Hot Starting Problem Driving Me Nuts

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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 18, 2014 11:33 am

85 psi is low, I've always gone with 100 as really the minimum you want cold. If it's starting well from cold it might not be an issue, but worth looking at. Put a drop of oil in the cylinder and see if it increases, if it does it's rings, if not it could be the valves.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri Apr 18, 2014 5:56 pm

Actually ive remeasured it, and its 75psi cold, not had a chance to get it going to measure hot....

DerryUK
Posts: 107
Joined: Fri Dec 03, 2010 11:24 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Fri Apr 18, 2014 10:11 pm

How does the compression feel on the kickstarter, hot vs cold? If you had zero compression when hot surely you'd feel it?

75/14.7 = 5:1 compression ratio which these days is low. You don't need compression to get things to burn, it is more of an aid to efficiency.

To get things to burn you need oxygen + fuel + ignition.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri Apr 18, 2014 10:23 pm

Why 14.7 out of interest? Is that really a reliable way to et a compression ratio?

There isnt much difference in feel on the kickstart hot or cold to be honest.

DerryUK
Posts: 107
Joined: Fri Dec 03, 2010 11:24 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Sat Apr 19, 2014 10:29 am

14.7 psi = air pressure at sea level

You never said how you stop your bikes engine?

Derry.

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 » Sat Apr 19, 2014 5:19 pm

5.1 is very poor compression and could be the cause, but I have run bikes with poor compression and still managed to have a wet plug.
When the bikes hot and won't start, remove the ht from the plug and try to start it, then remove the plug and have a look at it - it should be soaking. If it's not, then I would look once more towards the fuel delivery.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by Looper » Mon Apr 21, 2014 8:38 pm

Might be letting myself in for a roasting here but as far as I know almost all petrol engines need at least 100psi to start reliably. Poor compression led me a merry dance in the past with a bike that was a poor starter, because I felt I had compression when I kicked the bike over. After doing everything else, fuel system and ignition system I finally got hold of a compression tester and found I'd only 80psi or so. After a top end rebuild the engine had proper compression and has started reliably since.

With a fresh mag, new carb and poor compression, the top end is the logical place to look. It might not be the only problem but in my opinion it is a problem worth looking at before you spend any more time or money.

DerryUK
Posts: 107
Joined: Fri Dec 03, 2010 11:24 pm

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Mon Apr 21, 2014 11:55 pm

Remember it is hot starting that is the problem. If it was a case of just poor compression then it would bump start. What we don't know is whether the problem is fuel or sparks, hence my suggestion to try easy start.

If you have a spark but no fuel then with easy start the engine will burst into life then immediately stop (when the ether gets used up from the inlet.)
If the engine doesn't fire with easy start then you have no spark.

Derry.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Wed Apr 23, 2014 11:41 pm

I bought a can of easy start at the Ross autojumble last weekend on your advice. I will let you know.
As for the other query, the Gilera Saturno (for thats what we are discussing!) has a decompressor to stop the bike

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 8:37 am

Now you've mentioned the decompressor, how about removing it and blanking with a suitable size bolt or spare plug if it fits. The go for a run again and try starting from hot. It will eliminate any possibility of leakage from the decompressor when hot. Although saying this you would expect performance issues when the engine is hot and running, but as it doesn't require major strip it would be worth a try.

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