The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Baggy on 27.07. 2008 19:26

Title: Starting problems,
Post by: Baggy on 27.07. 2008 19:26
 hey chaps, right its hotter than a lizards bits in my garage and before I completely loose it can anyone help me out, my golden flash motor has been fitted with a mikuni carb and its a nightmare to start, it has a starting choke only, but after an hour trying last night,( and following the guy who fitted the carbs instructions to the letter)  and you know how hot it was she finally fired and ran as sweet as a nut, then she snuffed out and despite my best efforts and begging would not for love nor money fire again, I have a strong spark but appear to have no fuel. so today I stripped the carb out and made sure everything was clear and eventually again she fired up and ran very well then again snuffed out and haven't been able to start her again since, well ***** off now as she is almost finished and was hoping to be on the road this week, anyone have any ideas or have a carb that I can bolt on and will work, or any advice anything
that can help me out, would be greatly appreciated
many thanks
Title: Re: Starting problems,
Post by: bsa-bill on 27.07. 2008 19:36
Hi Baggy
The way you describe what's happening would suggest that your carb is not getting enough fuel from the tank or that the float chamber is not filling high enough.
These two I would eliminate first - have to say mind I know zilch about Mikunis

All the best - Bill
Title: Re: Starting problems,
Post by: fido on 27.07. 2008 20:00
Have you tried with the petrol cap removed in case the air hole is blocked?
Title: Re: Starting problems,
Post by: dpaddock on 27.07. 2008 20:17
Bill's comment is most appropriate. We assume the engine ran on idle and cutaway OK.
    First, check that the float bowl is vented to atmosphere. Likewise the petrol tank. It sounds like you have starved the engine by creating a vacuum in the petrol tank. Remove the bowl drain plug and see that fuel runs out continually when the tank petcocks are open.
    Fuel level in float chamber - not super critical but needs to be there. I run mine 3/8" below the bowl flange, using a piece of clear poly tapped into the bowl drain plug and run vertically alongside the bowl to check this. The factory method for checking this is confusing, at best, and sets the float level, not fuel.

Get back to us. Good luck.

Title: Re: Starting problems,
Post by: Baggy on 27.07. 2008 22:17
hey chaps, been through the fuel pressure checks, carb is venting to atmosphere, and tried with no cap on tank,checked tap and all sorts confused and knackered I'm 13  stone and stay in shape, this has killed me tonight  *sad2*
Title: Re: Starting problems,
Post by: Brian on 28.07. 2008 04:41
It doesnt sound like you are having much luck Baggy.
A couple of things, did the bike run ok before you fitted the Mikuni ? If it did then the problem is definitely with the carby. If you didnt  have it running before that makes things harder. I take it that it is hard to start and when you do get it running it stops. When you do get it to run will it run at low revs but die as soon as you open the throttle or does it rev up ok and then die out. If it starts and will only run at idle or just above then probably the jetting is way out, if it starts and revs up ok then dies it definitely sounds like a fuel supply problem. We need to try and work through what is happening, first fuel supply. Does this carby have a drain plug in the bottom of the bowl or can you remove the bowl while the carby is fitted to the bike and fuel supply. If so take out the drain plug or remove the bowl and turn the fuel on, you should get a constant flow of fuel. If it only drips or flows for a few seconds then stops then the problem is with the tap/fuel line/ needle and seat. If this checks out ok then you can be reasonably sure you are getting fuel to the carby. I take it you have checked the float/fuel level, this is not critical at this stage as long as it is somewhere around where it should be the bike should run.
Next to the starting, after you have been kicking for awhile and it hasnt started take out a plug and see if it is dry or wet. If its dry then once again this indicates lack of fuel, if its wet you could have an ignition problem. A simple test to do here is get some easystart, or can be called aerostart, here in Aus its called "Start You Bastard" [thats true, thats what it is actually called]. When the bike wont start give it a squirt of this stuff and if it fires up briefly then the problem is definitely fuel. Do not try and run the bike on this stuff, just a quick squirt to see if it fires. One thing I have just thought of is the fuel itself, is it fresh ? Modern fuels can go off in a very short time so if its more than a couple of weeks old try new fuel.
At this stage I would try some of these things and see what happens. One of the problems with fitting modern carbies to old bikes is that you cant tickle them, most oldies like a bit of a flood when cold to help them start. I like the original Monobloc and cant see any advantage in fitting a modern carby and if I did put a modern type on it would have to have an accelerator pump so you could give the throttle a couple of twists to squirt some fuel in before starting. Probably a pumper type Dellorto would be my choice, anyway thats getting away from what we are trying to acheive here.
Good luck with it and I hope between us all we can help.      Brian.
Title: Re: Starting problems,
Post by: dpaddock on 28.07. 2008 20:13
OK, it's not fuel.
Have a look at your ignition.
You apparently have spark when cold. How about when the mag's warm? Heat it with a hair dryer or (carefully) with a torch, and see if you still have spark. You talk about how hot it is in your garage . . .
BTW before you fitted the Mic, was the Flash running OK?
Title: Re: Starting problems,
Post by: Baggy on 28.07. 2008 22:28
Hey guys, the bike came with the Mikuni already fitted , the chap that fitted it is a brit bike mechanic and works with Mikuni he also rebuilt the engine when the bike was first built, it fired up again tonight, by pure chance I swapped a plug cap over so I could fit some spark indicators just to make sure it was sparking ( its hard trying to hold the bike kick it and hold a spare plug against the block  *eek*)  and she popped so I tried again and up she went, still snuffs out but did kick up again, I've noticed a couple of things that I'm unsure of how critical these things are but I will fix but could these cause me any of the symptoms with starting?? please accept my appologies for ignorance in advance, if I don't ask I'll never learn  *conf*

