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V50 stumble

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iansoady View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2018 at 12:17
Well it's not the 97 octane (not that I really thought it was). Just been out for a very pleasant ride for 45 miles or so with a 5 minute break in the middle. Not a sign of the cough in the first part. It did do it a couple of times on the return leg but not dramatically and was easy to ride around. What I have noticed is that it seems to happen when I've been on a closed throttle for a while - eg one of the incidents today was after dropping down a hill then entering a roundabout. I wonder whether that upsets the mixture at all?

Waiting for plug caps and plugs which I will fit anyway.


Ian
1952 Norton ES2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2018 at 12:47
Silly question time - are the valves clearances closing up to nothing when it gets hot? (Guess how I know!)

If inlet valves aren't fully closed may cause the spit back etc. I was blaming the carbs when it happened to me.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2018 at 14:39
I did set them to the recommended wider clearances so hope not. Worth a check though, although there is a satisfying tapping coming from both sides.

TBH it does seem much improved though I have no idea why.......
Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GC888 Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2018 at 15:32
Originally posted by iansoady iansoady wrote:

I did set them to the recommended wider clearances so hope not. Worth a check though, although there is a satisfying tapping coming from both sides.

TBH it does seem much improved though I have no idea why.......

Drop in ambient temperature by 10c ?

You have the same volume just slightly less of it due to a lower density on a really hot day (why engines always run better on a cold morning) 

The nitrogen is inert so the effect is from you getting more oxygen on a cold day i.e. its making the mix leaner or enabling the engine to burn more of the charge. 

Obviously the buggers up the theory of the spitting being caused by a lean mix as a cold day would make it rich. 

However pulling the cones so the carbs are open to air is a quick job for a test to see if it runs better.

What colour are the plugs after a good run? 

   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 30 Aug 2018 at 10:00
I'll be checking them when my new ones arrive (probably today). But today is mostly dedicated to further road testing of the Norton.
Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 31 Aug 2018 at 14:01
Plugs (the first is the left hand side):





Mixture looks pretty good from these although the right one does look a bit crusty. New plugs and caps now installed.

Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 31 Aug 2018 at 15:27
If it's only a momentory stumble, and if it's due to mixture, then it would be too short in duration to have any effect on the plugs.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GC888 Quote  Post ReplyReply Direct Link To This Post Posted: 31 Aug 2018 at 17:40
They both look OK but they are different and assuming they both went in new at the same time it suggests they were running differently at some stage. The deposits on the right plug can only be carbon but its has had a period of normal running to give it the brown 'normality'.

Back to the symptoms its only failing at a set speed and you think only one cylinder fails.
So you would expect it to be running normally and look ok, as most of the time it is.

However I would hazard an easy guess that its only the right cylinder thats doing the spiting!

Which is good as you have a spare everything to switch and test that you know is good and testing will not cost you anything! 

Gut feel I would look at carbs first, but that is just looking at a photo and I could be wrong.
Electrical tends to give different symptoms and not cause spitting, just misfires.

You have checked that the cutaway for transition between pilot and main is the same on both carbs and 'not worn' or have 'worn in the same way'?       








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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 2018 at 11:32
Thanks both. I agree that given the very transitory nature of the problem it wouldn't in itself show up on the plugs but the colour reassures me that the mixtures in general are not far off (although modern fuels can be misleading).

I don't actually know which cylinder it is - as it always happens when I'm trying to make a smart takeoff onto a roundabout etc I'm not inclined to start looking down - even if I thought I'd see anything! The effect is rather like switching the ignition off and on momentarily - which would lead me to think it's ignition related.

I haven't actually checked the cutaways but both look in virtually new condition. I would be surprised if they were different to each other but who knows?

It does remind me of a problem I had with my Commando many years ago in France where it popped and backfired, gradually getting worse. I spent ages by the roadside stripping the carb (had a single Amal fitted) looking for muck in the jets etc. Eventually I tracked it down to the Boyer ignition. Boyer had in their wisdom fitted those horrible pre-insulated crimps to the pickup which lives under a cover on the right hand side of the engine where the points would normally be. One of the crimps had been very poorly applied and was making intermittent contact. I pulled the crimps off and twisted the wires together which made it run perfectly till I got it home and fixed it properly.

Interestingly (or not) - when I first had the bike it often used to "cough" when I turned the ignition off. I know Boyer and the like generate a spark under these circumstances. It doesn't do it now. This may or may not be connected to my current problem.

All puns in this post are intentional.......

Ian
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1986 Honda XBR500
1958-ish Greeves/Triumph in progress
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2018 at 12:38
Just been out for another 40 miles to get Evesham Vale plums from a farm shop. The V50 behaved perfectly (although the tickover speed has increased by 1/2 a turn on both carbs!)

I'm reluctant to believe it was a simple as plugs & caps but unless I disturbed something else that's the conclusion I've come to.

A nice cheap fix!
Ian
1952 Norton ES2
1986 Honda XBR500
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