175 upgrade from 125 with running problems - HELP Please

[harps2]

Hi
As part of my first ever LI 125 project I decided to upgrade to 175 barrel/piston/head but still have the original 18 carb, std exhaust etc etc - I have upgraded main jet to 125 - scooter starts first kick and runs fine on idle but pull away is very sluggish and seems starved of fuel - excessive throttle causes it to die so just using very gradual throttle appears better - not really had chance to take it out of estate yet as not MOT or registered - any advice - bigger jet required ? - don't really want to change carb unless absolutely necessary.

Appreciate any advice/comments - thanks Alan

[CHRIS in MARGATE]

It should run fine.
Try: Air filter hose off
Air filter hose on with filter removed.
Possibly restricted air box.

Increase pilot jet.
Decrease main jet to 108

Consider looking for air leak around head and base gaskets with simple air leak test.

Did it run ok as a 125 ?
Exhaust blocked ?

[harps2]

It should run fine.
Try: Air filter hose off
Air filter hose on with filter removed.
Possibly restricted air box.

Increase pilot jet.
Decrease main jet to 108

Consider looking for air leak around head and base gaskets with simple air leak test.

Did it run ok as a 125 ?
Exhaust blocked ?

Hi Chris - will give those suggestions a go - pilot jet - which size do you recomend, and how about atomiser? - never ran as 125 for over 15 years I believe, exhaust is clear - revs OK at standstill just doesnt seem to want to when under load.

Thanks

Alan

[drivera]

As Chris says drop the main to 108 ish , 125 is far too big for an 18mm carb on a 175 , try that then see how she runs

[Warkton Tornado No.1]

I feel that both drivera & CHRIS in MARGATE are both correct in their advice.

Logic dictates that the SH1-18 will need different components to suit the conversion.

As a 125 it should have had:

Slide: 5899-1
Main jet: 99

Whereas the SH1-20 fitted to a 175 would utilise:

Slide: 5899-2
Main jet: 106


To my way of thinking you may need the 5899-2 slide but your main shouldn’t need to be too much bigger than 106.

I hope that helps.

[harps2]

Thanks everybody - will try all things suggested next week and let you know how i get on

Cheers

Alan

[Fireman Ash]

I have a 125 dl to 175 but with a dellorto SH/20mm, got it running sweet with a standard flat end clubman

[johnnyXS]

It should run fine.


Decrease main jet to 108

Consider looking for air leak around head and base gaskets with simple air leak test.

?

very good advice Chris.
I inadvertently fitted the wrong carb with a 118 main jet the last time I worked on my S3 150cc and wondered why it ran like a pig first time out.it barely managed 45mph and performance and pickup was as flat as a pancake.

One look at the spark plug told me something was badly amiss with the mixture and changing the main jet back to a 106 was like night and day. My 150 now cruises at an indicated 55mph with great acceleration and all round performance again.

An 18mm carb venturi is a little restrictive for a 175cc engine .If you are still using the original 150 inlet, any benefit you gain with the increase from 125 to 175 will be severely restricted by the original inlet . If you haven't already done so fit a 175 inlet manifold .

If you are still using the original 5889-1 Atomiser with the tiny 1.50mm dia bore ,You need to fit a 5889-2 Atomiser which has the larger 1.75mm bore.
You will probably need to experiment a little with the main jet as your setup is a little unusual but 108 would be a good starting point. let your spark plug colour guide you.

To get the most return on your 175cc engine upgrade I would advise you consider fitting a 22mm carb like a jetex with 50 pilot, 5889-2 Atomiser and 108 Main jet .A clubman type exhaust which together with the 175 inlet will give you better flow through your engine and a huge increase in power output

[harps2]

A great big thanks to all who offered the advice

Slide: 5899-2
Main jet: 105
Pilot 50

Running a treat so much so I took it for MOT and it passed today - thanks again for all the advice - there is a lot of great information on this site for sure! just need to get registration now.

Alan

[johnnyXS]

thats great news Alan .
Hope to see some pics sometime.

[Fireman Ash]

Nice one mate, it took a while to get mine just right but worth the pain, now enjoy riding it, that's what matters most

[CHRIS in MARGATE]

And a huge thanks to yourself for taking the time to write a reply because that will almost certainly help somebody else.
Now enjoy the summer.