Bogging down

[Dinny]

I had the same problem, mine accelerated ok at low speeds with small gradual throttle movements, if I moved the throttle quickly it bogged down.

I fitted new needles, pilot jets and reset the carbs. I was running in and running rich but think it was due to the richness. I modified my slides from 3.5 to 4.5 and that helped as it also leaned out throughout the range. After I got the mixture leaned with the idle screw and lowered the needles I then fitted two new spark plugs as I have found that the Champion N5's don't like running rich with modern fuel . Once new plugs were fitted no further problems, I found that once a plug starts missing no amount of cleaning will cure the problem. One plug on the rear cylinder lasted 25 miles which I put down to a rich mixture killing it.

I'm running 289's so slightly different but I looked at everything and was pulling my hair out so I hope this helps.

 

[Howard]

http://www.britcycle.com/Manuals/MonoblocTuning.pdf
The original Amal Monobloc tuning guide is here.

H

 

[macvette]

Thanks all, have all the Amal tuning guides. Re routed the kill wire and the issue is gone. I did know that BTH advise routing the kill wire away from the leads but ignored it for the sake of neatness. We live and learn.
Thanks Mac

 

[Martyn Goodwin]

Thanks all, have all the Amal tuning guides. Re routed the kill wire and the issue is gone. I did know that BTH advise routing the kill wire away from the leads but ignored it for the sake of neatness. We live and learn.
Thanks Mac

This was published a while back and along with a lot more Vincent material, will be republished in a future edition of the Oz Vincent Review.

BT-H Magneto Woes Begone?
Here is an extract from a recent thread from MiniVin @ the VOC Forums on the topic of an apparently unreliable BT-H magneto that, in utter frustration, was about to be removed from a twin:
<<QUOTE>> …
While in the process of removing the cloth tape that holds the HT (spark plug) 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 BT-H 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, engine started, and then finally twisted the cut-out line back together and...... it STARTED! On 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 realised 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 zero volt DC 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 BT-H cut out line was moved well away from the HT leads, I have had no further problems. Hopefully that is the end of the problems <<UNQUOTE>>

So dear readers – the message is clear – irrespective of what sort of ignition system you have, keep ALL low voltage and ground (earth) wires well away from the HT spark plug leads and where applicable, Coils.

 

[macvette]

Thanks MartynG that's the article I recall. My bike is a D and despite having the distributor rebuilt, I could not get the timing to be consistent. I had completely rebuilt the bike and it went well but not reliably. Last September , I finally stripped the distributor and found that the rebuild had been botched in that the pins holding the advance weights were loose and the nylon washer under the cam plate was too large a diameter and was hoopla hooping around the shaft interfering with the bob weights. This coupled with the loose pins explained the variable timing. I fitted the BTH and the bike was immediately easier to start and idled well. I rode it a little but not too hard because I was just coming to the end of running it in and put it away for the winter. It didn't show any symptoms.
When I started to ride this year and really open the bike up is when the hesitation started. In my case I could feel it at 60 mph in third and 70 in top. When I checked the plugs having tried to ride past this, the front plug was very sooty, the rear was fine. Having checked everything twice, I finally recalled the issue described above. I didn't think re routing the kill wire would work but in my case it has and the the bike now revs out freely, phew!
Again thanks for everyone's help, Mac

 

[redbloke1956]

Thanks all, have all the Amal tuning guides. Re routed the kill wire and the issue is gone. I did know that BTH advise routing the kill wire away from the leads but ignored it for the sake of neatness. We live and learn.
Thanks Mac

Hi Mac, I extended the kill wire, sheathed it, then ran it down from the mag - under the engine - then back up to join the main loom at the rear of the UFM, can't be seen and is very neat.
Cables carrying varying High Current or High Voltage can induce quite high Voltages into conductors running in close proximity causing all sorts of grief, especially to Electronic circuits (as in the BTH) So you should always keep High Tension wires away from every other conductor to be on the safe side. A small example of this phenomenon is to turn off a circuit breaker to a circuit in the home and then measure the Voltage on that circuit, you will almost always read a Voltage of sometimes up to 30Volts, this Voltage is induced into this otherwise "dead" circuit from conductors in close proximity.
Regards
Kev

 

[macvette]

Here's what I did . Mac

's what I did

 

[Bill Thomas]

Looks a nice one Mac, How about a full photo, Cheers Bill.

 

[macvette]

Here you go Bill