johnemms
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| posted on 29/11/11 at 09:32 AM |
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Crossflow - Starter - Timing
So.. I understand that the vaccume advance tube on a standard carb is conected to a special part of the carb which is located in front of the
butterfly so as only to only opperate when the butterfly is part open - if located behind the butterfly a constant vaccum would simply give full
vaccum advance 'all of the time'.
I also know that the timing on my crossflow should not exceed a maximum advance of aprox 32 degrees - so - using an ajustable timing light and rev
counter I have set revs to 4000 checked max timing at 32 degrees. My static advance has ended at aprox 8 degrees advance.
My inertia starter will not start the engine once the engine had been started and was hot so I have bought a high torque starter for £160. This will
start the car now but you can tell its having to work at it - (maybe it needs to be used a few more times to get the brushes & contacts bedded
in)?
Ok.. so.. if i connect the vaccum advance to the manifold it will be useless because it will give a constant & locked advance when the engine is
running..
So .. If i set my timing say to zero degrees static then start the car .. it reads 12 degrees advance.. so i now know my vaccum max is aprox 12
degrees.
So.. with my vaccum conected to the constant vaccum side of the manifold - when i crank my engine over with my inertia starter there is no kickback
anymore .. it starts like any normal car .. and as soon as the engine fires the vaccum locks and applies 12 degrees advance thus advancing it to its
almost correct setting...
My car was starting perfectly on the standard inertia starter & vaccum fitted at manifold because - I had set static at zero .. this stoped my
brand new engine with its high compression firing immediatly on the upstroke and putting a load on the inertia starter .. as the car fires the vaccum
increases and its 12 degree advance kicks in.
So starting a hot high compression engine which will fire on the first stroke - I figure pulling the advance back would be a good idea to get it
fire without kickback and then applying advance as it picks up and starts is a good thing?
If I do it my way with the vaccum then I can use a standard starter motor... If I do as i was told then I have had to buy an expensive £160 starter
which is still strugling to start the car and i fear may not last long...
Sorry for the long story.... all comments welcome 
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kendo
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| posted on 29/11/11 at 10:03 AM |
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I believe it's quite a common trait of xflows that if the timing is too advanced. So, its a balance between getting it to start and having
sufficient advance.
I had this issue and simply nudging back the timing until it started reliable seems to have worked and very little adjustment was subsequently made
when I had it rolling road tuned.
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johnemms
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| posted on 29/11/11 at 10:10 AM |
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Well it starts now with the new starter but i'm wondering on how long the starter will last..
It realy is easy to put the advance tube back on ..
rev to 4000 ..
set advance to max 32 degrees..
just wonder if anyone had a good reason not to do it this way...
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JeffHs
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| posted on 29/11/11 at 11:21 AM |
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I may be wrong, but I think you've misunderstood manifold vacuum. I believe it doesn't matter where the vacuum signal is taken as long as
it's downstream of the throttle valve. The vacuum in the manifold is not constant but influenced by engine speed (more suck at higher revs) and
the position of the throttle butterfly, so high speed, closed throttle (downhill, foot off gas) would give max vacuum. Low speed and wide throttle
would give almost no vacuum. It is broadly the difference between engine suck and atmosphere, so once the throttle is opened, vacuum is reduced.
Most manufacturers use a carb-mounted pipe for convenience, but a manifold mounted pipe would have the same affect as long as it is common, i.e open
to all cylinders. Once you get into twin Webers or bike carbs mounted on individual manifolds, then the vacuum signal is difficult, so people go to
non vacuum distributors with a different advance curve
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johnemms
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| posted on 29/11/11 at 11:25 AM |
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Vaccum pipe has to be atmospher side of butterfly .. hence a closed butterfly has almost no advance .. put it manifold side and.. Open or closed -
when the engine is running the manifold has a vaccum..
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britishtrident
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| posted on 29/11/11 at 11:35 AM |
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You can modify the distributor mechanism to give more centrifugal advance, if you do this you can set the advance at high rpm to give the correct
advance for maximum power but not have excessive static/very low rpm advance.
All that is required is to remove the shaft from the distributer and file or cut a few mm off the advance stop.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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johnemms
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| posted on 29/11/11 at 11:37 AM |
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Ahhhh /... nice one... will look into that..
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britishtrident
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| posted on 29/11/11 at 11:40 AM |
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Link http://www.starchak.ca/tech/pdfs/lucastuning.pdf
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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02GF74
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| posted on 29/11/11 at 12:46 PM |
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I gave up on the original post so not sure what the problem is - somethign to do with timing and problem starting the engine.