The header pipes are not sealed at all well and blow like buggery when running ?

how crucial is the setting of the throttle cable, mines sloppy at best, is there should the slider be tight against the bottom of the carb when trying to start ? or should it lift slightly?

Do I open the throttle when staring or leave well alone?

also as its a chop, she is at a steep angle when on the side stand ( to the right if on the bike), but all the pics I see of standard A10's they seem almost upright on the stand could this possibly be causing issues?

Finally and I thank you for taking time to read all of this, I do have the Amal carb that I assume was with the bike when first built, (( the guy who fitted the mikuni swapped this out and from memory said it was a later model that was a pain) if I was to re fit this carb does it bolt straight to the engine with a gasket or is there some form of isolater block to stop the carb getting to hot  like in early Austin cars?

sorry for so many questions, I hope you can understand my frustration as so bloody close to riding my first brit bike on the road  *smiley4*

Title: Re: Starting problems,
Post by: LJ. on 29.07. 2008 10:15
I have heard that some people seem to have problems with Mikuni carbs and I'd be inclined to refit the Amal that you have. Get the bike running in which it will, and then play around with the Mikuni later if you want to. Both my A10s have the Amal monoblocks and run fine, very easy to start usually without a tickle. I find that I *must* open the throttle just a little on first intial start and then after a few seconds i can let the throttle snap back and they will tick over nicely. You'll probably find much more help and info for the Amals as I think most A10s run quite happily with that type of carb.

Cable? I have mine tight, Just slacken off a little with the front wheel turned fully each way so that engine does not rev when turning. Use of nylon/teflon lined cables are a must I find. Finally I'd certainly try starting the bike as upright as you can rather than the steep angled side stand rest as you mention mine will eventually stop if bike is at an angle, again... with a Mikuni carb I cant really say.

Good Luck... Keep at it... Your nearly there!  *smile*
Title: Re: Starting problems,
Post by: octane on 29.07. 2008 15:50
she is at a steep angle when on the side stand ....... could this possibly be causing issues?
Hi Baggy steep is steep?
You put it it in upright position once you've started it ?

What type Mikuni is it ? Does it look like this: ? (flat-slide)


If so: I can't phantom that it will give you problems.
It's simplicity itself, very reliable. Starts first/second kick.
I've run it for 6 years with no problems whatsoever.

