Ignition timing for twin plug heads
- Thread starter vince998
- Start date
Hi
No clearance between front pipe and timing chest, or back pipe and front head. Had to make a sleeve to fill gap where exhaust sections join.
Performance? It's just a 1 5/8" standard Vin exhaust - all things being equal, it's the silencer that saps the power.
Re torque from high compression - never rode a Vin less than 8:1, but never knowingly been short of torque or flexibility on one either.
H
Hi Bill,
My bob weights have reduced movement (22° in total).
The ignition system is from Francois Grosset and set up for twin plug heads.
I´m running two 3 ohm Double Dyna coils, wasted spark. (on a re-wound 12 volt lucas E3L, electronic regulator and a 7 amp hour AGM battery. (Balances at 2000rpm with the the lights on full. Who needs modern generators)
Funny you should mention the silencer
I changed it for one from russel with a really small hole in the middle, then changed it again (cos the bike ran like poo) for one with a slightly larger hole (but still not straight through).
In the midst of converting to electronic ignition/twin plug heads/MKI concentrics, i´d forgotten about that
Time to make some noise then.
Dyna coils not recommemded with François ignition. Check that out.
Thanks Trevor,
Any idea why?
I´ve had them on for years, and although i had various other problems with Francois Ignition (all solved now) he never faulted the coils although with just about every letter i wrote to him i mention them.
He recommends 3 - 5 ohm with 5 ohm being preferable but 3 ohm usable.
Because i already had the coils i thought i´d keep them.
Will the primary resistance of the coils effect performance?
Thanks
Hi Bill,
I´ve been informed by Armours that it is only the heavy duty chromed exhaust that has the deflector plate. The stainless silencer is a straight through absorber type.
Not that it really matters anymore. Got home this evening, and stuck a torch up the silencer. Russel must have sent me a proper one cause i can shove a broom handle up there.
Breathing problems ade.
Think i´ll try the main jets next (as soon as i have repaired my fuel tank)
In terms of timing with twin plugs, my experience is with BMW airheads. Twin plugging is usefull as it allows you to run highish compression ratios but still use crap unleaded petrol. No increase in power, but the bikes are smoother and easier starting. The BMW consensus on timing is to run stock static timing, but to reduce full advance by 3 degrees. For bmws there ate a couple of companies that produce ignition systems that give you a choice of 15 different ignition maps.
Hopefully this helps
Charles
Hopefully this helps
Charles
Thanks Charles,
-3° would be 33° BTDC (on original settings for old fuel) or 31° BTDC on the new stuff, but this seems a little to much advance for the Vincent on twin plugs.
At 29 BTDC i only hear pinking if i crack the throttle open at stupidly low RPM in 3rd or 4th?
I seem to be able to reduce advance to 24° without any detrimental effects, however, the only way to really test is on a dyno i believe (there are just to many differing factors on the road)
Maybe to do with combustion chamber shape (I´m not sure if BMW use squish bands?
What you write about no more power is my experience as well, but as you state, starting and low speed running is a lot better.
A few comments on my own experience with a twin plug set up on a Vincent twin.
My engine has 7.3 to 1 compression ratio, what appear to be Mk1 cams or cams reground to a similar timing and 28 mm Mikuni carburettors.
The ignition system is provided by a BT-H electronic magneto. The unit has a MK2 advance curve that has a slightly slower/longer range than early units. I have the ignition set to 32 degrees fully advanced. I use ordinary NGK plugs, grade 6-7, gapped at 18-20 thousandths of an inch.
The engine starts easily and is normally run on whatever is the cheapest petrol found at the filling station. It returns between 50 and 60 miles per imperial gallon depending how it is being ridden.
I can't comment on top speed but it cruises easily at 70 mph and with considerate use of the throttle will run at 30 mph in top, two-up. I have never heard any pinking although I do wear ear plugs when riding.
I have run it in this configuration for approximately 15,000 miles.
Some observations of my own that may or may not have any foundation:
My compression ratio is low by modern standards and as the heads are standard there are no squish bands to promote better combustion. The shape of the combustion chamber with a higher compression would probably get more benefit from a twin plug configuration.
The early BT-H twin magnetos made pre- 2007 had a slightly shorter Mk1 advance curve. I have tried the engine briefly with this earlier curve and the engine felt perhaps a little sharper so in this instance there could be some benefit in in a shorter advance range to take advantage of better flame path. This also suggest that with a higher compression and more convoluted combustion chamber a shorter advance curve might be beneficial.
My engine has 7.3 to 1 compression ratio, what appear to be Mk1 cams or cams reground to a similar timing and 28 mm Mikuni carburettors.
The ignition system is provided by a BT-H electronic magneto. The unit has a MK2 advance curve that has a slightly slower/longer range than early units. I have the ignition set to 32 degrees fully advanced. I use ordinary NGK plugs, grade 6-7, gapped at 18-20 thousandths of an inch.
The engine starts easily and is normally run on whatever is the cheapest petrol found at the filling station. It returns between 50 and 60 miles per imperial gallon depending how it is being ridden.
I can't comment on top speed but it cruises easily at 70 mph and with considerate use of the throttle will run at 30 mph in top, two-up. I have never heard any pinking although I do wear ear plugs when riding.
I have run it in this configuration for approximately 15,000 miles.
Some observations of my own that may or may not have any foundation:
My compression ratio is low by modern standards and as the heads are standard there are no squish bands to promote better combustion. The shape of the combustion chamber with a higher compression would probably get more benefit from a twin plug configuration.
The early BT-H twin magnetos made pre- 2007 had a slightly shorter Mk1 advance curve. I have tried the engine briefly with this earlier curve and the engine felt perhaps a little sharper so in this instance there could be some benefit in in a shorter advance range to take advantage of better flame path. This also suggest that with a higher compression and more convoluted combustion chamber a shorter advance curve might be beneficial.
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Hi Eddy,
Thanks for the info.
Interesting point about the MKI / MKII ignition curves for the BTH.
the Francois Grosset unit i´m using has a mechanical ATD (similar to the original "D" distributor) based on what appear to be harley parts. ( Apologies if this isn´t the case Francois
)The good acceleration i get between 2800 & 4000 i ´ve put down to the bike "coming onto the cam". The fact that nothing much happens below 2800 could also be because the ignition is advancing to slowly (experiments are needed with weaker springs on the bob weights maybe)
I´ll see what Francois has to say about it.
Hi Eddy,
Thanks for the info.
Interesting point about the MKI / MKII ignition curves for the BTH.
the Francois Grosset unit i´m using has a mechanical ATD (similar to the original "D" distributor) based on what appear to be harley parts. ( Apologies if this isn´t the case Francois
The good acceleration i get between 2800 & 4000 i ´ve put down to the bike "coming onto the cam". The fact that nothing much happens below 2800 could also be because the ignition is advancing to slowly (experiments are needed with weaker springs on the bob weights maybe)
I´ll see what Francois has to say about it.
Actually the advance/retard unit is Honda. Also the note about Dyna coils is in the instruction sheet.