Ignition Timing & modern Fuel
- Thread starter Martyn Goodwin
- Start date
Yes i think Tim (Vibrac) is correct, i have fitted several of the newer ATD's and they do seem to have less overall travel than a worn original. realisticly you only want around 15 deg of travel or 30 at the crank for these engines nowerdays. I have found that if you use an 8mm or 9mm open end spanner you can simply bend the ATD ears inward and bend both the high and low stops about equally, as they only need about 1 mm or so. If you bend the low stop ears only, i have found you end up bending them too much, so it is better to bend them both (all four stops that is) it takes a little bit of juggling, but is easily achieved...........Cheers.....Greg.
Bending Completed, performed with ATD in a vice and a gentle squeeze on both sets of ears - ATD range is now 30 degrees at the crank - Have set the timing at 3 BTDC fully retarded and 33 BTDC fully advanced. Time (no pun intended) will tell.
M
The Pazon Vincent ignitions all use a start position of 0 degrees, as as advised by their consultant , Bob Dunn. This would imply that a standard ATwith 34degrees travel could be set as far back as 34 degrees total advance and still start fine. It should be noted that Bob Dunn chose zero degrees as the OPTIMUM start setting. Perhaps start position on a Vincent twin is not all that fussy, as long as it is not too far advanced for kicking?
Glen
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Glen,
I don't think it is very fussy. When I had manual Adv/Ret on my Rapide I found it used to start easiest with the lever was backed-off about 2/3rds from full adv - which I guess would have been about 10-12 crank degrees BTDC. It would also start on full retard - but not nearly so easily.
I never bother with where compression is, just a spirited kick with slight pressure on the decompressor which is released half way down the kick...
Perhaps someone with manual ignition on a std-ish Rap could corroborate my findings - or dispute them?
Peter B
Bristol, UK.
I don't think it is very fussy. When I had manual Adv/Ret on my Rapide I found it used to start easiest with the lever was backed-off about 2/3rds from full adv - which I guess would have been about 10-12 crank degrees BTDC. It would also start on full retard - but not nearly so easily.
I never bother with where compression is, just a spirited kick with slight pressure on the decompressor which is released half way down the kick...
Perhaps someone with manual ignition on a std-ish Rap could corroborate my findings - or dispute them?
Peter B
Bristol, UK.
That sounds Ok in theory, but it takes Bob Dunn at least 3 years to start anything.
Here is the Pazon advance curve they use for Comets
The advance curve for the ignition I ordered from Pazon shows a similar start point, possibly one degree higher at 3 degrees, if the above graph starts at two.
When it came time to order there was much discussion of the advance numbers with Andy, the owner of Pazon.I have saved all of the emails and those from Bob Dunn as well, just read thru them again. Andy informed me that the actual starting point for all the Vincent ignitions is zero degrees, but that it ramps up quickly to a few degrees at electric starter rpm perhaps 2- 300 rpm. For kick starting tho, zero is still the number.Why the charts show a couple of degrees is a mystery . I recall wondering about it at the time, but neglected to ask why.
I was a bit concerned about this as total advance for the unit (twin plug, twin cylinder, high ouput) was available in two types, either the 31degree type shown on the site, or a special 28 degree unit they had made up for A Bob Dunn race motor.
Armed with Roy Robertson's dyno info , I was concerned that even the lower 28 figure might still be too much total advance. My question to Andy was "Will the engine still start if I find it necessary to roll back timing another three degrees to 25 degrees total advance., making the new start position 3 degrees ATDC?"
He replied that it should be OK. I hope he is correct as the cost to make up a new advance curve is $500. I wish there were some ATD ears in there that could be bent!
Glen
When it came time to order there was much discussion of the advance numbers with Andy, the owner of Pazon.I have saved all of the emails and those from Bob Dunn as well, just read thru them again. Andy informed me that the actual starting point for all the Vincent ignitions is zero degrees, but that it ramps up quickly to a few degrees at electric starter rpm perhaps 2- 300 rpm. For kick starting tho, zero is still the number.Why the charts show a couple of degrees is a mystery . I recall wondering about it at the time, but neglected to ask why.
I was a bit concerned about this as total advance for the unit (twin plug, twin cylinder, high ouput) was available in two types, either the 31degree type shown on the site, or a special 28 degree unit they had made up for A Bob Dunn race motor.
Armed with Roy Robertson's dyno info , I was concerned that even the lower 28 figure might still be too much total advance. My question to Andy was "Will the engine still start if I find it necessary to roll back timing another three degrees to 25 degrees total advance., making the new start position 3 degrees ATDC?"
He replied that it should be OK. I hope he is correct as the cost to make up a new advance curve is $500. I wish there were some ATD ears in there that could be bent!
Glen
The chart in the previous post looks very suspiciously like the output from someone's ruler and pen, not actual measured data from a piece of electronics. As such it almost certainly is only an approximation of any given unit's actual response. Because individual electronic components have tolerances (e.g. +/-5%), there also will be unit-to-unit variations in the output. Whether those variations are larger than the width of the line drawn on the above graph could only be known by measuring several units, but I suspect they are.
The optimum advance curve for a specific motorcycle would depend on factors like its compression ratio, inlet port shape, and cam profile. While those factors could be dealt with, the variable properties of the fuel blend available in any given region of a country at any given time of the year (and it being different next year than it was last year...) make getting too deep into this fairly hopeless. However, if someone were concerned with having the optimum advance curve for their own motorcycle for a racing fuel whose properties they could count on as not changing, they would have to do dynamometer runs by varying the amount of advance at, say, 250 rpm intervals, then have a unit fabricated to reproduce the optimum results found.
It's only one small step from the above to installing fuel injection on a Vincent, which then would allow the advance curve to be altered at will as the fuel blends change. Kits actually exist to allow fuel injection to be added to any engine desired. A friend is currently reviving a damaged modern Ducati by doing that rather than buying the very expensive OEM components, but machining a simple pair of throttle bodies would let this be done just as easily (or with just as much difficulty...) on a Vincent.
The original Lucas atd was designed to have 17 degrees movement giving 34 degrees at the crank. The original timing was 38 before fully advanced giving 4 btdc fully retarded.
My twin still uses an atd. A few years ago the bike was getting harder to start. On checking the timing it was set to 34 degrees fully advanced but when I checked the retard figure it was 3 degrees AFTER tdc due to wear in the atd.
I fitted a new Roy Price atd which measures at 15 degrees movement. This allowed me to set the fully retarded timing to 4 degrees btdc and thus fully advanced at 34 degrees. The starting was greatly improved.
Another thing is be carefully bending the ears on the atd. The new Roy Price atd's use a thicker material, but I have seen original Lucas atd's with broken off ears which were of a thinner material. When you bend the ear you change the contact area on the ear from an full height contact to a point contact which by nature of the direction you bend it will be at the furthest point (which is bad from a mechanical point of view) from where the ears break off.
My twin still uses an atd. A few years ago the bike was getting harder to start. On checking the timing it was set to 34 degrees fully advanced but when I checked the retard figure it was 3 degrees AFTER tdc due to wear in the atd.
I fitted a new Roy Price atd which measures at 15 degrees movement. This allowed me to set the fully retarded timing to 4 degrees btdc and thus fully advanced at 34 degrees. The starting was greatly improved.
Another thing is be carefully bending the ears on the atd. The new Roy Price atd's use a thicker material, but I have seen original Lucas atd's with broken off ears which were of a thinner material. When you bend the ear you change the contact area on the ear from an full height contact to a point contact which by nature of the direction you bend it will be at the furthest point (which is bad from a mechanical point of view) from where the ears break off.