Scooterotica

Have an RB which is now run in (600 miles) and goes like a train in 1st, 2nd and 3rd but just dies in 4th no matter how many revs im pulling when i change up. Am using the following set up

LI150 box
30m delly (jetted by AF so still quite rich)
taffspeed crank
NK mid pipe

I am going to knock the mix down to 3% from 4% when i next fill up but i dont tyhink that will make much if any diff to the 4th gear problem. I have also tried a 34 delly but that was boggy throughout the range so went back to the 30.
Can anyone suggest what the issue might be, as im pulling my hair out. I will be trying a JL2 pipe this weekend as soon as i have made up somthing to help it fit but after that im out of ideas and exhausts...
The way i see it it either oe of these or a combination

Wrong pipe
Wrong sprocket set up
Wrong gear box

Anyone have any ideas,. mate had an RB with simailar issiues but he had a servetta box , swapped it for a pacemaker and problem solved even though the power band in 4th is right at the end of the range. I dont want to spend shed loads of cash unless i can help it and cant really see the point of getting it jetted until the 4th gear issue is sorted....Have aqsked about sprocket set ups earlier but general feedback was all over the place....

Help

Sef

Your gearbox is fine.....but what sprockets are you running?

NK tourer is not best pipe IMHO the NK race is better, and the Franspeed race is just about the best i think?

What jetting are you running on the Delly?

Also which RB 20 22 25

not a spanish LI150 gearbox is it?

cheers lads
its a RB20 with an italian LI150 box, not sure waht the jetting is as its been jetted for the RB kit by AF themselves, so suspect that its pretty rich. Having said that i have done a plug test and didnt appear to be that rich but what would i know...lol

Was on the phone to Taffspeed today (top blokes) as i know they do quite a bit with RBs and he said he suspected it was the the sprockets. He suggested the following:

15 x 46 with 80 chain or
17 x 46 with 81 chain.

Im currently running a 46 x 16

cmon lads put yer heads together as a sprocket set up solution is the cheapest option open dont want to start buying new boxes or pipes till i get the right combo..

Syd

Im suprised its not pulling a 16/46 Li150 box 4.9 ratio

Af tend to set up for 4.8

Putting 17 on will up the box to a 4.6 which I would think in your present state will make worst
Putting 15 on will drop the box to 5.2 which might help rev on.

Are you sure its Italian LI 150 & not a Italian Li150 special which has a big jump from 3rd to 4th

Standard 150 box althoughg i do have a 125 thati could try...Think I will go for the 15 sprocket first and see where that gets me. Going really well now its run in, was able to match me mates ts through 2nd and 3rd and then he sailed past. Hope when 4th is sorted i dont lose the the pull its giving now......

Hi i was running 4.8 ratio as well and it struggled with top gear on A roads or adverse conditions , i'm going for 5.1 ratio with af close ratio box , as the kit is a revvy mother think this will suit my set up ( franspeed race, 30 mm delly flatslide and 15 stone rider!!!)
Baz