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BSA M20 starting issue

Tried to start the M20 and having no luck, have a spark, changed the fuel, I checked the timing last summer, so nothing should of changed there but will have a look again, the Carb is a modern replacement, cleaned it and blew through the jets, it seems like I'm getting no fuel in the cylinder, plug always dry, seems like I'm getting a lot of pressure back through the carb, thinking it could be inlet valve or spring etc. ??

email (option): geoffdaviesltd@yahoo.com

Re: BSA M20 starting issue

May be worth checking that the petrol tank lid breather is working...?

email (option): jonsewell8@hotmail.co.

Re: BSA M20 starting issue

Problems with valve springs are virtually unheard of...If you have it set too advanced it will fire back in the carb..If you over flood it it will spit back in the carb..If you open the throttle too much as you try to start it, it will spit back in the carb.
If the oil has drained into the sump that will drag on the flywheels, slowing them down and it will kick back..

1st. make SURE it hasn't wet sumped...Remove the crank case drain plug to be sure...

Turn on the petrol and just hold the tickler down for a few seconds...Do not hold it down until petrol comes squirting out of the carb...Do not use the choke...

Try to start it with the timing set in the fully advanced position but do not open the throttle until the engine fires...When it does fire, then open the throttle to 'catch it' and get it to rev.

If during that procedure it kicks back then retard the ignition slightly...Repeat the start. If it still kicks back retard it a little more...The secret is to set the advance/ retard position with as much advance as you can without it firing back at you...Too much retard and it will be reluctant to start...You'll soon get the feel for the correct setting but take note of the other things I have mentioned, particularly the throttle...Do not kick and give it a big handful of throttle...

I'm assuming of course the points gap is correctly set, the ignition timing is correctly set, the plug is the right grade with the correct gap and the carb has the right parts in it and is set OK...It's worth checking the pilot air adjustment screw before you start the bike....Screw it in slowly until it bottoms out and then back it of 1 to 1 1/2 turns...That is a good base setting...Ian

email (option): ian@wright52.plus.com

Re: BSA M20 starting issue

Thanks Ian and Jon,

Ian, its not an amal carb, its a PZ27...... it was on it when I got it last year, I only left it on as it did start with it, in process of cleaning up the original Amal one that come with the Bike, everything was checked last year, had two laps round the garden then it was stored.

Will check the sump tomorrow....... something I never thought of.







email (option): geoffdaviesltd@yahoo.com

Re: BSA M20 starting issue

Hi Guys,

Ian......

Your information is sound advise.
i have learnt quite a few techniques from reading it, thank you!


I hope the bike is sorted easily, goodluck.
Please let us know Geoff your findings.

Cheers,
Paul

email (option): eastwood007@ntlworld.com

Re: BSA M20 starting issue

Quazaky PZ27...A 27mm Chinese carb....I have absolutely no experience of those. Whilst a carb is just a fuel delivery system and many different types can be set up to run on the 'wrong' bike I think you should consider the possibility that someone in the past just fitted what was cheap and available that would get the bike running and may not have taken the time to prove the entire set up...

Certainly when I have tried alternatives carbs I went for makes that are well known and for which all the required spares were readily available....I ran a Dellorto for example on one BSA and Mikuni carb conversions can be bought already set up for models such as the Gold Star and some twins....

However, setting up a carb from an alternative manufacturer and getting the bike to run really well without some base setting information can be a long and expensive exercise...Dellorto needles for example are pretty expensive, there are many of them and the Dellorto importer was able to offer little worthwhile advice on setting up a carb for a BSA....

So, it's a case of making a start and then adjusting everything gradually based on initial results...You can imagine, some familiarity with the entire process and a degree of patience is needed to get a really good result....

I concluded in the end that sticking with Amal was, for me, the best or certainly the easiest solution...

Amal carb wear rates can be relatively high but they are reasonably priced, spares are not too expensive and tuning information is readily available...Frankly, although much is said about wear rates, in reality most riders these days aren't covering enough miles per year for it to be a relevant factor...

What you decide to run with is your choice in the end but personally I would look to getting a correctly set up Amal on there to improve your chances of correct operation. You may find that the starting would improve immediately if the other carb has not been set up properly...Ian

email (option): ian@wright52.plus.com

Re: BSA M20 starting issue

A quick look reveals the PZ27 carb is marketed under multiple names and there are multiple copies of Keihin, Dellorto and Mikuni carbs manufactured by the Chinese...

I've no idea of the quality of these carbs or the degree of accuracy employed in their manufacture...They obviously work at some level though....My experience of Chinese manufactured goods to date indicates very patchy quality control with some things being OK and some not.
As yet the Chinese don't seem to have fully achieved the level of quality demanded by many Western consumers but their products do seem to be improving gradually...For example, it seems to be accepted their motorcycles have improved substantially from where they started and lots of them are now in use around the world...

It may be that these are good carbs...I guess the situation needs to be kept under review!!...Ian

email (option): ian@wright52.plus.com

Re: BSA M20 starting issue

If you're thinking of getting a new carb, an Amal concentric is a good all-round compromise. Buy a new one, not used. They run great and are very easy to set up.

email (option): cas.vanderwoude@gmail.com

Re: BSA M20 starting issue

Well, it started only just but it run, I'd gone over everything again, Ian the sump had about a mug full of oil.....still struggled, so took carb off and blew it out again and it went, unfortunately not for long as I'd rigged up bottle as a fuel tank, so very little fuel.

Just happy it went, I've the original Amal carb to clean up and replace some bits, wanted to get it running on Friday for a few Victory laps in the garden but too much on etc, plus by late afternoon I'd probably had more ale than my Grandad had 75 years ago.

email (option): geoffdaviesltd@yahoo.com

Re: BSA M20 starting issue

Hello,
In the past I had my old Amal overhauled and it still was not quite right. I then bought a brand new Amal 276c/1b and it completely transformed my bike. It starts, runs and idles so much better. Bite the bullet and buy a new correct carb for your bike, you won't regret it.
James

email (option): jamescusteau@yahoo.com

Re: BSA M20 starting issue

Thanks Jim,

To be honest the original one that come in the box of spares looks to be very good, just a few bits such as seals, it was replaced I'd say as the throttle valve sticks so need to investigate it more before I think of a new carb, unfortunately I don't know if I have a job to go back to in July, so cash for Guns, Bikes and Military radio is on hold..... its a case of make do at present except for the house extension, managed to make a good start on phase one of that.

email (option): geoffdaviesltd@yahoo.com

Re: BSA M20 starting issue

Had some free time this morning, so fitted the Amal carb that come with the bike, ( cleaned the carb and sorted the sticking slide the other night).

Took a bit but soon fired up, few laps of the back garden much to annoyance of wife (strange woman).

Thanks for all the tips etc. So one down, three to go, The WDC RE, AJS Model 8 and something too new to mention on here.

email (option): geoffdaviesltd@yahoo.com

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