running out of fuel?

[cchracer77]

Hello everyone.
This weekend I went and did some dune riding for the first time on my 2010 ec300. I encountered an issue I have never had on my normal singletrack trails. The bike runs great, plug reads good, float level is perfect. However at the end of a long wot pull the bike will lay down and lean out like it was running out of fuel. Two buddies on ktm 300's were also having this problem. The only idea we could come up with is that the bikes were "sucking the float bowl dry." Anyone else ever experience this sort of issue or have any other ideas?

 

[gasser]

Are you running much lower altitudes in the dunes? High altitudes require less fuel so you might not recognize a slightly low float setting until you put the motor under max load for longer periods of time at lower altitudes. Sounds like you need to readjust for the dunes. One thing you might want to do first is to check for good fuel flow from your tank and clean the fuel filters if needed.

 

[Jakobi]

Did anyone try going up a size or two on the main? The sand will put a bigger load on the engine plus as stated if you'd dropped alititude the bike will require more fuel also.

Is it one big surge as you come off WOT? A surging idle once stoping your long run? Or surging at part throttle after a WOT run??

 

[cchracer77]

That's why I'm confused. I jetted for altitude, the tank will drain quickly, float needle and seat are clear. I run the floats as high as possible without a continual dribble from the overflow. The bike will pull strong banging gears on the flats. On the long hill climbs it will pull hard through the top of third gear and hold good strong power there for about 45 seconds, then it gets about three good sputters and falls on its face, downshift to second without lifting and no change. Dump the throttle to turn out and within 1-2 seconds it will wind out again. As a test I got on the flat highway and let it pull in 6th for about 45 second and it does the same thing, dump the throttle and pin it again and it will pull. As stated the 2 ktm 300's were having the same problem. Altitude was around 5000 ft, 55 degrees f. I have a 40 pilot, N3CG needle middle clip, 165 main. Normally run a 38 pilot, same needle on second clip from top, and a 162 main at 6500ft +. Running Sunoco 100 octane and Motul 800 at 50:1. The ktm's were running 91 pump on junk oil, and Sunoco 118 with Bellray H1-R respectively. Second ktm running a 35 pilot, jd red needle, and a 162 main. It was jetted on a dyno at 5000ft.

 

[Jakobi]

Is that with a 38mm carb?? Thats a hella small main for a dual taper n3xx needle.

I personally run a 42P N3CJ#2 172/175 main in my 2010 EC300 with a high comp head. 98RON 300M 30+C (1000ft 86F). Jeffs runs 40 N3CH#2 with a 172 not sure on his temps or altitude. Considering you are running richer than us both on the pilot and the needle with that setup also makes me wonder why your bike would need 4 sizes smaller than us on the main.

Does sound like you're running out of fuel considering its running for around 45 seconds before cutting. I'd suggest throwing a fat main in just to check.

 

[cchracer77]

Dealer recommended a 158 main. The 40 pilot is rich on the air screw, but it gives better "pop" off the bottom. After fully warm, 30 min of hard riding to clean it out, a 20 second wot plug chop looks fat to me:

 

[Jakobi]

Yep yep

I run the leaner needle diameter with a bigger pilot. Its not as punchy but I prefer the cleaner smoother delivery of if. Still pleanty of torque for lugging hills.

Can't argue with your plug chop either. Is it a 38mm PWK?

With all bikes displaying the same symptoms perhaps you blokes just need to lay off the gas a little!

 

[cchracer77]

I assume its a 38mm. Its the carb it came out of the shipping crate with. It has no p#'s or markings at all other than the "Keihin" logo. Not an asII. Looks like a classic pwk. Of course I have come to realize that my bike must have been built on an overtime sunday! It has a combination of parts that the importer says didn't exist here in the U.S. The combination is closest to what everyone refers to as a "euro." These things have the consistency of Mona Lisa knock off's. As for "us blokes" I can't help it if i ride too hard!

 

[rgranger]

look on the top of the carb, should be a circle with a 38 or 36. my 2011 300 came with a 36mm.

 

[Jakobi]

look on the top of the carb, should be a circle with a 38 or 36. my 2011 300 came with a 36mm.

I believe the classic PWK has a plastic screw top cap. I've never owned one so have no idea how to verify sizes.

Heres a consideration though.. Still thinking about main jets here and maybe a little off topic.. You realise if you do have a 38mm carb that you are running the same size main as the ktm with a 36mm carb. Here in Australia the KTMs all run same as you described. 35/38 pilot. 158-165 mains. The gassers require 38-42 pilots and 170-178 mains simply because the smaller carbs have a higher velocity of air pulling more fuel through the same sized jets.

The 'Euro' model was marketted to Australia as a limited edition. Essentially it is a US EC300R with everything to be road reg (blinkers etc), which is what I have. White and black plastics. We all ended up with the ASII 38mm.

 

[cchracer77]

My bike is black with white graphics. Has red sachs 48mm forks, red sachs rear shock. It had all wiring and switches for road parts, but no blinkers. Had the stainless pipe like six days. But no guards.
I took the carb off last night here is what I found:
Has a black anodized screw on cap with no markings
Has "Keihin" logo horizontally on choke side of carb
Has 4 vent tubes on front of carb + 1 on rear + overflow
Has "Keihin" logo vertically on non-choke side
Says "PWK PRO" where there is normally a p#
There are NO other markings inside or outside the carb

I get more confused the more that I look. may also note that this carb looks nothing like the keihin on my cr500 honda, that bike likes a 168 main. I can't remember what pilot and needle it has, it has been over 5 years since I tuned it.

 

[Jakobi]

http://www.showandgo.com.au/carbie/carb12.htm?carb12_bf.html~mainFrame Which one does it look like??

