Boyer ignition problem

[Smokey_Paul]

Hi Dirk

I dont know of anyone having great success with the standard Boyer but as you will have seen you can order a special box directly with different curves.

Yes the Silk does kick, I always say you have to give it a brave deliberate kick to reduce the chance but Lumenition bikes are not as bad and wont start backwards as Boyers can do.

If you still have the standard parts I am building some Lumenition MK16 kits up to replace failed units. I can also test your units if you have them.

Regards Paul 

Sent from my Galaxy

-------- Original message --------

From: "Dirk [via Silk Motorcycles]" <[hidden email]>

Date: 08/11/2020 17:29 (GMT+00:00)

To: Smokey_Paul <[hidden email]>

Subject: Re: Boyer ignition problem

Hi,
i just got ready fitting the boyer to my no.112/114.
Mine is advancing as you rev up.
I started with .2“ advance with poor power, am now at .3“ with much better power.
BUT, it kicks back like a mule, no matter if set at .2“ or .3“ !?
....i cannot remember if my (all the others?) Silks tend to kick back in stock form (lumenition),
cause it is 5 years since i last drove it (shame on me the the boyer conv. took so long)

Also i am not sure if the engine is pinging under load esp in high gear.

Is there anybody in that forum who uses the boyer for more than a test ride?

yours
Dirk

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[Dirk]

....i already have the "silk-special" boyer box.
though i am not ready with trying to find the correct setting....
chances are i get it right. i will let you know.

thank your patience

Dirk

[Arthur Farrow]

Can you say please approx how many degrees it advances?

Anybody any idea how many degrees the standard mechanical system advances...mine is broken

I was sold a standard Norton one with plans to mount on silk by AO about 5 years ago only just fitted

Boyer are looking at making me a new “box” with the so called silk advance

Presumably this approved by mr silk himself when he bought one

Sent from my iPhone

Arthur Farrow

On 9 Nov 2020, at 09:43, Dirk [via Silk Motorcycles] <[hidden email]> wrote:

....i already have the "silk-special" boyer box.
though i am not ready with trying to find the correct setting....
chances are i get it right. i will let you know.

thank your patience

Dirk

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[Dirk]

so mine i made markings on the left engine side for ,2" and ,3";
when i run the engine, static timed at ,2", it does this advance from some about 2000 rpm.
Best setting i got is just before ,3".
I am not ready yet with trying to achive best setting. I keep you informed
 

....in degrees ,2" is around 25 degree and ,3" is round 35 degree;
( my degee-wheel is too big to get exact measurements)

[hendred]

I haven't measured the advance the mechanical unit provides and I don't really want to take it all apart again at the moment.  Looking at pictures of it I would estimate about 15 degrees but could be very wrong.  I asked Boyer Bransden for the technical details of the Micro Digital box developed for the Silk and they very kindly sent back the information requested.  The Boyer Silk box gives 20 degrees advance starting at 1000 rpm and reaching full advance at 4000 rpm. There is only a very slight increase in advance between 3000rpm and 4000rpm so essentially it reaches full advance by 3000rpm.  It also has no significant advance up to 1000rpm.  Assuming the measured and calculated figures are correct, full advance for 0.2" is 27 degrees and 0.3" is 34 degrees, then the starting advances are 7 degrees and 14 degrees respectively. Pretty similar to the mechanical advance if 15 degrees is correct.

I found the standard Norton Boyer Micro Digital advance curve here:

https://www.accessnorton.com/NortonCommando/electronic-ignition-advance-curves.21964/   

Look for the Rick in Seattle curves.  The data here is for engine advance for a camshaft rotating at half engine speed so everything has to be halved for a Silk installation. This gives 16 degrees advance at 2500 rpm.  The interesting thing about the standard Norton curve is the increase advance at 500 rpm for idle stabilisation.  This won't help with kickback on starting a Silk.
Hope this answers some of the questions.

[Dirk]

Thank you very much for that great research
After some road testing with the "silk-boyer-special" box, at ,3" , i think it is working quite well;
but i found from the throttle response and the way the engine puts out its power,
there must be something wrong with the carb......Amal 2038/303
so i put it apart and found:
main jet: 400
idle(air)jet: 50 installed down in the float chamber instead on the carb body
choke jet: 25
throttle valve: no.3
needle: 2F1, but in highest position
spray tube: the stepped up type (Nortons!?)

....looks like i have some work to do

[hendred]

Sounds like the Boyer is working ok which is good.  A few comments on the carb.  Do you know if this is the original carb fitted to the bike?  If you look in the Technical section of this site under Carburretor you will find the settings for the various carbs, including the 2038.  I believe the usual 38mm carb fitted was the 2038/302 which is a right hand 2 stroke carb.  2038/303 is a left hand 2 stroke carb and the jetting on your carb is similar to the baseline setting on the Amal website.
The choke jet and pilot jet appear to be the fitted in the wrong positions, the bigger jet is for the choke (enricher) , the smaller is for the pilot.  I now believe the pilot jet should be in the float chamber, not the body, it is prevent engine flooding - see new topic.
The spray tube is cut away on the 2 stroke carb, Amal part no 2622/148.  You will find a picture on Google.  Amal did make a special for Nortons and I believe it was used on Commandos with MKI concentrics.  

