Modern Vespa

I can't remember, I do remember needing to go up in jet size, I ran out of bigger main jets, to use with a 140 AC, went to a 120 AC, and started jetting routine over again. Having to go up that many sizes told me I was getting more air at WOT, I was already running no air filter. This was all done pre P200 and pre GSF dyno for me.

If you look at a Mikuni TMX30 carburetor or PWK carburetor as an example they have a bell mouth built into them.

Save waiting, get a spare AC, solder up the hole, drill it out to 1.2mm.
Then you can start working down the main jet.
As you reduce the size. The correct main jet is a size smaller than the one that revs out to max. There will still be an element of very minor splutter when correct. This is how 2 strokes work.

I have a 120 air corrector arriving soon with some more main jets. Will the 120 give less air than the 140 that is currently fitted? I will also order the other idle jet that you mentioned.I will fit all these new jets and see how it goes. If I don't get anywhere, then it's off to get looked at. I want a pressure test doing anyway just to rule out an air leak.

Do you have a number I can speak to you on? Be quicker than typing.

The air corrector works like needle taper does on a big boys carb.

Same as my one
https://www.buzzsolomoto.co.uk/scooters-parts.php/view/carb-bellmouth-vortex-kit-pinasco/id/004813

I have a 26/26 carb on my O tuned 200 and I think you should get the same. Swap yours to a P200 autolube pump and no need to add any oil to the petrol.

So the engine ran a ton better with the 130 (roughly) main jet in there. Spark plug was a bit white for my liking. So I upjetted it to 150 (roughly). Ran like a bag of shite as I thought it would. Both runs with filter off but cover on. I dont have any 1.4mm drill bits so I am stuck for now. I reckon this is going to take a 140 main or slightly lower. With the 150, the bike spluttered but sometimes picked up and revved out at around 6000-6500 rpm. Spark plug was black, as expected.

I will order some mains ranging from 136 - 142 and go from there. If this works I will just stick with the 20/20 carb for now and update to a 24/24 later. I dont want the absolute best from this engine as I will probably break it again. A nice and safe level will do. It ran so much better with that 130 in. Didnt pop and bang at all when lifting off the revs at 50-70 throttle. Still pops a bit at lower revs but it's always done that.

Can somebody confirm that a 130 main jet has a 1.3mm hole. 140 has a 1.4mm hole etc etc.

The answer is maybe, read this article. I picked SIP jets and bought a few kits so I would have them for tuning.

https://www.sip-scootershop.com/en/product/jetting-kit-dell-orto-105-128_40260000

Thank you.

How the hell did this bike run for so long before it seized last time. The new kit I fitted is slightly different to the old one that was on the bike when I got it. The old one had a 1.5mm spacer below the barrel. The head is the same (Pinasco 3703) with the 4 extra allan bolts. Maybe this RX barrel is different as it did not require a spacer. If the spacer was used, the ports were not lined up and the squish was over 3mm. Weird. Still surprising it ran for so long on a 105 main jet.

This may be part of the issue No? He's leaning out his mix into an already leaned out idle circuit isn't he?

The instructions say use 1% extra in the tank during run in for the first 500 miles. The idle circuit is no longer lean. It runs with mixture screw fully closed.

Don't buy any more jets until you change the air corrector to 120. It will all change for the better again and run smaller jets.
Now it's running a little better, im sure it's quite a bit faster already.

Yes it feels so much better with the 130 jet in there. Much more power. Sounds much better too. I will fit the 120 corrector and update on completion. I have ordered some bigger jets anyway, just in case. Shall I order that 55-160 idle also?

Yes, 55/160 will be better than now.

Hopefully once I have fitted the new 120 AC, 55-160 Idle and then found the correct main jet, I can then work on the idle. If I can't set it after all that then there must be another issue. Fingers crossed it all goes to plan so I can actually get out and ride this thing.

So I have fitted the 55-160 idle, BE5 Tube (always been there) and the 120 air corrector. Tried it with a 145 main and far too rich. Would not accelerate under load and very smokey. Dropped to a 140 and sputtering was less but still there at low revs as I wound it on and did not rev very high. Same with 138 and 135. The 135 was good but flat spots with spluttering when wound on. Settled on a 132 main which is still a bit rich but I don't have a 130 - 122. Next one down I have is a 120. That just did not feel right and the revs hung a bit and popped a lot when deaccelarating.

So I am almost there. It is rideable on the 132 but a bit rich. I think I will run it in on this jet and then get it dynoed to narrow down further the main jet required.

