Modern Vespa

I know my timing is set at 17 degrees as I strobed it. The smaller pilot jet must also be closer to what is best as it starts with less kicks. Choke used to start cold.

Yeah this test would help

I will do this on Fri and get back to you. I have my idle set to 1500 rpm. Its very steady and doesn't change much.

Thanks.

1500 rpm is a little high for stock ignition.

jack, where's your video where you have idle at 800rpm?

Someone needs to see it done… lol

Lowest it will rev comfortably is 1000 rpm but then will quickly stall when put into gear. I can manage 1350 minimum.

3 kicks stone cold is not unusual but hot should start on half a kick. Just a quick stab on the kickstart.

From your pilot jet experiment its pretty clear that it was (and still is) way too rich.

Next time you're out on it. Put in a bigger pilot (68/160 is fine. Not forever, just for the test). Keeping the AC120/BE4, drop the main jet one at a time until its too lean. This is when you open the throttle and it tries to cut out at WOT. When in this condition don't ride it like a knob, it will blow up. This will tell you where the low end is. I think you'll be surprised.

It always starts 1st kick when warm so that's good. I shall do your test at the weekend. So when it's too lean, I will know? It will be obvious at WOT? I don't want to damage it as you said.

Agreed. Compression is around 165 psi when cold and a bit less once engine is warm.

Yeah if it stalls when you pull the clutch… the idle isn't set right…

The aim is to get super smooth running with 2.5 turns… it should be only a quarter turn either way to compensate for slight differences in the hole size (wear, machining etc).

You're not suppose to set it to compensate for pilot jet sizes…

I think it's something like 4 turns out… the screw actually has no affect on the circuit.

And like most people, don't use the idle screw to up the rpm to compensate for wrong idle settings.

Compression readings for a Vespa doesn't mean much… you either have good compression (fresh engine) or you dont…

You would be measuring piston ring gap size to make sure the piston is sealing properly if the bike starts to bog

If you ride along steady at about 3000rpm in 2nd or 3rd. Quickly open to WOT. When too lean it will just bog. The correct main jet is somewhere between this lean number and 138 (assuming all jets are from the same box set).

One thing about closing the mixture screw to zero and cutting out. This doesn't work. This only reliably happens on air screw carbs.

Nice. I will use the same box of BGM. 118 up to 138 in 2 or 3 steps. Thanks for that. I am now clear on the process.

I will report my findings on Fri/Sat. Another exciting weekend ahead. Lol.

Yeah I don't think it's a good test to turn the fuel mix screw to make it cut out.

Although for me it's always run bad when you're no where near benchmark settings.

Whilst I am titting around this weekend, I will send you a pic of my vortex fitted and the marks on the underside of the lid where its touching. Could a worn box gasket be causing this? Gasket too flat?

I will go from 138 main to 128 to start with. I know the 132 does not bog or hesitate when WOT is quickly activated. Might even start 124 on the main. I will fit the 68/160 idle first before doing anything. Once I find the lean main jet, what does this prove and what next?

What's the benefit of the vortex ? A lot of posts I've read on here imply they are nothing but trouble . Why can't a standard filter and bellows to frame be sufficient with correct jetting for your kit? How much more HP does a vortex generate to be worth the faffing about?

I don't think I will fit the vortex. I don't run any air filter on the carb as the engine won't run with one fitted.

As you are having so much aggro with it why not stick a 24si on it and get the base jetting from the guys on here? They did me right sorting mine out and you are eliminating a whole load of mysteries going back to basics . Then you can follow chandlermans jetting guide on here and you can't go wrong really, you will at least get a running bullpark jetting set up then just small adjustment . You might have some air leak in which you will never be able to iron out with jetting.

I have a 24/24 fitted. The lads on here have helped me from the beginning. The bike runs fine but needs a little more carb work. I have done 1000 miles since the rebuild and dyno and all is well. No major issues.

Where are the pictures of your vortex?

I am not home until tomorrow so will send some pics then.

More rookie blab!

