Modern Vespa

What rpm before it slowed? How far in was the idle screw? Still the #7 slide?

Do this again but start with the mixture screw 4 turns out and idle screw mostly in. If the starting point is rich enough the idle will be at 1200 and speed up from there.

I'll give that a try tonight. Feels like I'm getting pretty close.

With the mixture screw 4 turns out and the idle screw turned all the way in, it idles at about 3500 rpm.

Maybe I misunderstood the test. I would expect the idle to be really high with the idle screw turned in that much even if the mixture screw was turned way out.

How far out on the idle before the rpm reduced?

Trying to determine how lean the 40/120 is running. If the mix screw is correctly rich, the idle fully in should barely run without throttle.

A 50/100 jet is an easy on to buy, as it's stock T5. Try this one next. Even if this is too rich it will still be the safest one to ride on.

I ordered a 50/120 today. The idle screw was maybe out 1-1/2 - 2 turns to get a regular idle speed.

#7 slide, 4 turns mix, 2 turns idle, drilled filter; 50/120 might not be enough but every jet is one of the complete set. It's going to be a lot closer and will probably be ridable.

Hmmm…I will throw the 50/100 in on my next order.

Also gonna check for leaks at the carb base and exhaust flange.

One thing I have noticed during my testing is that when I get to a stop light, the idle comes almost all the way down, but the last few hundred rpm take longer. Not sure if it's just the difference between a stone cold engine and a luke warm engine. Anyway, it's worth a check.

Jets should be arriving tomorrow, so I will have another crack at it. My tank was running low when I did some of these tests, so I will have to take them with a grain of salt. Low enough that it cut out as soon as I started up a hill. Stupid.

I was watching a video from back in the fall when I first starting jetting. I noticed that low throttle was actually not that bad once it was warmed up. The first 1/8 is rough, but beyond that, it's fine. In fact, most of that ride is around 1/4 throttle. There are several times when I try to open the throttle more than 1/2 way and it just sags. Main was definitely too small. At the time, jets were 42/140, 160, be3, 112.

Ok, I tried the 50/120; 4 turns out on the mix, 2 turns out on the idle. Idled between 1100-1200 rpm and sounded like it wanted to stall, but kept chugging. Smokey…

Progress. Up the idle to about 1800. Then, turn the mixture screw in until the chugging stops and rpm speeds up. How many turns is that? If its above 2 turns, take it for a ride.

Great! Thought it was getting closer to rich enough when my eyes started stinging.

I guess getting the right idle jet is a lot like the main. Rich and work down. I'm guessing that after getting the right pilot jet, the atomizer is used to distribute the mixture between the idle and main circuits.

The ride will have to wait as freezing rain has covered everything with ice.

It's never so easy. This jet will be closer. I very much doubt it will be the final one. Check how many turns to run clean at 1800rpm and go from there.
Record the adjusting and I can hear how close it is?

Ok. Set the tick over to 1800rpm. Mix screw 4 turns out. At about 2 1/2 turns back in it started to speed up. Went for a short ride around the block with the idle set at about 1100 rpm.

Still getting that 4 stroking sound, but it seems to pull better at lower throttle. The transition to 1/2 throttle is less of a jolt.

Took the Stella out for a good ride. Had it up to 65 indicated and it still had more to go.

Pulled better at low throttle and found myself at times cruising at 1/4 throttle. I get intermittent spluttering at higher RPM's where I didn't before but mostly it pulls. I threw in a sound clip. Easier than explaining.

Sorry, I missed the part about recording. Will do.

Well, it's definitely rich. However, as it's pulling well and riding ok, it might seem like it but it's not way too rich, just slightly. Sounds almost like it's stone cold and needs a good warm up.

With the engine fully hot try the mixture screw adjustment again. Turn the screw from 4 turns until it revs fastest. How many turns? This will help with the next jet.

Edit: before doing all that. Redo the main jet at WOT. Probably too rich there now.

Thanks Jack221.

I was thinking the main jet might need to be smaller as it was alternating between spluttery and clear at higher rpm's. First time I guessed right.

I think I'm hearing the difference between the rich and lean splutter at low throttle. Rich is a deeper sound and it pulls.

Getting the engine really heat soaked has been difficult. I didn't even crack 200F yesterday and it was one of my longer rides.

The 50/100 jet wasn't in stock at Scooter Mercato, so still looking for it stateside. I now have: 45/120 and 45/140.

Sticking with this, as we seem to be getting closer. It's a methodical process and much better than playing jet roulette. I can see how it would be easy to go in circles.

65 mph was good fun until hypothermia began to set in.

Should I still order a 50/100?

After a leaner main goes in. See how you get on with the fully hot engine mixture screw adjustment. What turns that is, Will indicate the next jet.
As the jetting gets nearer two things happen, starts to get faster and only needs low throttle to cruise around normally.

