FAQs

A selection of questions we have been asked.

Question 1: "Is the new BTH magneto 6 volt or 12 volt?"
Answer: Neither. The new BTH magneto generates its own power so it doesn't rely on a battery.

Question 2: "Will the new BTH magneto fit my nineteen hundred and frozen to death, XYZ Sport?"
Answer: If your bike originally had a Lucas or BTH magneto we will almost certainly have a model to fit.

Question 3: What is the magneto point’s gap?
Answer: The new BTH magnetos don't have any mechanical contact breaker points. The spark is triggered electronically so there is nothing to adjust.

Question 4: I like spending hours trying to adjust contact breaker points and ignition timing poking bits of cigarette paper in inaccessible places. What am I going to do with my time now that I have fitted my new BTH magneto?
Answer: You really do need to get out more. Try going out for a ride on your bike now that you have got the ignition sorted.

Question 5: Can I fit a manual advance lever to my new BTH magneto?
Answer: The simple answer is no. Your new magneto has an automatic, analogue, non-programmable electronic advance built in. You can specify fixed ignition if that is what you prefer.

Question 6: How long will I have to wait for my new magneto?
Answer: If we receive your order early enough in the day our standard range of magnetos is usually available for next day, UK delivery.

Question 7: Can I fit my new BTH magneto myself?
Answer: If you are comfortable removing, replacing and timing your old magneto you will find fitting your new BTH magneto very easy.

Question 8: Will I have to alter my carburettor settings?
Answer: Carburettors on old bikes are often set rich to keep the bike running because of old, worn parts or failing magnetos. Your new BTH magneto will fire a weaker mixture that may help your petrol consumption. If you have fitted a "new" carburettor don't assume that it will be OK because it is "new".

Question 9: Will fitting a new BTH magneto be the end to all my bike troubles?
Answer: We would like to say yes but realistically there are too many other factors involved. A correctly fitted new BTH magneto will solve ignition problems but here are a few things that our customers told us that our magnetos did not solve: Tight tappets, exhaust push-rod out, carburettor jets wrong, different length needles in twin carburettors, not enough petrol in the tank, plug leads on the wrong cylinders, timed on the wrong stroke and bike just simply worn out.

Question 10: Can I use suppressed plug caps on my new BTH magneto?
Answer: You can use 5 ohm suppressed caps but we strongly advise to use both the leads and plug caps supplied especially with twin spark set up.

Question 11: Does the body of the coil need to be earthed?
Answer: The coil body does not need to be earthed as the two leads fitted to the spade terminals on the coil supply continuity.

Question 12: What is the advantage of the timing peg?
Answer: The timing peg allows more accurate static timing as it locks the magneto in the correct fully advanced timing position during installation. Checking your timing with a strobe light, although not essential, is recommended for maximum accuracy.

Question 13: Is there something wrong with my new BTH magneto as the spark seems very thin?
Answer: This is normal as the spark from our magnetos is very high tension that produces good performance. It is sometimes difficult to see the spark at the plug gap, especially in bright light. Also see FAQ 14.

Question 14: How can I easily check that the spark is strong enough?
Answer: Remove the spark plug and put it back into the plug cap. Hold the plug by the plug cap or lead to avoid a shock. Hold the metal body of the plug approximately 1/4" (6mm) away from the engine while you or an assistant turns the engine over. The spark will jump the gap from the engine to the plug and the spark plug gap. If you can't see a spark because of the light conditions you will almost certainly hear the "crack" of the spark jumping the two gaps. (See Note 1.)

Question 15: Everything seems to be OK on the ignition side but it will not start.
Answer: If the ignition side seems OK look at other reasons. Have you got fuel? Is the fuel old? Modern petrol loses the volatile portions if left standing for more than a few weeks. (See Note 1.) Try some fresh fuel. Have you done a rebuild? What else have you changed, valve timing, valve clearance, carburettor, etc?

Question 16: Can I use an electronic rev counter with my new BTH magneto?
Answer: Several people are successfully using the self- powered the Scitsu electronic rev counter. Nick Brown, of A.J.S. Motorcycles, has sent us this advice. (See Note 2.) Another rev counter we have successfully tried is sold by Mick Hemmings. This simply needs a diode (IN4001 or similar) in the sensing lead and a12 volt supply.

Question 17: Can I use suppressed plugs?
Answer: NO, Suppressed plugs or anything with an 'R' have high resistance and can damage the CDI unit.

Note 1.
David Irvine in the U.S.A. had contacted us regarding a starting problem on his B.S.A. It had been laid up for a while. Tony Harris (previous owner) got this email:

Hi, Thanks for your speedy reply. My face is quite red with embarrassment. Right after I sent you the email, I checked your website hoping there might be some clues. Sure enough, an item in your FAQ list described the proper way to check for spark. By this time the BSA was indoors for the night, and out of the earlier bright sunlight. And sure enough I saw and heard the spark at the plug and jumping to the chaincase, just as the FAQ described. Anyhow, recalling that the BSA had sat idle all summer, I removed the Amal Concentric carb, dismantled it, and found the bowl and fine screen around the main jet coated with varnish; I'd failed to drain the bowl after the last run. Carb parts are now soaking in carb cleaner; I've been through this before and knew better. Thanks for your interest; I'll keep you posted as to results. David.

A little later we got another email from David:

Hi, A word to let you know the BSA is starting and running fine again. Its problem had nothing to do with your magneto but was entirely due to me letting it sit idle all summer long, letting the gas in the carb bowl turn to varnish (think there is a lesson here!). Again, my apologies for my magneto misdiagnosis. It's good to know you still retain an interest in your products long after the sale was completed. Best wishes, David.

Note 2.
Do not strap HT cables together allow a 1/4 air gap between HT coils (should not be touching)

Note 3.
Please be aware not to over tighten MD1R strap as this can lead to excessive clutch wear Note 4.

Re: Scitsu Tachometers: The single Magnetos use a yellow unit. The black model is recommended for you 360o twin with BT-H high output mag. You should connect the Tacho sensor wire to both HT leads. V twins are tricky because of the uneven firing pulse. the 1-2 space, 1-2 space, firing order can confuse the Tacho, so it is best to treat V twins like a single and try to keep the sensor wire away.