Scooterotica

To follow on from a thread a couple of weeks back..

Replaced the Simonini with Revolver on my scoot and, while it was like hot shite off a shovel up to third gear and about 50mph it just died when changing up to 4th and wouldn't go past 60.

So, been trying some different main jets. Started with a 130 (was 124) and it did the same. Went down to a 128 and it did the same. Got annoyed. Went for another ride and discovered that if i didn't rag it up through the gears it would happily chug up to 70. It's rideable as it is but any clues as to how solve this?? The plug looks ok i think, light brownish.

T5 4th gear?

SF

+1 T5 4th gear

I forgot to say it actually started slowing down too the more I opened the throttle, almost like it was missing, would changing the gearing make a difference to that?

fuel starvation maybe ,or just dirt blocking main jet .

I got a scorpion on mine and its just the same ,will do 60 odd in third and then just dies in 4th

Blistered Baz wrote:Went for another ride and discovered that if i didn't rag it up through the gears it would happily chug up to 70. It's rideable as it is but any clues as to how solve this?? The plug looks ok i think, light brownish.

Blistered Baz wrote:I forgot to say it actually started slowing down too the more I opened the throttle, almost like it was missing

Based on the above it could well be fuel starvation, as suggested by Sean. When your ragging it the float bowl is getting emptied out quicker than its being topped up. OK when initially accelerating when the bowl is full but by the time its got in its stride its not getting enough fuel. Throwing bigger jets at it won't work if it is fuel starvation.
Is it any better on a full tank? The added fuel load might push the fuel through to the carb more efficiently.

Things were probably not happening as quick with the simmo on.

Possible causes: Kinked fuel hose, blocked or restrictive fuel tap, blocked breather hole in fuel tank cap, low fuel level.

Possible cures. De-kink whats kinked, unblock whats blocked, fit a nice new shiny fast flow fuel tap.

SF

I' wouldn't adjust the jetting just yet: (stick with the 130 /128 on a standard carb)

1) Most likley over geared for the kit/pipe combo. Deploy T5 4th or 22 tooth clutch cog.

Is the inlet timing standard, or do you habve a race crank/worked inlet?

2) Adjust inlet timing/area if still standard

What is the cylinder head?

3) Check volume = compression ratio and squish. and optimise

4) Fine tune jetting

Spanish Fly wrote:

Blistered Baz wrote:Went for another ride and discovered that if i didn't rag it up through the gears it would happily chug up to 70. It's rideable as it is but any clues as to how solve this?? The plug looks ok i think, light brownish.

Blistered Baz wrote:I forgot to say it actually started slowing down too the more I opened the throttle, almost like it was missing

Based on the above it could well be fuel starvation, as suggested by Sean. When your ragging it the float bowl is getting emptied out quicker than its being topped up. OK when initially accelerating when the bowl is full but by the time its got in its stride its not getting enough fuel. Throwing bigger jets at it won't work if it is fuel starvation.
Is it any better on a full tank? The added fuel load might push the fuel through to the carb more efficiently.

Things were probably not happening as quick with the simmo on.

Possible causes: Kinked fuel hose, blocked or restrictive fuel tap, blocked breather hole in fuel tank cap, low fuel level.

Possible cures. De-kink whats kinked, unblock whats blocked, fit a nice new shiny fast flow fuel tap.

SF

Well, as it happens, the fuel tank was very low and my last run out yesterday was to go top it up. I didn't try the standing start again after that so i'm not sure if it had any affect on the problem. Might pop out today and give that one a shot. I think you're right on the jet, it made absolutely no difference but for safety I'm leaving the 28 fitted anyway. Failing that I'll have a run through the whole fuel system and see if I can find anything wrong, cheers!

Yanker wrote:I' wouldn't adjust the jetting just yet: (stick with the 130 /128 on a standard carb)

1) Most likley over geared for the kit/pipe combo. Deploy T5 4th or 22 tooth clutch cog.

Is the inlet timing standard, or do you habve a race crank/worked inlet?

2) Adjust inlet timing/area if still standard

What is the cylinder head?

3) Check volume = compression ratio and squish. and optimise

4) Fine tune jetting

I know very little of the history of the engine and actually what was done / fitted before I got to it. Apparently the polini kit was fitted and all set up by Taffspeed so it may have a few tweaks. It's very quick so I'm working on the assumption that it's a good job. Honest answer though is that I really don't know and won't until I pull the engine apart, which is probably about due anyway as I've had it for about 5 years now and done absolutely nowt with it other than ride it. I've got a Lammy too and that's where I spend most of my garage time, the vespa was supposed to be a reliable rally scoot! Which it was until I changed the exhaust.....