EC300 Idle Revisited.
 

OK guys, I'm ready to throw this POS carb in the trash. I've got the same issue he does: http://www.gasgasrider.org/forum/sho...highlight=idle

There is utterly no way I can get a consistent idle. If you even touch the idle air screw the bike will idle extremely high or almost not at all. This is not a needle, MJ, PJ, air leak or float issue. There is something fundamentally wrong with this carb. Surely somebody has figured out what to modify or what carb from another bike will properly work. The similar carb works perfectly on KTMs, why would it not on this bike? I don't buy for a second it's squish or head design, there is some kind of fueling issue that causing the carb to radically change AF with a very slight adjustment.

Is there a definitive answer for this carb or what's a good replacement? I thought I was very good with carb tuning and I have it working perfectly except for this one issue.

Thanks.

My bikes idle and carburate perfectly I'm guessing you have to rich of a slide. Try a #9 cutaway with a 35 pilot.The smaller cutaways have to much velocity over the pilot circuit.

Mine will idle forever leaning on a tree. However, I have seen a Keihin PWK38 on a KTM 300 with some casting flashing on the nozzle, and that bike was always a bitch to jet. Check that out and clean it up if present.

What else are you going to do for a carb? The Mikuni is a more of a PIA, we swapped it for the Keihin on my brother's Husky last year and never looked back.

If all else fails, call Ron at RBD.

I really hate to mess with the slide. Everything right off idle seems to be perfect.

One of my friends mentioned something about notching the slide. Currently I'm running a #7 but I tried a #8 with no noticeable results. What's driving me crazy is absolutely nothing I've done has had any real effect. Every other 2T I've ever had with this family of carbs has been fine. I swear this thing is almost as bad as the old Bings except it doesn't leak.

You could go to a Mikuni the tunability and tech support is outstanding but they are somewhat more complex as your now adding another system component ,the needle jet. You could prob pick up a vm38 round slide which is kind of old school but works very well for our applications and there a lots of snowmobile tuning manuals available for that carb. I pulled one off of a 92 wr 250, bored it to 39 mm and put it on a 94 cr 500 where it worked flawlessly with a big scary top end gain.

Didn't Yamaha or Kawasaki have a notched #7 on one of their motocrossers?

Might be worth a try.

Thousands of bikes run fine with this carb, its something with your particular specmin. Look for the problem in the carb rather than reinvent the wheel.

The idle circuit is very small, perhaps it is partially blocked by debris or flashing, or perhaps the casting is defective. Can you try ot on another bike?

300s most always prefer the #8 slide over the #7.

I could try it on a KTM 200 if it will fit. The carb is clean and no casting flashing or other obstruction that I can see.

Its what you can't see, inside the casting passages. Do you have access to an ultrasonic cleaner? I recently fixed a CV carb from an old Honda Vtwin street bike. Several hours in a heated ultrasonic bath broke something loose that nothing did before.

I didn't have ultrasonic but I tried some commercial carb cleaner and high pressure air. It seemed they were free.

I'm thinking there's something to Widebear's comment about fuel flow and intake velocity. An extremely slight slide adjustment makes a very large difference. That tells me it's either the design of the PJ circuit or something to do with the shape of the slide or the body. After a search I see some other members have had a virtually identical issue.

I was I could remember what the cutout #7 addressed on the motocrosser. It may have been a similar issue.