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1956 D1 Bantam engine starts but won't run
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Graham
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November 25, 2020 - 8:01 pm
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I'm trying to help a friend of mine who's inherited a 1956 D1 which will start readily but will not accelerate at all. - when the throttle is applied it "chokes" but does not stall. My instinct was a carburettor problem. I removed, stripped and cleaned the carb (Amal 361) - everything looked OK as per the manual with the needle set to the 2nd notch and checked it was responding to throttle - all OK.

I also checked points (Wipac) and set to .015" and plug (NGK B6HS) and set to .018".  I flushed the petrol tank and added clean fuel at a ratio on 33/1. Removed and cleaned the silencer as per the manual, put it all back together with exactly the same result. Am I missing something?

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dimitris
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November 26, 2020 - 8:22 am
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Hi there

Just asking, maybe electric problem with condenser or HT coil?

Experienced owners will have a clue.

BSA D1, 125cc (1952)---BSA D10 Sport 175cc (1967)---Triumph Cub T20 (1960)

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ZZ
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November 26, 2020 - 8:31 am
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You checked the points and plug, what about ignition timing?

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Graham
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November 26, 2020 - 8:41 am
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Both the Capacitor & HT lead look new (although I was concerned that the HT lead appears to be soldered to the coil?)

I haven't checked the timing - what's the easiest to do that?

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Stoo63
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November 26, 2020 - 8:55 am
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Hello factotum and welcome to the forum. There may be no easy fix to your issues or it may be a case of simply twiddling the stator palte round a few degrees. You need to have a good search of the Forum first as your issues have been discussed a million times before.

You will find just about everything you could ever want on the Forum via the FAQs and technical sections;  ** Please log in to view **

Have a really good nose around the forum and enjoy yourself. Looking forward to seeing your progress.

Good Luck!

All the best,

Stewart

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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Graham
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November 26, 2020 - 9:33 am
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Hi Stewart. Thank you, I appreciate the warm welcome. 

I will take a good luck around and search for D1 timing.

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sunny
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November 26, 2020 - 9:45 am
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hi Graham   your   rite  the    HT  lead  is  NOT serposed to be  soldered   on  a  small  rubber  band   is all  thats  needed   to  hold  it  tite   NO  resister spark plug  cap   is   used    try duck  tape  insted  of the   3  screws   holdin the  plate   so you can  move  the  timing   a  bit moor   ,.     id  check  the  carb  seting & seting   also

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dimitris
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November 26, 2020 - 10:05 am
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How to set timing on D1

I found some info with photos from my old topic about my D1's issue (couldnt set correctly the timing because crank shaft rotated in wrong position)

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I general:

1. Set the points maximum opening to .015" (0.4mm) using the screw holding the points

2. Remove cylinder head to find TDC (top dead center - maximum piston position)

3. Rotate engine back(anti clockwise) to lower piston by 4mm or 5/32" (can be done with a timing wheel, NOT SURE how many degrees back)

4. Untight the 3 stator screws and rotate the whole stator untill the points JUST begin to open. Tight them.

(i was adviced to use a thin cigarette paper to feel the moment it gets released from the contact points)

 

If this doesnt help, there also several other topics about timing

 

P.S. I AM NOT AN EXPERT. I learned everything from these guys here. Just had little more free time to write it down again

BSA D1, 125cc (1952)---BSA D10 Sport 175cc (1967)---Triumph Cub T20 (1960)

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JustinW
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November 26, 2020 - 7:29 pm
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Sounds like a tiny bit of crud in the main jet. When throttle opens it just can't give the juice. It might not be this this time but one day it will be 🙂

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Number6
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November 26, 2020 - 7:39 pm
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Hi,

"will not accelerate" - riding it, or revving it on the stand?

(I maybe far out, but I suddenly had memories of small Japanese 2-strokes that idle perfectly but go "bleuh" when twist grip is turned, close it, perfect idle again, open it, "bleuh", turns out to be fuel starvation)

What does spark plug look like, pale or sooty? May be a clue.

Could be carb could do with an overhaul kit. From Burlen this comprises of new main jet, jet holder (incorporating needle jet), needle, and clip (the needle and the needle jet can wear by rubbing together, this effectively makes the 'hole' bigger which makes the mixture somewhat richer than it should be, at low throttle slide position).

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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GlenAnderson
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November 26, 2020 - 10:04 pm
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I had issues with my '53 D1 that turned out to be a mis-matched/machined flywheel rotor. The magnets around the circumference weren't in the right place when the points opened and there wasn't enough magnetic flux in the coil to reliably fire the plug. I still don't know whether I had a flywheel meant for a battery ignition bike, or whether I had just been unlucky, because it appears it was a problem that the factory were aware of and issued special cams to compensate for. Whatever, changing the rotor cured the problem.