You say you have a strong spark;
Do you run a magneto ?...if not; what kind of ignition system do you run?
Title: Re: Starting problems,
Post by: Baggy on 29.07. 2008 16:32
Hey octane,
not a flatslide Mikuni, I will try and get a pic on when I've sussed my new phone software, the guy who fitted it reckons it would be way better than the amal that was fitted, I am running a mag for ignition, I am gonna sort the header pipes out tonight and put a block of wood under the sidestand and see how she goes with that as after chatting to the guys at Vale Onslow they reckon that the angle it sits at on the stand may well be causing at least some of my problem,
Title: Re: Starting problems,
Post by: octane on 29.07. 2008 21:20
... I am running a mag for ignition...
Hi Baggy.

My reason for asking about the ignition is, (and this might very well be a shot in the dark)
that at one point I was chasing, what I thought to be a carb problem,
as it did more or less what you describe and
every time I looked at the spark it was (sort of) good.....had to be the carb then...ei?

IF, and I say IF, your mag is not in real good shape,
you could have an OK spark when the plug is out,
but when under pressure in the cylinder, (and the windings heat up a bit)
it gets weak and will come and go at it own 'will'.
....AND as it happened to me: I could sometimes start it (sometimes not), and rather randomly
it would just stall.

My mag was tested and it turned out the insulation's between
the windings were breaking up.
Certainly not uncommon for old mags to do that.

So my question is
Do you have a nice FAT BLUE spark?....every time you kick ?
Do you know anything about the mags 'history' ? it original / has it been rebuild/rewound?

As I said; may be a shot in the dark?!


Here is a "HOW TO" check the magneto,
I did in another forum:


Title: Re: Starting problems,
Post by: Baggy on 30.07. 2008 21:37
hey guys, checked all I can and she fires up now on demand when cold or if i catch it a min or two after she snuffs out, left it for 20 mins or so, and no chance,spark is weak so its all pointing to a dodgy mag, ( by the way just to make sure made new leads, caps and plugs and tried before and after new stuff) before I spend money I haven't really got is there any other possibilities?if not is there anyone you can recommend to rebuild mine or sell me one fast as i really would like to get a week or two on a bike this summer  *sad2*?
cheers for all the help
Title: Re: Starting problems,
Post by: Brian on 31.07. 2008 01:15
Unfortunately Baggy there is no short cut for a crook maggy. Even if someone gave you another one it may not be any good or may fail soon after. Getting yours rewound is the only way to go. If you send it off to get reconditioned make sure you send it to a reputable place that rewind and fit a new condensor, not just clean it up and check bearings etc.
Title: Re: Starting problems,
Post by: RichardL on 31.07. 2008 07:38
I'm sorry I can't help in this regard, but it would be great if you could borrow (or, buy on trial) a known working mag to be sure the diagnosis is correct. Of course, rebuilding yours will result in a better overall bike, but might spend the money before the absolute need. I expect someone (or every one, but, surely, Groily) is going to chime in and say that it is better to do now than when you have the "absolute need" 200 km from home. On the other hand, if the mag is not the problem, you aren't going to get 200 km from home.

Title: Re: Starting problems,
Post by: groily on 31.07. 2008 08:48
Oh Yeeees, as Richard says . . . better now by far. Absolute need 200 kilometres from home can't be satisfied unless you have a spare mag in your pocket and really want to show off your imperturbable approach to breakdowns in the rain (of course) at the side of the road. . . 
The bad news is rewinds aren't cheap - but no point doing anything else. I suspect either windings have lost their insulation or the condenser's dying. You can get just an armature with modern condenser on an exchange basis for not so much (see SRM site for example) if you're confident that a) the rest of the thing is OK and b) you want to do the job. Good luck. Know how you feel having had loads of mag troubles myself this year.
Title: Re: Starting problems,
Post by: octane on 31.07. 2008 09:36
Hi Baggy
I agree with the others:
make sure it's the mag. They are rather terribly expensive to fix.

One thing; in your first post on this forum you write:
she fired up as sweet as a nut and sounds lovely.. I'm just thinking that maybe you could go 'backwards'
and check whatever you have done to the engine/mag. etc.
If it was OK back then and it's not anymore,
you must have been doing something that changed that.