I have not come across setting timing a 4,000 rpm!!
Timing is set statically - lightbulb method or dynamically, typically 1,200 rpm and done with out the advance connected.
please check you are setting timing correctly.
Are you using timing marks cast on the timing chain cover? These can easily be a couple of degrees out, may be worth finding TDC and then attaching a
timing marker.
Are you using vernier timing gear, if so, if this set correctly?
I have a couple of timing charts at home and from memory, a tuned engine does not need as much advance (or is it other way round) so do nto start
filing away the tabs in the distributor.
What carbs are you using? If twin DCOE then what is the mixture set up?
How tuned is your engine?
I have 1660 engine with 1300 cc pistons, a slightly wackier cam so that is higher CR than standard and it starts ok with tiny gel battery.
Stating the obvious, but fat are your starting leads? Are the connections to battery/starter/sally noyd good? Are the crimping of connectors good?
Are earthing points clean and good? Is battery getting fully charged and ion dood condition?
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Autosri
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| posted on 29/11/11 at 01:10 PM |
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I am a little confused as I set the timing at 1000rpm with the vac disconecred as thats befor the ignition curve starts this is on a pinto with dcoe
webers to stop the carbs spitting back i use 14btdc and that's fine for running but is a bitch to start on cold days so im collecting the bits
to get megajolt working as it's got a cranking ignition timing and an idling timing so set it low for starting but as soon as it starts it will
jump to the normal timing
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johnemms
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| posted on 29/11/11 at 01:28 PM |
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As I said.. if you connect your vaccum directly to the manifold you will get 'full vaccum advance all the time'
If you set your static timing to zero - then connect the vaccum it will jump to aprox 12 degrees advance.
Therefore - starting the engine - you will have almost no advance alowing the starter to throw the engine easyer.
Once it fires the vaccum will be immediatly held to its maximum of 12 degrees.
Being able to back off the advance while turning over the engine removes kick back..
[Edited on 29/11/11 by johnemms]
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Dingz
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| posted on 29/11/11 at 01:34 PM |
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quote:
Vaccum pipe has to be atmospher side of butterfly .. hence a closed butterfly has almost no advance .. put it manifold side and.. Open or closed -
when the engine is running the manifold has a vaccum..
Atmosphere side of the butterfly will always read atmosphere. Vacuum Advance should be connected the manifold side, when the throttle is closed it
will see a high vacuum cos the engine is sucking hard. when the throttle is opened the vacuum drops. Vaccum advance only works at small throttle
openings to improve driveability and economy at full throttle it should have no effect. I think you are worrying too much about it over advancing the
curve. If you are still worried just leave it off.
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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Autosri
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| posted on 29/11/11 at 01:34 PM |
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But what happens when you open the throttle a bit your timing will shoot back to 0 degrees
Say 800rpm throttle closed you will have 12btdc so hats fine but what about 1000rpm with part throttle vaccum drops and it drops back to say 4btdc
then what happens if you boot it at 2000 revs you will be at 18btdc then you loose all vacuum and your down to 6btdc
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johnemms
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| posted on 29/11/11 at 01:41 PM |
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The vaccum pipe should be conected to a special drilling on the carb.
This hole is just 'in front' of the butterfly...
It works by a tiny amount of vaccum..
If you connect directly to the manifold - even a slight vaccum gives full advance..
Twin carbs do not have the special drilling - this is why we normaly leave it off.
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britishtrident
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| posted on 29/11/11 at 03:47 PM |
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Setting the timing at 4,000 rpm or any other RPM after the centrifugal advance is at maximum was a fairly standard procedure with tuned engines.
The problem with a lot Ford engines is the distributor only has 10 (distributor) degrees centrifugal advance at the distribute shaft ie 20 degrees
measured at the crank pulley.
10 distributor degrees advance wasn't a lot compared with other comparable 1960s engines Rootes/Chrysler UK engines generally used
distributors with about 14 distributor degrees centrifugal advance (28 crankshaft degrees)
With a 10 degree distributor 12 degrees static advance is require to give 32 degree at 4,000 rpm ie 32 - ( 2 x 10 )
With a 14 degree distributor only 4 degrees static advance is required to give 32 degrees at 4,000 rpm ie 32 -( 2 x 14 )
[Edited on 29/11/11 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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