Cutting out when hot and then not responding to starter switch

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John Breay
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Cutting out when hot and then not responding to starter switch

Post by John Breay » Fri Jul 13, 2018 6:34 pm

Just done a carb re biuld which included the needle lift/vacuum hole drill out to 3.2mm. Got it running sweet but another problem has reared its head. Took it out to fetch fish and chips just now and on the way home it stuttered, back fired, cut out and then wouldn't respond to the starter switch. After a few minutes it gave a few little tweeks of the engine and then after another minute or so it started and ran fine. Any ideas?
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Wirralman
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Re: Cutting out when hot and then not responding to starter switch

Post by Wirralman » Fri Jul 13, 2018 7:08 pm

The only time I've had something similar was in torrential rain, which WD40 sorted out. If you had been through rain maybe waiting with the engine hot would be enough to evaporate moisture

If it was bone dry, I'd check all electrical connections, starting with earthing point behind the horn During the course of checking you may find a dodgy wire or connectors
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FordPrefect
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Re: Cutting out when hot and then not responding to starter switch

Post by FordPrefect » Fri Jul 13, 2018 7:53 pm

I agree with Wirralman, it sounds electrical to me. Inspect your connections and buzz things through with a meter. One tip I'd give is if you're looking for a break in a wire don't rely on the continuity *BEEP* to tell you all is well, actually read the resistance value on the meter. A wire can be broken in the sheath and still make enough contact to beep but not enough to be of any other practical use. You should get something between 0 and 3 ohms depending on your meter if the contact is good.
If you don't find anything obvious Joth's guides show how to electrically test the bike ignition.
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1993 MT350 bought August 2017

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hounddog
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Re: Cutting out when hot and then not responding to starter switch

Post by hounddog » Sat Jul 14, 2018 3:06 am

Sometimes if the valve clearances are too tight ,as the engine gets hot expansion will stop valve closing and will stop the engine. . The starter motor will still operate but it won't fire up . Once it's cooled down all fine again.
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Ian
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Harley Davidson MT350e
Armstrong MT500e
Armstrong MT500 - next project

John Breay
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Joined: Thu Jun 14, 2018 5:46 pm
Location: Northampton

Re: Cutting out when hot and then not responding to starter switch

Post by John Breay » Sun Jul 15, 2018 2:51 pm

Thanks folks. Ran Joths tests this morning and all was fine. Went for a spin just now and it conked out on the way back 500 yards from home. This time it did respond to the starter switch but wouldn't fire up so I did the walk of shame home with it. Ripped the seat and tank off straight away and retested the low speed trigger(black and blue, engine side) which was just over tolerance on the high side. What ever it is it doesn't like the bike getting hot! I've order some tank cleaning stuff as its not very clever in there and also an in line filter as none is present. Guess once I have these bits i'll have to have the carb off AGAIN and give it a good blast with carb cleaner and compressed air. Any one ever had a low speed trigger fail that manifested itself when the bike gets hot? I'm suspicious but being a tight arse I don't want to do the scatter gun thing...
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John Breay
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Re: Cutting out when hot and then not responding to starter switch

Post by John Breay » Sun Jul 15, 2018 4:05 pm

Just had a peep at the earth behind the horn, twas crappy, corroded but still no dice. Cleaned the one behind the battery box too which was in worse fettle. Had a quick look at the valve clearances but engine is still hot so that will be a tomorrow job, there was a bit of movement there so I'm thinking it isn't that. The joys of MT ownership eh, good job I get on well with my spanners!
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Wirralman
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Re: Cutting out when hot and then not responding to starter switch

Post by Wirralman » Sun Jul 15, 2018 8:01 pm

If your earthing points had corrosion, you may have corrosion elsewhere Fiddly to go around every electrical connector and connection but as you say the joys of an MT

Someone will be along soon to explain why there's no electrical connection when hot but there is when cooler
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FordPrefect
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Re: Cutting out when hot and then not responding to starter switch

Post by FordPrefect » Mon Jul 16, 2018 5:51 pm

Wirralman wrote: ↑
Sun Jul 15, 2018 8:01 pm
If your earthing points had corrosion, you may have corrosion elsewhere Fiddly to go around every electrical connector and connection but as you say the joys of an MT

Someone will be along soon to explain why there's no electrical connection when hot but there is when cooler
Heat increases resistance in a circuit but, I shouldn't have thought it could make much difference here. Not unless there are some particularly naff corroded contacts somewhere that are getting hot and increasing resistance on an already poor connection. That is a very long shot in the pitch dark however!
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1993 MT350 bought August 2017

Wirralman
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Re: Cutting out when hot and then not responding to starter switch

Post by Wirralman » Mon Jul 16, 2018 8:14 pm

FordPrefect wrote: ↑
Mon Jul 16, 2018 5:51 pm
Wirralman wrote: ↑
Sun Jul 15, 2018 8:01 pm
If your earthing points had corrosion, you may have corrosion elsewhere Fiddly to go around every electrical connector and connection but as you say the joys of an MT

Someone will be along soon to explain why there's no electrical connection when hot but there is when cooler
Heat increases resistance in a circuit but, I shouldn't have thought it could make much difference here. Not unless there are some particularly naff corroded contacts somewhere that are getting hot and increasing resistance on an already poor connection. That is a very long shot in the pitch dark however!
You're right about increased resistance when hot but an MT loom getting that hot on a run to the chip shop ? As said, a long shot but the answer will probably be a long shot and maddeningly simple when it's tracked down

I've certainly come across a dodgy MT ignition key switch, the guard protecting the key slot was stuck allowing water into the switch A good soaking in WD40 sorted out the guard, problem solved


John, I've sent you a PM
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FordPrefect
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Location: North Lincolnshire

Re: Cutting out when hot and then not responding to starter switch

Post by FordPrefect » Tue Jul 17, 2018 6:13 pm

Wirralman wrote: ↑
Mon Jul 16, 2018 8:14 pm
FordPrefect wrote: ↑
Mon Jul 16, 2018 5:51 pm
Wirralman wrote: ↑
Sun Jul 15, 2018 8:01 pm
If your earthing points had corrosion, you may have corrosion elsewhere Fiddly to go around every electrical connector and connection but as you say the joys of an MT

Someone will be along soon to explain why there's no electrical connection when hot but there is when cooler
Heat increases resistance in a circuit but, I shouldn't have thought it could make much difference here. Not unless there are some particularly naff corroded contacts somewhere that are getting hot and increasing resistance on an already poor connection. That is a very long shot in the pitch dark however!
You're right about increased resistance when hot but an MT loom getting that hot on a run to the chip shop ? As said, a long shot but the answer will probably be a long shot and maddeningly simple when it's tracked down

I've certainly come across a dodgy MT ignition key switch, the guard protecting the key slot was stuck allowing water into the switch A good soaking in WD40 sorted out the guard, problem solved


John, I've sent you a PM
I've problem solved all manner of things down the years, if it's taught me anything it's to leave no possible avenue unexplored, no matter how remote the chances.
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1993 MT350 bought August 2017

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