Poor starting on new Amal and BTH Magneto

[nkt267]

If I remember correctly from a previous lenghty thread, the BTH does not show much of a spark when the plugs are out.
Unfortunately it seems that what works for one bike may not work for yours..My Comet does not like to be tickled and prefers to be on the weak side for starting.If all was well with the old carb I would fit it just to prove where the problem lies..John

 

[greg brillus]

Yes without a doubt there seems to be no two bikes that are the same re starting. Some like a rich mixture and some not so rich....the latest Comet i finnished off had standard Lucas mag ignition and a new 289 Amal...was hard to start after fuel on, tickle carb, choke lever closed, kick over comp using decomp lever a couple of times, and then go to start.....after about 10 kicks gave up and pulled the plug, to discover it wet...left till next day....fitted new plug with 18 thou gap per normal, Ok try again with different technique...fuel on, tickle carb for a few seconds only and not enough to pee "as it were" choke lever closed, kick passed comp a couple of times, this time open choke, and kick away....started first time.....I think the starting on anything will always vary from machine to machine, but having good carburration and well set and functioning ignition contribute immensly.....If you think about the various older bikes that people own, generally i have found that the ones that always sit in the shed unused are the ones that are hard to start, or hard to start when they are hot.....this is a shame, but unfortunately true for obvious reasons..............and even more so if that bike is a "Vincent"................Cheers.....Greg.

 

[minivin]

Morning Gents and Ladies, I have to now admit to an EMC Fopaux that I should have known better about, since being an electrical designer on aircraft systems I have to account for this every day.....

While in the process of removing the cloth tape that holds the HT leads to the oil line on the cylinder head AND cutting a number of tape strips that held the cut-out line to the port side HT lead (which was the most inconsistent when it came to firing) for about a foot in distance (I was using the HT lead to hold the cut-out line away from the exhaust pipe and cylinder head), I then cut the kill line just in case it was shorted and I thought to myself "I'll give it one more chance before I remove the BT-H".

Low and behold, with the garage door down and in darkness for the tenth time that morning, there was sparks! thousands of them, like Zulu's.

I then went through the stages of strapping the lines back on, first the starboard HT lead, engine started, then the port HT, started, and then finally twisted the cut-out line back together and...... STARTED.


Now, after going out on the bike for the rest of the day and putting twenty miles on it, with about five first-time starts and three two-or three prodders, it got me thinking that I must have had a partial short in the kill-button. However on further reasoning and thinking how the port ignition lead had pretty much never fired, and once the kill line had been removed from it it now fired every kick, I had unfortunately created a massive EMC loop on the ignition kill switch.

What we have with the HT lead is a "very" Emmisive line in EMC terms, it's throwing out lots of electro-magnetic interference which has always been known about in the past years when TV sets would get very upset when a vehicle would go by outside with no suppression on the ignition system. While what I had strapped to it for about twelve inches was a "Susceptible" line in EMC terms (the cut-out line), which is looking for a signal (a OVDC ground line in this instance) to tell the Magneto electronics that its requirement to fire is no longer needed. What I had created was a perfect induction loop that was inducing noise down into the BT-H, which was upsetting the brain within the magneto and causing it to go mad!. Once the line was away from the HT lead, I have had no problems either since.

Hopefully that is the end of the problems, however I do have some design issues, I'm going to start a new topic on that though.......

 

[timetraveller]

It is an interesting thing about some modern ignition systems that they throw up problems that those of us brought up on mags, or even those new fangles coil things, never had to learn about. A few years ago I was helping Roy Robertson with his racer at a local rolling road. It was our first trip there and the readings were off and a mess. It was only later that we found that the 'rev counter' on the rolling road was picking up massive inteference from Roy's modern ignition system which, like minivin's, was broadcasting radio frequency interference everywhere.

 

[vibrac]

Who would produce ignition systems for 70 year old bikes? all that effort and then have to sholder the blame every time it doesnt start.no wonder this forum is littered with "I have gone to coil ignition"," I have gone to pazon" "HD ignition coils","refitted my K1F" .etc etc I think the BT-H is worth every penny

 

[TouringGodet]

I think the BT-H is worth every penny

Me too, it does wonders for my twin. Mags are okay too, the Comet is quite happy with one.

 

[ossie]

when my shadow [magneto] was ticking over my freinds harley would fail to start turn off vincent and his harley would go.?? happened a few times as well.
OSSIE.

 

[nkt267]

Mags are okay too, the Comet is quite happy with one

Mine died today in Newmarket.sob..sob..john

 

[davidd]

I think it is tough to make the transition from magneto to electronic ignition. As I mentioned above, I had trouble on the initial set up and it is difficult not to blame the ignition that you have not experience with. Many owners prefer the stock set up because they know how to make field repairs and there is not possibility of a field repair to an electronic ignition, unless it is a wiring issue. Congratulations to Minivin for catching an installation issue.

The issue of the spark is always tricky. The spark of the BTH appears to me to be a high frequency spark like the one I see when I try and TIG weld, but forgot to hook up the ground. It is not always easily visible (as Tim has mentioned.) I tried to find some information on the spark itself and I was not altogether successful. I was most interested in finding out if a big blue spark was an indication of anything that could provide useful information. If what I read is correct, the visible spark that we can see is not the spark that ignites the charge. This does not answer the question well, but it does suggest that the spark we see is the coldest part of the ignition. I ran across the following on the Briggs & Stratton site in the Ignition Theory section:

"Briggs & Stratton ignition myths:

A bright blue spark is best. A yellow/orange spark signifies weak ignition. Not true. Spark color determines virtually nothing. The hottest spark is ultraviolet which we can't see. Blue spark is cold in comparison to ultra-violet. Orange and yellow come from particles of sodium in the air ionizing in the high energy of the spark gap.

Laying the spark plug against the block and pulling the engine over can adequately test ignition coil output. Not true. The ignition coil will only generate enough output to jump the gap of the plug. When under compression, the plug requires twice the voltage to fire. This check is not an accurate test of the coil and can be misleading.

An armature air gap that is too wide will prevent spark. Not true. Well, sort of not true. Briggs & Stratton air gaps cannot be made too wide to prevent spark providing the coil is healthy and the engine is spun over fast enough. A wide air gap, say .030" will ever so slightly retard the ignition timing as the magnetic field takes longer to build within the coil windings."

If anyone knows more about the sparks, I think it might be helpful.

David

 

[vibrac]

When we put the racing Comet on Methanol the then owner of BT-H said the higher demands made by the compression and the mixture will strain the electronics it will only last a season or so. Mid-way through season 2 she stopped as predicted. as BT-H was on the way to Mallory we popped in and he sorted it fast enough to get to practice.
Never finding a great advantage to Methanol (Our engine was way cool anyway) we dropped the compression and reverted to petrol at the end of the season BT-H is still fine 3 years later