1980 Vespa Grande starting issues

Asparagoose Lamichhane /

Hey all,

New to the forum and new to mopeds. Bought a 1980 grande a few months back, owner stated that it ran last year and had been sitting. Has ~3k miles on it.

Gas tank was in good shape but I flushed it anyways and made sure gas was flowing into the carb.

Cleaned the carb twice with carb cleaner and compressed air, including idle circuit. Held a flashlight up to confirm that the gap through jet and up into the needle is clear.

Compression tester shows ~150 pounds, can get it up to 200 if I keep pedaling. Of course it won't rise unless I let go of decomp lever, but once it is up to 150, 200, squeezing decomp again doesn't release the pressure. Is this supposed to happen?

It has spark when I pedal and hold it to the fins. I also tried a new spark plug, both have spark. No lights.

Plug smells like gas after I've tried pedaling.

Spraying carb cleaner or putting a little 50:1 premix directly into the plug hole, then replacing the plug/boot and pedaling does nothing.

Motor can sometimes be kind of difficult to turn by hand after I come back the next day. A little bit of blaster temporarily solves this. Also kind of hard to pedal but maybe that's normal for grandes?

Starter clutch stutters pretty frequently, I can always get it to engage and start turning the motor if I keep pedaling but maybe something I have to keep an eye on, or maybe related to the high compression number?

Choke changes nothing, throttle makes it make a deeper sound but still doesn't start. Trying to start with no air filter changes nothing.

This video is not me (from an old post with some guy and his Bravo) but similar to my situation. Anything that can be gleaned from the sound?:

Looking for any advice on next steps or things to look at, thank you!

Re: 1980 Vespa Grande starting issues

Ľ̷̝̽͒i̶̛̼͑͠ȁ̸̧̛̽m̵̻̟̯̀̅ ̷͎̙̽̊F̶̲̺͑̓ F /

Is the starter clutch rubbing? Or the rear wheel? Or the flywheel? That’s what it sounds like

Re: 1980 Vespa Grande starting issues

Dirty30 Dillon /

If you haven't replaced the singular motor seal on this, you should automatically do that before going any farther.

While it's apart confirm timing and spark, you haven't mentioned that at all.

Re: 1980 Vespa Grande starting issues

> Dirty30 Dillon Wrote:

> -------------------------------------------------------

> If you haven't replaced the singular motor seal on this, you should

> automatically do that before going any farther.

>

> While it's apart confirm timing and spark, you haven't mentioned that at

> all.

He said he had spark, but checking timing and replacing the seal basically guarantees that it will start

Re: 1980 Vespa Grande starting issues

Dirty30 Dillon /

> Nick MBC Wrote:

> -------------------------------------------------------

> He said he had spark.

You right. I must have glossed over that, even went back for seconds to make sure it wasn't in there.

To be fair, I don't even try starting a vespa motor anymore without a complete rebuild. For the cost and time, it's not worth me killing myself over small issues when I can KNOW a bike has a 100% tight motor and move on with my life (edited)

Re: 1980 Vespa Grande starting issues

so much bs with your post, stop smoking. 150 psi that climbs to 200 psi only if i keep pedaling...decomp raises compression? get it together man cant help without the facts.

Re: 1980 Vespa Grande starting issues

Yeah I assume the decomp not dropping compression is due to his compression gauge, I've used many that hold the highest compression that it read...

Re: 1980 Vespa Grande starting issues

Dirty30 Dillon /

Comp Gauges will always hold the reading, that's why it has it's own vent button. Once you've pumped it up, it won't matter if you release decomp on the bike.

Re: 1980 Vespa Grande starting issues

Asparagoose Lamichhane /

Ah oops I didn't realize that about the compression gauge that makes sense thank you . I'll order a rebuild kit then and will plan on checking timing. Could the seal be bad enough to prevent starting even with a high compression reading?

Re: 1980 Vespa Grande starting issues

> Asparagoose Lamichhane Wrote:

> -------------------------------------------------------

> Ah oops I didn't realize that about the compression gauge that makes

> sense thank you . I'll order a rebuild kit then and will plan on

> checking timing. Could the seal be bad enough to prevent starting even

> with a high compression reading?

Yes, what you could do is a leakdown test to see how bad the seal is

Re: 1980 Vespa Grande starting issues

Asparagoose Lamichhane /

Alright, I did a rebuild, new bearings, seal, gaskets. New spark plug too. Still won't start (using drill on the stand). Tested spark and compression again, and plug smells like gas. Flywheel doesn't turn super easily, is that normal? I can turn it by hand but drill doesn't sound like it is getting up to max rpm. When turning flywheel by hand it feels like it goes past a slightly tougher spot once every revolution. Could plug be sparking against the cylinder but not once I put it back in?

Re: 1980 Vespa Grande starting issues

Asparagoose Lamichhane /

Also I checked the timing, it was right about 19 degrees like manual says

Re: 1980 Vespa Grande starting issues

pardon me for going off earlier, but 150 psi on a stock vespa is unheard of. Id spray some premix in the plug hole and drill start, thats after cleaning and setting points again and again.

Spark on a vespa goes thru your brake switches and your brake bulb to ground so wise to check those components as well.

Sometimes when a motor first get put together its a bit off...bearings, case halves, new seal, etc. I usually take a smalll block of wood and whack it a few times and then spin to make sure the only resistance is the new seal, if its periodic like you say then check for rubbing against the subframe or worst case scenario is you dropped the crank or nicked the crank lobe and everytime it passes your intake patch its gouging it up, terrible.

Re: 1980 Vespa Grande starting issues

Asparagoose Lamichhane /

right, I don't know what was happening before the rebuild but now I get 110-115 psi every time. and gotcha, wire from internal ignition coil going to brake light was fucked so I just cut it and grounded it. Turns out where plug wire attached to HT coil was not consistent connection either (rattled around when using drill to turn over engine, didn't notice until it fell off completely. cut a bit off for a fresh end and reconnected). Also, the rubber cover for the points wasn't seated properly and was rubbing.... Lol. Last thing I had to do was take the pipe off. It finally starts but only when the pipe is off so I guess I have to unclog it or buy a new one.

thanks everyone for the help!

Re: 1980 Vespa Grande starting issues

So from the sound of your video, you don't have enough spark. You have spark, means your wires all work, but there is not ENOUGH spark. Your wet plug is the perfect evidence of that. Simply setting the plug on the fins and spinning will tell you if spark exists, but not strength. Spark outside the cylinder requires less energy than spark inside the cylinder because compression forces the air/fuel molecules closer together.

I use an adjustable gap spark tester to ensure that my spark is strong enough. It's a cheap tool and ensures that you absolutely have enough spark to run your bike. I shoot for spark that will jump a 1cm or 1/2in gap.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account