Poor starting on new Amal and BTH Magneto

[minivin]

Good points gents, additional details as follows:

i) The BT-H is an auto advance and has been timed at 32 degrees as per their instructions. This is 6 degrees less than the Richardsons recommendation.
ii) The spark plugs are NGK B7EV.

Now, as I have a Vokes air filter here after getting a new Comet mounting stub made on a rapid-prototyping machine, I think I will try Greg's thought's on putting an air filter on first to help richen the mixture.



Now after that, I'll have a look at the ignition timing as the 32 degrees goes against all your experiences.....

 

[minivin]

I have a twin spark BTH I think 34 BTDC is a good place to start my Racing Comet is at 32 but its higher compression my carb is a Gadrner carb not reccomended for kick starts The float level is aproximate the low down running is poor but she runs like smoke where it matters. but that is of little help for you, me? I have a foxley roller started

Ah, now that is typical, someone who has had no problems with ~32 BTDC ;-)

 

[TouringGodet]

My experience with my Rapide and other British bikes is that with everything else correct, the key to good starting is the tickover setting.

I certainly had this situation recently on my Comet. It started very easily when cold, but when hot, I couldn't start it at all. Stock carbs and magneto. After touching only the air mixture screw, it now starts very easily cold or warm. I have the spring on the air mixture screw, but I noticed it was backed way out. I screwed it in until it was just snug, then backed it out one or two turns, and that did the trick.

 

[minivin]

Unfortunately I have found the first problem, the BT-H is weak! I have to kick the bike really heavily to get either plug to spark. Gonna go get another set of plugs and see if it's the Platinum plugs that are putting up too much resistance, I very much doubt it unfortunately......

 

[minivin]

actually no bollocks it, I'll do as David suggested and make a bonding lead first before I spend any money. Considering the surface area of the mounting, this shouldn't be the issue. But as I don't fancy damaging the regulator or BT-H with my Megga bonding tester set (it shouldn't, but I know my luck at this moment), I think this is the first step

 

[minivin]

OK, I finally have given up with the BT-H, with a bonding lead fitted it still struggles to fire. I have just gone and brought a pair of B7ET plugs and it still struggled to fire with them out of the engine. I have therefore concluded the BT-H is not fit for purpose and I am going to have to fit the K1F I have sat here.

Fortunately in some ways it is manual advance, so all I need to do is unbolt the BT-H and slot-in the K1F. But to say I am annoyed is an understatement, £600 annoyed to be precise

 

[vibrac]

I have never seen a spark on either of my BT-H mags (twin and single) but a piece of paper between the plug electrodes comes out with minute holes drilled in it.
I have raced both for many years
I have a product from the prince of darkness I will willingly swap fror your BT-H

 

[Gerry Clarke]

Only modern ignition experience was with a Pazon that did not want to work - KR was very pleasant giving a full refund. On reflection, I am much happier having a rewound magneto and an Alton for the lights.

I have original 289 carbs. and the original Lucas mag., rebuilt with slack wire manual advance/retard and timed at 35 degrees. I removed the chokes as they never made any contribution to starting on this current C Rapide or my previous D Rapide with moboblocs. Much easier to route the throttle cables. I make my own cables and take great care with synchonization. The carb. settings are book standard and the plugs look fine, with no. 1 cylinder just a hint rich for cool, unstressed running. Tick-over when warm is fine and starting is first or second kick - needs ticklers depressed for a count of three, that's enough to raise the levels and not spill out. Apart from the usual prime kicks and easing over no. 1 compression (can hear the rear carb. gurgle) with the valve lifter, it needs about one third throttle and off she goes. No trouble starting and riding in the cold weather we've been having, including mornings leaving home at -2C.

Gerry

 

[craig]

so you are pulling the plug after 5-6 kicks and it is wet with fuel because it (they) didn't fire?

 

[davidd]

Like Tim, I am a little surprised. In my experience the BTH either works or it does not, there is no in between. However, changing the ignition will tell. A friend who just built a Norvin and fitted a BTH was going through the same thing last weekend. The rear cyilinder would not fire. He spent all day building an ATD and fitting a stock magneto. The rear cylinder still did not fire. It turned out that the rear cam was 180 off. The BTH worked fine.

Sorry it is so much work, but you will know soon!

David