Author Topic: A7 Shooting Star burning rich on one cylinder  (Read 260 times)

Offline Terryb

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A7 Shooting Star burning rich on one cylinder
« on: 19.04. 2020 19:18 »
Ok Guy's

What causes burning rich on one cylinder. I have the situation and it's been prevalent for some time. That the colour of my spark plugs show that the number one cylinder burns richer than the number 2. What are the possible causes?
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Offline Triton Thrasher

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #1 on: 19.04. 2020 19:33 »
It’s a problem inherent in feeding two inlets and cylinders, which are not identical, with one carburettor.

Does the bike run ok?
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Online morris

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #2 on: 19.04. 2020 20:25 »
Here's an explanation and a (maybe?) solution, information snitched from; http://bsa-info.nz/us-dealer-info/#HapAlzinaBulletins
Anybody ever tried this?
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Online RDfella

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #3 on: 19.04. 2020 20:42 »
Thought the usual remedy was a wedge between carb and head to slightly offset the carb towards the weaker cylinder.
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Offline Terryb

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #4 on: 19.04. 2020 21:02 »
When the plug doors up it starts to missfire under load.
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Online muskrat

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #5 on: 19.04. 2020 21:14 »
G'day Terry.
The anti-bias gasket is to remedy that. https://www.a7a10.net/forum/index.php?topic=7720.0
As also mentioned in that topic ignition bias can be a cause. try running a hotter plug in the rich cylinder.
Cheers
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Offline Terryb

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #6 on: 19.04. 2020 21:19 »
It starts fine, ticks over fone, but as soon as the plug doors up it starts to misfire under load.
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Offline Scott and Jay

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #7 on: 20.04. 2020 04:04 »
Hi there, terryb

I went through these symptoms. I realized that tappets weren't set evenly. That didn't fix it, but then realized I had a difference of 5 degrees in my ignition timing, between cylinders. I did run one hotter plug on one side, and I also timed it at the mid-point between cylinders. However, upon my top-end rebuild in 2017 I go the same symptoms. Our engineer had, by then, refaced the magneto cam - so it was exactly the same timing, both sides. There was no other explanation but the classic induction bias - which is now fixed by Cake Street Classic's anti-bias gasket...
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Offline Terryb

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #8 on: 20.04. 2020 18:52 »
Hi All, thanks for all the input.

The back ground of this thread is that I have owned my 1955 Shooting Star now for about 6 years, completing in that time some 7,000 miles plus and I have always had an issue with mixture problems between cylinders. Initially I had a traditional Mag for about 1 year and then converted it to electronic (Thorspark) after the mag. gave up, so I believe the problem isn't a timing issue between cylinders. I've always run the engine with a lean carburettor set-up, which has worked and I've tolerated the occasional spitting back in the carb.

Over the winter I've renewed the bottom end and satisfied myself that now the engine is mechanically sound, but the tuning of the engine is proving to be more difficult than pre-refurb. So now is the time to try and resolve the in-balance between cylinders, so I've taken some of your advice and ordered Anti-Bias Gaskets from Cake Street Classic's. Together with a different spark plug set-up, I hope there is an improvement. So, watch this space for the next instalment. *smile*
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Offline Terryb

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Re: A7 Shooting Star burning rich on one cylinder
« Reply #9 on: 24.04. 2020 13:52 »
I just like to thank all you guy's and the existence of this Forum for your help and knowledge, magic.

Gasket from Cake Street came today and installed. Changed spark plugs to N4C on No.2 and BP6ES on No.1, re-adjusted timing a  gnats c"ck and bingo. Went out for a 5 mile test run and she didn't miss a note and pulled well, checked plugs on my return and as near as dam it both were the same colour, a greyish brown *smile*
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