might help in knowing what will happen when you disable it. The pilot and needle jets have small holes (emulsion holes) in them that adds air to the fuel that is drawn through them. This atomizes the fuel. Makes the mixer right is a nice way of saying it. This air comes through the air jet....at about 19~20psi of vacuum the diaphragm is pulled back (vacuum comes through that small hole that we are plugging) against the 18+pound spring, in the AJCV and the little plastic door that the diaphragm held open; closes cutting off the needed air. This is designed to soften deceleration...The AJCV makes the idle on deceleration richer, except that there is no extra fuel added, the AJCV does nothing more then turn off the air NEEDED, to make the pilot jet mixture atomized right. There might be more fuel pulled through the pilot, do to the loss of air but, I don't know how much that would be. The un-burnt fuel will pop as it hits hot fuel still burning in the exhaust. When this happens, the rich mixture makes a dead cylinder, less vacuum on the intake stroke and still burning on the compression stroke. Somehow this makes less engine braking compression. . Why you would want to soften the engine braking on a race bike is beyond me. Mikuni, Edelbrock, and the FCR carburetors do not have this...maybe because they were made for race bikes. If you are going to ride the street then this would be good but, you might have gotten a XR650L. As in what you use to plug the hole is up to you RTV works ....I got lucky and found these real small rubber plugs that were to be used for one of my kids toys.....he lost them...they look like little top hats and fit perfect in the hole.......hole plugged no vacuum diaphragm doesn't move bam disabled. Leave the spring in or this won't work. There is fuel that leaks into this small vacuum hole when the bike is laid over (crash/bike falls over) so, whatever you use has to be fuel proof. You should readjust the idle mixture screw once you do this modification.
There are a lot of carb's that have the mixture screw being an air screw but, this is mostly on the small 4 strokes and two strokes. If the idle screw is in the front it's a fuel mixture screw like the XR650R is as you know, an Idle fuel mixture screw. If it is in the back it's an air mixture screw. The big thing that is needed to make the AJCV disable trick work is to jet richer pilot (because you can) and adjust the idle mixture screw to work right. Turns out from full in....
2~2.5 for the 68s, 1~1.5 for the 70 and .5 to almost 1 turn for the 70s. depending on the bike.The other reason is to load the carburetor up for smoother idle while coming to a sudden stop and still being able to run the bike lean to pass AQME standards (smog). The bike does not pass smog if you run it rich enough to run right. Having this AJCV lets Honda run the pilot lean but, not have the bike stall coming to a stop as often.
The big confusion comes from some of the first guys on some groups, getting my modification backwards and cutting off the tit to the diaphragm, cutting the air from the air jet off all the time making the bike run bad. There would be no air going to the pilot emulsion holes at anytime. Some did this and had to buy new diaphragms to fix it and are sour on any talk about the AJCV. Make sure it will resist fuel, fuel will get in that hole if the bike is stalled and on it's side. The diaphragm when pulled out by the vacuum, closes a plastic block cutting off the air from the air jet. AJCV is not needed or wanted for most racing. Having the air to fuel mixture right at all times is the goal for most.
http://www.cyclewareables.com/pages/air_cutoffValve_replacements/aircutoff.htm
http://www.cbxman.com/detail.aspx?ID=598
http://www.hawkworks.net/manual/4.html


Setting the Float on the stock Carburetor:
Float level should be 16mm from gasket flange to bottom of float
with carb inverted. I ran mine almost 17mm to help it stop peeing on it's kick stand on a hill.
Jetting
The difference between pilot jet with and without the "S" after the number

Starting a flooded bike.

There are two drills to starting a downed pig But, First if you crash...lay it down, fall over (that last one is all the time for me). Make sure you don't have GAS coming out of the air box. This is where most of the argument will come form.

Most will tell you to hold the decompression lever in, while holding the kill button and kicking the bike through 3~5 times, up to ten times to clear out the fuel. Then at times if it was a real good spill there is so much fuel in the cylinder this can still not work and you start all over again.

The Race way:

You pick yourself up off the ground in a daze wondering where the bike is. Find the bike and pick it up. Fight the pain and hope you are pointing the right way. You pull the throttle wide open and grab the front brake! This is important....it stops the throttle from moving while you kick the bike over. Find TDC and kick as hard as you can and go! I have had a few argue with this but, once it is done without the throttle moving it works!

The main thing to know is the bike has way to much fuel in the cylinder to start so, you need to add lot's of air to get the fuel to fire. If you kick the bike over slowly to clear the engine and the spark lights the fuel the bike is on fire! Starting the bike the Race way pulls everything into the cylinder not back firing into the air box.

Some of my good friends that I ride with didn't believe it and it did not work for them. But, once they got the front brake thing down it was almost every time one kick...two at the most....

