Xr650l cutting out off idle throttle

[Arxr650l]

Here's what I have done ,10.5.1 comp piston stage 1 hot cam ,k&n filter desmogged, Dave's carb mod. After rebuild I rejected carb with a 55 and 160 jets, off idle if I quickly give it gas it will cut out then take off I've tried different settings of the mixture screw with no luck ,any advice would help

[SoCalXR600Rmonkey]

i have a stock motor and had a off idle flat spot like you describe. i ended up with a #60 idle jet and the mixture screw out ~1 turn...  not ness the way it's supposed to be but it's so much better now. i also tweaked the piston lifter arm to remove all the free play so that as i open the throttle the lifter arm moves the piston in synch

[XR650L_Dave]

It cuts out as in misses or stalls, or there's just a momentary pause before the revs go up?

[EarthCruzn]

Sounds like CV delay.................

Most people say they actually did not need much more jetting after the piston and cam.......... 158 main is a Dave's Mod centerline.

With the 55 pilot put the mixture screw to 1/2-3/4 of a turn out...........start the bike and slowly turn out the mixture screw until you get a good smooth idle..........STOP

Did you count? If not ..............count the screw rotations while turning the screw back in.................. now simply set the mixture screw out to that count position

 

If it is more than 3 1/2 turns you are lean on the pilot.................. if its about 2 - 2 5/8 you are in the game.............if its 1/2 - 1 Turn out you are rich on the pilot

With a 55 pilot you should be about 1 1/2 - 2 turns it should start getting smoother.............. little rich BUT still in the game as you have room for adjustment.

 

At 4 turns the mixture screw is just about in full open position .......any more turning out is useless.

If there is dust in your area get rid of the K&N and get a foam / oil type filter............... even on the street you can get dust,,,,,,,,,

Edited August 23, 2019 by EarthCruzn

[EarthCruzn]

The CV (constant velocity) carb requires vacuum "to build" to raise the carbs piston and needle...................... nature of the beast.

 

It is a mechanical delay ......which can be shortened by two mostly commonly used methods:

 1) enlarging the piston vacuum hole(s) as Dave's Mods does 

  2) By replacing the piston slide spring with a weaker / less resistant spring.

[Arxr650l]

Sounds like CV delay.................
Most people say they actually did not need much more jetting after the piston and cam.......... 158 main is a Dave's Mod centerline.
With the 55 pilot put the mixture screw to 1/2-3/4 of a turn out...........start the bike and slowly turn out the mixture screw until you get a good smooth idle..........STOP
Did you count? If not ..............count the screw rotations while turning the screw back in.................. now simply set the mixture screw out to that count position
 
If it is more than 3 1/2 turns you are lean on the pilot.................. if its about 2 - 2 5/8 you are in the game.............if its 1/2 - 1 Turn out you are rich on the pilot
With a 55 pilot you should be about 1 1/2 - 2 turns it should start getting smoother.............. little rich BUT still in the game as you have room for adjustment.
 
At 4 turns the mixture screw is just about in full open position .......any more turning out is useless.
If there is dust in your area get rid of the K&N and get a foam / oil type filter............... even on the street you can get dust,,,,,,,,,

I am getting a different filter this one was one it when I bought it

[Arxr650l]

Just checked plug ,looks to be running lean

[Arxr650l]

Just installed #60 pilot jet still is cutting out off idle

[Arxr650l]

It cuts out as in misses or stalls, or there's just a momentary pause before the revs go up?

It misses

[XR650L_Dave]

60 pilot is probably too rich.

Could cut out from too much fuel too. Did you try tuning with no airbox cover?

[Arxr650l]

60 pilot is probably too rich.
Could cut out from too much fuel too. Did you try tuning with no airbox cover?

Yes I've tried with no air box cover on ,could it be spark plug gap too wide

[Arxr650l]

Or could the after market needle have anything to do with it

[XR650L_Dave]

It's a fussy carb, there's no doubt of that.

It pays to stick to one of the nown good recipes

Plug gap too wide or weak spark yes could do it. Might be worth checking spark plug cap resistor.

[baldy110]

Go with 52 pilot and no more than a 155 main your to rich.  I built up a XRL engine with a custom cam, 102mm 11.5-1 compression piston, ported head, FMF full exhaust, ect..  When I was using the stock carb it ran the best with 52 / 155. Most people think when they modify their engine they have to go richer on the jets.  That's not the case by adding a bigger piston with more compression the engine will need no change to the main jet or at the most one size up.  The bigger bore and higher comp will draw in more fuel which richens the mixture.  I know it sounds counter intuitive and against what most people say but based on my experience of building motorcycle engines it works.  The stock carb on my current XRL performs great starts easy idles good no flat spots unless I twist it really fast then there is a slight hesitation it carberates clean from sea level to over 12,000 feet.  It's a good carb.

Edited August 30, 2019 by baldy110

[XR650L_Dave]

When comparing, tweaks may be necessary to compensate for ethanol content.

I was in CT when they switched from MTBE to ethanol as the oxygenator and I had to go a couiple additional steps on the jetting.

[Arxr650l]

I'm about to order a pumper carb lol,thanks everyone for your help I will keep you updated,also I notice it takes awhile for it to return to idle

[baldy110]

You got a vacuum leak.

[Arxr650l]

Imma try to find it

Is there any common places for them to leak

[EarthCruzn]

On ‎8‎/‎29‎/‎2019 at 1:10 PM, Arxr650l said:

Or could the after market needle have anything to do with it

DynoJet needles............ NEED to run with DynoJet main jets.......... they do not play well with others..............

Mixing of needles and jets by different manufactures will cause strange behavior..........

[Arxr650l]

Checked for vacuum leaks and cant find any