86 250r jetting fmf silencer and pipe

[stevo936]

Looking for some advice on my jetting.  I pulled the carb and checked jets.  I have a 150 main and 50 pilot jet.  

The issue I'm having is it seems like off low end 1/4 to half throttle i have a little stumble and then it takes off.  I kno this is two-stroke but it seems like it should be smoother.  

The bike starts great when cold first kick with the choke on and no throttle, and idles well.

I did notice i have a little leak on the front two piece exhaust and need to seal that, also when i ride for a few minutes and shut if off gas sometimes comes out of the drain on the bowl.  What could this mean?

The bike is 1988 with 86 motor.  Stock motor FMF pipe and silencer, stock filter with one inch hole drilled, running 40:1 klotz oil.  150 main and 50 pilot

Thanks

[StrokedAZ]

Is it the stock carb?  If so the pilot seems a little big, stock is 48. What elevation are you?  I run a 45 main when I go up in elevation.  I would take it apart and clean it real good and make sure it has the correct needle in it first.  Any exhaust issues will make the situation worse, that needs to addressed as well. A little RTV sealant stuff goes a long way.  Just my 2 cents

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[stevo936]

Yea it is the stock carb I'm around 2000 above

[StrokedAZ]

Same as me. Switch to a 48 pilot with 1 and a half to 2 turns out on your air screw What is wrong with the pipe?  Is it leaking at the junctions or is the pipe damaged?  If it is just spooging at the junctions I would put a thick bead of high temp rtv at both the junctions when u install the pipe.  I did it and it sealed mine up pretty good, the springs by themselves wouldn't cut it on mine.  You could also check the packing.  If the packing in the silencer gets saturated it can affect your jetting and cause it to run rich.

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[team palmer 34]

i'm running a 162main 50 pilot i got stock carb fmf sst and power core 2 silencer ans v force 3 reeds and 1 1/2 turns on air screw runs great

[fearlessfred]

Use the air screw to determine what pilot you need by raising idle and turning airscew all the way in and opening slowly(allowing motor to catch up to changes) until you find the point that it idles highest return back to the point were you got highest idle .If you have to go very much past two turns with screw to find highest idle you will need a smaller pilot .air and fuel are mixed in the slow circuit and your looking for the correct ratio and trying not to open screw so far that spring does not hold it secure or on the oppsite end damage seat .There is no one setting for all bikes

[Jerry Hall]

Do you know if the stumble is caused by a rich or lean condition?  

If it is a lean condition, the engine will hesitate without any power strokes occurring.  Listen to the noise coming from the muffler

If it is a rich condition, the engine will hesitate with the engine initially having intermittent firing cycles and making a transition to firing cycles occurring every engine revolution.  This condition can also be heard by listening to the exhaust note coming from the muffler.


A rich condition is the most common cause  of a stumble at 1/4 throttle as the needle jet and needle ware.  A lean hesitation is very common on the Keihin carbs when the throttle is suddenly opened from an idle, if the air screw setting an or pilot jet is too lean.

Turning the air screw in causes more suction to be placed on the pilot jet making the pilot jet flow more fuel.  Turning the air screw out makes the pilot jet circuit leaner.

If the needle jet is worn, you will need to replace the needle with a needle that has a larger initial diameter or replace the carburetor.  Not being able to replace the needle jet is one of the disadvantages of owning a Keihin carburetor.

[team palmer 34]

when i rebuilt my carb and its a kelihin pj i replaced my needle with a dgh needle works great and running a 162 main with 50 pilot and 1 1/2 turns out on air screw