EC300 Idle Revisited.

Ud_luz

Ud_luz

New member
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/showthread.php?t=3183&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.
 
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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.
 
Yes the Kawasaki MX bikes have the notch in the slides. You can get them for about $55 online in a 7 or 8 size but I dont think that's the issue really. I do want one of those notched slides to do some comparison tuning.

You could have an air leak in the throtte body where the needle jet and idle circuit assy attaches with those tamper proof torx screws. The choke plunger could be leaking air. A guy on KTM Talk went so far as to completely block the choke hole in the bell housing and found the carb worked better but would still start.

I say you need to get someone elses 38mm carb and swap it into your bike with your jets and see what happens. This will quickly determine if the carb has a problem.
 
I talked to Ron at RB. He said that it's unlikely it's the carb after I told him what all I have done. In his opinion it's a classic case of a squish issue. I told him I'd send him the head and the carb but he told me to save my money and do the head. If that didn't clear the issue up, and he was pretty certain it would, then send the carb in. He told me this carb is more sensitive than what I'm used to with the KTM version but from my description this is head related.


I'm off to take the head off and send it in. I will follow up with a report.
 
oldgoat said:
Well ???. Did the head mod fix it ???
Click to expand...
Well, me being the "I'll get around to it" and having a garage full of other dirtbikes to ride, I haven't sent it in. Actually I'm dealing with a kind of weird low compression issue before I send the head in.
 
thats the problem with having more than one bike .. if one breaks you just go ride a different one .... eventually you end up with four or five broken or ill running machines!!
 
An update. An o-ring was missing in the jet block. I replaced the carb with a new JD AS but couldn't stand not knowing what was wrong with the old one. I replaced the o-ring and made a new gasket, reinstalled the carb and the bike ran perfectly.

Who would have thought?
 
Ud_luz said:
An update. An o-ring was missing in the jet block. I replaced the carb with a new JD AS but couldn't stand not knowing what was wrong with the old one. I replaced the o-ring and made a new gasket, reinstalled the carb and the bike ran perfectly.

Who would have thought?
Click to expand...

Hey,
Can you be more descriptive with the adverse symptoms and exactly what,where parts were missing.
The only reason I ask is a guy I ride with is have similar jetting issues with his 09 ec 300.

It has a hanging idle that gets worse as the bike heats up...wack the throttle a few times and it will drop.
It's jetted with a 45PJ 180MJ and a cck needle...my 08 is jetted pretty close to that and it runs great.

So, we threw in a 48PJ and it still has the hanging idle, I played with the air screw and I can get it to idle down but then it almost dies and stalls a lot....with a 48PJ it should be way on the rich side.
My first thought was some sort of air leak....I wonder if his carb as the same missing part(s)
I tried to find the jet block o ring in a exploded view of the carb, but it's not shown ???
Let me know
Thanks !!!
 
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I assume you have to remove the security screw (Torx?) and remove the nozzle assy.
 
moto9 said:
I tried to find the jet block o ring in a exploded view of the carb, but it's not shown ???
Let me know
Thanks !!!
Click to expand...

mikesxs.com lists a pwk jet block gasket and o-ring. i also ordered a float needle from them. the float needle was the wrong one. i have not opened the jet block up to see if the gaskets they sent me are correct...

you do need to remove the security torx - the last jet block i opened up was on a mikuni tmx, and it was trashed in there. after that i found out you cannot order a jet block gasket for a tmx. urrghh..
 
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