Brian,
The vacuum connected gives a false reading since the engine is not
under load and has a high vacuum which it would not have if the engine
was under load pulling the weight of the car. Fro example in your test
you probably did not have the throttle open anywhere near where it would
be if the car was actually doing 4000rpm in 4th gear. The wider the
throttle is open and the more load on the engine the less vacuum there
is. An advance of 32 degrees with no additional vacuum advance simulates
the most advance there will be when the engine is working its hardest
and will normally give the best power without causing the engine to
knock ping or overheat.
Under lighter loads the vacuum advance mechanism allows greater timing
and improves gas mileage and driveability.
You should have your 8 - 14 degrees of initial timing set first then see
how many degrees you are advanced at 3500 rpm. All the centrifugal
advance should be in by 3500 rpm or a little under. If the total advance
is greater than this it should be limited by the stops on the
distributor base plate not by retarding the initial advance, if the
advance is less, then the base plate is binding or the springs are too
strong or the weights are too light.
So what you are looking for is an initial setting of 8-14 degrees, and a
total centrifugal advance of 32-35 degrees at 3500rpm. With the vacuum
attached you will probably pick up as much as an additional 10 degrees
depending on load, Light load = higher vacuum = more advance = better
gas mileage.
As far as gas mileage I do not have much experience with webers or
dellorto's but there are a couple midgets around here with similar specs
and 10.5 to 1 compression using stock SU's that are pretty peppy and get
about 25 mpg city driving.
The timing marks jumping around are normally a sign of a worn
distributor or worn timing chain or plug wires allowing spark to jump
between them. You could switch back to points to eliminate the
electronic ignition from the picture. I use a Crane XR700 on my car with
no jumping around of the marks.
Hope I did not confuse you too much.
Peter S.
Charlotte NC
59 Bugeye
71 Midget
71 Fiat 850 Spider
Bryan Vandiver wrote:
>
> Peter,
>
> No, I didn't have the vacuum disconnected when I timed at 4000rpm. I didn't
> think I was supposed to. Doesn't it need to be connected to make sure the
> engine is timed at 'full advance', or am I missing something here. Would that
> also explain why I two distinct timing marks with my strobe light?
> In any case, what exactly am I shooting for?, what is setting the timing at 30
> degrees supposed to do for me?
>
> regards - Bryan
>
> >X-Accept-Language: en
> >MIME-Version: 1.0
> >To: Bryan Vandiver <Bryan.Vandiver@eng.sun.com>
> >CC: spridgets@autox.team.net
> >Subject: Re: Speed timing, and gas mileage
> >Content-Transfer-Encoding: 7bit
> >
> >Did you have the vacuum advance disconnected when you did the 4000 rpm
> >total advance?? The engine is not under load so would have a high
> >vacuum. The total advance should be done with the vacuum disconnected,
> >and should be around 32~36 degrees.
> >Peter S.
> >Charlotte NC
> >
> >Bryan Vandiver wrote:
> >>
> >> I have some questions about 'Speed timing' my 1275 engine in my bugeye.
> >> First of all here's ,my setup.
> >> Freshly 'rebuit' 1275
> >> - .020 over piston
> >> - Kent md266 cam/springs/lifters set. (timed in at 7degrees from TDC)
> >> - 12g940 head (mildly ported, and port matched to manifolds) w/K&N filter
> >> - dellorto DHLA 40 (simular to weber DCOE)
> >> - Maniflow LCB for 1275
> >> - 1.75 exhaust system
> >> - Ignitor electronic ig in stock Distributor ('71 1275)
> >>
> >> When I timed the engine by ear, my timing setting ended up being between
> >> 18-21Deg at 1000RPM, with smooth idle, and plenty of power between
> 2-4000RPM.
> >> I then speed timed the engine at ~4000RPM and the setting from above showed
> it
> >> was running 40+ degrees at full advance.
> >> I then reset the timing to ~30 degrees at full advance.
> >> Now I have a much rougher idle, and It seems like my power band shifted to
> >> between 3500-6000 RPM. The timing mark at 1000rpm with the vacuum advance
> >> disconnected, is now at about 6 deg.
> >> I also noticed when speed timing that my timing mark wasn't 'jumping around
> >> randomly, but that I saw two pretty stationary timing marks about 5 deg
> apart.
> >>
> >> The car does start and idles well, although a little rougher than I'd like.
> I'm
> >> wondering if now I'm running too retarted at low rpm.
> >> Anyone have any experience with this that they'd like to share?
> >> Please remember this is a 'street' car, NOT for track.
> >>
> >> Also, even though my plugs look good after 2-tanks of gas, (nice tan
> deposits),
> >> I'm getting less than 18MPG! this sounds way too low for a car/engine of
>this
> >> size. Not to mention the fact that this is with a 5-speed OD 210 tranny.
> >>
> >> Regards - Bryan Vandiver
> >> San Jose, CA
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