Author Topic: A65 SPITFIRE KICK BACK  (Read 708 times)

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johnjag

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A65 SPITFIRE KICK BACK
« on: 10 February, 2019, 18:47:01 »
Hi - not been on here for a while. Have recently bought a 1966 A65 Spitfire fitted with a John Hill alloy 750cc barrel and an Electrex self generating ign/lighting system. My problem is on starting, it kicks back so fierce as to break my ankle! Now I am no novice at these things but this has got me stumped. Initial thoughts of course are too far advanced ign timing. This is spot on but I have tried continually retarding it to no avail. However if I do not give it any throttle it never kicks back but will only fire once or twice but not start. If I give it just the slightest throttle on starting it kicks back. If I screw in the throttle screws a little and kick with no throttle it starts with no kick back but is then ticking over far too fast. The Electrex system has been returned to the factory where it was given a clean bill of health. John Hill was the previous owner of this bike and says he never had any problems, which I doubt. Once I can get the bike started it runs fine. Has anyone any ideas as I am at my wits end.
Thanks
John.

Caulky

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Re: A65 SPITFIRE KICK BACK
« Reply #1 on: 11 February, 2019, 09:04:12 »
Today's fuel is different to that of the 1960's, so the ignition timing should be retarded a shade.
Clean the idle jets (physically) and use new fuel.

berniej

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Re: A65 SPITFIRE KICK BACK
« Reply #2 on: 11 February, 2019, 09:37:54 »
I haven't used the Electrex system but believe that some after-market electronic ignition systems can have a tendency to fire a bit too advanced when the supply voltage is low. Maybe worth checking that you have a fully charged battery - or leaving a charger connected while you try to start it - to make sure that isn't part of the problem.

Cheers,
Bernie
'49 M21/B31 hybrid
'56 M21 combination
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Mike Farmer

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Re: A65 SPITFIRE KICK BACK
« Reply #3 on: 11 February, 2019, 09:49:48 »
 :)

Maybe weak mixture--

Mike

johnjag

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Re: A65 SPITFIRE KICK BACK
« Reply #4 on: 13 February, 2019, 09:06:00 »
Hi all - thanks for the fast response. Caulky first - as I said I have kept on retarding the ign until I have run out of adjustment as this was my initial thoughts too. No joy.   Berniej - The Electrex system is completely self generating and so needs no battery even for the lights. So no joy either.   Mike- The carbs are brand new premium concentrics and I have upped the pilot jet on the advice of Amal Carbs. This has not cured the kickback but has made the bike easier to start just on tickover (when it does not kick back) but it is still a bit hit and miss for me to rely on just that to start it. However I think the carb settings may be a step in the right direction. Thanks to all of you. John.

Servodyne

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Re: A65 SPITFIRE KICK BACK
« Reply #5 on: 13 February, 2019, 09:20:51 »
Hi there.
It sounds very much like an issue with the timing and not the carbs.
Once you get the bike started have you tried strobing it?
This is the only sure way of checking the timing correctly, and you will also be able to see if its advancing correctly up to the timing marks. It sounds as though it's stuck on full advance to me.
 

JulianS

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Re: A65 SPITFIRE KICK BACK
« Reply #6 on: 13 February, 2019, 09:35:03 »
Some digital electronic systems have a stabilising function where at low rpm to avoid engine stalling it advances the timing.

No sure if Electrex has this function built into the chip.

Servodyne

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Re: A65 SPITFIRE KICK BACK
« Reply #7 on: 13 February, 2019, 19:27:42 »
Some digital electronic systems have a stabilising function where at low rpm to avoid engine stalling it advances the timing.

No sure if Electrex has this function built into the chip.
If it has there's no mention of it in the Electrex instructions that I have. I bought one a while ago for a Norton but have never fitted it.
Interestingly there's no mention of using a strobe in the instructions, Just set the crank to the correct position using a timing disc or a dial gauge and align the FA mark on the rotor with the red dot on the stator. Electronic advance at 5000rpm is 21deg.
I think I'd still be checking it with a strobe though.

Mike Farmer

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Re: A65 SPITFIRE KICK BACK
« Reply #8 on: 13 February, 2019, 19:32:13 »
 :)Ho agin. It might be worth a a try kicking it over a couple of times with the ignition off in the same way they used to "prime" the old aircraft engines. I have always done this with the old big hand started tractor engines. We used to pull them  every piston through compression stroke. Maybe helpful---who knows.

Mike 8) 8) 8)

Editor

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Re: A65 SPITFIRE KICK BACK
« Reply #9 on: 14 February, 2019, 09:26:45 »
For what its worth there is an effect on Boyer Systems where when the voltage is low, the advance 'curve' shifts to more advanced so it will kick back. Charge the battery up and its fine. I know the Electrex is self generating but it may suffer from the same effect??
Have you tried calling them for advice?

Caulky

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Re: A65 SPITFIRE KICK BACK
« Reply #10 on: 15 February, 2019, 10:08:07 »
Are the float levels set-up to 0.080" below the cusp?
Easy to adjust with 'stay up' floats.

johnjag

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Re: A65 SPITFIRE KICK BACK
« Reply #11 on: 16 February, 2019, 10:10:33 »
Hi all - and thanks for the further imput. I have checked the timing with a strobe as suggested by Electrex and the timing is spot on the mark and advances perfectly. As I said in my first post I have sent the unit to Electrex who say it is perfect. I am still convinced it is carb related as it does spit back through the carb when it kicks back and it only kicks back when I try to start it with a slight throttle opening. If I screw the throttle screws in slightly it starts first time with no kick back but then of course it ticks over too fast. On the road it pulls like a train and is very quick.
John.

DerekAnderson8

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Re: A65 SPITFIRE KICK BACK
« Reply #12 on: 16 February, 2019, 10:48:33 »
I fail to see an issue here, my bike A65 which is totally std kicks back if i try and start with throttle slightly open.

why cant you screw the throttle in slightly and then adjust after its running, surely a small compromise on what is probably quite a tuned and very enjoyable A65.

 ;)

derek

Caulky

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Re: A65 SPITFIRE KICK BACK
« Reply #13 on: 17 February, 2019, 11:03:59 »
As Mike Farmer said further back in this thread, 'weak mixture'.
Opening the throttle slightly brings the needle jet into operation.
Raise the needles one notch, by using a lower notch on the needle.
The pilot screw should be 1 1/2 turns out to begin with, then tune the carbs.
I use the Hughie Hancox method for tuning. i.e. treating each cylinder as a single.
About 4 mins into this video:
https://www.youtube.com/watch?v=cjUU1eDyesI&list=UUZSGgAoIUtPZfo8Y0qTNW0g&index=10 

johnjag

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Re: A65 SPITFIRE KICK BACK
« Reply #14 on: 18 February, 2019, 17:20:44 »
Hi Derek Anderson 8 - but there is an issue. If it won't start normally then something is wrong. Yes every time I start it I can screw in the throttle screws and then when it starts I can screw them back but that is hardly a cure. If at the end of my investigation that is what I have to do then I will pack a small screwdriver and do it but I think in the meanwhile I will continue with carb adjustments. At the end of the day it is just an old 750cc motorcycle (albeit with an alloy barrel and a superior ignition system from when it was new) and I should be able to start it without breaking my ankle. Also even though it runs fine I worry I will end up with a hole in a piston or worse because the set up is not as it should be.
Thanks for your input.
John.