after a total rebuild on the engine,valves ,guides magneto rewound etc it wont start! set magneto at 3/8" btdc,new monoblock ,cables ,what is the degree setting for the mag ? as i will have to take it apart to check it again ,many thanks

Try swapping the HR leads over. They might be the wrong way around.

 already took of ht leads from mag  , checked compression ,2 bar both sides ,bores were .5mmo/s honed new rings this is my first twin , causing a bit of head scratching .if anyone has the degree timing ,i would appreciate it ,   

Hi Mick,

See attached . This is from my 'filing system'.

This might sound a bit basic but are you getting a spark and is fuel getting through to the cylinder.  Usually the ignition timing can be a bit out and a bike still start.

Dave.

Digging further into my 'filing system' I found BSA service sheet 216. It should be the definitive info but I'd like confirmation from other SR owners.

My Rocket is timed at 35 degrees BTDC at full advance as recommended by SRM. I timed it with a strobe light and it runs fine.  I found conflicting information as to 35 degs = 5/16" and 35 degs= 3/8" and I don't know which is right. As a matter of interest I have electronic ignition on it and both cylinders fire at 35degs and before using the mag the left cylinder fired ay 35 and the right at a shade over 32

Baza

Hi,

I think the 5/16 probably refers to the A7.  I would suggest that the 3/8 recommended by SRM is correct.  Also, with the electronic ignition it is quite easy to try slight changes to get the best running -  a bit more involved with a mag and points.  The other advantage of the electronic ign. is the 'wasted spark' which means that the HT leads are always the correct way round unlike a mag.

Going back to mashermick - is it running yet?  If, when you put the leads back on the mag. did you try swapping them on the opposite plugs?  Bear in mind that with a twin mag. it is possible to set timing 180 degs. out and that is why swapping  leads on the plugs only can determine if this is the case.  So if it is sparking and you have fuel this is one of the first things to try.

Dave.

thanks Dave ,checked mag by takeing of ht lead and seeing the brass p/up I know its on the right cylinder ,, after checking timing with a degree wheel ,i also did the pencil in the plug hole marked at 3/8 "  .points were on the just opening mark! tempory fuel supply ,flooded ,kicked over a dozen timess and got a kickback so i MUST BE GETTING NEAR going to take of ht caps and try bare wires next     

Just had a flash back to a time when my A10 would not fire/start.  Having done it many times before I could  not see where I was going wrong.  Eventually a second opinion was sought.  So repeating what I had done with a witness the exclamation was almost instant.  "You are turning it backwards you wally!!!!". 
Ooops!  Ten minutes later the bike was running perfectly.  As I had the timing cover off to change the mag. I had, for some reason, turned the engine backwards so timing was 3/8 ATDC instead of BTDC.  The thing that confused me was that it did fire a bit as there would still a bit of fuel about.
A true story.

Dave.

 

Dave.

That's brilliant, I do love to hear from honest men. I wish more folks would publish their "screw ups" it would be a help to all of us.

Mike

ok ,so here where its at, took plugs out and wired on to plug directly good spark,kicked over about 12 times getting about 100 psi. dont know if thats enough .fitted new rings on rebuild after bore honed, fitted hepolite rings ,somebody told me they dont seal well,had a kick back but still wont fire up,having a cupper to recouperate my weak knee !

Mick,

Had look at A65 pressures and with 7.5:1 compression it should average 120/125 with a first kick of 65/70.  Allowing for new rings that need bedding in, 100 psi, although a tad low, should be enough for an A10 to start and run.  I know you have probably done it already but go back to the start with the timing procedure.  Is there anyone near to you who could help? 
See my post from the other day.  Sometimes another pair of eyes can help.

Dave. 

Forgive me if you've already checked this but if an auto advance mag have you wedged to full advance to check timing? Obviously if a manual advance you set to full advance. HTH

many thanks for replys, going to go back and check timing marks on pinions etc again ,keep you informed !