Modern Vespa

Hello,

First time posting here — thanks in advance for any assistance.

I have a 64 VBB with a 15/20 Dellorto carb, I installed a Mazzuchelli racing crank years ago and have never had an easy time with consistent starting.

I'm thinking I may need to modify my ignition timing from 28 degrees BTDC to work best with the much wider combustion chamber of this crank.

Any recommendations for what may be a more effective timing setting (or other tweaks) is greatly appreciated.

*g

28 degrees seems awfully advanced. Even with points, I think you should be at like 22.

The timing is determined by a combination of ignition type (points or electronic) and top end.

Can you tell us more about the rest of your motor? Are you sure the issue is not something like weak spark, fouled plug, or low compression? Those seem more likely to cause hard starting than to much timing advance.

What cylinder is this bike running? Is it a dome or deflector piston?

thanks for your replies chandlerman and GlickSpeed.

It's a stock set up (minus the crank) with a deflector piston. The coil (stock) and stator and have been replaced over the last couple of years the condenser is new. The bike's been generally off the road — unregistered for years.

Compression (can't recall reading) seemed ok when I checked it last. Cleaned and rebuilt the carb about 6 months ago.

I have noticed an intermittent weak charge recently coming from the spark plug wire — doesn't fully shock my finger when touched and kicked over. Maybe the coils gone bad again.

The difficult running has been happening longer than this recent potential coil issue (even when the coil was new). I can usually restart after running it for a while (ride around the block), but if I then let it sit for 5 minutes or more, it will be then very hard to start.

I'll try the 22 degree setting chandlerman and report back.

Hope this helps — and thanks again!

It’s “Gick.”

Motor needs to be ran at 28 btdc. Changing the crankshaft does not changing the ignition timing. I would be looking at compression, then ignition. Ignition can include flywheel magnet issue.

Thank you GickSpeed!

Looks like it's time to start wearing those reading glasses I just got.

The compression test didn't get above 100... I think I damaged the helicoil in the plug hole taking out the spark plug.

I have heard of instances where degrees get shaved off or added to the ignition timing depending on the modification done. I know 28° is the factory recommended setting. This crank adds (I'm guessing +20°) to the area of the fuel charge opening (forgot the technical term for this area).

will report back when helicoil is repaired or head replaced.

thanks again.

"helicoil in the plug hole taking out the spark plug."
VBB...


is it a bodge by any chance?

Unlikely in that it has a deflector piston, and a little earlier than the standard “bodge 64-69 years”.

Either way, have the head repaired properly or source a decent replacement. Helicoil on plugs is bullshittery. Time-Serts are marginal at best.

No doubt. The Viet’s would have changed that out decades ago. Needs Timesert on the head.