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Discussion Starter · #1 ·
Can the ignition of a T140 be set with a dwell meter?
If so, what angle setting and how is it accomplished as I've never seen a 2 cylinder dwell meter?
 

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Don't mean to be sarcastic but seen too many burnt pistons etc.
If you want all kinds of headaches use any other technique you want. If you want to set your timing and be sure it is dead on use a timing light - period. If you want to forget about timing issues permanently, get a Boyer.
 

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Discussion Starter · #3 ·
Talking two different things there.
Dwell meter sets the points, not the timing.
I use both dwell meter and timing light on the old car.
 

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Hi Guys,I'm a newbie overhere:) so Hello again:)never had an old trumpy but plenty of time on BSA twins,I always thought dwell was the time contact points stayed open ? Yeh that sounds right,,,? ie the position of the breakers in relation to the cam lobe,with 2 sets of points putting a dwell meter on em could be done in theory-the way its been done since time immorial as you know is to have both sets opening at the top of the lobe-15 thou I think ?,locking it THEN TIMING IT,So to answer your question-dunno:)J.B.
 

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In my limited experience with points, surely the dwell is set by the gap.
Bigger gap-longer dwell and vice-versa.
Or are you asking if the timing (the point where the breaker begins to open) can be set normally, but the length of time until closing can be varied? I`m just asking myself why anyone would want to do this?
 

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Nah your missing the point,the dwell is how long the contact points stay open and this is dictated by the position of the points in relation to the housing,if it stays open too long it'll bump over and you wont get a true timing on both cylinders ie one cylinder will run hot,your bike will start running on 1 piston,you'll check fuel,you'll probably look at your plugs,coils etc,most parrell twins have got a coupla firing spots..anyhoo thats why I use the the elektick stuff :)J.B.
 

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Discussion Starter · #7 ·
I think most are onto the idea, and I should have said "set the points" via dwell meter.

We used to do that all the time with the dual point Mallory distributor on the old Chevy hot rod.

So does anyone doe that on their Triumph and if so, with what meter and how.

I am thinking a 2x multiple of a 4 cylinder meter reading, but not too sure.
 

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Hey Beemie I'm with ya man. I have been trying to find out the answers to the question you are asking for years now without success. The method you are suggesting (dwell meter and timing light) made tuning my old Honda 750-4 so much easier and effective than just checking the contact points gap with a feeler guage. I'm certainly not here to challenge those who prefer the tried & proven way the Triumph manuals suggest. I'm just aware as you suggest, that there are other ways to confirm the dwell of your points are correct and equal with each other on Triumph twins, it's just nobody seems to know what that dwell angle should be and if there is a dwell meter out there capable of use on a twin cylinder engine? I'm glad I'm not the only Triumph owner that has pondered this question and am now more determined than ever to see if I can make this work.
JQ
 

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Dwell meters actually show the ratio between points-open and points-closed time - that is, how long the points are open for, compared to how long they are closed for. On the Triumph twins, this is determined by both the points gap (minor contributor), and by the cam lobe (the major conrtibutor to the ratio). You'll notice that the Triumph twin lobe is shaped in such a way as to close the points about 100 crank degrees before firing (to "charge" the coil) then open at firing time. The points are kept open until the next compression cycle so as not to overheat the coil(s) and waste current. This ratio (6.2:1) would make a dwell meter reading fairly useless.

Dwell meters are really designed for multi-cylinder, single points set, distributor based engines with multi-lobe points cams. They allow the setting of the optimum points-closed to points-open ratio, which in these multi-cylinder engines is much more reliant upon points gap. They also fairly clearly show up lobe wear if the points gap is set correctly in these types of ignition systems.

My advice is to forget dwell meters on the older Triumphs, and persist with points gap (15 thou) and timing using a timing strobe. If the timing is out between cylinders, either vary the points position (on the newer plate) or vary the points gap on one point set (on the older plate).
 

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Discussion Starter · #12 ·
If the dwell meter method was appropriate for our old dual point hot rods, it certainly could apply.
A little variety in life keeps it interesting.

A bit of research into the theory is in order to see how to apply the dwell meter readings.

There is always the simplist way of getting the appropriate readings working backwards by getting the engine perfectly setup by conventional means and then seeing what the dwell readings are.
 

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If the dwell meter method was appropriate for our old dual point hot rods, it certainly could apply.
A little variety in life keeps it interesting.

A bit of research into the theory is in order to see how to apply the dwell meter readings.

There is always the simplist way of getting the appropriate readings working backwards by getting the engine perfectly setup by conventional means and then seeing what the dwell readings are.
Dual point distributers in the old hot rod were still used by only one coil, doubling the input current to the coil. These bikes have no distributor. Each point plate half operates a single cylinder. I think everybody would get a different dwell reading (and all be right) as it would be so varied by the difference in eccentric screw settings and such. If you were to try to match each point dwell setting, it probably would be all out of timing. There isn't a whole lot of "out of tune" room on these. I spent a week trying to get the timing perfect, and it still isn't. One of my cylinders is still about 1-2 degrees advanced, and if I move it a hair, it's the same, 2 hairs, and its way retarded. We are, in essence, just lucky they run at all. Just my $.02.
 

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Yes.. one method of getting the timing spot on with points is to use only one set and fire both coils but it involves making up a cam.

As a point of interest, I always thought that a Dwell meter measured the charge time of the coil, this is the time the points are closed. This is really the time or angle you are interested in.
 

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The japanese bikes of the 70's used 1 point and 1 coil for 2 cylinders, and 2 points and 2 coils for 4 cylinders. They are so easy to time too. 2 cylinders would fire simultaneously with a "wasted spark" to the non-compressioned cylinder. The the point plate ran off the crankshaft. But again, these are unique bikes for today, and I wouldn't trade for a Honda. I just wish I had an old Honda too, and a Norton, and a Bonnie T-100, and a ...
 
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