RVF400 Tyga Twin Stack

[Malc]

Stock mains are 108, aftermarket exhausts don't usually need big changes in jetting. Remove at least one shim from the needle, and aim for 110-112 on the mains.

[wogstaa]

Full exhaust system will need bigger jets than 112 for sure.

I've picked up some 122 and 118 jets, I'm gonna give the 122s a try since that's the next size down from what's currently in there.

Full throttle performance is very good, it's part throttle at that mid range that's the big problem.

[Malc]

Just going on past experience.

You say full throttle is very good, so why are you choosing to mess with mains if this is the case? Part throttle is mostly needle taper and clip position, so if rich with two shims, you need to drop the needle surely?

[wogstaa]

The a/f chart is on the rich side as it is, it could probably do with smaller main jets anyway.

I ran the same setup with 1 shim prior to the dyno tune and it was worse than with 2 shims, borderline unrideable.
It was also mentioned to me that it could be an issue when transitioning to the main jets. With the little riding I've done it seems like that could also be a legit cause.

[gavins]

As already stated, midrange issues like that will almost always be needle related but main jet size and float height will also effect it to a much smaller degree.

125 mains does sounds a bit on the large side to me for RVF carbs, have you checked the float height as well?

Drilling the hole in the bottom of the carb slide out from 2mm to 2.5mm will also help pickup once the jets and needle heights are set right - one 0.5mm shim with stock needles is normally sufficient in my experience. Have you made any mods the the airbox?

[wogstaa]

Cheers guys,

My airbox is stock.

I've done a bit more research and I think it's likely a combination of a few things. I was planning on working on the bike today but we're having insane weather in Sydney right now, so I don't have anywhere to work on it.

My plan will be to get the carbs off and check the float heights, set idle mixture a little leaner (it's starting way to easy in the cold without choke and it definitely smells rich) and drop 1 main jet size and see what that does.

I've already tried 1 shim under the needle, it was too lean, even with the HRC springs which should have the same effect as drilling the slides.

The current setup is the best I've had so far.

[saltysealion]

Any updates on this?

[wogstaa]

Damn, I haven't checked here for ages, so sorry for the delay.

I was pretty happy with running 122 main jets and 2 shims under the needle.
It seemed almost spot on to ride, still had a tiny hesitation but it wasn't very noticeable.