Author Topic: Starting problems,  (Read 4513 times)

Offline Baggy

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Starting problems,
« 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
Baggy

Online bsa-bill

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Re: Starting problems,
« Reply #1 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
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline fido

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Re: Starting problems,
« Reply #2 on: 27.07. 2008 20:00 »
Have you tried with the petrol cap removed in case the air hole is blocked?

Offline dpaddock

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Re: Starting problems,
« Reply #3 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.
David
 
    
  

David
'57 Spitfire


Offline Baggy

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Re: Starting problems,
« Reply #4 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*
cheers
Baggy

Online Brian

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Re: Starting problems,
« Reply #5 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.

Offline dpaddock

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Re: Starting problems,
« Reply #6 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?
David
'57 Spitfire


Offline Baggy

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Re: Starting problems,
« Reply #7 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*
cheers
Baggy







Offline LJ.

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Re: Starting problems,
« Reply #8 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*
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
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Offline octane

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Re: Starting problems,
« Reply #9 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

..how 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;
but;
Do you run a magneto ?...if not; what kind of ignition system do you run?

Offline Baggy

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Re: Starting problems,
« Reply #10 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,
cheers
Baggy.

Offline octane

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Re: Starting problems,
« Reply #11 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' ?....is it original / has it been rebuild/rewound?

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


BTW:

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

CLICK


.

Offline Baggy

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Re: Starting problems,
« Reply #12 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
Baggy

Online Brian

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Re: Starting problems,
« Reply #13 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.

Online RichardL

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Re: Starting problems,
« Reply #14 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.

Richard
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