Hope this helps you sort out the carb

[Dirk]

my carb was replaced in the 80‘s, when the first owner won a bike rally, with a new carb donated by amal.
From the documents i got with my bike, he ordered the 2038, that had been sold to silk.
Amal wrote back, that they had not been involved by silk about the final settings/jetting of the carbs when fitted to the bikes....
For the spray tube, isn‘t the 622/075 the one for 2 strokes ?

[hendred]

Sorry I got the pilot jet position the wrong way round, it should be in the body to prevent flooding.  I believe the 622/075 is the spray tube for a MKI Concentric. 2622/148 is a spray for a MKII.  For some reason Amal don't list the spray tube as a spare part on the exploded diagrams but you can find them if you know the part number. I found a picture of the 2622/148 on a US part suppliers site.

The Amal comment about not being involved with Silk settings explains the baseline setting of your carb.  The main difference between Silk and Amal settings is the smaller slide cutaway, bigger main jet and I think a different needle. As I said earlier it is all in the technical section on this site. The slightly larger slide cutaway may be beneficial on modern fuels as my bike tends to 4 stroke at very small  throttle openings with a 2 1/2 cutaway.

 Do you have original manual supplied with the bike?  Not much help with carb size or jetting but it would be interesting to know what ignition advance setting recommended for your Silk.

[Arthur Farrow]

Would it not be better to start a new topic on carburation?

Sent from my iPhone

Arthur Farrow

On 21 Nov 2020, at 11:09, hendred [via Silk Motorcycles] <[hidden email]> wrote:

Sorry I got the pilot jet position the wrong way round, it should be in the body to prevent flooding.  I believe the 622/075 is the spray tube for a MKI Concentric. 2622/148 is a spray for a MKII.  For some reason Amal don't list the spray tube as a spare part on the exploded diagrams but you can find them if you know the part number. I found a picture of the 2622/148 on a US part suppliers site.

The Amal comment about not being involved with Silk settings explains the baseline setting of your carb.  The main difference between Silk and Amal settings is the smaller slide cutaway, bigger main jet and I think a different needle. As I said earlier it is all in the technical section on this site. The slightly larger slide cutaway may be beneficial on modern fuels as my bike tends to 4 stroke at very small  throttle openings with a 2 1/2 cutaway.

 Do you have original manual supplied with the bike?  Not much help with carb size or jetting but it would be interesting to know what ignition advance setting recommended for your Silk.

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[Fredvincent]

If it is any help, my carb is a 2038 303 on a one owner late bike with no record of the carb being changed.

[hendred]

That's interesting.  Doesn't really make any difference whether it is a 302 or 303.  It would be good to have confirmation of the jetting on an original 2038 carb.  I think the main jet on mine had been changed at some time.

[hendred]

That's interesting.  Doesn't really make any difference whether it is a 302 or 303.  It would be good to have confirmation of the jetting on an original 2038 carb.  I think the main jet on mine has been changed at some time.

[Fredvincent]

My 2038 has Main Jet 480, Needle Jet 108, Needle 2F1 on second groove from top, Slide 3, Pilot 25 in top of float bowl. This is as the manual for my bike states, except needle in middle groove. The needle was dropped one notch in service. The bike has done 12000 miles so it was running OK up to 2012. May need a bigger main jet now with current fuel available.

I checked my manual for ignition timing. It states 37.5 degrees, 0.3 in BTDC at full advance. This is for a late bike built in February 1979 which is I assume a Peter Green ported bike.

The engine data listed on the forum states 7mm BTDC for Mk 1, 5mm BTDC for Mk2 and 7.6mm BTDC which is 0.3 in for late Mk2’s.

[Dirk]

.....again one year has passed to find the time for my silk.
GOOD NEWS; after i corrected my jetting on the amal,
there is no more kicking back
so from this experience, the boyer ingnition with the silk special box is well worthy
-starts easily,-no kickback( needs just a brave deliberate kick, like smokey Paul mentioned),
-no pinging.
my kickback problems were all from the wrong jets in the carb

Thank you all for your help and patience; i'm happy to be part of this community

Dirk

[Dirk]

.......damned.......
it's two years till i got back to my silk problem.....

[Smokey_Paul]

Time flys

[Arthur Farrow]

Dirk

It would be good to have details of your carb model and the jets you fitted !!

[Dirk]

you'll find that info in the thread "carburation" (two threads of course).
Mine is now fitted like hendres's 2038 amal. I might try the main jet 490

Dirk