Could you maybe tell us exactly what you've done ?

is there anyone you can recommend to rebuild mine or sell me one fast....
Depends on where in world you are located.
If you're in Europe I'm afraid I'd disagree about using SRM for a rebuild.
I did; and it was an altogether bad experience.
Week after weeks of delay, unanswered emails and
when they finally got around to shipping it to me, the packaging was so
ridiculously inapt that the cover of the mag. had broken in two.
I got the local mag.-guru to check it (he didn't have time to rebuild it back then)
just the other day, and he was NOT impressed.

This is what my SRM-rebuild mag looks like.
That's the high tension lead.
Waaay to small, according to him


Should be like this:


This is the various soldering
around the condenser etc.


..which according to him should
be protected and kept from
shaking loose, by means of some sort of
epoxy or silicone

like this:


IF indeed it's the mag that's your problem
 and you're in Europe
and you don't want to wait for weeks
and you have money to spend;

Check this: MAGNETO Exchange (

I do not know about their mag. rebuilds, but I do know that they are to be trusted for good and fast service,
like; I ordered some parts this Sunday....received an email Monday afternoon that the parts had been send.

..but as I said: be sure it's the mag.
That's an awful lot of money, but it IS a total rebuild including everything: bearings, slip-ring etc.
not just a rewind.

Here's a place in UK that will do a rewind for 85£+ vat: Independent Ignition Supplies (

...if you remove and send them the armature. (Not difficult to remove. I'd be glad to walk you through the procedure)
Title: Re: Starting problems,
Post by: groily on 31.07. 2008 12:34
Ah well, very happy with my K2FC from SRM with 2 year warranty. It did take a week or so longer than I'd hoped -  including post from France and back it was a month when I was hoping for 3 weeks. Always answered e-mails and phone, and packaging was fine - maybe they learnt something from Octane's bad experience! Have to admit I haven't opened it up to look at the thickness of the HT wire, the soldering round the wotsits or the gunge/lack of round the condenser but presumably it will look like Octane's pix if the same bloke did it. I don't have much to compare it with either, apart from old armatures awaiting refurb for other ongoing projects. Anyway, it works very nicely but it WAS expensive. Had I not needed a slip ring plus all the consumables, I'd just have got an armature for less than half the money.

Reason I suggested them was because Baggy wants to ride the thing this summer - and an off-the-shelf exchange is faster than have-your-own-rewound.

I'd have suggested Independent Ignition if they still offered the exchange rewind service because that would be quick too - but seems to have been suspended for quite some time now. Couldn't do me one a few months back, and site still says 'Sorry, service withdrawn'
Few more suggestions:
Tony Cooper on 0121 5592405 (UK)
Sean Hawker -
These 2 are both highly recommended by others, but haven't used them myself. Tony Cooper would have been quite a bit cheaper than SRM I discovered subsequent to despatching mine.

Also look at (in Gloucestershire) about whom I know nothing more.

One or all of these folk would be able to sort you out if it's the mag that's the culprit.

Good luck again!
Title: Re: Starting problems,
Post by: Baggy on 31.07. 2008 14:13
Hey Guys, I Have spoken to Tony cooper, and he can turn it round for me in 7 days and is only half hour trip from me, he was really helpfull and his costs are very competitive, I will take it off tonight and drop it over to him tom, he will check it for me just to make sure,
hopefully while thats been sorted I can finish the other bits and bobs
will let you know the outcome,
Title: Re: Starting problems,
Post by: octane on 31.07. 2008 14:54
.., I Have spoken to Tony cooper, and he can turn it round for me in 7 days and is only half hour trip from me, he was really helpfull and his costs are very competitive..
Oh, that's great.

I'm anxious to hear if the mag. is indeed faulty.
I hope I haven't led you astray with a wrong 'diagnosis'.

If so; I apologize.