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Stoo63
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November 26, 2020 - 10:12 pm
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So, as you see, Graham, these oh-so-simple wee bikes throw up a blizzard of possible issues. Johnny Nash in '72 had the hit with "More Questions Than Answers" but thankfully it was from the album " I Can See Clearly Now"!  Fingers crossed it's something nice and easy like the timing but after so many years and the make-do and mend repairs of previous owners, you can never be sure of what you're working with or what you'll find. 

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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dimitris
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November 27, 2020 - 6:35 am
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GlenAnderson said
I had issues with my '53 D1 that turned out to be a mis-matched/machined flywheel rotor. The magnets around the circumference weren't in the right place when the points opened and there wasn't enough magnetic flux in the coil to reliably fire the plug. I still don't know whether I had a flywheel meant for a battery ignition bike, or whether I had just been unlucky, because it appears it was a problem that the factory were aware of and issued special cams to compensate for. Whatever, changing the rotor cured the problem.  

Wow...thats interesting! Sorry for interfering, but where can i find these rotors? Or modified cams! Mine was something like 10 degrees out, and couldn't set the timing correctly. Forum users found the solution for me, and i removed the key from the rotor to set it in corrrect position..

BSA D1, 125cc (1952)---BSA D10 Sport 175cc (1967)---Triumph Cub T20 (1960)

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cocorico
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November 27, 2020 - 8:54 am
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Stoo63 said
... it's something nice and easy like the timing but after so many years and the make-do and mend repairs of previous owners, you can never be sure of what you're working with or what you'll find.   

dimitris said

...Mine was something like 10 degrees out, and couldn't set the timing correctly. Forum users found the solution for me, and i removed the key from the rotor to set it in corrrect position..  

Dimitris' 'saga' was some time before you joined Stoo, I think, or you wouldn't have referred to D1 timing as nice and easy (though it should be). It should be fixed by the keys on the generator and cam, but if the crankshaft has moved in the flywheel various things can be done. Best hope it is not that, but worth looking for Dimitris' topics on it.

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Stoo63
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November 27, 2020 - 10:21 am
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Indeed, Bob, I'm also a victim of the vagueries of BSA timing but I'd meant that it may just be a case of rotating the stator fingers-crossed

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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dimitris
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November 28, 2020 - 1:05 pm
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cocorico said

but worth looking for Dimitris' topics on it.  

Better NOT! I was looking at them the day before, and got so confused. So many pages, and my knowledge for sure wasn't helping.

I realised how big was my frustration those days..

I think we must better write a new clean guide of the solution, for that problem! read-manual

laughlaugh

BSA D1, 125cc (1952)---BSA D10 Sport 175cc (1967)---Triumph Cub T20 (1960)

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JustinW
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November 28, 2020 - 7:32 pm
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Check the points post hasn't got any wobble. That causes weird effects.

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Graham
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November 29, 2020 - 1:17 pm
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Thanks to everyone for your responses - I thought I'd give an update on what I've found out over the past couple of days. I completed static ignition timing and all OK. I then did the obvious thing and completed a compression test;

Cold: 40 psi, Warn: 40 psi, Warn and with oil down the barrel: 50 psi.

Obviously low! At 6.5:1 ratio I'm guessing it should be circa 90 psi?

Removed the head and barrel and checked tolerances on the bore, rings etc and all pretty good - from what I can gather it was rebuilt within the past year and it certainly looks that way! No obvious lip on the bore,  clean +40 piston fitted and clean within tolerance rings. No discernible play in flywheel / conrod.

There is carbon build up on the head compression chamber which I will clean and polish, the head Gasket looked OK (I will fit a new one - are they all non metal?). The Base Gasket, although not torn, looked like it have it could be passing oil, is this possible and would that effect compression? 

The part that does concern me is that I cannot confirm if it's ever run since the engine rebuild!!

What else should I be checking that could cause compression to fall? 

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GlenAnderson
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November 29, 2020 - 2:20 pm
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The D1 didn’t have a head gasket, the head and barrel were just lapped together to get a seal. Fitting a gasket just lowers the compression even further than it starts out from. You only need a gasket if you skim the head and up the compression ratio, and even then, on a D1 with its relatively large clamped surface area to bore ratio, it’s arguable that it’s necessary. I don’t have a gasket on mine and I’ve taken 0.100” (2.5mm) off the head face. 

As for low pressures, how are you cranking it over? If it’s just on the kickstart I’d doubt you’ll ever get close to a true figure. Stick it in gear and bump it down the road. 

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GlenAnderson
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November 29, 2020 - 2:23 pm
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Something else worth bearing in mind, quoted from another thread:

Maico490 said
"I purchased a cheap compression tester and this indicated a very low compression, now i knew this couldn't be right, a member of the club came round with his trusted snap on compression tester, and i had a really good compression on both sides , the cheap gauge was reading 55 psi the snap on one was reading 125 psi."

I've had a bit of experience with this from working on chainsaws. You need a tester with a Schrader valve inside the adapter which connects to the cylinder. Without this the volume of the hose leading to the gauge is added to the combustion chamber volume. On larger car engines this doesn't matter but on smaller cylinders the results end up being way off.   

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