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Have Allstate VNA piston ported 125.

Had trouble starting, low compression around 89 PSI. Got new rings checked old ring gap was huge, put new rings in and ring gap right at correct gap. Also did a full engine rebuild while I had the motor out. Did airleak test, passed.

Problem is it is still hard to start. Will start with starting spray and run fine . Once running, can hit the kill switch and kick again and starts up. Thoughts I have.
1. Compression even after new rings is at 90-91 PSI (I can't figure out how this can be other than maybe a leak at the head? However it passed my leakdown?)
2. Is it stator related? Weak spark, spark is there and visible.
- This is the internal ignition coil. How to test what it is putting out?
- Replaced condensor

Just spitballing and need some people to bounce it off of what could be causing the difficult to start issue.
Do I tackle stator first?
But what is causing my low compression?

Cheers for any response.
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parallelogramerist
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How hard are you kicking over the lever? You can do it if you put your foot into it.

How many times are you kicking over the lever? Keep kicking it over until the gauge reading quits going up.

Preform a "wet test". Squirt a little bit of oil down the spark plug hole, then perform another compression test. If the compression is higher, that means it's the rings (or a severely scored cylinder wall).
@subetherbass avatar
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1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
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What is your SQUISH CLEARANCE MEASUREMENT.
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SubEtherBASS wrote:
What is your SQUISH CLEARANCE MEASUREMENT.
I have not measured this. I will do some searching on the best way. It is a bone stock 125 Piston Ported. Used the piston in it as it was in great shape and cylinder was nice and clean.

To answer WhoDats
I am a 215lb, 6.3 dude kicking will all my might. I usually kick over about 6-8 times until the guage stops moving, with the throttle open.
Will try the wet test as well. I just did it with the throttle open and the fuel on.
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rfman81 wrote:
I have not measured this. I will do some searching on the best way. It is a bone stock 125 Piston Ported. Used the piston in it as it was in great shape and cylinder was nice and clean.

To answer WhoDats
I am a 215lb, 6.3 dude kicking will all my might. I usually kick over about 6-8 times until the guage stops moving, with the throttle open.
Will try the wet test as well. I just did it with the throttle open and the fuel on.
i build these engines all the time; one of my favorites. first thing that comes to mind is the engine runs off a true choke, unlike the SI carbs that have a fuel enricher circuit. there is a flap on the carb box, when you pull the choke handle up, does the flap cover the entire hole??? have you tried starting the bike by removing the carb box and closing the venturi with your hand??
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even with new rings, if the ring gap is too big it could be you're just beyond the wear limit for the bore. maybe you need to go to next overbore to get good sealing. but with the real oldies like these, what is the expectation on compression? I'm guessing it's lower than newer engines.
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GickSpeed wrote:
i build these engines all the time; one of my favorites. first thing that comes to mind is the engine runs off a true choke, unlike the SI carbs that have a fuel enricher circuit. there is a flap on the carb box, when you pull the choke handle up, does the flap cover the entire hole??? have you tried starting the bike by removing the carb box and closing the venturi with your hand??
Thanks for responding Gick I was hoping for some of your sage advice.
So I have fiddled with the chock to get it fully cover but not tried closing it with my hand. Will try that and see if it starts then.
What is the actual compression psi for these older Vespas?
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rfman81 wrote:
Thanks for responding Gick I was hoping for some of your sage advice.
So I have fiddled with the chock to get it fully cover but not tried closing it with my hand. Will try that and see if it starts then.
What is the actual compression psi for these older Vespas?
90-95 on a fresh bore for the VNA engine.
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Ah see, ask an expert before assuming. Your compression is good, by the sounds of it.
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Chap at my scooter shop told me barrels wear kind of banana shape, so it becomes impossible to get any sort of compression. I had exactly Same problem on my lammy, and still have. I have bought a new barrel and piston as I was 4th oversize anyway.
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L4NFF wrote:
Chap at my scooter shop told me barrels wear kind of banana shape, so it becomes impossible to get any sort of compression. I had exactly Same problem on my lammy, and still have. I have bought a new barrel and piston as I was 4th oversize anyway.
?

It's a deflector piston with lots of CC's in the combustion chamber. nothing "banana" about it.
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What I meant was he said the barrel wears unevenly, if you check your rings towards the top or bottom of the barrel they could have a different gap than if checked in the middle of the barrel. So if you set your ring gap at the top of the barrel you may have a larger ring gap at the middle of the stroke so not getting adequate compression.
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