My turn for carb problems

[vfrman]

Need some help guys. I have tons of info to toss into this, but some of it is fairly random stuff.

Basically my bike is running rich and doesn't pull out of corners very well. This is a race bike. It is so rich that it spits black juice out the exhaust. You can see it on my number board on the tail...



This is a rear plug:



Now for the stats...
The bike:
108f/112.5r main jets
Float height and idle screw are set to spec
stock airbox with the block plate on the bottom of the airbox
Stock filter with K&N element instead of paper
Crazy gold needles that I have no idea what they are.
Some aftermarket 3/4 exhaust, brand unknown. You can see straight through the silencer.

Environmental:
HOT! I'm in a high mountain desert where the ambient temps are anywhere from 26 to 40 centigrade. Good thing is humidity is usually down around 10 to 15 percent. The altitude at the track is about 1341 meters ASL.

Check out these needles...The gold one on the left is what is in the bike now. The middle is a 8ZF needle and the one on the right is unknown.



Now take a look at these dyno graphs. One thing to keep in mind is that these were done at about 1615 meters ASL when I lived in Albuquerque, NM.





Look at that A/F crash and power drop at 5k when the metering transfers to the mains...and then the A/F turns into a roller coaster.

This last one is kind of interesting...the operator held the throttle steady and then at 12 seconds, he rolled to WOT. The A/F mixture goes from lean to rich. And at my lower altitude, the lean condition shouldn't be as dramatic. I guess I need to get the bike on a dyno here, but I want to get it pretty close first.



OK. So my thoughts...

With the mains down to 108f/112.5r and the size of that needle, I'd be lean. But I'm not. I'm thinking of putting in the 8ZF needles and dropping to 110 on the rear. That might fix it...

[Neosophist]

nc35 ?

small jets for nc30

wow looks like my magna plug.. thats driving my nuts too.


id start with stock needles, they are sometimes lean with the stock shim hence the extra shimming, so might help you lean it out.

all carbs the same?

[Tim400GB]

Thought about taking the material out of the airfilter just leaving the grill?

[vfrman]

nc35 ?

small jets for nc30

wow looks like my magna plug.. thats driving my nuts too.


id start with stock needles, they are sometimes lean with the stock shim hence the extra shimming, so might help you lean it out.

all carbs the same?

This is on an NC30. I'm pretty sure the carbs are also NC30 carbs.

[Neosophist]

you'd have the weird shaped sliders if it were nc35 carbs :D

i just read your still at altitude! I thought you had come back down to normal sea level..

shouldnt post half asleep

http://www.ultralightnews.ca/rotax503/r ... nchart.pdf

nice simple chart here for jetting correction.

If we go on the basis that 115/118 are stock jets for your bike then

108 / 110 might be a little on the lean
110/ 112 might be a little on the rich depending on weather.

Id consider a 110 instead of your 112 if your keeping the 108.

Overall they seem roughtly ballpark, shouldnt be that black unless something is really up, varying the sizes by such a small amount is only going to make the difference between crisp and flat

bin those needles and get stocks put in there and go from there..

[vfrman]

bin those needles and get stocks put in there and go from there..

That is the plan. I think I'll also put 110 in the rear instead of the 112 and see what happens. A co-worker that is also a motorhead seems to think that the plug is showing oil contamination as well. Not sure on that one tho. I need to pull a front plug (isn't that a grand time) and see what they look like.

[micpec]

Steve, +1 to convert back to usage of stock needles. Leave the gold and pointy ones aside.

What brand of main jets are you using in current set-up? I believe that stock Keihin jets are correct based sizes while Dyno ones are slight bigger compared to Keihin although size numbers matches.

I would still advice to start from the bottom-up, that's full stock and go from there.

[vfrman]

Steve, +1 to convert back to usage of stock needles. Leave the gold and pointy ones aside.

What brand of main jets are you using in current set-up? I believe that stock Keihin jets are correct based sizes while Dyno ones are slight bigger compared to Keihin although size numbers matches.

I would still advice to start from the bottom-up, that's full stock and go from there.

I'm going 90% stock...still gonna keep the K&N and start with 108/110 jets. I'm not sure what the brand is, but I am sure the jets are not Keihin. Good thing Slo1 has stock needles for me.

[TyeNoodle]

Blimey and I thought I was having troubles with my VFR! (well, I am...)

Those gold needles look to have quite a thick shallow taper. How do they compare in length to the 8ZF's? I've done a couple of NC30's now that have responded well to having stock needles put back in, the HRC style ones being far too rich for some reason. But your mains should be lean if anything with your current setting.

Are your float valves in good shape? Clutching at straws a little, me.

What spec is your engine?

[vfrman]

Blimey and I thought I was having troubles with my VFR! (well, I am...)

Those gold needles look to have quite a thick shallow taper. How do they compare in length to the 8ZF's? I've done a couple of NC30's now that have responded well to having stock needles put back in, the HRC style ones being far too rich for some reason. But your mains should be lean if anything with your current setting.

Are your float valves in good shape? Clutching at straws a little, me.

What spec is your engine?

Float valves are good. The engine is stock.