The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: owain on 06.08. 2018 19:27

Title: Difficult to start
Post by: owain on 06.08. 2018 19:27
My 1950 A10 plunger is very difficult to start. If I run down the road and drop it into 2nd gear then it starts and rides nicely. Kick starting it is a real lottery that seldom results in the engine starting. The K2F magneto was recently reconditioned by APL magnetos in S.England but I'm not sure what the issue is. Carb is an amal concentric 930 with 280 main jet, a .25 pilot jet, needle position at 3 (i.e. lowest notch), needle jet .106 and 3 1/2 throttle body (Does that sound roughly right for a 1950 iron head A10)? The timing is spot on, All valves have clearence 0.015"...It should start first kick but it's not? Any ideas? *conf2*
Title: Re: Difficult to start
Post by: JulianS on 06.08. 2018 20:02
280 is probably too big for a main jet. Try 240.

Does you carb have a pressed in pilot sleeve (Unless it is a new Premier model). Most 4 stroke concentrics from the late 1960s have one and do not need a screw in pilot jet. If it does have the pressed in sleeve you can see it if your remove the air screw and look in the hole.
Title: Re: Difficult to start
Post by: RichardL on 06.08. 2018 20:16
Have you watched for spark across a plug gap with the plug body making earth? If you have spark, is it bright or faint?

Compression good and about even for both cylinders?

Clean pilot jet? (Technique described elsewhere.)

Too sure about the timing?

Copper plug wires? (Should be.)

Noise suppressors in plug caps? (Should not be.)

Clean slip ring?

Brushes properly seated in the pickups?

No spark leaks through cracks in pickups? (See LJ's recent post.)

Excellent plug wire connections in the pickups and plug caps?

Plugs gapped properly and not fouled?  (This basic I'm sure you must have checked.)

Next time you try starting it after sitting for a couple of hours, don't tickle it. Try a couple of kicks no throttle, then half throttle. No go? Tickle until you see gas around the tickler, then a couple of kicks no throttle, half throttle, 3/4 throttle. No go? Pint of Guiness.

Richard L.
Title: Re: Difficult to start
Post by: muskrat on 06.08. 2018 21:01
G'day owain.
How old is the carb? Concentrics have a habit of the slide binding if the nuts are too tight and thus wear the slide/body and create a lean mixture.
Cheers
Title: Re: Difficult to start
Post by: Billybream on 06.08. 2018 21:44
Do you tickle It, always find my concentric needs plenty from cold.
Title: Re: Difficult to start
Post by: chaterlea25 on 06.08. 2018 21:50
Hi Owain,
It sounds to me as though the plugs are on the way out  *ex*
My SR goes into hard to start mode every now and again *sad2* needing a push or downhill run to start
a pair of new plugs and all is well again
The modern crap fuel is hard on plugs

John
Title: Re: Difficult to start
Post by: owain on 06.08. 2018 22:24
wow fast replies, thanks!

The carb is pretty old (bought it from an autojumble) and doesn't have a pressed in pilot sleeve. All of the components on the magneto were replaced, new pick ups, windings, bearings, etc. Except for the points. Yep, I'm getting a spark from the spark plugs when removed and earthed. I'm also getting an orange flash from the spark plug tester when the spark plug is in the cylinder and under compression. It's a good spark but not super strong like I would hope for from a newly reconditioned magneto. I keep reusing the same spark plugs. I bought them a few weeks ago but have fouled since i've been tinkering around. So I just heat them up until they are cherry red under a blow torch and reinstall them. I think you're right about the main jet being too large. I checked the original 276 carb and that is running a 120 main jet with .106 needle jet. Although I don't know whether this jet configuration could be the same for the 930 concentric. My current idea is to put the old leaky 276 carb back on the bike and give that a go :/...might put some fresh spark plugs in too
Title: Re: Difficult to start
Post by: RichardL on 06.08. 2018 22:56
I'm no expert in our carbs, so must ask Julian, is the main jet even in play when starting the bike?

Richard L.
Title: Re: Difficult to start
Post by: duTch on 06.08. 2018 23:19

 
Quote
........ is the main jet even in play when starting the bike?

 I wouldn't have thought so either.... but will await expert opinions  *conf2*
Title: Re: Difficult to start
Post by: chaterlea25 on 06.08. 2018 23:43
Hi Owain,
Quote
I bought them a few weeks ago but have fouled since i've been tinkering around. So I just heat them up until they are cherry red under a blow torch and reinstall them.

That was the way to clean the plugs in my Dad's TVO Ferguson  *eek*
But that was almost 50 years ago *sad2*

Modern plugs will not recover once fouled  *problem*

John
Title: Re: Difficult to start
Post by: coater87 on 07.08. 2018 01:15
Owain,

 Like John I have not seen the torch on the tip trick in a long, long time.

 Probably back to the days of myself and my brothers taking turns holding the high tension lead on our family rototiller every spring. That's how dad figured out if the spark was sufficient.
 My lord how us boys hated that f#$%[#% rototiller....

 Lee
Title: Re: Difficult to start
Post by: BSA_54A10 on 07.08. 2018 08:26

 
Quote
........ is the main jet even in play when starting the bike?

 I wouldn't have thought so either.... but will await expert opinions  *conf2*

No.
Main jet does nothing till you are on the parallel section of the needle and that is around 3/4 throttle.
Title: Re: Difficult to start
Post by: BSA_54A10 on 07.08. 2018 08:29
Sounds like the carb is idleing & starting on the slide and not on the pilot jet

Next time you start it try adjusting the pilot air screw.
If you can turn it more than 1/2 turn in either direction and the engine keeps n running then the pilot circuit is clogged.
Title: Re: Difficult to start
Post by: RogerSB on 07.08. 2018 14:41
Maybe some help.
Title: Re: Difficult to start
Post by: stev60 on 07.08. 2018 21:24
For what its worth, I put a new 626/300 Premier 26mm concentric on my 51 A7. 107 needle and a 220 main (probably could go bigger) Starts and runs perfectly, always on the first kick and thats just effortless push down, , with bowl flooded.
Title: Re: Difficult to start
Post by: edboy on 07.08. 2018 23:54
928 concentric with drilled pilot bush on my plunger and runs and idles lovely