You're going to have a hard time with that 68/160 without the venturi. CHT dropping with the 55-60/160 coasting off throttle, no popping, plug looks not dangerous -- seems good from here. Pretty sure the 68/160 is made for use with a venturi.

Judging by your videos and "if I were you" I'd keep that venturi on the shelf until next season. For riders like you and I who just want to ride, the gain vs jetting complications aren't worth it, for the season at least. Mine is still on the shelf and there is no season here.

Don't tell Jack, but trying to find lean sounds a bit nuts for someone who rides all-balls like you. Dial in your mixture screw as best you can on the road with the 60/160, then dial back your mj's. If you drilled your own bowl passage, you may want to confirm that passage is actually through at some point.

New total guess as to why the lurch:
Too big mj, leading to not-atomized-enough fuel burning off throttle.

BTW thanks again for the video's. Went through covid and couldn't ride when you posted.

Hello there.

I checked the hole into the bore by shining a torch down whilst sticking the 2.5mm drill bit through. I could clearly see the drill bit at the bottom where the main jet resides. I will still try what Jack has suggested but only on a small bit of flat road and only for tiny bursts to find the lean point. Once I hit this point with the biggest main jet that causes this lean hesitation, I am unsure what to do next.

I will start with a 128, 10 sizes down from the same manufacturer and go from there. The vitext will be staying off but I will fit and post some photos as it does not quite fit and contacts the air box cover when fitted.

I am glad you like the videos. I will upload some more once I get the time.

Thanks for the advice. It's always welcome.

So I fitted a 118 main jet as its the smallest one I could find. Does not hesitate when riding. Engine revs up to 11000 revs. Didn't feel much different to ride. Maybe a bit more snappy. What now? The bike sounded very different with the 118 main in. Like a hollow, quieter sound. The 138 sounds more crisp. I have just rode back from my test area with a 60/160 fitted @ 2.5 turns and 138 main. It felt much better with no lurching. With both the 118 and 128 fitted, there was a lot more popping mid range. Sounded unsettled.

I will until it cools down and see how that 60/160 is for kicking it off. The 55/160 starts cold after three kicks. There is slight popping on the run down below 3700 rpm. Strangely with the 68/160 and 128 main jet fitted, there was no popping at all. Weird.

And what was learnt. Even 118MJ is not lean enough to be too lean. And probably wouldn't even seize up there....for a while. Would be somewhere under 110MJ before the classic bog lean symptoms started.

138MJ is too big. Keeping AC120/BE4 and 160/160 put in the main jet that doesn't splutter at 3000rpm and see what that is and sounds like.

0 Yes, I am very surprised, but you did call it. What idle jet should I leave in, you wrote 160/160. Did you mean 60/160? Thanks.5

60/160 should do.
When you set the mixture screw. Fully hot ridden round the bypass, engine. 4 turns out mixture screw. 1000rpm tickover (and tickover screw mostly in to achieve this). Slowly turn inthe mixture until it speeds up and stop there. 2.5 turns. Tickover down to 800 rpm.

When way over rich it wont be as quick and will use loads of fuel just going slow.

I am off out now for a ride to my testing spot. I will report back on completion.

Thanks again.

Right. The 60/160 and 125 main are not good. After a decent WOT run, the engine continued to rev after I went back to idle. Revs took a while to come down. The only way I can get it to tick over at 1000 revs minimum is with a 68/160 and 132 main jet. I bet it takes ages to start from cold with the 68/160 idle jet.

It's all getting very confusing. Must be the mentioned 'overlap' of the idle and main jet. 68/160 seems huge. I think it's best for me to leave it where it was 55/160 and 138 as it ran ok with no major issues. I just can't seem to dial it in.

Update. Had to take out the 68 as it takes about 8 kicks to start. I have put a 62 in and now it starts after 2 kicks cold. Main jet is 130. I could probably fit a smaller main but it seems to run OK.

Jetting is more normal now. See how this goes. The hanging revs just sound like an air leak.

Defo no Air leaks. Pressure test was fine only last week. I will see how it goes.

