I have been testing my ignition coil with a multimeter and coould someone say if these readings are ok. using the ohms setting at 200 Iam getting a reading across the positive and negative terminals of 5.2 changing the setting on the multimerter to 20 I am getting a reading of 8.1 when taken from each terminal to the center. THe reason I am asking is the bike a 1970 Starfire is difficult to start carb is Ok timing OK tne plug and HT lead are new. Fuel is fresh. After a few kicks if I take the plug out it is wet with fuel and the plug seems to spark ok when kicked over.When I do get it to finally start it will tick over perfectly for about a couple of minutes then without any warning it just suddenly stops then takes ages to get started again no problems with fuel blockages or the vent inthe petrol tank being blocked.I do not want to go to the expnse of buying a new coil if this one is ok Thanks.
Coil figures seem to vary a lot on coil and points ignition bikes, and the ultimate test is to substitute yours for a known good one.
As a friend was reminded recently, Starfires could be sods to start sometimes even when well set up.
Thanks for the reply what I failed to add was the bike has Pazon electronic igntion not points, but that was what I was hoping to avoid buying a new one then finding out it was not really needed.
Hi,
The wet plug could indicate flooding. When started can you rev the engine to get it off the primary/pilot circuit and on to the needle?
Dave.
To test any component you must completely disconnect it from everything.
Meter on 20 ohms scale
Primary connection + to - around 4.5 ish ohms , maybe 2.5 ish.
Change scale to 20k and leave 1 clip on 1 of the connections and put other clip down centre ht post.
Should be around 4.5k ish
Thanks for those replies. When started it will rev Ok and release the throttle it will tick over OK for about maybe a minute then without warning will cut out, then difficult to restart but when it does it will just repeat tickover then suddenly cot out. Asregards the coil testing the coil was fully disconected both positive and negative wires and also removing ht lead. using multimeter set at the 200 setting across positive and negative terminals a reading of 5.1 then connecting between positive terminal using the 20 setting on the mulimeter and the other to ht terminal a reading of 8.1 same reading using the negative terminal and ht terminal.
You must , I think allow the meter to read the resistance correctly by choosing the correct scale.
Most meters have
20
200
20k
What this means , is that the thing being measured will go up to or exceed each scale , forcing you to choose the next scale upwards.
So you're getting 5 ohms on the 200 scale for the primary , but you need to choose the next scale upwards before you move 1 of the leads to the ht terminal.
Electrical issues often run for a minute or 2 then fail.
Cool down , work for a minute then fail.
Have you tried the condenser ?
The scales on the meter I was using were first the 200 that got a reading of 5.1 then used the 20k which got readings of 8.1. The condensor is not in use because it has Pazon electronic ignition. Having ruled out any fuel problem I am left with electrical and I suspect the coil, but not being very electrically minded I have checked the coil with a multimeter but on checking on the internet some people are saying that the readings I should be getting are approx 3 across the positive and negative and 9or 10 when across the ht and other terminals,my coil is not giving those readings so that is why I suspect the coil. Thanks I do have a very old spark plug tester must 40 years old it is v shaped plastic you connect the plug on one end and the Ht lead to the other then you kick the bike over while gradually moving the contacts apart it has a coloured scale to it goes from red to green then white inthe red you have a problem inthe green you could have a problem and in the white all Ok. When in the white the contacts are about 10- 12mm apart and when kicking over the spark jumps the gap with a good blue spark.
Ah ok.
Blue crack is good
Sometimes a spark will jump , laying on the head , but fail under compression.
Can you substitute coils side to side (if twin) or another machine.
Some twin bikes use 6v coils in series which are different ohms to 12v coils
As I have said in my first post the bike is a 1970 Starfire 250cc. I have owned a number of BSA bikes in recentyears mainl twins 1957 Gold Flash 1956 A7 1964 A65 1957 C12. Until a couple of years ago I had both the A65 and the A7 but because of age now coming upto 83 the big twins were becoming to heavy get on the center stands and move around in the garage. Still enjoy riding so bought the Starfire All previous bikes after setting up correctly were either first or second kick starters the Starfire is the exception never a first or second kick starter even after spending time making sure all set up OK. Maybe this is something that I will have to live with. Done some checking on the web and found out that coils can be tricky they test out Ok but can still cause problems when running the bike, in fact it can give the impression that the problem is fuel related. That is why suspect a possible coil problem as I have eliminated every thing else. When I had it out last summer it runs perfectly Ok on arun it is just the initial starting that is the problem and this sudden cutout after ticking over for about a minute.
Coils are about 25 quid so worth a try
I had a Lucas Coil on a Royal Enfield go faulty. The only indication that it was wrong was that it was taking 6 Amps instead of the usual 3 Amps. This proved that some of the turns of the coil were short circuited, which prevented the magnetic properties working correctly. btw.. It was a long push home..!