I do hope you get it running real soon.
Title: Re: Starting problems,
Post by: groily on 31.07. 2008 20:38
That confirms the good things I have heard - be very interested to hear the result in due course - and the £££!!!
Title: Re: Starting problems,
Post by: Baggy on 31.07. 2008 22:59
its £125.00 ish with £135.00 maximum and he runs BSA's so I have total confidence in him, ( even as a newby to BSA I told him what was happening and he told me how to split the cover, remove the mag, and be sure to make a template of where the bolts in the timing cover go,also he would walk me through setting it all up when back on the bike, what a star, simple but bloody invalueable advice thats rare these days)I will let you know tom night how I get on,
Title: Re: Starting problems,
Post by: groily on 01.08. 2008 12:09
Well that's a very fair price indeed - and sounds as if it comes with a lot of extras! I'll go to him for my next 2, which are sitting on the bench waiting for me to make a decision . . .thanks for letting us know.
Title: Re: Starting problems,
Post by: Baggy on 01.08. 2008 14:25
Hey, been over today, guy is a bloody gem, put my mag on tester, showed me what was happening, spark, intermittent, dies quickly on one pot, altogether shot, so he will re build it and I can pick it up next thursday, he is so helpfull, and has some crackin bikes that he uses, brilliant,
Title: Re: Starting problems,
Post by: octane on 01.08. 2008 15:14

Baggy; I'm so glad the source of you problem was found.

showed my what was happening, spark, intermittent, dies quickly on one pot,...
Just like mine did.

You'll be on the road in no time.

Title: Re: Starting problems,
Post by: GuyboA10 on 02.08. 2008 04:43
g'day. hey Octane & co. have u bought from Degroot bsa parts? I just recently found their website and am impressed with the goods they sell. How is the $ compared to others(srm)? cheers guybo.
Title: Re: Starting problems,
Post by: octane on 02.08. 2008 09:49
g'day. hey Octane & co. have u bought from Degroot bsa parts?
Hi Guybo

Yes I have.
As I said:
but I do know that they are to be trusted for good and fast service,
like; I ordered some parts this Sunday....received an email Monday afternoon that the parts had been send...
So as you can see; they deliver very fast.
..which is more than I can say about any other Brit-bike parts dealers that I know of,
certainly including SRM.

So far, I've been happy with the goods I've received.
... I'm thrilled that they have a web-site ordering system
that allows you to actually see photos of the parts
...the prices seams fair

No I haven't compared the prices to those of SRM's.

If you do, please let us know the outcome.
Title: Re: Starting problems,
Post by: Baggy on 09.08. 2008 19:28
Hi Chaps,
Picked my newly sorted mag up on thursday, tony put it back on the machines that highlighted the problems and the difference was untrue, fat strong sparks across the rev range constant on tickover etc, came with new leads, caps, pick ups, holding clips, gasket,swapped the bits that were wrong on the mag , looked brand new, the whole lot ready to fit, he also lent me the tool to set the timing and all instructions, bloody brilliant, so today fitted & timed, first kick, no joy?second kick, backfire, timed it up on the wrong pot, swapped the leads over ( as in instructions by Tony) ........................
third kick and she burst into life strong and sweet, idles beautifully warmed her up and shut down, walked away, now the acid test hot sart...................

first kick and away she went revs strongly, idles perfectly, been wiring the bike up for the rest of the day. I now have all the nec lights, horn,etc, so kicked over many times and first time kick and she starts I'm so impressed, the total charge for all this was £140.00, if anyone needs a mag rebuild I cannot recommend him highly enough, so I am now about 2-3 hours away from a bike ready to take for its MOT, well pleased.
A big thanks for the help guys, really appreciated, will post some pics soon,
Baggy  *smile*
Title: Re: Starting problems,
Post by: a10gf on 09.08. 2008 20:26
 *smile* Congrats! Good to read about success after all the work you've done.
Title: Re: Starting problems,
Post by: LJ. on 10.08. 2008 10:22
Now there's one heck of a happy chappy! Reading this kind of news makes me smile ear to ear. Dont it make a difference in reading of ones sucesses after ironing annoying problems. Well done Baggy! Now go ride that machine eh? Thanks for posting.  *smile*