Carb Vacume at Idle

[rdrguru]

Hey everyone, wrapping up my mods to my 1982 v50iii. Before my engineer anal retentivness kicks in, it is running great, nice and smooth and accelerating nicely. I think the timing is a slightly retarded as I fell it should be a little snapier than it currently is, but I don't have a timing light. I am running a Dyna Electronic ignition with Dyna coil coils. I was syncing the carbs on Friday and was pulling about 42 mmHg, and I can't find the spec, does that value sound about right?

Thanks!

 

[V700Steve]

I haven't seen info on how much it is supposed to be, just equal. Borrow a light for timing, you need to sync it also at full advance.

 

[rdrguru]

Thanks, they are equal, I am looking to base line it currently to try and determine if I'm having any valve or piston ring leak. On acceleration the vacuumed needles reactly, as well as my eyes can tell, simultaneously, so they do appear to be balanced as well. I do need to borrow a timing light though, that is no doubt! Thanks again!

 

[john zibell]

Thanks, they are equal, I am looking to base line it currently to try and determine if I'm having any valve or piston ring leak. On acceleration the vacuumed needles reactly, as well as my eyes can tell, simultaneously, so they do appear to be balanced as well. I do need to borrow a timing light though, that is no doubt! Thanks again!

The vacuum drawn won't answer that question. A leak down test is what will tell you if you have ring or valve leaking. Timing lights aren't expensive, just buy one. I have inductive pickup one I've been using for over 40 years.

 

[Paul Brice]

As John says, the vacuum draw isn't going to tell you anything about valves/rings etc & you need compression & leak testing to check that. Just for info, my V50 3 (when balanced & set for stable lowinsh idle) will pull a vacuum of -4inch Hg or -101mmHg. I have video but they are too big, so here are screen grabs...

 

[rdrguru]

Yep, mine is not that high, and again I'm almost sure the timing is retarded. I'm going to check that next, set it to spec and check it again. When I took it for a test ride, I couldn't get the rpms any higher than about 6000. I know my needle is set correctly and I have full range on my slide. I pulled my plugs after the ride and they look good, so not too lean or rich.

 

[Paul Brice]

Definitely get a strobe & do your timing & check the advance bobbins are working (marks moving on rev rise)....lots of carburation & ignition problems have the same symptoms

I've gone up approx 20% on main & pilot jets to compensate for lack of airbox. Before that the engine would also struggle at higher revs as too lean - plug colour didn't really help as much of the time I was also just bumbling around town at low revs or on idle !

 

[dbarale]

Did you time it statically?

 

[rdrguru]

No, like an idiot I trusted that the guy who owned before me had that all set up correctly...Well that would have been the only thing because so far just about everything has had issues.

 

[dbarale]

Just for reference as I was recently dealing with the same thing and I had the picture in my phone.
When the right and left timing marks on the flywheel are lined up, the magnet on the rotor (I added the sharpie lines because I can’t see crap anymore) should be lined up with the pickup sensors (little square bumps on the pickup modules).

Ignore the melting charging wiring at the bottom. That will be addressed next.