Engine Won't Start

[Alan @Ncl]

Finally got round to starting the Flash after all these years.  Very very difficult process but eventually, it 'took off' and ran for a couple of minutes on the stand.  Obviously running hot as pipes started to blue, even for this short run so I stopped.  Suspected weak mixture (possibly blocked pilot jet) as any attempt to run without full-choke or slightly opening the throttle, resulted in engine stalling.

Took carb off again and stripped it right down and cleaned it up but found nothing obvious.  Could not resist gently pushing some 5 amp fuse wire down the pilot jet (is this really such a dreadful crime, as seems to be indicted in the Haynes manual?).  Reassembled and refitted carb with pilot screw 1.5 turns open and stop screw just lifting the slide off the bottom but it just will not start at all now. 

Carb flange seems sealed. Timing is spot on at 3/8 BTDC fully advanced (used a 12v timing light to detect points opening, having removed the centre bolt from the contact breaker).  Spark showing at plugs (not exactly Blackpool illuminations but not bad).  On removal, thought plugs seemed quite dry to mildly damp, especially considering the amount of carb tickling done.

Took compression tests and got 135 psi both sides (rising to 170 when some oil was squirted in the bores to seal the rings). Given the years of standing this does not seem too bad.  Does anyone know what the readings should be with 8. somethingish pistons? 

Eventually retired from the fray exhausted and temporarily defeated.  So now, having trawled the site, its out to the forum to see if any of you gurus can suggest a way forward as I seem to have come to a dead end.

[muskrat]

G'day Alan,
               check the float height. What carb has it got? Will it fire with some aerostart or similar?
Cheers

[jfligg]

Hi Alan 

  I would think that 130 per side would be OK.  Does the bike start by holding the throttle open a little bit.  Is it trying to start at all.  I would be tempted to try new spark plug.  Has the mag been rebuilt?  This in my opinion is the Achillis Heel of this machine.  If you are going to use the bike you should overhawl the mag.  Good Luck and keep us posted.  Jeff

[Alan @Ncl]

Thanks Jeff
Its not really even trying to start.  Have tried different throttle positions but no good.  Mag is a replacement (but not rebuilt) for the one that was originally on (which had a grooved slipring and open circuit secondary; see my earlier post).  It seemed ok as far as resistance tests indicated.  Also good enough spark when spun by hand.  I think I may indeed try new plugs and perhaps leads too but given the sensitivity to throttle and choke during its brief run, I am still suspicious about the fuelling side.

[Alan @Ncl]

Still working on this but in response to Muskrat's suggestion (thanks again M), I rigged up a bit of plastic pipe pushed/screwed onto the protruding end of the pilot jet and let it level out like that (filled chamber from a plastic bottle through the normal feed pipe).  You can see the level on the attached pic; its just about level with the A in Amal and about 35mm measured from bottom of float chamber outside.  How does this look do you think?

Also tested to see where it flooded.  This happens about 50 mm which is about level with the top screw and in line with the primary air hole, as you would expect.  This leaves about 15 mm for the venturi effect to lift the fuel. I am conscious of previous posts about the different SG of modern petrol (or the substitute they sell at the pumps).  On the web it said petrol is now SG=0.737.  Does anyone know what it was in the 'good old days'?

[muskrat]

G'day Alan,
               just did a bit of searching re float height. I haven't had much to do with monoblocs.
Found this, Monoblocs can handle 15 degrees of downdraft without modification and fuel level should be at the small 'pimple' located on the center of the float chamber cover about .100 inch below the embossed AMAL lettering.
And this, the 'dot' is generally in between and immediately below the bottom of the legs of the M & A (2nd&3rd letters of AMAL) which makes it about 3/16" below the bottom of the mixture screw level......
 So looking at your pic it seems about right.
Cheers

[Alan @Ncl]

Thanks again M for this useful info.
As you say, it seems my level is not far out then. 