Thanks for all the replies butnobody has said if the readings that i am getting are OK i do not know how much leeway is alloed from what I can gather across the terminals ou should get 3ohms and acroos the center to each terminal 10 ohms I am getting 5.1 and 8.1 respectively so are these readings accetable.
Below is a test sequence that I came across a few years ago and saved for reference. It gives details of a few very simple tests you can do to determine whether the alternator is ok.
Testing the Stator
As it is a coil of wire it must have two ends (Yes I know a lot of our stators have three wires) so our first test is, is there continuity through this coil? 1 to 3 ohms is the ball park figure. While at the same time this coil should not have any connection to the earth of the bike. If you don't have a multi-meter then a bulb test is very good, often a bit more instructive.
Disconnect the alternator wires from the bikes wiring. Use a headlamp bulb; you know - the one with one filament left! Fit the bulb up with a pair of wires so that you can connect it to the alternator wires. Start engine and at a modest tickover the bulb should light up enough to see that a rev up would blow it! Use the other wire if you have three, and a similar result should be obtained. Do not worry about how bright or what wires to use, just make sure that all wires are used to give an output at some time. If the bulb does light up but is less than 'brilliant' then you might have weak rotor magnets, more anon.
Finally connect one end of the lamp to the engine and the other end to any one wire, there should NOT be any bulb lighting. This would indicate a good stator. Three wires? Time and again, I am told that 'I have a 'three phase alternator'! No sir. The sign of a three phase stator is nine pole pieces, ie the grey metal pieces inside. Output Hi or Low? 6V or 12V? only the part number can help us now, there are quite a few, so look for the 47*** number, this will tell all. You don't have such a list? I do!
The Rotor /Testing
The early 70mm outside diameter rotor came in different widths at times, but as they are all tired by now and we need more output, do not concern yourselves with these rotors too much, if it is there and it works, fine. The later 74mm are just about all the same thickness and they all have 6 magnets, ie they are all the same electrically (magnetically) despite different numbers, 54212006 being the most common and most prone to failing.
Condition? Mostly sorted by giving it a good looking over. Is the centre steel tube coming loose? Is there grey powder 'throwing' from the centre? Does it show signs of having touched the stator? (shiny bits and deep scoring). Are the magnets coming adrift? Is the woodruff key slot worn? Are the magnets any good? The latter needs a magnetic probe (I have one!) but there is still plenty you can check. Hold out a medium spanner or large screwdriver, will the rotor hold its own weight on all six magnets? If not then it is not worth putting back on the bike. (Kick it under the bench now it's on the floor!) For a real test of magnetism we do a full output test.
Full Output test
Now we have to be a little more electrically clever, do you have/can you use a multimeter? Have you got a friend who has/can? You need a 10AMP DC range on you meter. You do NOT need a 1 ohm resistor (Lucas suggestion). This test is the same for 6V and 12V and 3 Phase and High Output (with a little reservation we are coming to). Find the output terminal of the Rectifier or Regulator/rectifier. Disconnect its output lead. This might be a BROWN/BLUE wire and will be the Negative terminal if we have a Positive earth system. Connect the 10A DC meter between the output terminal and the wire you just pulled off of it. Lights on should NOT cause any current to flow, if it does then you've got the wrong wire (you might be on a battery lead). Start the bike, and put on all the lights. Rev up to 3000 or so and for the RM21 you should see close to 9 amps. If you have some 3 phase or high output then you should pass the 10 amps about 2500 revs.
The rotor/stator gap should be a MINIMUM of 8 Thou, any less will cause contact, heat, electrical output failure and huge expense to say nothing of a seized engine and even an accident!
Neg to pos ohms around 3 , this is primary windings, using the 20ohms scale on meter.
Either of the neg or pos to the centre ht using the 20k scale should be around 4.5k ohms
Give or take
You have a new pazon, no condenser and if your bikes ht coil is the remaining original part, then I'd change it anyway frankly
An update on this problem starting it would seem that the problem was nothing to do with the coil but a dodgy plug, the reson why I discounted the plug in the first place was the plug is practcally new it has done less than 200 miles.What happened was I tried to start the bike a couple of days ago and kicked the bike over at least a dozen times to know avail took the plug out it was wet and was sparking on kickover, so in desperation I found a couple of old plugs from an old bike that I had some years ago they were not the correct type being NGK b7es the starfire is NGK b8esbut I fitted one anyway and the bike started after 2 kicks and ran perfectly. Have decided to abandon NGK and have ordered acouple of Champion plugs N3c which is the equivalent of the old N4 plugs.
There are dodgy , fake ngk out there certainly.
The n3 champion is a petty hard/cold running plug,compared to the n4.
Depending upon your riding, you may find n4 better choice
Champions , the lower numbers mean colder/harder plugs, which may foul up if riding gently
From what I can find out the N4 is no longer avaiable it has been replaced by the N3c.
Green spark plug co
Just over £2.40
N4c plugs are available but are un glazed as are N3c. If after flooding the carb the bike doesn't start first time the unglazed plug will soak up thr fuel and short out.