Thanks again mate. Much appreciated.

How did your CHT respond on that ride?

Back-out the mixture screw a 1/2 turn and see how it returns next time out.
Again, there is no turns-out rule on Spaco carbs! You have to take it out and adjust it on the road.

BTW all three kitted bikes in my garage will die at 1000 idle. Maybe not at first, but somewhere during a hiccup they will. I set mine at 1150 or so to prevent stalling in the middle of traffic, which can be very dangerous here.

Hi Roody76 I feel your pain when it comes to carb jetting we both have Pinasco 190's. It looks like the case transfer ports are slightly larger on yours with center plug head and a more skeletal piston. Not sure if you modified the intake mine has 187 degrees.

Don't want to step on anybody's toe's you've already received solid advice from the resident tuners. I'll share this as my experience maybe you can get some insight. I had a heck of a time figuring out the main and pilot because the middle was too rich. After I made that discovery the main and pilot became easier. I would try a BE3 atomizer as a 'test'.

I'm running a 48/100 pilot. A T5 for example runs a 50/100. I would start with a 55/160 pilot and 128 main jet. If this is more rideable work the main jet up/down size by size. If this is worse forget everything I said.

Look into the SIP T5 air filter they are free flowing maintain the health of the rotary pad, piston and have a small venturi built in.

https://www.sip-scootershop.com/en/product/air-filter-sip-si-2424g_40200000

The CHT always rises high when in 4th gear and cruising off WOT. Rises to about 170 C. This only happens in 4th gear because I never ride WOT. I don't need to go that fast. When cruiing about the roads, te,ps get to around the mid 130s. It ran hotter with the 125 main and did not respond at all well when I lifted off from a 5 second WOT run. The engine kept revving high for a good few seconds. I set my idle quite high at 1400 rpm.

Is the BE3 leaner than the BE4? The bike runs fine. No spluttering when accelerating. Only time it splutters is when I am riding it and then apply very slight throttle, and I mean very slight. Twist a bit more and the 4 stroking stops. I like the way it rides.

I just bolted the kit on. I had to build up an area with JB Weld on the flywheel side and use a home made paper gasket so I could seal the transfer port. The carb and intake seemed to match so no work was done on widening that. I think the previous owner had this done. I have the Pinasco air filter under the seat. I have a 60/160 and 132 main. Runs ok.

So should I try a 55/160 with 120/BE3/132 for a start? When I go any richer than a 60/160, it takes a lot of kicks to start the bike, like sometimes 8 or 9. With a 60, 58 and 55/160, it starts after 2 or 3. Would this indicate the bigger jets are to rich?

Chandlermans atomiser chart

Jack suggested the 120/BE4 combo is a must. BE3 is very lean compared to BE4. Maybe the BE3 would be far too lean for my bike. I have a BE5?

Nope, a lot of Malossi 210 kits end up using BE3.

all depends on the air corrector you end up using…

If the case transfers are not matched seems unlikely the rotary valve has been touched leaving any change on the new crank. Based on that there probably isn't the time or space even with the large cylinder transfers to need main jets larger than 120's.

"it splutters is when I am riding it and then apply very slight throttle, and I mean very slight. Twist a bit more and the 4 stroking stops"

This is why I suggested testing the BE3. If you are having trouble discerning pro's and con's of 118 vs 138 MJ you might not notice if a BE5 is better or worse than a BE4.

I've never heard of the under seat Pinasco filter until reading about it here and know of no one using one. LML had an under seat filter most owners removed upon delivery. Seems like the Pinasco filter may squelch air flow easy enough to remove for tuning and re-install later if necessary.

I've just changed from a 140 be5 124 to a be4 122 and seriously ironed out my mid range vibration and this sort of dry running feeling . It's a bit rich on pilot now , so a bit of pilot mixing adjust, but finally got my plug that lovely dark chocolate colour rather than light sandy coffee which worries me as that's heading lean imo. I'm not messing about now , just going to get my clutch up cog and like it.