From what I have now seen on the web it seems modern fuel (typically SG = 0.732) is marginally higher than leaded petrol (0.72) which is only about 2.5% difference.  If this is right it implies that the level should settle a bit lower than design point (Archimedes and all that) but only marginally.  Still, it supports the notion that everything else being equal, engines will tend to run a bit leaner on the modern stuff. Also, if its a bit denser, this will presumably make it harder to lift for a given choke depression so exacerbating the weakening effect.  All quite marginal and theoretical but I wonder if the reality bears this out?

Alan

[wilko]

I know i keep harping on about this, but it's retarded timing that causes overheating and spitback, especially if just at low revs.Of course at middle to high revs lean jetting will do it too, but when there's no load well....

[muskrat]

G'day Wilko,
                OK it's your turn  . Seems like carb might be OK so yes timing is next on the list.
Alan, check the timing at retard, I think it should be around 10 degrees. Is it manual or auto advance?
Cheers
 PS, I went electronic 20 years ago.

[Alan @Ncl]

Thanks Wilko and Muskrat
I too tend to associate overheating primarily with retarded timing but I have checked it a few times now and its spot on when fully advanced.  I even wondered if it was sticking on retarded (its got an autoadvance but it seems free enough).  I measured the retarded position as corresponding to about 8 degrees before TDC which does suggest its a bit retarded relative to your 10.  Ironically, I was half expecting to have to retard a bit more when/if I ever get running, due to the fuel issue (I think the pistons are about 8.5 on my bike).

Also, my main problem at the moment is simply getting it to start (it wont), rather than overheating.  Would excessive retard prevent starting?

Spitting back is not a problem in my case but during today's 'assault' it did kick back weakly at one stage which, ironically, I took as potentially promising.

Stripped and cleaned the carb again and checked all the sizes.  Have set the throttle stop so the slide is about 1/16th inch open with the twistgrip fully closed. Is this OK?

I also got new plugs and leads today so will be try fitting those tomorrow, following up a suggestion by Jeff, earlier in the week. Will check plug caps too as I have seen on this forum that they need to be non resistor types.

[Stu55Flash]

I've been through similar, the basic fuel/air mixture should be 14:1 and you may need to adjust the needle position to get this. Try lifting by one notch. If the plugs are sparking you should get some splutter at least if the timing is somewhere near. The mags are the weak spot but usually its when hot this old technology is at its worst. The throttle has to be open slightly to draw some fuel from the main jet on kick over. With the air slide closed.

Duno if this helps?

Stu

[Alan @Ncl]

Thanks for your comments Stu
The needle is on position 3 at present and there are only 4 notches on my needle which is surprising as I thought there were usually 5 (it seems to be stamped with number 15).  So this seems OK and corresponds to where it always was (used to run a bit on rich side anyway, by memory).  When it did run briefly the other day, I thought maybe the main jet was blocked so that on cracking throttle the additional air would take the mixture way above stoichiometric with only the pilot jet providing.  Was getting a spark at atmospheric condition but that may not be enough for 'in the pot'.  Hence looking in that direction next.

[muskrat]

Starting as far as the carb is concerned is pilot and slide. Timing, the further retarded (to a point) the easier it should be to start. The compression could be blowing the spark out, throw a new set in. Hook a timing light up to a lead and external battery, give it a kick and see if you get a flash. No flash = no spark.
Cheers

[BSA_54A10]

Go and buy your self a colour tune.
They are made b a company called Gunsons.
Shove it in and you can check that there is a spark at combustion pressure. Saves a lot of hours chasing down that electrical problem in the carb.
Also used for checking carburation and setting pilot jet , cut away & needle position.

Modern fuels leave sticky conductive deposits on plugs so it is a good idea to burn off the plugs to eliminate that possibility .

Shane had a pair of plugs go foul in 3 kicks. The A65F fired once then stopped and never even looked at starting again.
After much nagging from me he swapped plugs with the Bonnie, just to shut me up.
Results,
Firebird running like a pearler, Bonnie dead as a door nail and these were brand new plugs straight out of the box.
He was flabbergasted .
We burned off the plugs, they went back into the now warm engine & he has done 2 rallies on them without problems.

[Beezerman]

Hi
I got this spark plug tester from e-bay  http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250657870145 works really well just fit between spark plug & plug lead kick over the bike & you will see a spark great for a fiver.
Ron.