Sounds good. I found the 50-100 and ordered it anyway. Good to have one in the war chest even as a point of comparison.

It's definitely getting faster, especially in the top end. 3rd will easily get to 50 and 60 is no sweat in 4th. This past fall, 4th wasn't doing too much. Gotta remember to turn on the gps.

It takes a while to get the jetting perfect but approximate, is how yours will be when this pilot is done. And approximate will be good enough speed and reliability if left there.
With high bhp and big carbs it really takes time. But for me that's the fun part, so I always like to have a jetting project to ride around.

Approximate is just fine. It would probably do better with a bigger carb, but the reed valve would need opening up. Timings and squish are kind of bland and the ports aren't matched, but it's all fine for this engine.

Anyone know how to free a stuck seat latch. It's not locked, I just can't free it from the Kaiser helmet bit. It's a P series seat. Thanks.

Went down to a 118 MJ and went for a ride. Revved cleanly at WOT in 2nd. Mixture screw speeds up idle at 2 1/2 -3 turns in (from 4 turns out). 60 mph is actually 52 on the GPS.

Seems to go well for what it is. Appears like the power tops out early, so might benefit from a further up gear.

When adjusting the mixture screw, you're not going in far enough. Should go in until it starts to sing. If at the last half turn it will sing anyway but mix screw a few turns out and revving highest and just clean when the idle is almost all the way in is what is needed.

When pulling away there is a rich splutter. This should not be there. After that it goes lean, meaning the jet is too small. Will need the 50/100 after all.

I hear you on the mixture screw. There is a point where the idle starts to speed up a little when turning it in. Turning in further and the speed really takes off. I guess that's the point you meant.

50/100 should arrive Monday.

This is my Make it Go 101 engine as well as my Learn to Ride (again) ride. Still not used to riding at 50+ mph but getting there. I ride mostly on mountainous back roads with spotty phone service, so getting home again is the priority.

Just to clear something up…

When adjusting the mixture screw.

When I turn it in from four turns out.

The point where the idle picks up significantly is what I'm looking for.
And it should be 2+ turns in from 4 out.

And that's where I set it and leave it for riding.

I think you also said that I would know the pilot jet is right when it idles at about 1200 rpm with the idle screw almost all the way in and the mixture screw out around 1.5 turns or less.

I have also noticed that it run better without the air filter, though I haven't tried it lately.

Can I run it like this with the cover on?

Thank you.

That's the only way to run it, IMO. If you're riding in really dusty conditions, you might want the filter, but for normal street riding, bellows-to-frame is plenty.

Thanks. Surprising how well it runs without it. I don't ride in a particularly dusty environment.

2 opinions to share.
1. On right track with making sure it's heat soaked before making decisions on jetting. Hard to be patient - but no way to really get it right without being fully warm.
2. I am a no filter guy also. It's probably not great for the rotary pad - but they just love to breath easy. ¯\_(ツ)_/¯

To each their own.

Yeah…Not even cracking 200F in these temps, but hoping to get it close enough that any changes will be small and I will know what direction to go in. This scooter is a reed valve Stella, so no rotary pad to damage and reeds are pretty cheap in comparison.

It will jet in with the filter on or off. It's not exactly filtering much anyway. If you take off the filter re do the main jet from splutter again. It will change.

The final pilot jet should leave the mixture screw at 2+ turns.
The pilot jet is worth trying if 4 turns out, needs all but a turn of the idle screw to hold 1200rpm.
Turn in the mixture screw until the rpm picks up and continue to fastest rpm, which will be fast, likely over 4000rpm.

Got it. Thanks.

The 50/100 arrived yesterday, so I'm giving it a try. It's much shorter than any of the other pilot jets I have so I'm not sure if it's the correct one.

Got it from scooter west: 50/100 SI carb for T5.

Ok, mixture screw 4 turns out. Idle screw out 1/2 a turn out I'm at 1180 rpm.

Went for a ride yesterday after getting the engine warmed up. It was 60*, so I couldn't resist. I will redo the mixture screw test today. Thinking I might go down 1 on the main jet. I had it up to today 57 mph gps and it felt comfortable.

Here is a better video of the mixture screw test. Idle screw turned all the way in and turning in the mixture screw from 4 turns out. The idle is not picks up after 3 1/2 turns in, so on the last half turn until completely closed.

The 50/100 you have is for a G carb, like on a T5. Should work similar to the E version if no air filter fitted.

Sounds like rich all round now. Go back to the 50/120 and adjust the mix screw better. The first 1/8 throttle relies on the mix screw.

At least it's going faster. Must be doing something right.

Thanks!

Yes, definitely.

Where do I set the mixture screw? I'm thinking about 1/2 a turn out from where the idle speeds up. I didn't reduce the main jet. Still revs out cleanly in second at WOT.