Anyone Seen Carb Needle Wear Like This? 86VFR700

I've read that the brass and aluminum are pretty close in hardness which is why they both tend to wear as opposed to only one or the other wearing. I'm sure there are slight variations though.

If the factory needle is shimmed too high it will get stiff, but not these adjustable ones. The clip stays in the same location down low and the spring pushes down on the clip. So regardless of the needle height, the spring tension stays the same. Now you could add washers on TOP of the clip to add spring tension.

As far as preventing needle tip wear like mine, maybe the spring tension should be a bit higher? That would keep the needle from being pushed sideways from the incoming air. Or would it? It may not be possible to prevent needle tip wear (besides never revving the engine, but what fun is that?)

I know if the spring tension is too high the slide will get stuck and not go down all the way.

I don't know. I'm not gonna worry about it. The bike runs great, so it's no biggie getting poor gas mileage.

(Let me go through a couple tanks of gas with my new carb mods and adjustmants. Who knows, maybe my mileage will be improved)

 

Mmmm bugger. Sounds like the wear is not readily fixable.

 

Just a side note. I found a great diagram of a downdraft CV carb at howmotorcycleswork.com. It's not exactly like the Keihin VD series, but it's close. Differences include slide shape, velocity stack, angle of mixture screw, the number of transition holes, etc...
I corrected a few errors and made some enhancements. Check it out.

 

I recently pulled my carbs and checked all 4 needles and photoed all 4 needle jet holes for analysis. Luckily the other 3 holes are in good shape, it's only that needle jet from post #11 (rear left carb) that shows any wear.

I've got 2 needles that show wear in the middle, one that has wear on the tip and one that looks okay. Here is the worse of the 2 needles that have wear in the middle. Can you believe my bike runs great with this needle? All I can think is it will run even better and stronger when I get these replaced. Woohoo!




I checked my pilot jets which were genuine Keihin #38. I had a drill bit that measured 0.36mm that fit fine and a 0.40 that did not fit so I'm pretty sure mine are still the stock 0.38mm size.

The main jets were quite strange. I could have sworn I saw 118 on them, but they are actually unmarked. I didn't even see scrapings were a stamping could have been ground off. It's very strange and I looked at all 4 really close. I had a drill bit that measured 1.175mm and it fit 3 snugly while 1 was an easy fit. A 1.23mm bit did not fit any of them so the main jets are probably 1.18mm. Not Keihin 118's, but more like Dynojet 118's which are measured by actual size. So they are bigger than stock.

I also checked my main jet emulsion tubes and discovered all 4 were the same. Is that correct? I thought there were 2 front and 2 rear tubes where the holes were different heights. Maybe not for the 86 VFR bikes?

 

If you do go with the 02 sensors, I would love to hear more about it.
I'm considering the same but not sure where to locate the bungs. It would be a PITA to get at the rear exhaust headers.

 

It's been done before on one of these bikes. He had a 4-1 exhaust and placed the bung right where the pipes came together to a single pipe, near the foot peg. Here is a link to the thread.

http://vfrworld.com/forums/showthread.php/22392-carb-help-on-an-86-vfr-700


I also remember a guy adding 4 bungs on a different style bike and plugged 3 while using the 4th. He could swap the O2 sensor around to verify each carb, but only one at a time. Beats paying for 4 wideband O2 sensors.

 

This is just a fuel mileage update. With my needles in the same position (same as when I got the bike 3 years ago) I recorded the last 2 tanks of gas and both had the fuel light come on at 118 miles and I switched to reserve at 126 and it added up to 29 mpg. So that's very consistant.

After raising all the needles 1 notch, K&N filter and open air box I was expecting poorer mileage or about the same. It actually improved! layful: The fuel light came on at 126, I switched to reserve at 137 and got 33 mpg. That's awesome getting an extra 10 miles per tank.

I'm hoping to get some newer needles any day now and I'll test and do plug checks and report back.

 

I used another tank of gas and the mileage is even better.

The fuel light came on at 131, I switched to reserve at 143.

This is great, but can anyone explain why my fuel mileage is better? Is it the filter and airbox letting it breath better or maybe raising the needles moved an unworn section (larger diameter) of the needle to the spot were the bike cruises at? I don't know.

I just swapped out my 2 most worn needles (worn in the tapered area) with some better/newish ones. The tiny hiccup I got when opening the throttle at 5500 rpm is gone. Midrange torque is still strong. I'm hoping the fuel mileage will be better still.