mystery miss
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mystery miss
I have a '52 G80S fitted with a 389/1 monobloc. All was well until I had the magneto re-built. The bike starts and runs well, pulls strongly, but at a steady 50mph there is a from time to time a slight hesitation, like a half miss! The plug, with the re-built magneto has gone from dark brown to light grey (NKG B5ES), so I thought perhaps the mixture was a little lean with 250 main jet and went to the standard 260. This hasn't solved the problem perhaps made it more pronounced. I'm reluctant to fit a softer plug. Perhaps I'm barking up the wrong tree and looking in the wrong direction. Any suggestions?
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Re: mystery miss
Hi
I'd be tempted to raise the needle one notch and see if things improve.
Regards Mick
I'd be tempted to raise the needle one notch and see if things improve.
Regards Mick
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Re: mystery miss
If the carburation was all right before you had the mag done it will be the same now. Did you check the point gap when before you fitted the mag I made the mistake once of not checking the gap which was almost nil had the same problem. Good luck hope you solve your problem soon.
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Re: mystery miss
Hi, My 53 G80 fitted with new Monoblock and recon mag ran well up to around 50mph and them seemed to run out of puff. After a bit of experimentation it seemed to indicate that it was running weak at the top end. Fitted a larger main jet and now it pulls really well at all throttle openings. I put it down to modern fuels having a lower octain rating. Going up one or two sizes on the main jet may have little effect, I jetted the carb up a few sizes and worked from there.
I do agree with the comment regarding the checking of points and timing before making any other changes. If these are correct, then go for the carb jetting route. Main jets are not expensive and you may even be able to snaffle a couple from a friend to try before buying new.
I do agree with the comment regarding the checking of points and timing before making any other changes. If these are correct, then go for the carb jetting route. Main jets are not expensive and you may even be able to snaffle a couple from a friend to try before buying new.
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Re: mystery miss
Thanks for the suggestions. I'll try them and see how I go.
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Re: mystery miss
Notwithstanding the suggestions already made above and if you haven't already done so, the very first thing I would have done is to try a new plug, (not necessarily a softer one).
EDIT LATER.
Just noticed this:
EDIT LATER.
Just noticed this:
In my 350 and 500 singles I've always used B7 or B8 ES in NGK or preferably Champion N5C (as Clive mentions below)Trefor wrote:.........from dark brown to light grey (NKG B5ES),......
Last edited by SPRIDDLER on Thu Dec 10, 2020 10:03 am, edited 5 times in total.
'There is a tide in the affairs of men
Which taken at the flood............'
Which taken at the flood............'
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Re: mystery miss
And forget NKG somehow our magneto bikes don't seem to get on with them. Try Champion N5C from a known reliable source such as Green Spark plug company.SPRIDDLER wrote:Notwithstanding the suggestions already made above and if you haven't already done so, the first thing I would have done is to try a new plug, (not necessarily a softer one).
clive
if it ain't broke don't fix
if it ain't broke don't fix
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Re: mystery miss
That's a rather sweeping statement Clive. I use NGK in all my bikes, both magneto and coil, and have had no issues whatsoever. I certainly wouldn't use a resistive plug or plug cap with a magneto but any genuinely sourced plug should be ok.clive wrote: And forget NKG somehow our magneto bikes don't seem to get on with them. Try Champion N5C from a known reliable source such as Green Spark plug company.
For my G80S I use a B7ES.
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Re: mystery miss
Always used the Champion N5.
Johnny B
Johnny B
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Re: mystery miss
But this is my experience (and others who have been experiencing problems which go away when changing to Champion), sweeping or not, perhaps there are a lot of fake NGK around.Reynard24 wrote:That's a rather sweeping statement Clive. I use NGK in all my bikes, both magneto and coil, and have had no issues whatsoever. I certainly wouldn't use a resistive plug or plug cap with a magneto but any genuinely sourced plug should be ok.clive wrote: And forget NKG somehow our magneto bikes don't seem to get on with them. Try Champion N5C from a known reliable source such as Green Spark plug company.
For my G80S I use a B7ES.
clive
if it ain't broke don't fix
if it ain't broke don't fix