Anyone Seen Carb Needle Wear Like This? 86VFR700

I missed this 3 years ago when I first cleaned these carbs, maybe they weren't worn then? The tip of the needle is worn now. I assumed these needles were stock because of the taper and until today I never removed the needle from the slide. I was surprised to see they were notched.




Here are some pictures with the needle rotated 90* each time.


The normal angle.



Left side of tip worn.



Flat side of tip.



Right side of tip worn.



3 years ago I did notice a slight notch worn near the top of the needles. It wasn't too bad. I took an emory board and took the sharp edges off and smoothed it out.



I'm wondering where these needles came from. Has anyone seen a jet kit with aluminum needles that looked like this?

I thought about replacing them as the stock needles seem to still be available for about $15ea, but the bike really runs well, so why bother?

 

Those look like Dynojet needles, I always replace them with stock needles when I come across them.

 

If the needles have been changed then the jets most likely were too. Most after market are a set. You may want to check the main jets to see what they are.

 

Dynojet, huh? I was hunting for pictures, but came up dry.

I knew something was up with this bike as the airbox lid has like thirty 1/2" holes in it, but they were all covered in thick aluminum tape making them useless. Snorkel is still in place.

I checked the jet numbers when I had it apart. 38 pilot and 118 main, but I did not verify the hole diameters as it's not easy to do. Next time I pull the carbs my plan is to fab a slightly tapered rod, insert in main jet, mark location it stops then measure that diameter. A Keihin carb 118 jet should measure about 1.13mm-1.15mm. Any bigger than a measured 1.16-1.18 and I'll know it's been drilled.

For the pilot jet I can use drill bits to measure. I have .37mm .40mm and .45mm.

Then I'll know for sure about the jetting.

The bike runs pretty great, but mileage is below average 25-30 mpg. Does it sound like the needles are the mileage culprit?

 

Yes they could be. Drop them one notch and see what happens. Remember you're leaning it out a little so watch the heat, surging at cruise and listen for detonation under load. That might do the trick as far as mileage goes.

 

Let me provide some more background. The bike has run well for the 3 years I've had it except for having a slight weak spot around 5500 rpm on the freeway when opening the throttle. That was with an opened up stock exhaust. A few month back I experimented by restricting the outlet size to match stock and I got a bit more power under half throttle. If I twist more than half, the power goes away. It makes passing in 6th gear kinda bothersome. I recently switched to a Yoshimura 4-2-1 small can exhaust with 1.5" outlet and I seem to have a little more power right at 5500rpm on the freeway, but still only under half throttle. It's finally time I looked into fixing this.

I've been discussing this annoying little issue with Squirrelman and we both thought raising the needle a little would be good to try. Yesterday I moved the clip down 1 notch raising the needle (just on the rear 2 slides with the carbs still mounted to see if it got better or worse) It helped in that area, it also improved power below that in the 3-4k rpm range. It moves a lot quicker at less throttle which is pretty fun. When I do pull the carbs off I plan to do the same to the front needles. I think the bike will pull even harder still in the midrange.

If I have some extra cash laying around in the future I may just buy all 4 new needles. Is that what everyone suggests? It will run better and maybe get better fuel mileage with new stock needles?

 

Oh yeah, I suppose the slides could have been drilled out as well. Does anyone know what size hole the stock slides should have or what size Dynojet suggests to drill them out to?


I'm considering investing $130 into a APSX D2 Digital Wideband O2 AFR Controller & Gauge & Sensor Kit. I can weld the bung in the exhaust right where the 2 sides join the single pipe. I'd just use the setup temporarily to dail in the carb, then remove it and plug the sensor bung. It's cheaper than a dyno session and I can learn a lot about tuning.

 

Yeah, those look like Dynojet needles. Needle wear isn't too unusual due to the needle bouncing around with the intake pulses. So you do get some even with stock needles, but the stock needles are usually anodized so they don't wear so quickly. I'd replace them with unworn needles if tuning gets to be very problematic.

I would imagine the slides are also drilled if this is indeed a Dynojet kit. You should be able to tell by looking at the inside bore of the hole in the slide. It won't be smooth like a factory part, and you should be able to see slight imperfections, and the very top edge of the hole won't be radiused, but most likely a sharp edge instead.

 

Damn, that's some odd wear pattern! Never seen that, although I've never seen Dynojet needles either. I'm sheltered, I guess.

If you do the WBO2, I'd also recommend a data logger. The numbers tend to fluctuate a lot...at idle or full load they're pretty accurate, but otherwise it's not worthwhile glancing at it on the road. Take some notes after a short ride, and you should see some patterns start to emerge. Anything that distracts while you're riding is a bad thing IMHO. Too many cell phones!

Carbs are tough to get good data since no other sensors can easily be captured. I'd want to strap on an MS with a TPS and a MAP sensor...and maybe a laptop or a smartphone paired over BT to a serial output...convert the bike into a rolling dyno, LOL.

 

If you've got that wear on the needle then you probably should be looking at the emulsion tube too. Ideally you want both to be perfectly circular and the needle to have a smooth taper. My guess is that the wear pattern that you have would more likely lead to rich running as the orifice formed between the worn needle and tube will be a bigger area than if the part was unworn. Your high fuel consumption would be part of that pattern.


