Avanti gearing advice

[coaster]

Hi, just in the process of rebuilding my reed valved Avanti which has been running with 20 x 47 sprockets and Li125 Special gears (4.7) It did run really well and felt like it would pull higher. The rebuild includes a Grand Tourisimo 60/110 crank which I believe will add a little to the torque so was thinking of gearing for around 4.4:1 ratio. I will be buying an AF Road clutch and also have an Li150 (Italian) gearbox I could use.

Just wondering what others thoughts on gearing choices are before ordering. I note the AF clutches come in 46, 47 and 48 tooth so numerous ways of getting the top ration but what about the gaps between the gears?

Any thoughts gratefully received

[MickYork]

The exhaust will be a major factor, that needs to be decided before picking the gearbox.......or do you pick an exhaust to match the gearbox

[Adam_Winstone]

^...wot he said.

[coaster]

Oops, I meant to put that in the post

Exhaust id a Franspeed Super Tourer
Carb is a 30 PHBH mounted on a ScootRs Atomic Ultimate reed inlet which uses the Yam reed block.

[Adam_Winstone]

TBH my experience of the Supertourers is that they like to rev-on and I think that you may find 4.4 too long. I run 4.8 on mine, piston port with advance/retard ignition, and it pulls very nicely through the range and is perfectly happy high speed touring. 4.6:1 might be OK with the reed and stroke but I think that you'll lose more than you gain at 4.4

Adam

[bike grim]

For a few months last year I ran a Supertourer on a tuned TS1 230 (60/107) at 4.45 (19/46+pacemaker) when it was on the pipe it’s was brilliant but you had to rev it. When it was sat at group riding speeds so around 55- 65 mph I was forever downshifting to 3rd to keep in the power. No roll on acceleration to speak of in top gear and hills or headwinds were a 3rd gear affair. It needed around 4.8 I reckon but never tested it.

However, I have also used the same pipe on a torquey 283 Pro Porting kit for over 11000 miles and it pulled 4.12 (19/46 +LI150) no problem at all in all gears but did have a rich point at 4300- 4600 rpm that I could never jet out.

I don’t know if that is helpful or not but I’ve typed it now, haha

[coaster]

Thanks for the feedback so far, any thoughts about Li150 versus 125 Special gear sets?

[MickYork]

My original Avanti set up was 4.6 with a gp box and a Ron Moss clubman (possibly the last one ever made )

It pulled fine with that set up and i changed to a Franspeed Tourer (not the Super) and it also handled 4.6 ok although a few more gear changes were required with hills.

I never had the reed block or longer crank/stroke which would give better low down grunt so you may be in with a chance.

[holty]

if i remember correctly the 125 special box is the same in top as a gp200, but first is so short you might as well set off in 2nd, ive not used the 150 box myself, but if your hoping to run as low geared as possible a close ratio box will help, ive got a af close ratio in my rb250 and its spot on, your sprocket choice will be dependant on how much pulling power you have and your size and weight and riding style, im guessing the new af5 speed will be even better, close ratios do work well with expansions as well.

[corrado]

I'm in a similar situation with my Muggy 225 with Atomic reed and ADS3 exhaust. Pulls 4.7 easily, Li150 box with 17 x 47 but 18 x 47 is 4.44 which might be a bit too tall. 17 x 46 is 4.6 but as I run an LTH clutch I'm not about the change the clutch in a hurry, though I am tempted by the new LTH alloy crownwheel in 46.

[coaster]

if i remember correctly the 125 special box is the same in top as a gp200, but first is so short you might as well set off in 2nd,.

Yes, its exactly the same as an Italian GP200. I'm thinking I might use the Li 150 box with 18 47 which will give me the same as Corrado, 4.7 is a slight improvement on the current 4.8