300 won't idle. Please help!!

[stemplin]

I have an 08 300 that won't idle and I'm about to pull my hair out.

I have searched and read through pages and pages of posts but still no solution.

I ride at 0-500 ft elevation with 70-100 degree temps most of the year.

My bike has the RB head and carb mods, Gnarly pipe, and Q stealth silencer. When I got the carb back from Ron, it was jetted pretty much dead on (178 main, 42 pilot) and ran like a top.

Over time it has gotten worse and will hardly idle now. Idle screw is completely bottomed against the spring to get any kind of idle. The choke, idle screw, and air screw seem to have very little effect at all. There is a bad flat spot at around 1/4 to 1/2 throttle. I have to really push through the flat spot to get it on the pipe and gas mileage has gone to crap. 20-25 miles and I'm switching to reserve. The bike spooges like crazy.

I've tried pretty much everything I've read in the posts that I've searched and nothing seems to have helped so far.

I raised the needle clip a notch with little effect.
Brand new NGK BR8EG plug
Clean air filter
disassembled and cleaned Powervalve assembly
Carb is spotless, cleaned multiple times
Float height seems ok as I can lean bike either side with no fuel overflow
Re routed horizontal carb vents up and into the airbox
Brand new reed valves
brand new rubber boot between reeds and carb.

I don't suspect an air leak as the idle never races or anything.

If anyone has had these problems or knows anything else I can try, I'm all ears.

Thanks everyone.

 

[noobi]

Loose/dirty electrical connections can cause symptoms similar to what you describe, particularly the big flat spot. I had this happen and the bike would start and idle, and run wot but nothing else, ended up being a loose spade connector on the coil.

 

[Jakobi]

Reading the title I was getting ready for the ol use the search engine answer. While reading I then thought Reeds for sure, but after reading your extensive list of things you've done to try and resolve this issue one thing stands out.

PISTON + RINGS!!

How many hours have you got on the top end? How'd the piston look through the exhaust port when you serviced the powervalve? Any blow by past the rings? Don't under estimate the effect that a worn piston can have on jetting and power. Paaaaarticularly off the bottom end!

 

[stemplin]

Noobi,

I havent thought of electrical yet, I'll go through all my connections and see what i can find. Thanks

Jakobi,

I have questioned the piston/rings but I've had the cylinder head off and jug looks great. Looking through exhaust outlet doesnt show any blow by. I creeping towards time for a top end but by no means overdue for one. Would the bike still run strong up top if it needed piston and rings?

 

[Jakobi]

Thinking about spooge here. Has it been burning trans oil? Any chance of a blown seal?

Did you measure you ring end gap when you had the jug off?

From my experiences worn top ends usually result in the bike losing its snap in the lower throttle openings. Once you rev the tits out of them they still run alright. In a 4T easily diagnosed because you'll be burning oil. Can't really use this to check on a 2T

 

[stemplin]

I don't believe it's burning trans oil. I was thinking spooge was unburnt fuel from what seems to be really rich condition.

I didn't have jug off, just the cap so no I didn't measure ring end gap. If I do pull the jug, do you know what ring end gap should be?

 

[stainlesscycle]

spooge is generally really rich which is probably why it won't idle. i would check piston and rings - you said no blowby though. bike will still run great up top with bad rings, it will rev out fine, just have less power. the bottom end will suck with bad rings.

the silencer also could need a repack.

are you fouling plugs or hard to start (cold or hot)?

if all this doesn't help, and you have good rings/piston, silencer, reeds, fresh fuel and plug. you gotta start at the beginning. the air screw will have no effect if the idle screw is all the way in. set air screw at 1.5. make sure there is slack in the throttle cable, so the slide goes all the way down and you can feel it hit the idle screw. back out idle screw till the slide no longer hits it. then turn the idle screw in about 1.5 turns. this is about where it should idle.

the flat spot should go away, but it probably won't idle.

i would think deal with the flat spot first, then get it to idle. try moving the needle 1 clip in each direction and see if that fixes flat spot.

turn idle screw in another .5 turns. turn air screw out 1/4 turn at a time, pausing 5 - 10 seconds until it races. stop. don't go out more than 3 turns.

if the air screw has an effect, then you just need to reset your idle. then you can tweak throttle response...

 

[stainlesscycle]

whoa - just noticed this one. the choke has no effect? is the rubber bumper on the bottom of the choke assembly ok?

 

[Jakobi]

whoa - just noticed this one. the choke has no effect? is the rubber bumper on the bottom of the choke assembly ok?