Hold the throttle wide open, holding the front break.....find Top Dead Center and kick!





Once you use a pumper the stock carburetor just isn't any fun! If you don't mind the trouble of the initial setup (lot's of jets) the Mikuni was two years trouble free for me and it's a better (smoother) carburetor. I have owned and ran all three. I made the stock carburetor work....it can work but, it is nothing like a pumper...If you haven't ridden a BRP balls to the wall, drop offs, popping up and over walls, just looking for the edge, then you might never know the difference. The Edelbrocks biggest fame is how easy it is to tune and its ability to get the Oinker started and keep it running, no matter what! I have my Edelbrock pored out to be a 40mm X 42mm and it rips on my bike. The Mikuni TM40 can be tuned to perfection but, that takes major time and effort but, it is worth it! It is power on everywhere all the time, never lagging always spot on through out the throttle movement. But, a pumper is not needed for the casual weekend warrior or fire road rider but, it still is nice even there!

Out of curiousity, has anyone plugged the hole on the air jet cut off valve cover? Wonder how your carb has worked since?

Ogilvie told a guy in Ty Davis shop there was a longer emulsion tube for the really rough sections of a race course. I think it was back when the A team and B teams were contractually prevented from talking to each other and ran somewhat different setups. I've tried long and hard to run down the emulsion tube but never found anyone else who'd heard of it. Perhaps it was an A team only mod because PC managed only the B team bike in the beginning. And I know the B team ran some mods that the A team wasn't aware of. Perhaps one could be made or sourced off another carb?

I have problems with Mikuni TM40-6. I have bought new the complete set modernised for XR650R. I have established the carburettor on XR650R 2006 with standard an exhaust and the standard air filter. I cannot will get rid of shots in the muffler at return throttle even when the motorcycle does not move. I do not understand, why frequency of turns of the engine strongly depends on motorcycle position? If vertically turns 1200, in inclined position (on side stand) - 1600. Somebody can had experience on adjustment of this carburettor? Specify please the size Pilot Jet, Pilot Air Jet, Main Jet and position Jet Needle for the best work of the carburettor. Specify how much early it should switch on and off pump (position of screws of regulation). Define, this carburettor how much smoothly worked. Thankful in advance for the help.

Michelangelo wrote:Out of curiousity, has anyone plugged the hole on the air jet cut off valve cover? Wonder how your carb has worked since?

Yea - used some RTV in the hole - The hole is really small - It would be pretty hard to find a plug to fit - I think using RTV is better anyway.

Carb works fine after the mod - Definitely like how the bike decels when comming off the throttle/down shifting vs before - Alot more compression braking

AJCV
I have a hanging Idle that I believe is related to the AJCV
Witch hole do you plug? The one under the diaphram, or the one that comes off of the carb body and passes through the cover?

2000 xr650r
uncorked
elevation 500'
68s
172
2nd clip

Antcap,

I just checked, Moscow's altitude is around 200m HASL, so that is 'sea-level'.
On the net you will find quite a bit of jetting-info for the TM40 mated to a Pig, and I'll give you mine (below).
However, NO carburettor will have zero backfiring on a big thumper like the Pig, even if the exhaust is a full 100% sealed.... and this is probably one of your problems, air leaks somewhere into it causing some rumbling or backfiring - which as said is 'normal' up to a certain extent. Often the slipjoint between header & muffler leaks a bit, and a little sillicon may help here, but also, if you mounted a different exhaust/header then be sure to use NEW gaskets.
The idling-change when leant over is not normal, and I suspect your float-level is set wrong or out a bit. But also, make dam sure you've mounted the carb 'vertical' when the bike is, as it's easy to set this out a bit.
The TM40 is a good upgrade over the stock carb, and the pumper helps it to respond 'crisper', the front wheel lifts on command.

Mine's jetted (at 1400m HASL, some 25deg Celsius):
Pilot 25, Airjet 1.1, Screw ~2.4 turns.
Y2 Needle-jet with Jet-needle Y01, Main jet 145.
I have a modified side-cover and run a UNI or TwinAir filter, with XRsOnly headers with a T4 ProCircuit silencer.

You may also want to try a 27.5 pilot coupled with a 1.2 airjet, and others often mention they prefer the Y4 Needle jet. And, at your altitude you must try a slightly bigger main if your bike is similar to mine, but best would be to find a dyno for this.
Hope this helps!

Hi guys
I have a problem with my bike.When I want to start it and I turn the choke on the engine does not rev itself at all therefore sometimes hard to start it.After a little ride when the bike reached the operating temperature it's not problem.If somebody knows the answer please let me know.
Thousand thanks.

