help needed my series 2 dies in fourth

[smoore-gt225]

hi i think i need some advice on my gearing, it gets through the first 3 gears great then put into 4th and it dies
here is my set up it is a tuned 175 it has a li125 gearbox, running on 16x46 sprockets and a sterling pipe
it wasnt to bad on the old 42mm clubman i had on it
if im reading af's chart right i have got a ratio 5.3 and really need 5 ratio is this right how would i achieve this
any advice would be appreciated
cheers steve

[Stokie]

Put a clubman back on or avoid using 4th gear ............ you're welcome

[DaveTomo]

http://www.tonycassidy.com/Gearbox_Visualiser.html
17X46 would give you 4.9,17X47 would give you 5.09,download the above and have a play,its good fun

[Doom Patrol]

Sorry; I don't quite get this. If it's dying in 4th why are you attempting to make the gears taller? It would make it even harder to pull surely?

[coaster]

Sorry; I don't quite get this. If it's dying in 4th why are you attempting to make the gears taller? It would make it even harder to pull surely?

I agree, if you go in that direction you'll have trouble pulling 3rd When you say it's 'tuned', do you know what has been done to it? It sounds as if it's too peaky and the Sterling pipe won't help. As said above, either put the clubman back on or if you want an expansion you'll need something more llike a JL3.

[DaveTomo]

Just looked at the replies ^ and I just put down the visualiser without really looking at your problem ,but as said above if it wont pull 5.3 it certainly wont pull lower as is.If you're going to keep the expansion maybe better to go 15X46 which would give you 5.65,or put the clubman back on, or change the gearbox (LI150 ?) or change the expansion -which ever your funds allow.Good luck & let us know which way you go.

[smoore-gt225]

Hi Thanks for info i have put the 15 back on but havnt got a chaincase gasket in the shed so cant finish it
to go and test it will have to wait till tomorrow
cheers steve

[crooky]

I have same set up on my series 2 af stg 4 175 but with clubman i found the 15 sprocket just rev'd its tits off with low top speed. Decided i'd put a 17s on but unless conditions were spot on ie flat and no wind it struggled and i'm only 12 stone. Read a few of Adam Winstones posts on other forums and put a 16s on for a 5.3 ratio with it transformed it (as his posts said it would!!!). Just ran it first time to morecambe it sat nicely in the 50s and pulled really well uphill without the need to be changing down and stiil felt like it had a bit more in it. I did get carried away with the theoretical speeds on the gear chart and opted for the 17s rode it to brid and nowhere near as quick or rideable as the 16s. As I say if you do a search on the lcgb and look at some of Adam's posts on the subject it makes sense.
Good luck with it

[Doom Patrol]

Adam is a mine of information on this sort of thing and what I've learnt has shaped my thinking on the subject. As I understand it an expansion pipe will push the power too high up the rev range and with a tall gearbox your engine will never develop the revs to utilise the power fully. That's why you are struggling in fourth gear basically. You need to bring that power down into the lower rev range.

[smoore-gt225]

hi its all sorted put the 15 back on an its flying well its flying for a 175
cheers steve