Bow chicka bow wow!! This would definately result in a super rich condition across the board. By bike does't even like to rev well under choke though. I'd definately check this. $13 part and easy as pie to pull out. If its questionable you could run some grease around the seal and see if it runs better breifly.

I doubt that the rings would be shagged.. I think 0.8mm is out of spec for a 300. 0.4mm is ideal. You would expect to see some blow by as well. The main reason that I thought along these lines is that you said its progressively been getting worse. Usually a good sign of a part wearing as opposed to something broken.

 

[stemplin]

What exactly am I checking for on the rubber bumper at bottom of choke?

 

[gasser]

My son's bike has much the same problems you describe - smokes badly, loads up on the bottom, and has to get on the pipe to keep running. His bike is pulling trans oil into the engine somehow. I suppose it's a bad crankcase seal on the right side or perhaps a bad case gasket (is that possible)? Anyway it is definitely pulling oil out and burning it. A 2-3 hour ride burns about half of the tranny oil.

 

[Jakobi]

Use a 14mm open ender and unscrew the whole choke plunger. You'll see how it works. Basically just a shaft with a plunger on the bottom. The plunger is a rubber seal that closes the choke circuit. As you pull the choke up the circuit opens. If the rubber is perished, chipped, cracked or warped out of shape it will won't work as it should. If its completely damaged it will be like always having the choke on, pulling the choke on will have little to no effect, the bike will run really rich and fuel econonomy will suffer.

 

[hannesd]

i personally,wouldn't touch jetting if your idle progressively got worse.
if the conditions are still the same, id look for wear on something like indeed choke rubber or maybe crank seals or even reeds...
alltough with broken reeds i didn't really have a flat spot in my case,only no idle.

hannes.

 

[hannesd]

FYI : i've had a mopet once that had the rings broken in 4 pieces (both) and it still ran, alltough i had to rev it to the moon
that's how good a 2 smoker is

 

[stemplin]

I went ahead and pulled my jug and there was some blow by that couldn't be seen from the exhaust outlet. Cylinder still looks good with visible cross hatch marks but ring end gap measured 0.95 mm so I guess it's time for a top end.

The piston that was in there is marked "D 71.97" and the back of the jug is stamped "B". Any suggestions on a place to source a good top end kit? I've found a complete Wossner "C" kit with gaskets and everything for $239.00 on Ebay.

Any thoughts on the D piston would be greatly appreciated.

 

[Jakobi]

I went ahead and pulled my jug and there was some blow by that couldn't be seen from the exhaust outlet. Cylinder still looks good with visible cross hatch marks but ring end gap measured 0.95 mm so I guess it's time for a top end.

The piston that was in there is marked "D 71.97" and the back of the jug is stamped "B". Any suggestions on a place to source a good top end kit? I've found a complete Wossner "C" kit with gaskets and everything for $239.00 on Ebay.

Any thoughts on the D piston would be greatly appreciated.

Nice find. How'd the D piston looking? Does it show much wear around the skirts? Not sure where you'd get a replacement D from. Maybe ask around some of the places selling the kits and see what they say. They might be able to order you one in, or possibly suggest just running a C. I found the Wossner A I dropped in my A cyl was a better fit than the Vertex A I pulled out at 75hrs. The rings were still only 0.4 and 0.5mm respectively. I pulled it down due to piston slap. Go figure. The Wossner now has 75hrs on it and sounds much better.

 

[stemplin]

The skirts actually look really good, not many wear marks at all and i wasn't hearing any piston slap. I've been reading that different manufacturers piston sizing varies. I was thinking of using the wossner c kit but I have no idea what brand the current D piston is.

 

[Jakobi]

You could always just try and source a set of rings for it, but might be hard not knowing what brand.

If the nikasil is still in good shape then odds are the C will fit nicely in the B cylinder. The difference between a C and a D is 0.02mm. If the D had of been slapping or showing wear on the skirts you wouldn't even consider down sizing.

The right way to do it is to take it somewhere with the equipment to have the piston to bore clearance measured.

 

[stemplin]

Does anyone know if the wossner's have any identifiable markings on them. I know I've seen "w" on wisecos before but all I can find on this one is the "d 71.97" and and arrow towards the exhaust port.

 

[Jakobi]

Does anyone know if the wossner's have any identifiable markings on them. I know I've seen "w" on wisecos before but all I can find on this one is the "d 71.97" and and arrow towards the exhaust port.

The S3 Vertex I have here has its brand printed on the top along with size and arrow.

I can't remember what my Wossner had. Looking at pics it appears they have a part number only.