Modern Vespa

Hey Guys,
Newbie question:
Just installed SIP's Sport (variable electronic) ignition. Love the more solid lights and the "feel" of the throttle.
Set timing to 18 BTDC on a tuned p125x with a Malossi 166 kit, SIP Road 2 exhaust.
The idle is unstable though.
Should I work more on the timing (set it without timing light), or back to jetting?

Idle is unstable as in what way? Needs to be revved up higher to stay running? Speeds up and magically slows down?

Starts fine and stays running at idle.
But just like you say. Speeds up and slows down.
Thanks!

While you definitely should strobe your ignition as incorrect timing could lead to a holed piston, I’d say start with the easy stuff before focusing on electrics.

Clean your carb, check your gaskets, check the air fuel screw at the back of the carb, make sure the air box screw is tight to the cases and that your air filter is clean.

If that doesnt solve it, it could just be your motor spitting back/ worn rotary valve affecting the idle. Sadly theres no easy repair for that one.

As long as the scooter runs well and returns to idle quickly I’d live with it. If the idle hangs/ too lean I’d keep at it and change the air/ fuel screw/ jetting/ find the air leak.

MJ has some good advice on all the other stuff you gotta watch out for.
As for timing the VAPE - everyone has their own method.
Here's mine:

- Have a look at the advance curve shown in the manual (see below)
- Note that it will advance as it leaves idle - before starting to retard.
- Its really hard to strobe at idle - because just a few hundred RPM advance it significantly - and these things don't idle at a dead steady state - so it will jump all around.
- Same can be said as you get up to about 4500RPM - it starts to retard precipitously.
- So I prefer to set the timing by revving to the area that the timing is in a steady state - about 4K RPM. Here it stops jumping and hovers for you so you can actually read a number.
- I take a timing read at this hovering point - the farthest advanced its going to go. Then just subtract about 2.5 degrees for the 1000 RPM idle number.

The other thing I do is I am vigilant with pulling the plug and looking for any tiny balls of aluminum. These will look like sand granules or acne on your plug around the electrode. That's bad. If you see it - retard 2 degrees and repeat.

My $.02

-CM

you didn't specify the RPM's you're setting 18 deg BTDC at. That's obviously critical, as CM2 pointed out.

I use pretty much the same technique he does, but you need a timing gun with a tach in it so you know the RPM's, and that they're steady. Plus, you want and really need an adjustable timing light for setting the variable timing because it's soooo much easier to validate the timing at not just steady 4k, but also that peak power is the expected value (in your case, 18 BTDC).

There have been a couple threads on this topic if you want to search

I do agree with the method of setting up variable timing. Whichever variable timing anyone has, the method is the same.

However, determining where to set it is very specific to an exact engine set up. 18 degrees may well be the best setting but very unlikely to be so easy. Anything from 10 to 30 will run...... and might appear to run fine......at least for a while. Determining the correct setting for your engine takes some trial and error (often quite a bit of error). Timing is opposite to jetting and should begin low and increased with caution.

Find "0" and mark it first.

Use a timing light for a two stroke motor.

My factory marks were several degrees off when mixing and matching parts like you are. I'd have to look but something like 6 or 8 degrees.

Wow, thanks Guys.
My timing light arrived today. Looks like I'm advanced 3 degrees at idle, based on Charlieman 22's suggestion. Unfortunately it's a bare bones strobe light, but I think I got it.
I'll try adjusting it tomorrow and follow-up.

Is the light made for a two stroke motor? Mine has a setting for two and 4 stroke motors.

Ensure your confident in where TDC is, a lot rides on that. I use cheaters (white pen) marks on the stator to track my movements as I try to find the optimal desired timing point at RPM.

Below is my favorite article on advance timing for these scoots. I have read it many times to keep the info straight in my head.

[url=https://www.mbscooters.co.uk/info/mb-*-tech-articles/engine-tech-*-advance-boxes+282.html] Link fails to codes but does work if you copy and paste[/url]

Well done for posting this Captcha
https://www.mbscooters.co.uk/info/mb--tech-articles/engine-tech--advance-boxes+282.html
Old article but facts very accurate. A must read for anyone setting up variable timing.

Okay I was able to correct the timing to 18 BTDC with the new strobe. I'd done the markings on the fan but when I unscrewed it I realized it could be put back a number of ways on the flywheel. Had to find TDC again...
It's running well. Thanks again to all of you guys.

On a side note, SIP's website says both a timing light isn't required and be sure and check the timing with a light after setting

Ok, going to ask what everyone else is thinking; At what rpm did you set the timing to 18 degrees? 18 degrees at 6000 rpm would most likely be pretty good. 18 degrees at 4000 rpm likely to be a lot less good.

Judging from the SIP graph, I'm guessing it's in the 4k to 4.5k range, as that's where it's most stable. Unfortunately I don't have a tachometer (yet). I rode yesterday in the hills and it ran better than ever. Rode again today on flat streets, and now I see it's 4-stroking/unhappy at 1/8th throttle. Not sure if this is a timing issue or something else.
Thanks

I wouldn't be riding much, and especially not pushing it, until I had confirmed the timing was 18 BTDC at 6,000 RPM's. You should take a peek at the piston and make sure there's no signs of detonation or pitting on the piston crown once you are confident in the setup.

Also, how did you find TDC?

(I ask because I really don't want you to learn the hard way what happens when you ride to failure with the timing too advanced).

I think I said this earlier in the thread, but if you're going to run variable timing, you should invest in an adjustable timing light. It'll have a tach built in, and you can both more accurately and more easily validate that everything is working as intended.

I'm as close as possible, finding TDC with an adjustable piston stop and a well printed carboard degree wheel. I can't be more than a degree off.
So time to get another timing light.. Neighbors are going to kill me.
Thanks!

