Hard Starting When Warm '48 Rigid G80

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Locked
User avatar
Iron Head
Member
Posts: 277
Joined: Sun Jan 24, 2016 7:19 pm
Location: BERKSHIRE UK

Hard Starting When Warm '48 Rigid G80

Post by Iron Head »

This post is partly prompted by the recent magneto one referencing hard starting when warm, but I'm pretty certain it's fuel in my case. The bike will start first or second kick from cold (with choke) and runs fine but requires major flooding to start even between switching off and then immediate re-starting. Can't seem to get the plug wet even by what would normally be considered serious flooding from tickling. Has a nice old bronze Amal 89B/1AK which I'd like to keep using and has been stripped and every orifice cleaned on several occasions. Magneto is rebuilt and healthy. Float is NOS could it be sticking shut somehow?

Any thoughts appreciated as always.

Iron Head
Tigercub
Posts: 16
Joined: Fri Sep 29, 2017 11:17 pm
Location: Warwickshire England

Re: Hard Starting When Warm '48 Rigid G80

Post by Tigercub »

Something that slipped my aged mind in the magneto thread was that when warm my bike seems to have lost its compression. It pushes over past TDC too easily for my liking. Certainly don't need a valve lifter. I can stand on my tiger cub kickstart at TDC but not the Matchless. Strange, why only when warm. This of course means less 'suck' as well...? Just a thought.
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Hard Starting When Warm '48 Rigid G80

Post by Mick D »

Hi

I wonder if both these issues could be related to the exhaust valve clearance and differential expansion of components in the valve train. The significance of it only happening when warm could be down to the fact that certain parts will come 'up to temperature' quicker than others.

May be worth checking the exhaust valve clearance and opening it up a little if possible.

Regards Mick
User avatar
Iron Head
Member
Posts: 277
Joined: Sun Jan 24, 2016 7:19 pm
Location: BERKSHIRE UK

Re: Hard Starting When Warm '48 Rigid G80

Post by Iron Head »

Thanks for a good suggestion guys. Mick, I had wondered about valve clearances particularly as I haven't re-checked after the top end rebuild and a tight exhaust valve clearance might well be the culprit. I have plenty of compression and I do seem to get a sound each time like it is firing once but the 'firing' may be fuel in the exhaust?

Regards

Iron Head
User avatar
Iron Head
Member
Posts: 277
Joined: Sun Jan 24, 2016 7:19 pm
Location: BERKSHIRE UK

Re: Hard Starting When Warm '48 Rigid G80

Post by Iron Head »

Checked clearances last night and the exhaust was certainly tight using the ‘check exhaust with inlet just opening' and vice versa procedure in the manual for my year. Will run up tomorrow and report back.

Iron Head
User avatar
1608
Member
Posts: 2493
Joined: Mon Oct 05, 2009 1:00 am
Location: ESSEX UK

Re: Hard Starting When Warm '48 Rigid G80

Post by 1608 »

Difficult starting when warm can be caused by running too rich. Loss of compression can be caused by sticking exh valve due to valve/guide clearance closing up when warm due to burnt oil deposits. When engine cools the valve re-seats.
Just another thought, could it be fuel evaporation. Is there a Tufnol spacer fitted on the carb.
desmo
Member
Posts: 20
Joined: Thu Jan 01, 1998 12:00 am
Location: BADEN-WUERTTEMBERG GERMANY

Re: Hard Starting When Warm '48 Rigid G80

Post by desmo »

I had the same issue on my 1948 G80.
As far as I`m concerned,the spacer between the head and the carb was made of aluminium in these years
Swaped it for a more usual pertinax / plastik spacer and voila,
that took care of that, no more hot starting ploblems anymore.

Of what material is the spacer on your bike made of?

Regards,
Norman
User avatar
Iron Head
Member
Posts: 277
Joined: Sun Jan 24, 2016 7:19 pm
Location: BERKSHIRE UK

Re: Hard Starting When Warm '48 Rigid G80

Post by Iron Head »

Thanks for the carb spacer tip Norman. Mine is aluminium so probably well worth a try! No change to hot starting with the tappet adjustment just more tappet noise?!

Iron Head
Locked