RVF Carb Issue

[wogstaa]

I took it for a quick ride, it's definitely better now than before I put the 115s in.

The problem seems to be at full throttle, it stumbles from around 6000-8000rpm then takes off. If the throttle isn't wide open it goes past that spot smoothly.

[Ben_OB1]

According to the Keihn carb guide, main jet sizing is the primary influence on WOT response (assuming correct float height). Identify the minimum main jet size for smooth operation and then go one size larger for ideal engine durability.

Have you checked that you have standard taper jet needles? if these are non-standard (fatter at the point) the WOT fuel flow through this path might be reduced also.

Where are you - sea level or in the mountains somewhere? My RVF at sea level (Adelaide) has 112s all round, it has non-standard needles with 1mm shim (I don't have the needle designation handy) a Tyga full system, 2-1/2 turns air correction, standard pilot jets. It hasn't been dyno'd but it makes good progressive power with no flat spots... bum dyno suggests its making high 50s BHP. I need to download the Bosch iPhone dyno ap :-)

Also, have you synchronised the carbs? I've not touched the sync on mine yet but have obtained a set of vac gauges.

Good luck,

Ben.

Ben.

[wogstaa]

Thanks!

I'm in Sydney.

I've just checked the needles and it's running 1 0.5mm shim under each needle and they looked stock





As for carb sync, I haven't touched it yet. I've installed brass adapters to the ports with covers so I can make it an easier job for later. But it idles smooth enough for me to assume they're not way out.


So my current setup (yet to be tested) is: HRC replica springs, 0.5mm shim under needle, 1 5/8 turns out pilot screws, stock pilot jets, 115 mains, float height 11.8mm with a TSR 3/4 system.

Before I modded anything it was: stock springs, 0.5mm shim under needle, 1 5/8 turns out pilot screws, stock pilot jets, 108 mains, float height was around 10.5mm, TSR 3/4 system. It had the issue in the same rev range but it was very minor.

[wogstaa]

Good signs with the setup I just mentioned. At least with no load it's not stuttering at all.
1 cylinder was missing at idle, but I think it cleared up. I will double check it though, but it is idling very smooth, better than before.

Still need to ride it but from idle to just before the redline, it revs clean.

[Ben_OB1]

That is a fat looking needle, hard to tell for sure though as cameras with wide angle lenses do all sorts to perspective!



Next time you have the needles out have a look to see if they are designation "J8VA". I will check my needle designation tonight and report back...

Out of curiosity - Why is it that you've fitted HRC replica springs - as I understand this has the same effect as drilling the balance holes in the slides. I haven't heard of many people doing this mod on the RVF carbs?

Ben.

[wogstaa]

Next time you have the needles out have a look to see if they are designation "J8VA". I will check my needle designation tonight and report back...

Out of curiosity - Why is it that you've fitted HRC replica springs - as I understand this has the same effect as drilling the balance holes in the slides. I haven't heard of many people doing this mod on the RVF carbs?

Ben.

I had a look at the needles they have J8VA on them.

I put the springs in for a bit better throttle response and I thought it might have helped with the flat spot I had before and I didn't really want to drill the slides.


Thanks for your help!

I took it for a spin, it feels pretty good. So I guess lowering the float height fixed my issue.
Does that mean I might actually need bigger mains if I put the floats back to stock heights?

[Ben_OB1]

Excellent news, feeling "pretty good" is a good start. How is the colouring of exhaust residue in your exhaust pipe?

Here is the Keihn tuning guide I mentioned:

http://www.showandgo.com.au/carbie/info ... nginfo.pdf

I corrected my flatspot (which wasn't too bad) by adding an extra 0.5mm washer under the needles... that said, I don't use much WOT so the midrange tuning is the most important for me. I am getting more curious about my needles now!

Ben.

[wogstaa]

Thanks for the link.
I'm happy with it after a really quick ride.

I've got it all back together now, hopefully I can go for a longer spin after I finish work tonight to confirm it's running as good as I thought it was.

If you've got the needles raised 1mm with a full exhaust system, they shouldn't be too different from stock.
I would've put another 0.5mm shim under my needle if it had a fueling issue at part throttle, but it seems fine (maybe because of the springs).

[micpec]

That is a fat looking needle, hard to tell for sure though as cameras with wide angle lenses do all sorts to perspective!



Next time you have the needles out have a look to see if they are designation "J8VA". I will check my needle designation tonight and report back...

Out of curiosity - Why is it that you've fitted HRC replica springs - as I understand this has the same effect as drilling the balance holes in the slides. I haven't heard of many people doing this mod on the RVF carbs?

Ben.

Hey, that is my pic I took this pic when I had some carb reset done last year whilst carbs dismantled for ultrasonic cleaning and ended fitting new honda carbs seals.

Had some jetting issue too, with old spec with 2.00 turns out for pilot jets, #116 main jets (dyno), dynojet needles as pictured the left one and double shims. I went back to stock settings at 1 5/8 turns out, lowered to #112.5 main jets (dyno), stock needles J8VA, 1 shim 0.5mm, new RO hrc springs, and float height 12.5mm, and for sure again balanced the carbs, and combined with the TSR system lovely!

[micpec]

By the way....there is some thread about the differences in between standard genuine Keihin jets and for example Dyno jets. Here it is: viewtopic.php?f=24&t=26528&p=188936&hilit=+keihin