Hot Starting Problem Driving Me Nuts

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moriniboy
Posts: 43
Joined: Wed Apr 03, 2013 7:59 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Thu Apr 24, 2014 12:03 pm

The decompressor cable is very slack and barely works unless squeezed fully at certain points of the engine cycle. Im sure its not that

Willpower
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Joined: Sat Feb 21, 2009 2:56 pm
Location: St. Annes on Sea

Re: Hot Starting Problem Driving Me Nuts

Unread post by Willpower » Thu Apr 24, 2014 1:49 pm

Just can't understand why the plug stays dry when the motor is hot. If fuel is being delivered and the spark is good, you'd expect it to fire. Piston rings/cylinder bore & valve problems would likely make the bike smoke even from cold. So when its hot, where is the fuel going if he piston is not getting wet?
One other easy check would be to remove the plug when hot and give the engine a good crank over on the kick start and get a mate to watch the plug hole for fuel vapour. You could also try this cold first to compare results.

moriniboy
Posts: 43
Joined: Wed Apr 03, 2013 7:59 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Thu Apr 24, 2014 5:23 pm

Well this is the point, I wonder if fuel is being delivered properly. It takes a bit of starting from cold, and is a nightmare hot. having said that, Im now on my second carburettor, having replaced the original RDF remote-float carb (like an Italian pre-Monobloc Amal or Amac) which was no better, with a modern PHBH as fitted to Morinis, Guzzis and even with appropriate 2-stroke atomiser, more modern Aprilias and racing Lambrettas etc

Looper
Posts: 98
Joined: Fri Mar 20, 2009 11:04 am
Location: Ireland

Re: Hot Starting Problem Driving Me Nuts

Unread post by Looper » Thu Apr 24, 2014 9:12 pm

If as you said, the plug is a good colour and there's no problems while it's running the fuel supply must be ok (at least until you stop the engine that is). That's the bit that doesn't make sense to me, if it is a fuel issue I'd expect there to be problems while the engine is running as well. If you have a lifter on the exhaust valve there could be carbon deposits under the seat of the valve stopping it sealing properly. I know I keep banging the same drum but until you have good compression all other diagnostics are compromised. If I had a troublesome engine that was only developing 75psi I'd be taking the head off for a good look inside. In my experience poor compression can cause all sorts funny symptoms that can look like fuel/ignition problems. I really would look at sorting out the one thing you know isn't right and see where you are then.

moriniboy
Posts: 43
Joined: Wed Apr 03, 2013 7:59 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Thu Apr 24, 2014 10:42 pm

Yes, Ive come to the conclusion that you are right and its time for (at least) a re-ring and valve/seat grind/repair...

Looper
Posts: 98
Joined: Fri Mar 20, 2009 11:04 am
Location: Ireland

Re: Hot Starting Problem Driving Me Nuts

Unread post by Looper » Fri Apr 25, 2014 12:11 am

First thing is to lift the head and have a look, shouldn't be too hard on an old single. Any obvious scoring of the bore or rings, signs of a head gasket leak or badly seating valves can be seen once you open it up. There could well be one small thing causing a leak. A full topend rebuild is the worst case, an afternoons fettling might be enough to bring the compression back to being good enough. As I said it might not be only issue causing the hot starting problem but it will certainly help.

Willpower
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Joined: Sat Feb 21, 2009 2:56 pm
Location: St. Annes on Sea

Re: Hot Starting Problem Driving Me Nuts

Unread post by Willpower » Fri Apr 25, 2014 5:01 pm

Before you start the strip down, it could be worth trying to start the hot engine with the petrol tank filler removed. Who knows, the engine could be doing enough sucking whilst running to keep it going, but the tank may vapour lock when the engine stops.

moriniboy
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Joined: Wed Apr 03, 2013 7:59 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri Apr 25, 2014 7:17 pm

It leaks petrol all over the tank if full so unlikely but a good thunk!

Detour Rd.
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Joined: Fri Feb 20, 2009 3:13 am

Re: Hot Starting Problem Driving Me Nuts

Unread post by Detour Rd. » Tue Apr 29, 2014 2:59 am

I see you have a compression release. On my singles out in the woods if I have a get off or a stop it would get stubborn to restart. Try shutting off the fuel and ignition, throttle wide open, pull on the compression release and kick through several times. Fuel still off ignition on and I would get a start. Try it,

moriniboy
Posts: 43
Joined: Wed Apr 03, 2013 7:59 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Tue Apr 29, 2014 9:00 am

Ive tried it all, believe me. Tho with my mag I cant switch the sparks off

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