Hot Starting Problem Driving Me Nuts

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

Hot Starting Problem Driving Me Nuts

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

Ive been wrestling with this for several years and it's not gone away!

I bought a post-war single which it transpired had a warm/hot-starting problem. I could be outside the pub one pint later, kicking it for half an hour before it suddenly decided to start with no warning. Bump starting seemed to make no difference. So I:
replaced the old remote float Dellorto-carb for a modern Dellorto PHBH of the same venturi size, put a tufnol spacer between inlet and head to keep heat away and even had it put on a dyno to check fuelling. The bike runs GREAT from cold and the plug is a mouthwatering biscuit-colour
BUT
it still wont hot start.
SO I
had the mag rebuilt. Lovely blue spark, even when it wont go, which it still wont when it's warm/hot.
Valve clearances are spot on, no the exhaust valve isnt being held open.
"Change the plug" said Brian Silver/Moto Marianna and various other people, so I did, and am using a palladium racing type, still no different.
The plug always seems to come out of the cylinder bone-dry, and today after a rapid 20 mile ride,back home and it as usual failed to start one cuppa later, so I dipped the plug tip in petrol and it started first kick, and seems to start when warm if I squirt a bit of petrol down the plug-hole. "Cant be the carb, youve tried two" says the Man from Dellorto in Reading, but Im not so sure and am now wondering if it can be float weight (the height is correct) and so Ive put in an 11g float instead of the 8g that was in there, and now when I drain the float-bowl, noticably more fuel comes out than before but thats as far as Ive got.
Any suggestions?

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 11, 2014 2:09 am

Wish I hadn't looked at this post because after sitting here thinking for fifteen minutes it's still bugging me and I want to get to bed. If you've got spark when it's hot, and enough fuel's getting in to run when hot then surely it should start. I presume you've tried giving it choke. My triumph sometimes wants choke even when hot. You could do a compression test cold and then hot, maybe something is causing a loss of compression. Of course the compression should increase as it gets hotter but you never know. The only other thing would be to adjust it to run rich and see if that helps, I'm running an old single rich and it seems to like it. Good luck and good night.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Fri Apr 11, 2014 3:36 am

Does the mag have a kill switch? You could try disconnecting that in case it's iffy.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Fri Apr 11, 2014 3:30 pm

No, no killswitch on the mag

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triumph5ta
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Re: Hot Starting Problem Driving Me Nuts

Unread post by triumph5ta » Wed Apr 16, 2014 3:47 pm

When you try and kick it over when hot does it pop or cough at all? Or is it completely dead sounding?

moriniboy
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Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Thu Apr 17, 2014 6:40 pm

Dead-sounding until, with no warning, after 15-20 mins of kicking and on occasion being pushed to no avail, it just fires

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by DerryUK » Thu Apr 17, 2014 9:13 pm

If you don't have a kill switch how do you stop your bike?

The only case of poor hot starting I've had was when I bought a second-hand mini. Nice car went well but unless you restarted the engine immediately (ie filling with petrol) it would not start when hot. It was so bad that I used to leave it for a couple of hours before I tried again. I cured it by adjusting the SU carb, it was running rich when idling. After adjustment it would start hot or cold no problems.

Another thought, try some Bradex Easy Start, £4.50 from Halfords. I used it many years ago with good results on a hand cranked diesel that was impossible to start hand cranking. Easy start always got it going. It used to be based on ether I don't know about the current stuff. I used to give the old diesel a squirt in it's inlet and it always started. Being based on ether if forms a volatile vapour that won't flood your engine but will start to burn as soon as you look at it.

My thinking is if your bike doesn't start with easy start when hot then you have an electrical problem, if it does start then you have a fuel problem.

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

Re: Hot Starting Problem Driving Me Nuts

Unread post by moriniboy » Thu Apr 17, 2014 10:13 pm

Well that's certainly logical (im not being sarcastic, I promise!)

Im currently mucking about with float height/weight, and as Dellortos have a choice of 'Starter jet' sizes and ive got a usually dry plug, Id be daft not to try a bigger one

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 17, 2014 10:46 pm

I really would recommend testing the compression. If you've got spark, you've got fuel (while it's running at least), the third part of the holy trinity is compression. If an engine is hard to start but will run once started it's the first place to look. I don't know why you'd be loosing pressure when it's hot but for the sake of a compression tester and ten minutes it's always worth it, if only to rule it out.

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 8:20 am

I wondered about compression and was one of the reasons I double checked the tappet clearances,. Also I wondered whether when cold the (iron) barrel/bore was 'tight' enough to provide enough compression to get started and keep running, but hot, it'd expanded enough to break the seal between bore and rings. Is that a possible scenario? It is purely hypothetical o my part
It is suspicously easy to kick over. I will check it hot. It is about 85psi cold - I do have a comp. tester.

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