31K Carbs on an 86+ (1UA)

[RD4ME]

Hi Folks,

I've got my 86 RZ all back together and have begun testing it around the neighbourhood.
The bike runs rich but starts and idles perfectly and delivers decent power up to about 7K. Above that, it is being held back and while the revs will climb - there's limited top-end power (but a decent cloud of blue smoke).

I'm using a stock set of 31K carbs not the factory 1UA carbs with the powerjet. Other than the carbs, the bike/exhaust is stock with freshly rebuilt motor.

I know that the carbs types are different but I'm not sure where to start adjusting i.e. air screw, needle position, main jet size, etc.

Wondering if anyone has had any experience with this and could share some advice?

Thanks!

31K YPVS................................................1UA YPVS
Main jet 240...............................................Main jet 185
Air jet 0.7..................................................Air jet 0.8
Needle 5K1................................................Needle 5L20
Clip from top 4...........................................Clip from top 2
Pilot jet 22.5..............................................Pilot jet 27.5
Air screw 1.25 turns out..............................Air screw 1.5 turns out
float height 0.5mm........................................float height 0.5mm
...............................................................Power jet L/H 65
...............................................................Powerjet R/H 60

[MK]

That should work without huge problems.
The 31K is pretty equal to the 1UA regarding WOT setting.
Only thing is you'd benefit from using the bigger idle jet and the 1UA needles.
(The 1UA pipes require a richer setting at low rpm & load)

If the bike has issues above 7k, then there's other reasons.
PV not working, working the wrong way (cables attached wrongly), carb main air jets clogged (those behind the brass balls), float height / fuel level.

[RD4ME]

Thanks for the feedback MK.
The bike does run above 7K - it just doesn't pull as hard as I would expect. There's no hesitation or stuttering as the revs build - it just feels choked-up.
So agree it could be PV. At this point I've been keeping to my neighbourhood and it's pretty hard to hit the RPM range required to test the PV without looking like a complete lunatic!!
I can see that it does move slowly when I rev it in the garage - but think I need to set-up a Gopro and check it on a longer stretch of road. I have noticed that when I turn-on my bike, my PV rotation seems very sluggish compared to others that I have heard.

Cheers.

[RD4ME]

So I switched the stock 1UA pipes to a set of DG Pipes and took the bike for a spin.
I made no changes other than switching the pipes and it has really made a difference. The bike still runs rich but the WOT/top-end power is much improved.
Previously, there wasn't any kick above 8k and revs would climb slowly. With the DG pipes it really pulls at the higher revs.

I even notice that when I'm in first gear and accelerating, the front end will lift on the power alone when it gets close to 10K rpm. It was a big surprise the first time it happened as I was not expecting it - so I kept trying it - and it does it every time.

I did notice some unburnt fuel is coming out of exhaust manifold and dribbling down the header pipe on the right side. I'm going to check the float height and give it a clean. If that doesn't solve it I think going down one on the main jet might be next - but open to suggestions.

[MK]

Well that's a common observation.
Some 1UA pipes sometimes peak at short above 8k, so if you expect a powerband of 6 to 10k, you'll be kind of disappointed.

I've had that on a 1UA I ported in the mid 90's. After fitting 31K pipes, everything was on normal level again.

[kpke]

Glad to hear it's running better. That exhaust spooge is normal and is more than likely coming out of your interconnect from the expansion chamber to the slip in exhaust manifold. On non-O-ring manifolds that interconnect needs to be cleaned very well and then packed with high temp silicone before you carefully slip the pipe into the manifold. It can also come from worn-out power valve seals. But if it was not happening with stock pipes it is probably your pipe joint as I mentioned above.

[RD4ME]

Thanks - the spooge is definitely coming from the manifold - which makes sense as I didn't use any sealant when I put the pipes on.
I didn't realize the 1UA pipes had such a short powerband. My tach is very lazy - but with the DG pipes the bike pulls hard from 5.5K - 9k - which might be 6.5k-10K if the tach were measuring correctly!

Here's a video of me giving it a good thrashing https://youtu.be/R0CIB5hwFWU