Any further advice or does it all sound good?

What max revs should I be aiming for under load? I want to stay on the safe side. It has the ReedSpeed CDI so unrestricted.

Thanks.

Mark.

Good progress. What happened to the new BE4? The BE5 is a little lean usually and will affect lower rpm.

How's the idle now?

I never had the BE4. Always been a BE5 which I thought was rich. The idle has always been ok but it's a lot better now. The mixture screw now actually has an effect on the revs. I have set this to 2.5 turns out. Is it worth buying the BE4?

Thanks.

Be5 is leaner than be4:
Lets talk atomizers

I will buy and fit the BE4. This is leaner top end though. Will that matter?

I'm not quite sure what you are asking

Will it make it much leaner at high revs?

I think the debate was never resolved with full agreement in any threads I've seen on how it affects WOT behavior. You'll probably not feel much difference. I think of it more as a tool to tweak the midrange and low-mid transition, where the idle jet and main jet are kind of pegging each end of the spectrum. IMO (others may disagree), I would use the main to define wot behavior, then change the stack if unhappy with something intermediate, and confirm you're still happy with the main mixture after doing so (because the two work together to affect the end result)

Hi.

Thank you for your advice. BE4 ordered. I will fit it and give it a go.

Good luck! Will be interested to see how you like it compared to the 5 with your setup

To be honest, I am not sure what to expect. How different can it be? I am curious now.

It helps to have many varieties of brass bits, then you can fail in many more entertaining ways. Ask me how I know .

I am slowly building up my collection. You never know.

You need the BE4. With the AC120 any atomiser will work (start, ride, feel not terrible) but only the BE4 is rich enough to go fast and do no damage. Rolling off the throttle at 70mph on a 190 kit needs a BE4.

Pilot sorted. Main jet not lean. Must be feeling better already. Main will end up 128 by the sounds of it.

You definitely know your stuff. Best forum I have been on for advice. The BE4 is ordered and also the main jets from 122 - 130. I am looking forward to running it in and getting it on the dyno to fine tune. The help given to me on this forum has been second to none. I really appreciate it.

It feels so much better. The pick up and sound are immense. A real pleasure to ride.

Bit of a strange question. At the base of the cylinder on the flywheel side, if I spray a little carb cleaner in that area, the engine stops. Could this be a leak or is the carb spray affecting the stator and spark? I found this out by accident when trying to clean that area of the bike a little. I used a standard gasket and used that blue sealant stuff either side of the gasket.

Thanks.

Serious About Air Leaks

only way to know is to pressure test it

I have no means of pressure testing it. I don't have the equipment to do so. I have a compression tester for the head and that is it.

I would have the carb box cover on and ruhber boot between the box and frame connected before worrying - you want to make sure you aren't getting mixed signals due to the fumes getting sucked in "the normal way" via the carb. If the carb intake is isolated well and you spray the base there and it still sputters out... I can't really think of another explanation besides an air leak.

You're gonna have to redo all the jetting if you've been building around a big leak like that 😉

What a pain in the arse but interesting. I am going to take the engine to be pressure tested and go from there. I don't want to ruin this new cylinder kit. Although I have done about 500 miles on it so far with no issues. Lol. The carb cover and rubber boot have always been on. It spits a bit of fuel out of the intake so without the air filter on gathers in the box and leaks down to the floor. Should it spit fuel out of the carb?

I believe there is something wrong with the bike. I don't have the time or some of the tools to fix it. I am taking the engine to a specialist tomorrow who will take a look at it for me. Finspeed scooters. Good reviews and a good lad. Hopefully he can tell me what is wrong with it and what needs doing. He has already mentioned fitting a 24mm carb and getting rid of the autolube. See how it goes.

To keep the argument balanced, don't get a 24/24 and don't get rid of the autolube. Get a 26/26 and a PX200 autolube pump. This is the best solution if not having a reed block. Anything less is time and money wasted. And most importantly will be slower and what's the point in that.

This was my plan with an 187 lml kit. 26/26 auto lube carb. You saying it's necessary to swap out the oiler gear for a p200 oiler gear when you go to this larger carb? Figured it was no difference.

The pump gears are different between models. There is a write up somewhere on here.
I just did a malossi for a mate and put this set up on it. It's a 177 now but will be 187 on the next rebuild.
And of course have the same setup of 26/26 and 200 autolube on my O tune for the last 8 years, all on the same piston and all wide open for miles.