Since 351 install, if idle speed is below 1500, and I crack the throttle quick, engine stalls..
Im running:
twin air filter, kdx snorkle
megabomb header
main jet 135
pilot jet 40
dynojet needle 3 notches
air fuel mix screw out 3 turns
(ive tried 2.5 turns, 3.5 turns, 4 notches from the top) all the same result.. had dam carb out and in 8 times!

ive tried 128, 132, 135, 138 main jet
why is this happening?

 

How's it run otherwise? Does it have a hard time clearing it's throat at low rpms? If it stalls but doesn't die does run cleanly once it catches? Does it do this consistently? Did you adjust your idle too?

Maybe lower your needle. I had a problem where my bike (still a 250) ran like crap, would run rich and load up at low speeds, but run great at wot. Turns out my main needle was too short. I'd ordered a NITC needle for a KLX300 and the durned thing was 5 mm or so shorter than the stock needle. I kept fiddling with the jets - nothing. Swapped the original needle back in, with one washer for a little lift, and problem gone. So if what I described is what you're experiencing try messing with the needle height. And then there float bowl level adjustments. I don't have much of a clue how those work.

Taking the carb out of the KLX reminds me of heart surgery. Not that I've ever done that, but I've had the carb out a number of times.

 

ha ha Heart Surgery .. !

It runs like a bear otherwise.. if I open the throttle slowly with say.. 1200 to 1400 rpm idle.. no prob.. but if I crack it open fast... dies.. every time..

If I run the idle 1500 and above, no problem.. I just want to idle like it was stock.. I like it LOW like 1200 rpm

 

Main 135, Pilot 40 should be correct. I'd drop the needle down at least one washer. Also might tighten the air-fuel screw in a bit. I'm guessing you're too rich.

 

I'm using a 132, 40, and clip on 4th spot down I believe. Then the air screw adjusted to run smooth.

Runs like a bear. Well at least it did. haha

 

I was running a 132 main, stock pilot at 2.5 turns, dynojet needle some where in the middle.

Your problem is not a big enough flywheel. Turn the idle up to 1500 and smile. I like is slow too, but the higher (12.5:1) compression, bigger cylinder and more air flow make the 351 need a faster Idle.

At least that was my conclusion.

Are your valves within spec? Spark plug gap correct? It does NOT HAVE TO BE JETTING causing your problem.

There is always the pumper carb.... It gives it a KICK in the *** when you crank the throttle.

David

 

Could a small vacuum leak, or even pinhole in the diaphragm act like this? Usually, these make it too lean, but, big main, decent sized pilot, and three turns out on the air/fuel screw maybe can make up for most of the near-idle lean condition, and therefore have this flat spot?

 

Have you "drilled the slide"?

CV should not care how fast you the whack the throttle open, slide goes up only as the vacuum builds up -> mixture doesn't drop lean.
But if the slide slams open (like in a direct lift carb) then the mixture can momentarily drop really lean when the vacuum drops.
That's why 4-stroke direct lift carbs better have the accelerator pump.

Do you have an un-drilled slide to try?

--
Mikko

 

Its undrilled slide..

Did I mention that I still have all the emissions hosing hooked up still?

 

Emission hoses have nothing to do with it.

I did get to go 1/2 turn leaner on the pilot when I put a plug on the vacuum port.

I think its telling you to let it run @ 1500 RPM. Perhaps you should listen to it.

David