Ok just to be clear, am I not supposed to be at 18 BTDC at both 2200 and 4500 rpm's? If I set the timing to 18 degrees at 6000 rpm's it will be 22 BTDC at those rpm's, according to the SIP graph that came with the kit.
(The DIY "bolt-on kit that doesn't need a timing light" )

I totally forgot that at the same time I ordered the Vape ignition, I also ordered a rubber airbox cover gasket and a plug for the hole left where the auto-mix tube at one time went through the carb box. Not sure if this made a big difference, but adjusting the idle jet mixture screw corrected my original idle issue. Offhand this makes little sense, since there is the considerably large hole feeding the carb. Is this like the short vs long straw analogy?

Okay, so I set it at 18 BTDC with a strobe & tachometer.
Engine was still "unhappy" at 1/8 throttle.
Funny story:
Looked up the Malossi 166 instructions. They recommend 95 octane fuel, but without reading glasses I read 85! Filled it with 87 and now it runs smoother than ever.
So this timing is retarded for my setup, right?
P125x engine
Malossi 166
SIP Road 2
23/64 upgear
24/24 Spaco, 3 1/2 turns out. No leaks
55/160 idle
118 Main, B3, 160 Air
'59 Allstate with 8" wheels
Revvy as 'ell. Most cruising is done at 1/8 or so throttle. Climbing fairly steep hills in 4th gear now

(Picking back up as I'm catching back up)

Yes, you're reading the graph correctly. if it's at 18 BTDC at 6,000 RPM's (~3.5 degrees from baseline, which is the recommended timing for the cylinder), it'll be ~0 from baseline at 4,500, so call that 21.5 BTDC and also at 2,000 RPM's.

The magic, as Jack has noted and the dragonfly75 article details, is in determining the correct RPM's to set the baseline at for maximum performance, but without blowing up the top end or holing the piston.

And if you're unsure, retard it a degree.

Also worth noting that with timing, it's entirely possible to stay under "safe" temps and still destroy the motor. A CHT will not help you here like it will with carb tuning, and an EGT will only get you so far, too, although if I'd started running one sooner, I'd have avoided at least one incident where I blew up the motor by delaminating the Nicasil from the bore around the exhaust--no seize required. Just get off the highway and it dies on the ramp.

I'm a 0/5 Stars ("Would not recommend") on that experience.

After lots of rides, tweaking a degree here and there and then more rides, it seems my setup likes 18 degrees BTDC at 4000 rpm's.
Assuming it's safe there.
More torque, surprisingly reliable starts, and more confidence in it as a daily rider.
Took off the cylinder head. Smooth as a baby's butt after a wiping down with break cleaner and rag.
Will post if something comes up.
Thanks again to all of you guys

I get it now, I feel your pain

Glad you're sorted!

You should still have a degree or two of advance if want to take advantage of it, but if you're happy with how it's riding, then think of it as safety margin and go on.

My neighborhood is very hilly, and there's a VERY steep hill I've made my "bog tester," at least that's where I tested jettings before the Vape.
Tried advancing a degree or two and bogged a bit on that bog tester hill. Later I hooked up a tachometer and the rpm's there are 3900 in 2nd gear.

That’s strange... it should be better for hills if you’re at 20deg btdc at around 3900

I sense you’ve not jetted properly...

To be honest, this bike is a true mystery.
Is there anything else that can affect timing?
Gas octane (87 to 91 here)?
Crank length (Mazzuchelli cut crank)?
Px engine running on 8" tires?

Did you re-jet/re-tune the carb because you advanced the extra 2 degrees?

You need to identify if the bogging is because the jetting is rich or lean...

No jet changes until yesterday, but each timing change I made before required idle adjustment.
Ordered ANOTHER set of jets. Pretty sure my idle jet is rich, since one step up made the feared hill-bog worse. Also made the barely-open-throttle 4 stroking worse.
It's gotta be close, timing wise. Not much change a degree or two in either direction. For now it's 20 btdc at 4k.

Im going through the same exercise now...

Advancing 6 degrees now and i'll be re-jetting everything... gets tedious, after the 5th pilot change and 10th needle change... lol

A (leaner) 48/160 idle jet did the trick. Running great for the moment. "Bog hill" test result, 9 out of 10. Lots of pull.
Would love to clear out the four stroking at barely open throttle someday.


Maybe explains my original question

You are running a very similar setup to mine although drastically different main stack. Do you have an air filter in or are you running fully without air filter?

I see you are on a 48/160 idle. I was considering using that as well today but its a very lean idle so i held off on it. I also have the barely open throttle four stroking. Currently trying to work it out experimenting with atomizer to see if it is crossover richness.

Tried to fight crossover richness with both a BE2 and a 185 air corrector, individually. No luck
Running with a new (drilled) air filter. Replaced the flyside oil seal.
The 48/160 idle jet did the trick. Kinda worried though..

SIP have a good video on variable timing now.

At least I think it's good, because I agree with how they recommend setting timing and the implications.

Loved his px build videos. His workshop looks like a kitchen.
Best quote of that video:
"This time, I really promise not to go full throttle..."
The next video in the series is carb tuning. That will be interesting.
Interesting too that you can switch between a static and variable timing by just changing the CDI coil.

I also loved that he dyno'ed all the changes. The weaker power output of the variable ignition in the overrun was especially interesting to me.

It reminds me that that Pinasco Flytech stops retarding at 7,000 RPM's, (IIRC) which I never understood until seeing this video.

Great talking point, that video.

Another reason for buying a Kytronic. All overrun retarding is controlled.

And proof that variable ignition can be better than fixed.