1st gear lacks power

[Snails]

Finally I have my GP back on the road and MOT'ed
Its been off the road for a while as I changed the engine. Replacing the std one with a new block fitted with a SR175. The MOT run was the first drive of substance that I'd under taken and what I noticed was that I was really having to quickly open the throttle quite far in first gear to get enough power to accelerate properly. It seems ok in other gears but I am still running in so was not trying to rag it anyway

I've checked that the throttle cable is adjusted properly so that its not me having to wind the throttle open before the slide moves.

Full spec

25 mm dellorto
pilot 45, starter 60 mail 122 (on the big side I know but should not affect it until I open the throttle fully)
Af Reverse cone clubman (sick of it already)
Gearing is Indian gp125 with stretched chain
Tuning I did myself but was nothing drastic.

Now it could just be me, my vega has a quick action throttle and the only other scoot I've really ridden in the last 10 years is this GP in std form but I dont remember it needing to be like this. maybe some scoots just need you to do this once you start messing around with them in terms of changing them from std? Thoughts please

[HxPaul]

Some "sr" kits have the exhaust port cut in the wrong place,some have the inlet ports cut in the wrong place,some have both and some are ok.Its the luck of the draw with things made in India.

[Snails]

This is a real SR kit if that's any better. Bought from Scooter Restorations.
Not an easy one for me to check or do anything about but I will bear that in mind.

[Snails]

Well the barrel was. The piston and head I purchased separately. From memory the head is just std 175 and this piston an Asseo or is it Asso..not sure where that leaves me in respect to the profile..

[Scooterdude]

I'd do a compression test followed by checking your squish, and as you've had your piston from a different source I'd be inclined to check piston and ring gap, this would be a good starting point.

[Snails]

Thanks. I did check the squish when I built it. I cant remember the figure off the top of my head but it was at the top end of the advised range if I remember rightly. I checked the ring gap when I built it and it was fine.

I recently bought a compression tester and it was on the low side. I think a qtr of what I was told to expect (25 bar?), however I've not followed this up as it felt fine when kicking over - certainly not a qtr of what I would expect so I'd left thinking it might be me misreading it. I will double check that at the weekend.

What are the possible reasons for loss of compression other than broken rings please?

[Scooterdude]

25 bar is 360 odd psi!! If your running that no wonder you have no power as your head has just been blown off!!

You want to be looking at a reading of between 125and 145 psi, I've found (through my oun misfortunes) that if it drops to 75 psi it will still run and sound ok but will have less power, if it drops below 75 psi it probably won't start.

[Chris in Margate]

Recheck your compression first. Mine is 105 psi and perfect. Engine on bench is 110 psi. Your figure is very incorrect.

[holty]

i would suspect you have some set up issues with your carb, your idle jet maybe to small, or needle in the wrong position, what clip is your needle on ?

[Snails]

Ok I mean s5 psi not bar. It still runs, which is why I was thinking it was misreading somehow. pics and detailed description to follow - possibly next week.

I did think my engine was running lean so I have the needle (d29) with the clip on the richest I could set it.I've changed my opinion on whether its running lean, think i was just miss reading the colour of the plug. I will adjust the clip and see if it helps.