Standard carb?
And if so, it still has the springloaded small flap in the choke?
If yes then remove this thing, just take it out - or, replace by a small plate with a hole in like XRsOnly sells.
My hunch is that this will solve your prob.

Hi
Thanks for your response.Yes it is a stock carb but why sould be removed that flap? Do you think its went wrong?
or is it normal that the idle is low when the choke on?Thanks

You need to read-up a LOT on your bike still I conclude: Yes, that flap MUST come out, your engine will eat it in the future otherwise, and that will cost you plenty of money.
Also it sounds like your bike runs too rich when starting, and this may help in solving this.

What yearmodel bike you got? 2002 or earlier? Then open it up and make sure you have the improved clutch-bushing, this will seize otherwise.... with again a nice bill to settle.
Read up my man, there is plenty of info on the net on this bike, it will make you and your bike better.

My bike was made in 2004. Honestly I don t realy know which flap you mean maybe the flat piece of metal ( we say "butterfly valve" ) which blocking the air passage? I have downloaded the service manual before just you know it doesn't contain the real issues. I think i am gonna save up for a new carb. ( mikuni tm 40 or Keihin fcr )

Yes, the choke-butterfly valve has a small springloaded valve in it - and this thing must come out. It wears and will come loose, and backfiring will ruin it.... and then your engine eats it.
XRsOnly offer a fixed replacement plate (which will NOT hinge/move at all) with a/some hole(s) in, however you won't really need this. The simple fact that they actually offer this thing should make you think I think...

There's nothing wrong with the std carb, however it isn't a pumper (acceleration jet mechanism). The TM40 is way easier to jet than the FCR, and also there's loads more info on the net for this carb.
Add that's it readily available, cheaper too..... so am not surprised to hear I've got one too. More instantaneous reaction, easier wheel lift over ruts etc, I'm glad I replaced the std carb - but the gains are not absolute, as said the std carb does things quite well.
Your choice of course, depends on what you need or want.

Ok I get it now, but one more question if you don't mind.What if I remove the butterfly valve flap and later I will need this staff at cold start?

You won't need it, that's the whole point. But if you think you will buy the small alternative from XRsOnly (small plate with a hole or 2 holes, can't remember) and it will 'choke' better with fully closed choke.
However, a real fully closed choke one never uses, the risk of drowning the engine is too big. That's why I suggest to put the choke on first click only, with a properly jetted carb you won't need more.
If your livingroom is in arctic circles then you might want to kick it once or twice with fully closed choke, then 'up' it a bit, then whack it into life.

Ok thank you very much your help.

Hi
I need your help again.I disassembled the carb because my bike has stoped during riding and I'm pretty sure due to the improper settings. ( idle improper, the exhaust spits )
What do you think should I change the jets also or leave them? Currently I've got:

Main jet : 175
slow jet : 65s

Cheers

Idle jet should be a 68s, unless you're miles in the air altitude-wise.

But before you change it check following, the connection of carb into the rubber inlet manifold.
Idle the bike, take a gas burner, and wave the opened gasflow on & around this part - no flame eh, just the gas.
If the idle goes up you have found a leaking rubber boot, which you need to replace of course - by the "open" type (big round hole), not the restricted one (just a slotted opening).

Ok Hi !
My bike is european version so its opened, I'm using the HRC muffler the O type carb insulator. I asked a quotation from my dealer but I am litttle bit stranded now because I cannot decide which part this item: B53E .I hope you can approve it.
The needle which is in the top side of the carb or it is the needle seat which holds the main jet? If it's the last one I think I 've got this one so I only need the 68s solw jet. and I would like to thank you for your help I really appreciate it.

Tom,

bear with me: a jet-needle always works with a needle-jet - confused|? You darn well should be, and by the sounds of it are.
However, the jet needle is a tapered needle which sits in the slide of a carb, and it slides in an opening.... which is the needle-jet, jet for short: a bushing with a hole in it in which the needle slides.
You onlyneed to replace the (jet-)needle, and this is that 53-something part yes.

Have a look at this thread http://www.xr650rforum.com/t1402-uncorking-my-brp-today-march-18-2012 as it lists all the parts youneed for uncorking & carb. Decide which you need and take it from there?

Mind though...... do that check with the gas on your bike!!!!!!!!
I hunch your bike sucks "false air", which basically means your carb-boot leaks.
That gas-trick will tell you immediately, so take that as a beginning >> do this first!

Hi
Yesterday I got the new part ( 68 slow jet ) put it in the carb set the pilotscrew as well ( maybe ) and than I could start it up .Took it for a short ride, it seems everything all right. Although at cold start the idle is stil low but I start to think its quite normal.Anyway thanks your help and enjoy your ride.

Yes, they idle cold a bit lowish, just adjust the screw temporarily.
Have fun riding it!