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The part that wears isn't the emulsion tube as they are easily removable. The part your refering to is the needle jet. That is the non removable piece the needle slides in and out of.

I took some photos of one of the needle jets so I could blow it up and see more detail. It does seem to have a small amount of wear as I've tried to highlight in the pic below.




The wear seems pretty small, but may be part of my low fuel mileage. As far as I know, these needle jets are not replacable nor does anyone make these for this carb. Correct me if I'm wrong.

I saw that Factory Pro has a $280 service where they can replace certain needle jets, but they don't show our bikes.

I just recently added a K&N filter and did some test riding, things went fine. Then I removed all the aluminum tape from my airbox lid to expose all these holes (37) that a previous owner had drilled out and later covered back up.



She ran better than ever. Pulled like a raped ape! Plus the intake sound. Geez, do I love that sound. I've been cranking the throttle every chance I get just to hear it roar.

I pulled the rear plugs (the same ones I raised the needles on) and they were fine. Maybe a tad browner than the normal tan, but at least it's not white. So now I know the current setup works. I'll pull the carbs, raise the front needles to match the rear and do an overall check. Make sure all the tiny orifaces are still clear and button it back up.

I don't think there is much I can do about the mileage except buy another Dynojet stage 1 kit and swap the new needles in place. I doubt it's the needle tips that are causing the poor mileage, it's more likely the needle jets (can't fix) and upper part of the needle (that is shown in the pic below).




I'm not too worried about the mileage as it's a fair weather bike only. Currently it runs great, sounds great, makes more power from 3k-6k than I've ever felt before and is super fun to ride now, so I'm all good. :triumphant:

 

I'd just replace the needles and ride it that way. If the plugs look good and the bike runs well, I wouldn't worry much about fuel mileage.

Those needle jets are just pressed in, I wonder if they'd be easy to remove? I picked up a Kawasaki Eliminator 600 last year with Keihin CVK carbs. I was surprised to find that the air jets are removable. When one jet fell out I thought I'd broken something, LOL.

 

It'll definitely be rich at small throttle openings because the jet needles have worn (and then been smoothed) to a smaller diameter, and the needle jets are significantly ovalised to a larger diameter. In tandem with that wear, the slide guide and even the slide will be worn. A new set of jet needles and needle jets are a minimum fix, but they won't last long since the slide guide is also worn. This lets the slide flop back and forth, and with it the needle in the jet. Also, if the slide holes have been enlarged, that will cause the slide to bounce more (less damping) exacerbating the issue.

Mikuni BST's are renowned for this problem. They have the needle jet machined in the end of the emulsion tube, so they are replaced as one item. In my Hinckley Triumph 900, I had new needles and emulsion tubes as a 20,000km interval service item. I really like the Factory Pro gear, so I will put their jet kit in my 4th gen sometime soon-ish. It's got 70,000 miles on what is probably the original needles and jets, and I reckon it is too rich at small throttle openings. Fuel economy will improve, and I will get a bit more snap to the throttle when the over-richness is corrected.

Beware the seat-o-the-pants dyno. If you have created a hole in the power delivery, it will feel really strong as it climbs out of the hole, but you may only have lost power and not gained anything.

If your needles and jets are running horribly rich, then adding heaps of air by opening the airbox may fix it - that is, lean it back off - at some throttle/rev combinations. If it was my bike, I'd get that airbox sealed back up, and a new set of needles and jets. That's the easiest path to a silky smooth fat power curve the V4s are renowned for.

 

Why would you assume the slide guides are worn? They are fine, no flop.

I can pick up another Dynojet stage 1 for $90. Maybe less if Dynojet sells just the needles.

How would you suggest replacing the needle jet? Do you know someone who makes a replacement?

I'm only asking this because at some point in the future I may want to improve the fuel mileage.

 

I have spares that match. PM me and I'll fire a couple in the mail. Kudos.

 

Needle is a soft alloy while main outlet is more durable brass, so far less wear on that.

A major factor in needle wear is a solidly-mounted needle that's been jacked up too far for stock setup. If needle is too high it can't float around as it was designed to. Best solution is to take some length off the tit under needle holder cap that locates the spring.

 

I had a bad case of brass emulsion tube wear on my Suzuki RF900, but the needles were fine. It ran poorly at low and midrange revs with the worn tubes, occasionally fouled the plugs and developed an unhealthy appetite for fuel. I used FactoryPro tubes and these were a simple and very effective fix.

 

I would assume the slide guides are worn, because it's a bearing surface. What did you measure the wear as? See
http://www.moto-lab.com/gallery/view?itemid=263 for some pics.

I'm not familiar enough with these carbs yet to know the details - these are just things I know from experience are consumables.

 

There's some comment on FactoryPro's web site about needle tip damage.
http://www.factorypro.com/tech/needle1.html

Says it could be from the wrong needles - too long - so they bottom out.

 

These carbs do not have replacable needle jets. FactoryPro doesn't have anything to fix this.

Okay, I think your assuming the Keihin VD carbs have replacable, plastic slide glides. They don't. The slides move up and down in an aluminum hole bored in the carb body.