Hot Starting Problem Driving Me Nuts

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Tue Apr 29, 2014 1:39 pm

I guess you haven't tried the easy start yet?

Derry

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 11:15 pm

Havent had a chance, been too busy with work, plus the weather's been generally terrible

Pete R
Posts: 81
Joined: Sat Jul 07, 2012 8:04 am

Re: Hot Starting Problem Driving Me Nuts

Unread post by Pete R » Fri May 02, 2014 3:54 am

If the compression pressure is really only 85 psi cold,you should try this.
*Adjust valve clearances and remove the exhaust pipe from the head.
*Start the engine and give it a few rev-ups.Open the throttle hard,then fully close it before the revs get too high.When it slows down,do it again.Keep doing that for about 30 seconds.
*When the engine cools down again,set the valve clearances again and fit the exhaust pipe.

Do another compression check and see if it hasn't improved by 30 psi or so.It probably will.

Measured compression pressure is not (CR x 14.7).If the charge was not heated during compression,a 5:1 engine would have 5 atmospheres absolute pressure at TDC,which shows as 4 atmospheres above atmosphereic pressure (58.8 psi gauge pressure).This is not the case,and it could show 90 psi or 95 psi gauge pressure (above atmospheric).

The gauge pressure you get in reality,because the charge does become heated,is more like ( [CR to the power of 1.2] -1) x 14.7 psi.An 8:1 compression engine could show 160 psi,but it also depends on valve timing and intake valve closing point.

I'd always be suspicious of a bad condensor on an engine that won't start hot.Take a spare spark plug and gap it to 5mm.When the engine won't start,connect that plug to your plug lead and see if your ignition can throw a 5mm spark.If so,you can forget the possibility of an ignition problem.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri May 02, 2014 11:33 am

Blimey sounds drastic and neighbour-annoying.What does that do?
Your surname isnt Roper by any chance is it? I ask as a Guzzi owner...

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Fri May 02, 2014 8:59 pm

Well until Pete tells what he is trying to do I will put his technique down to witchcraft! I agree with him about the capacitor. I've had two failures in my lifetime though neither gave hot starting problems. On one occasion (Hillman Imp) the engine just stopped and I found a broken capacitor lead. On the other occasion (Mini) the engine would suddenly start misfiring and spontaneously clear itself. Just changed the capacitor for a cure though it took me months to find it.

I can't see compression being a problem from what I've read so far. Though I'd do a test just to OK the rings. Pour some oil (half a cup) in the plug hole, wait 5 minutes, kick the bike over to clear excess oil then immediately do a compression test. If the pressure goes up, worn compression rings, if it doesn't, leaky valves.

Still, now the weather is OK perhaps Moriniboy can get out and do an easy start warm start test?

Derry.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri May 02, 2014 9:08 pm

Next week. promise!

Pete R
Posts: 81
Joined: Sat Jul 07, 2012 8:04 am

Re: Hot Starting Problem Driving Me Nuts

Unread post by Pete R » Sat May 03, 2014 10:31 am

DerryUK wrote:Well until Pete tells what he is trying to do I will put his technique down to witchcraft!
It doesn't matter if it's witchcraft,as long as it works.I've seen it work so many times during the last 40 years or more.It's not unusual to get 20 psi or 30 psi improvement.
It especially works on an engine that's been laid up/unused for 6 months or more,or engines that have ever been run with tight valve clearances.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Tue May 06, 2014 7:43 pm

Right, I dug the Saturno out again and the compression tester. Ive not started the bike, but cold the pressure tester read 90psi (not 80 as I previously posted, sorry). I put oil down the ploghole and the reading went up to about 92-93psi (gauge isnt that clear, but what is clear is that the oil doesnt make much difference)

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by Looper » Tue May 06, 2014 8:17 pm

90 psi isn't too bad, and there clearly isn't a problem with the rings. Still think it would be worth testing the compression when it's hot and wont start. Should be higher but if not, it's possible either the valves or the head joint are opening up as they expand with the heat. If the compression hot is ok then you're right back to fuel.

Coxy
Posts: 202
Joined: Sun Mar 29, 2009 11:05 am
Location: Sydney Australia

Re: Hot Starting Problem Driving Me Nuts

Unread post by Coxy » Sun May 25, 2014 1:15 am

This bike is how old?? and has likely had how many owners.
My money is on the Cam Timing being out which could also explain the Low Compression, So after all you have done check the cam Timing then look elsewhere, Not forgetting that the specific gravity or density of fuels have changed over the years and Carburettor Jets are fixed but if the fuel is effectively more Viscous it will not flow the same as Fuel from when the bike was new meaning it will be lean.

At work on the Dynometer older engines designed for the long gone Leaded fuels in Australia benefit greatly from re jetting to suit modern fuels, I have seen such results as an old CX 500 go from 18 HP to 36 HP a full doubling of power once sorted and with 650 Bonneville 'motors they start around 35 HP and end up closer to 50 after sorting for modern fuels.

A couple of points to think about there.

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