A quick google "PWK Pro" turns up referrences to 41mm carbs.. and the plot thickens. Any chance you can measure it up while its off the bike?

You weren't wrong when you said you got a mixed bag bike..

 

[cchracer77]

So, I think I have a pretty good theory about what this thing is. Measurements of the carb body indicate that it is a 36mm quadvent. (176.6mm tall). However, the throat is polished all of the way through and snap gauge indicates 38.2mm. Old mechanic buddy suggested that it was a flawed 36mm casting keihin "cleaned up" to 38mm. He mentioned that this was a common practice for Mikuni back when. Just a theory though.
As far as jetting ect. goes, I talked with a couple more GG dealers around and they all believe that a 165 is too rich with the N3xx needles. I got recommendations ranging from 156 to 162. I measured up the three needles that I have (N1EF, N3CG, NECG) and plotted them in excel. The N1EF is the richest, the NECG is just a bit leaner in the last 1/8, and the N3CG is substantially leaner from 1/2 up. Thinking about trying the NECG a clip lower than the N3CG to lean up the midrange and provide a softer transfer onto the main?

 

[Fred1956]

So, I think I have a pretty good theory about what this thing is. Measurements of the carb body indicate that it is a 36mm quadvent. (176.6mm tall). However, the throat is polished all of the way through and snap gauge indicates 38.2mm. Old mechanic buddy suggested that it was a flawed 36mm casting keihin "cleaned up" to 38mm. He mentioned that this was a common practice for Mikuni back when. Just a theory though.
As far as jetting ect. goes, I talked with a couple more GG dealers around and they all believe that a 165 is too rich with the N3xx needles. I got recommendations ranging from 156 to 162. I measured up the three needles that I have (N1EF, N3CG, NECG) and plotted them in excel. The N1EF is the richest, the NECG is just a bit leaner in the last 1/8, and the N3CG is substantially leaner from 1/2 up. Thinking about trying the NECG a clip lower than the N3CG to lean up the midrange and provide a softer transfer onto the main?

Post up a picture.....

 

[Jakobi]

As far as jetting ect. goes, I talked with a couple more GG dealers around and they all believe that a 165 is too rich with the N3xx needles. I got recommendations ranging from 156 to 162. I measured up the three needles that I have (N1EF, N3CG, NECG) and plotted them in excel. The N1EF is the richest, the NECG is just a bit leaner in the last 1/8, and the N3CG is substantially leaner from 1/2 up. Thinking about trying the NECG a clip lower than the N3CG to lean up the midrange and provide a softer transfer onto the main?

Screenshot? I've played with all the needle tapers listed above also. Findings are all in the jetting section.

For me N1EF was too rich off the bottom (possibly due to the F diameter). NECx was clean off the bottom and then richened up and needed a 170-172 main due to the richer 3rd taper. N3Cx runs nice off the bottom, then leans out hard from 1/2 throttle to WOT. The 2nd taper gives a nice hit as it comes onto the pipe. Requires a fatter main to fuel the leaner needle taper.

The NECx does give a very smooth transition everywhere, but somewhat lacks the mid range snap.

A quick look through the jetting database doesn't show too many people using mains in the 160 range let alone the 150. Only references I can find are people using a 36mm carb.

We've gone a bit off topic now. Any other ideas how to identify if your bowl is running dry and how you'd fix it?

 

[cchracer77]

This chart shows diameter vs. Length from bottom clip, the taper of the three needles. As for the float bowl I thought of trying one of the older boyesen "no slosh" parts. The shape and size should allow for a lower float height without the fear of sucking it dry. The only concern I have is that based on pictures I've seen these don't have an overflow tube. Wonder if anyone else has tried one of these?

 

[rosco]

I think you are way too lean on your main. At that altitude and temp running in the heavy sand I would try a 180 main with a n3eh needle in the middle position. You could probably stick with the 40 pilot. If you have problems with it wanting to drop back down to a decent idle after a hard run you could possibly jump up a step on the pilot as well. The n3eh is a lean needle so it really cleans up the mid range but you need to make sure your main is plenty fat for when you are under a hard load. Give it a try I think you'll be impressed. Remember air temp and humidity seem to have way more of an effect on jetting than altitude. There is a big difference between running at 55 degrees and say 95 degrees. We've had to run as high as a 185 on the main under certain conditions.

 

[Jakobi]

I think you are way too lean on your main. At that altitude and temp running in the heavy sand I would try a 180 main with a n3eh needle in the middle position. You could probably stick with the 40 pilot. If you have problems with it wanting to drop back down to a decent idle after a hard run you could possibly jump up a step on the pilot as well. The n3eh is a lean needle so it really cleans up the mid range but you need to make sure your main is plenty fat for when you are under a hard load. Give it a try I think you'll be impressed. Remember air temp and humidity seem to have way more of an effect on jetting than altitude. There is a big difference between running at 55 degrees and say 95 degrees. We've had to run as high as a 185 on the main under certain conditions.

The N3CG he is running in clip 3 is only a half a clip leaner than what you suggested. The diameter is one step richer which essentially has the same effect as what you suggested by going a size larger on the pilot. I agree that the main sounds waaaay off too.

I personally run a 42P N3CJ#2 (lean and crispy) and a 175 main. This is at 300-900M 30+C and humidity between 60-100%. (1000ft - 3000ft, 86+F)

 

[swazi_matt]

Not sure if you have checked this, but is the fuel tank breather pipe allowing full flow, may be partially blocked

 

[Jakobi]

Not sure if you have checked this, but is the fuel tank breather pipe allowing full flow, may be partially blocked

On all 3 bikes though?